JP5423693B2 - Carbon fiber bundle - Google Patents

Description

  The present invention relates to a carbon fiber bundle having processability into chopped fibers, bundling properties suitable for handling of chopped fibers, and opening properties suitable for water-based processes represented by papermaking processes.

  Carbon fiber reinforced composite material with carbon fiber and matrix resin is excellent in lightness, mechanical properties, electrical conductivity and dimensional stability, etc., so it can be used in automobiles, aircraft, electrical / electronic equipment, optical equipment, sporting goods, and construction. It is used in a wide range of materials and other fields.

  Many molding methods are known for carbon fiber composite materials. One method for obtaining a base material used for molding is to process carbon fibers by an aqueous process typified by a wet papermaking process. For example, chopped fibers are dispersed in an aqueous medium and processed into paper or nonwoven fabric, and then various resins are used as a base material to form a composite material base material. An electrode base material of a fuel cell is manufactured by this paper making process.

  In the wet papermaking process, paper is made by dispersing chopped fibers in an aqueous dispersion medium. In order to improve the quality of paper products, it is required to have carbon fiber bundling and openability in an aqueous dispersion medium. Convergence is important in making the fiber length uniform at the time of cutting and processability when feeding chopped fibers. The spreadability is a characteristic for dispersing the fiber bundle at the single fiber level, and directly affects the papermaking quality. The better the convergence and spreadability of the carbon fiber bundle, the better the mechanical and conductive properties of the carbon fiber reinforced composite material.

  From such a background, in a carbon fiber bundle used for an aqueous process, a specific resin is usually attached as a sizing agent to improve the bundling property and the spreadability.

  Patent Document 1 discloses an aqueous process carbon fiber to which a sizing agent mainly composed of a surfactant is attached. Patent Document 2 discloses a carbon fiber for papermaking in which a hydrophilic compound composed of polyoxyalkylene and an aliphatic hydrocarbon is attached as a sizing agent. Further, Patent Document 3 discloses a carbon fiber to which a sizing agent composed of a surfactant having an HLB value of 9 to 17 and a polyvinyl alcohol-based water-soluble thermoplastic resin is attached.

  However, it is not easy to achieve both convergence and spreadability. In particular, when trying to obtain a paper with a high basis weight by increasing the carbon fiber concentration in the aqueous dispersion medium, the fiber spreadability is insufficient, There is a problem that the quality of the base material is deteriorated due to agglomeration and the mechanical properties of the molded product cannot be fully exhibited.

  By the way, urethane resin is often used as a fiber sizing agent because it is excellent in elasticity, toughness, adhesiveness and the like. For example, Patent Document 4 discloses a carbon fiber bundle using polyether polyurethane or polyester polyurethane resin as a sizing agent.

  Although this fiber bundle is intended to improve adhesion to thermoplastic resin by attaching a polyester polyurethane resin with a breaking elongation of 400% or less, the disclosure also suggests that it exhibits excellent properties in an aqueous process. It has not been done.

  Further, Patent Document 5 discloses a carbon fiber chopped strand that uses a mixture of an aromatic polyurethane and a non-aromatic polyurethane as a sizing agent and is excellent in handleability, mechanical properties of the composite material, and conductivity.

  However, it is neither disclosed nor suggested that the carbon fiber chopped strand described in Patent Document 5 exhibits excellent properties in an aqueous process.

International Publication No. 2006/018139 Pamphlet JP 2006-219808 A JP 2000-54269 A JP 2007-231441 A JP 2003-247127 A

  Thus, there is a demand for a carbon fiber bundle that achieves both convergence and spreadability with an aqueous dispersion medium. In the case of a carbon fiber reinforced composite material, the greater the proportion of carbon fiber, the better the mechanical properties and conductivity. Therefore, a better substrate can be obtained if it can be processed at a high carbon fiber concentration. In addition, handleability when manufacturing and processing the fiber bundle is also important, and flexibility when winding on a bobbin and heat resistance when passing through a drying step are characteristics that are always required for the fiber bundle.

  An object of the present invention is to provide a carbon fiber bundle that has good handleability when producing and processing a fiber bundle, has excellent sizing properties, and has excellent fiber-opening properties in an aqueous dispersion medium even at high concentrations. .

As a result of intensive studies to achieve the above object, the present inventors have found the following carbon fiber bundle that can achieve the above-mentioned problems. That is, the present invention relates to a carbon fiber bundle comprising carbon fibers and a sizing agent, wherein the sizing agent comprises 73 to 98% by mass of polyoxyalkylene units, bis (2-hydroxyethyl) terephthalate or bis (isophthalate) ( 2-hydroxyethyl) containing 0.5 to 15% by weight of aromatic ester unit and 1.5 to 10% by weight of aromatic urethane unit. It is a carbon fiber bundle adhering at a rate of mass%.

  The carbon fiber bundle of the present invention is excellent in handleability when manufacturing and processing the fiber bundle, and further achieves both the fiber convergence and the openability in the aqueous dispersion medium, when the carbon fiber concentration is increased. However, uniform dispersion at the single fiber level is possible, and a papermaking substrate excellent in mechanical properties and conductivity can be obtained.

  The carbon fiber bundle of the present invention is obtained by attaching a sizing agent comprising a polyoxyalkylene unit, an aromatic ester unit and an aromatic urethane unit to a carbon fiber. First, these components will be described.

  As the carbon fiber, PAN-based, pitch-based, rayon-based, and the like can be used, but PAN-based carbon fiber is preferable from the viewpoint of the balance between strength and elastic modulus of the obtained molded product. These are available as commercial products. The carbon fiber may be subjected to a surface treatment in order to improve adhesion to the sizing agent and form a uniform film. Examples of surface treatment include chemical oxidation, electrolytic oxidation, or gas phase oxidation in the liquid phase, but the electrolytic oxidation in which the carbon fiber is used as the anode in the aqueous electrolyte solution is simple and suppresses the decrease in strength. preferable. The electrolytic treatment solution is not particularly limited, and examples thereof include inorganic acids such as sulfuric acid and nitric acid, inorganic bases such as potassium hydroxide and sodium hydroxide, and inorganic salts such as ammonium sulfate, ammonium carbonate and sodium carbonate.

  A carbon fiber bundle is a form in which single fibers (filaments) of carbon fibers are bundled, and the number of filaments is usually about 1,000 to 60,000. From the viewpoint of handling and opening properties of carbon fibers, 3,000 to 40,000 are preferable. More preferably, it is 6,000 to 24,000.

  As for the diameter of the carbon fiber (filament) which comprises a carbon fiber bundle, 3-15 micrometers is preferable, More preferably, it is 5-10 micrometers.

  In addition, the carbon fiber bundle of the present invention may contain a small amount of other fiber types as long as the object of the invention is not impaired. Examples of other fiber types include carbon fiber, glass fiber, aramid fiber, alumina fiber, silicon carbide fiber, boron fiber, metal fiber, and other high-strength and high-modulus fibers. Also good.

  The sizing agent of the present invention can be obtained by condensing an aromatic diisocyanate with a polyol containing a polyalkylene glycol and an aromatic ester. Here, the polyol containing an aromatic ester is obtained by dehydrating and condensing a glycol component and an aromatic dicarboxylic acid component. An aromatic diisocyanate and a polyol containing a polyalkylene glycol and an aromatic ester are condensed so that the aromatic diisocyanate has an aromatic urethane unit, the polyalkylene glycol has a polyoxyalkylene unit, and the polyol having an aromatic ester has an aromatic property. Constructs a group ester unit.

  Since the condensation of isocyanate and alcohol is a polyaddition (addition polymerization) reaction and does not involve the generation / separation of low molecules, the polyoxyalkylene unit, aromatic ester unit and aromatic urethane unit constituting the sizing agent of the present invention. The mass ratio reflects the mass ratio of the raw materials constituting each unit. That is, the mass% of each unit in the present invention is the mass% of each raw material with respect to the total mass of the three types of raw materials.

  The polyalkylene glycol that can be used in obtaining the sizing agent of the present invention needs to be hydrophilic in order that the carbon fiber bundle exhibits high openability in the aqueous dispersion medium, for example, polyethylene glycol (PEG), Examples include polypropylene glycol (PPG), PEG / PPG block polymer, PEG / PPG random polymer, and the like. Of these, polyethylene glycol is preferable.

  Moreover, the compound which has other hydroxyl groups except water can be contained in the range which does not impair the handleability of a sizing agent, bundling property, and fiber opening property. Examples of such compounds include ethylene glycol, propylene glycol, butylene glycol, glycerin, pentaerythritol, trimethylolpropane, sorbitol, catechol, bisphenol A, and the like.

  As described above, in the present invention, the polyoxyalkylene unit constituting the polyurethane resin used for the sizing agent is preferably composed of polyethylene glycol. However, the term “consisting of polyethylene glycol” described here means It means that polyethylene glycol is 90% by mass or more of the total alkylene glycol component.

  From the viewpoint of the balance between the handleability of the carbon fiber bundle, the bundling property, and the spreadability in the aqueous dispersion medium, the weight average molecular weight of the polyalkylene glycol is preferably more than 6,000 but not more than 21,000. The polyalkylene glycol component varies in hydrophilicity and film flexibility depending on the molecular weight. When the molecular weight is in an appropriate range, it is possible to obtain a sizing agent that exhibits higher spreadability and more excellent convergence and handling properties.

  In addition, the polyalkylene glycol component can also be used by mixing a plurality of types having different weight average molecular weights. In this case, the weight average molecular weight of the polyalkylene glycol can be obtained by the following formula.

  Here, Mw represents a weight average molecular weight, and W represents mass% of the polyalkylene glycol component.

  Polyols containing aromatic esters can be obtained by dehydration condensation of glycols and aromatic carboxylic acids. Examples of glycols that can be used for dehydration condensation include ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanediol, and the like. Examples of the aromatic dicarboxylic acid component include phthalic acid, terephthalic acid, isophthalic acid, diphenic acid, ubido acid, 2-methyl terephthalic acid, 4-methyl phthalic acid, and naphthalenedicarboxylic acid.

      The glycol component is preferably ethylene glycol, and the aromatic dicarboxylic acid component is preferably terephthalic acid or isophthalic acid because a sizing agent having an excellent balance between bundling properties and spreadability can be obtained. Therefore, as a polyol containing an aromatic ester, bis (2-hydroxyethyl) terephthalate or bis (2-hydroxyethyl) isophthalate which is a condensate thereof is preferable.

  Moreover, other glycol, aromatic carboxylic acid, and its dehydration | condensation condensate can be contained in the range which does not impair the handleability, bundling property, and fiber opening property of a sizing agent. Such compounds include, for example, the glycols and aromatic carboxylic acid components that can be used to obtain polyols containing aromatic esters.

As described above, it is important that the aromatic ester unit constituting the present invention is composed of bis (2-hydroxyethyl) terephthalate or bis (2-hydroxyethyl) isophthalate. "Consisting of bis (2-hydroxyethyl) terephthalate or bis (2-hydroxyethyl) isophthalate" means that the aromatic ester component is 90% by mass or more of the total aromatic ester component. .

  The aromatic diisocyanate in the present invention means a diisocyanate containing an aromatic ring in the structure, and constitutes an aromatic urethane unit by condensation. Aromatic diisocyanates include phenyl diisocyanate, methylene diphenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, and the like. Tolylene diisocyanate is preferred because a film having more flexibility and toughness can be obtained.

  As described above, the aromatic urethane unit constituting the present invention is preferably composed of tolylene diisocyanate. However, the term “consisting of tolylene diisocyanate” described here means that the tolylene diisocyanate is a wholly aromatic diisocyanate. It means 90% by mass or more of the component.

  In order to achieve both convergence and spreadability of the carbon fiber bundle, the composition ratio of the polyoxyalkylene unit, aromatic ester unit, and aromatic urethane unit, which are components constituting the polyurethane resin, is important. The polyoxyalkylene unit imparts hydrophilicity to the sizing agent and improves the opening property of the carbon fiber bundle to the aqueous dispersion medium. The polyoxyalkylene unit needs to be contained in an amount of 73 to 98% by mass with respect to the total mass of each unit. If it is less than this lower limit, the sizing agent is insufficient in hydrophilicity, so that the dispersion of the sizing agent itself cannot be produced, or the fiber-opening property in the aqueous dispersion medium is not sufficient. Further, when this upper limit is exceeded, the handleability and convergence are insufficient. Preferably it is 85-97 mass%, More preferably, it is 89-94 mass%.

  The aromatic ester unit improves the heat resistance and bundling properties of the carbon fiber bundle. An aromatic ester unit needs to contain 0.5-15 mass% with respect to the total mass of each unit. If it is less than this lower limit value, the heat resistance of the carbon fiber bundle is lowered and the process passability is affected, or the convergence is lowered. On the other hand, if this upper limit is exceeded, the hydrophilicity of the sizing agent will be insufficient, and sufficient openability will not be exhibited. Preferably it is 0.8-9 mass%, More preferably, it is 3-6 mass%.

  The aromatic urethane unit makes the film formed on the surface of the carbon fiber flexible and tough, and improves handling and focusing. An aromatic urethane unit needs to contain 1.5-10 mass% with respect to the total mass of each unit. If it is less than this lower limit, the flexibility and toughness of the sizing agent are lost, the film becomes brittle, and the handleability and convergence are lowered. If this upper limit is exceeded, the hydrophilicity of the sizing agent will be insufficient, and sufficient openability will not be exhibited. Preferably it is 2.3-6.5 mass%, More preferably, it is 3-5 mass%.

Thus, in order for the carbon fiber bundle to exhibit good handling properties, bundling properties, and fiber opening properties, it is important that the polyoxyalkylene unit, the aromatic ester unit, and the aromatic urethane unit are included in a specific ratio. It is. About the composition ratio of these units, it can measure from the absorption wavelength and intensity | strength of IR spectrum, for example besides the weight ratio of a raw material. For example, the polyoxyalkylene unit is 1070 to 1150 cm ⁻¹ (C—O—C stretch), the aromatic ester unit is 1717 to 1750 cm ⁻¹ (ester C═O stretch), and the aromatic urethane unit is 1690 to 1720 cm ^{−. 1} (urethane C = O expansion / contraction) shows a characteristic absorption, and the composition ratio of the polyoxyalkylene unit, the aromatic ester unit and the aromatic urethane unit can be known from the absorption rate and the like.

  The constituent component of the polyurethane resin used for the sizing agent of the present invention may contain a small amount of other units as long as the object of the present invention is not impaired. Examples of other units include polyamines such as low molecular weight alkylene glycol, cyclohexanediol, and hexamethylenediamine.

  The sizing agent in this invention can be manufactured with the following method, for example. That is, dicarboxylic acid and alkylene glycol are heated and dehydrated to form a polyol containing an aromatic ester. After adding polyalkylene glycol and cooling to an appropriate temperature, diisocyanate is added and polyaddition ( It can be obtained by proceeding the addition polymerization reaction.

  In the present invention, the adhesion amount of the sizing agent to the carbon fiber is in the range of 0.5 to 7% by mass with respect to 100% by mass of the carbon fiber bundle from the viewpoint of the balance between the bundling property and the spreadability. is important. When the adhesion amount is less than this lower limit, film formation becomes insufficient, and the converging property and opening property of the carbon fiber bundle are insufficient. On the other hand, when the upper limit is exceeded, the fiber bundle is hard and the handleability is insufficient, and the cost is disadvantageous. Preferably it is 1-5 mass%, More preferably, it is 1.2-3 mass%.

  The sizing agent of the present invention includes an antifoaming agent, an emulsifier, an antiseptic, a slime inhibitor, a crosslinking agent, an antioxidant, a heat stabilizer, an epoxy resin, an acrylic resin, and various kinds of materials, as long as the object of the present invention is not impaired. You may contain components, such as a thermoplastic resin. Moreover, a well-known sizing agent can also be added.

  Carbon fiber sizing treatment is usually performed by immersing a continuous carbon fiber bundle in a solution or dispersion liquid (sizing liquid) of a sizing agent in an aqueous medium, or dripping, spraying or spraying the sizing liquid onto the carbon fiber, and then drying the dispersion medium.・ We do by removing.

  In the carbon fiber bundle of the present invention, when the drying temperature is 180 ° C. or higher, the convergence property and the fiber opening property are more excellent. The reason is not clear, but it is considered that the sizing agent from which volatile components have been removed exhibits fluidity and uniformly coats the fibers. In order to raise the temperature of a drying process, the sizing agent needs to contain the aromatic ester unit. The aromatic ester unit improves the heat resistance of the sizing agent and suppresses thermal decomposition in the drying process. When the aromatic ester unit is not included, the thermal decomposition of the sizing agent proceeds, and unevenness is formed in the formation of the film, so that the convergence property and the fiber opening property are lowered.

  The heat resistance of the sizing agent can be determined by measuring the thermal weight loss (TG) of the pure sizing agent. The thermogravimetric measurement is a measurement of a change in weight when a sample is allowed to stand under a specific temperature condition. If the heat resistance is insufficient and thermal decomposition proceeds, the weight loss increases. When the thermal weight reduction of the sizing agent at 230 ° C. for 15 minutes is 30% or less, thermal decomposition is suppressed even in the temperature range of the drying step, and higher convergence can be obtained.

  When the carbon fiber bundle of the present invention is used in a papermaking process, the roving, which is a continuous fiber to which the sizing agent is attached, is a chopped fiber cut with a known cutting machine such as a guillotine cutter. Although the length of this chopped fiber is not specifically limited, It is preferable to cut to about 1-20 mm. By making the cut length within this range, it is possible to obtain a base material excellent in the balance of paper processability, mechanical properties and conductive properties.

  In addition, the sizing agent used in the present invention can maintain the openability even when the concentration of carbon fibers in the aqueous dispersion medium is increased, and can prevent re-aggregation of single fibers once dispersed. It is considered that the excellent opening property is exhibited because the sizing agent has a high affinity for the aqueous dispersion medium and also has an excellent affinity for the carbon fiber. That is, the hydrophilicity of the polyoxyalkylene unit and the aromatic ester can be obtained by configuring the polyurethane resin in an appropriate ratio of the hydrophilic polyoxyalkylene unit and the hydrophobic aromatic ester unit and aromatic urethane unit. In addition, the balance of the affinity of the aromatic urethane unit to the carbon fiber is well controlled, and it is considered that an excellent opening property is expressed.

  Since the carbon fiber bundle to which the sizing agent of the present invention is attached is excellent in bundling property and spreadability in an aqueous dispersion medium, a carbon fiber sheet uniformly dispersed at a single fiber level can be obtained by a papermaking process. . This carbon fiber sheet can be suitably used for an electrode material, a planar heating element, a static electricity removing sheet, and the like. In addition, a carbon fiber composite material having excellent mechanical characteristics and conductive characteristics can be produced using a known resin as a base material.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, the following Example does not restrict | limit this invention.

  The measurement method of various characteristics of the carbon fiber used in the description of the present invention is as follows.

(1) Adhering amount of sizing agent About 5 g of carbon fiber to which the sizing agent was attached was collected and put into a heat-resistant container. Next, this container was dried at 120 ° C. for 3 hours, cooled to room temperature while taking care not to absorb moisture, and the weight of the weighed carbon fiber was set to W ₁ (g). Subsequently, the entire container was placed in a nitrogen atmosphere at 450 ° C. After heating for 15 minutes, the mixture was cooled to room temperature while taking care not to absorb moisture, and the weight of the weighed carbon fiber was defined as W ₂ (g). Through the above treatment, the amount of the sizing agent attached to the carbon fiber was determined by the following equation.
Adhering amount (% by weight) = 100 × {(W ₁ −W ₂ ) / W ₂ }.

(2) Evaluation of convergence The carbon fiber bundle is cut and about 70 g of chopped fibers [weighing value M (g)] is collected and put into a 500 ml graduated cylinder. Next, the graduated cylinder is inserted into a rubber sheet having a thickness of 4 mm. Then, after tapping treatment from a height of 2.54 cm to 60 times, the volume V (mL) of the chopped fiber in the graduated cylinder was read. Through this treatment, the filling bulk density was determined by the following equation.
D: Filled bulk density D = M / V
The number of measurements was three, and the average bulk density obtained by dividing the filling bulk density by the number of measurements was evaluated in four stages A to D. A to C are acceptable and D is unacceptable.
A: The average bulk density is 0.4 or more.
B: The average bulk density is 0.3 or more and less than 0.4.
C: The average bulk density is 0.25 or more and less than 0.3.
D: The average bulk density is less than 0.25.

(3) Evaluation of spreadability (A) Evaluation of spreadability (normal)
0.05 g of chopped fiber cut to a length of 6 mm is put into 300 mL of water, stirred gently for 20 seconds, and then allowed to stand for 20 seconds. The dispersion state of the carbon fibers was visually observed, and the spreadability was evaluated in four stages A to D. A to B are acceptable and C to D are unacceptable.
A: The number of unopened bundles is less than one.
B: The number of unopened bundles is 1 or more and less than 5.
C: The number of unopened bundles is 5 or more and less than 10.
D: The number of unopened bundles is 10 or more.

(B) Opening evaluation (high concentration)
2 g of chopped fiber cut to a length of 6 mm is put into a container with a diameter of 150 mm containing 1000 mL of water, stirred gently for 60 seconds, and then allowed to stand for 60 seconds. Water was filtered off and three small pieces of 2 cm × 2 cm were cut out from the obtained sheet-like carbon fiber, and the number of unopened bundles was measured by microscopic observation. Observation was performed on both the front and back sides of the small piece, and the spreadability was evaluated in four stages A to D from the total number of unopened bundles. A to C are acceptable and D is unacceptable.
A: The number of unopened bundles is less than two.
B: The number of unopened bundles is 2 or more and less than 5.
C: The number of unopened bundles is 5 or more and less than 10.
D: The number of unopened bundles is 10 or more.

(4) Heat resistance evaluation (thermal weight reduction)
Using a pan-type differential differential thermal balance (TG-DTA), a thermogravimetric measurement was performed at 230 ° C. in an air atmosphere for 30 mg of a pure sizing agent, and TG% after 15 minutes was measured. From the weight reduction ratio, the heat resistance was evaluated in five stages of A to D. Insufficient heat resistance is not preferable in terms of safety and environment, as well as a decrease in processability associated with the generation of pyrolyzate and a decrease in the convergence of the carbon fiber bundle.
A: Thermal weight loss is 10% or less.
B: Thermal weight loss is more than 10% and 20% or less.
C: Thermal weight loss is more than 20% and 30% or less.
D: Thermal weight loss exceeds 30%.

Reference Example 1 Preparation of Sizing Agent Aqueous Solution (a-1) 2 mol of ethylene glycol and 1 mol of terephthalic acid were heated and stirred at 180 ° C., and dehydrated and condensed until the acid value became 1 or less. ) (BHET) was obtained.

  Heat 96.2 parts by weight of polyethylene glycol (PEG) (weight average molecular weight 6200) and 0.99 parts by weight of BHET to 120 ° C., add 2.86 parts by weight of tolylene diisocyanate (TDI), and stir the alkylene glycol / An aromatic ester / aromatic urethane polyaddition product was obtained.

  The obtained polyaddition product was diluted with water to a concentration of 10% to obtain an aqueous sizing agent solution (a-1).

Reference Example 2 Preparation of Sizing Agent Aqueous Solution (a-2) Same as Reference Example 1 except that 93.7 parts by weight of PEG (weight average molecular weight 6200), 2.56 parts by weight of BHET, and 3.72 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-2) was obtained.

Reference Example 3 Preparation of Sizing Agent Aqueous Solution (a-3) Same as Reference Example 1 except that 89.2 parts by weight of PEG (weight average molecular weight 6200), 5.49 parts by weight of BHET, and 5.31 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-3) was obtained.

Reference Example 4 Preparation of Sizing Agent Aqueous Solution (a-4) Same as Reference Example 1 except that 85.1 parts by weight of PEG (weight average molecular weight 6200), 8.14 parts by weight of BHET, and 6.76 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-4) was obtained.

Reference Example 5 Preparation of Sizing Agent Aqueous Solution (a-5) Same as Reference Example 1 except that 96.6 parts by weight of PEG (weight average molecular weight 7000), 0.88 parts by weight of BHET, and 2.55 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-5) was obtained.

Reference Example 6 Preparation of Sizing Agent Aqueous Solution (a-6) Same as Reference Example 1 except that 90.3 parts by weight of PEG (weight average molecular weight 7000), 4.92 parts by weight of BHET, and 4.76 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-6) was obtained.

Reference Example 7 Preparation of Sizing Agent Aqueous Solution (a-7) Same as Reference Example 1 except that 80.0 parts by weight of PEG (weight average molecular weight 7000), 11.62 parts by weight of BHET, and 8.43 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-7) was obtained.

Reference Example 8 Preparation of Sizing Agent Aqueous Solution (a-8) Same as Reference Example 1 except that 97.6 parts by weight of PEG (weight average molecular weight 10,000), 0.62 parts by weight of BHET, and 1.80 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-8) was obtained.

Reference Example 9 Preparation of Sizing Agent Aqueous Solution (a-9) Same as Reference Example 1 except that 93.0 parts by weight of PEG (weight average molecular weight 10,000), 3.55 parts by weight of BHET, and 3.43 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-9) was obtained.

Reference Example 10 Preparation of Sizing Agent Aqueous Solution (a-10) Same as Reference Example 1 except that 90.2 parts by weight of PEG (weight average molecular weight 10,000), 5.35 parts by weight of BHET, and 4.44 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-10) was obtained.

Reference Example 11 Preparation of Sizing Agent Aqueous Solution (a-11) Same as Reference Example 1 except that 85.1 parts by weight of PEG (weight average molecular weight 10,000), 8.65 parts by weight of BHET, and 6.28 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-11) was obtained.

Reference Example 12 Preparation of Sizing Agent Aqueous Solution (a-12) Same as Reference Example 1 except that 96.4 parts by weight of PEG (weight average molecular weight 20000), 1.84 parts by weight of BHET, and 1.78 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-12) was obtained.

Reference Example 13 Preparation of Sizing Agent Aqueous Solution (a-13) Same as Reference Example 1 except that 91.9 parts by weight of PEG (weight average molecular weight 20000), 4.67 parts by weight of BHET, and 3.39 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-13) was obtained.

Reference Example 14 Preparation of Sizing Agent Aqueous Solution (a-14) 97.7 parts by weight of PEG (weight average molecular weight 6200) and 2.33 parts by weight of TDI were used under the same conditions as in Reference Example 1 without using BHET. By polyaddition, an aqueous sizing agent solution (a-14) was obtained.

Reference Example 15 Preparation of Sizing Agent Aqueous Solution (a-15) Same as Reference Example 1 except that 98.1 parts by weight of PEG (weight average molecular weight 10,000), 0.28 parts by weight of BHET, and 1.61 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-15) was obtained.

Reference Example 16 Preparation of Sizing Agent Aqueous Solution (a-16) Same as Reference Example 1 except that 98.8 parts by weight of PEG (weight average molecular weight 20000), 0.31 part by weight of BHET, and 0.91 part by weight of TDI were used. Thus, an aqueous sizing agent solution (a-16) was obtained.

Reference Example 17 Preparation of Sizing Agent Aqueous Solution (a-17) Same as Reference Example 1 except that 69.5 parts by weight of PEG (weight average molecular weight 4000), 17.67 parts by weight of BHET, and 12.83 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-17) was obtained.

Reference Example 18 Preparation of Sizing Agent Aqueous Solution (a-18) According to Reference Example 1 of Patent Document 1 (International Publication No. 2006/018139 Pamphlet), the number average molecular weight 600 represented by the following chemical formula (I), HLB 11.3 A surfactant (A) prepared by mixing 80 parts by weight of polyoxyethylene oleyl ether and 20 parts by weight of polyoxyethylene alkyl ether having a number average molecular weight of 1300 and HLB17 represented by the following chemical formula (II) is 20% by weight. It prepared to aqueous solution and obtained sizing agent aqueous solution (a-18).
_{C 18 H 35 O- (CH 2} CH 2 O) 8 -H (I)
_{C 12 H 25 O- (CH 2} CH 2 O) 25 -H (II).

Reference Example 19 Preparation of Sizing Agent Aqueous Solution (a-19) Same as Reference Example 1 except that 89.0 parts by weight of PEG (weight average molecular weight 2000), 2.8 parts by weight of BHET, and 8.2 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-19) was obtained.

Reference Example 20 Preparation of Sizing Agent Aqueous Solution (a-20) Same as Reference Example 1 except that 94.2 parts by weight of PEG (weight average molecular weight 4000), 1.5 parts by weight of BHET, and 4.3 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-20) was obtained.

Reference Example 21 Preparation of Sizing Agent Aqueous Solution (a-21) Same as Reference Example 1 except that 90.6 parts by weight of PEG (weight average molecular weight 4000), 3.8 parts by weight of BHET, and 5.6 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-21) was obtained.

Reference Example 22 Preparation of Sizing Agent Aqueous Solution (a-22) Same as Reference Example 1 except that 93.6 parts by weight of PEG (weight average molecular weight 25750), 3.7 parts by weight of BHET, and 2.7 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-22) was obtained.

Reference Example 23 Preparation of Sizing Agent Aqueous Solution (a-23) Same as Reference Example 1 except that 87.2 parts by weight of PEG (weight average molecular weight 25750), 7.8 parts by weight of BHET, and 5.0 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-23) was obtained.

Reference Example 24 Preparation of Sizing Agent Aqueous Solution (a-24) Same as Reference Example 1 except that 94.7 parts by weight of PEG (weight average molecular weight 31500), 3.1 parts by weight of BHET, and 2.2 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-24) was obtained.

Reference Example 25 Preparation of Sizing Agent Aqueous Solution (a-25) Same as Reference Example 1 except that 89.3 parts by weight of PEG (weight average molecular weight 31500), 6.5 parts by weight of BHET, and 4.2 parts by weight of TDI were used. Thus, an aqueous sizing agent solution (a-25) was obtained.

Reference Example 26 Preparation of Sizing Agent Aqueous Solution (a-26) 96.2 parts by weight of polypropylene glycol (PPG) (weight average molecular weight 6200) was used instead of PEG, and 0.99 parts by weight of BHET and 2.86 parts by weight of TDI were used. A sizing agent aqueous solution (a-26) was obtained in the same manner as in Reference Example 1 except that it was used.

Reference Example 27 Preparation of Sizing Agent Aqueous Solution (a-27) 6.62 parts by weight of methylenediphenylene diisocyanate (MDI) was used instead of TDI, 88.2 parts by weight of PEG (weight average molecular weight 10,000), 5.23 parts by weight of BHET Except having used the part, it carried out similarly to the reference example 1, and obtained sizing agent aqueous solution (a-27).

Reference Example 28 Preparation of Sizing Agent Aqueous Solution (a-28) 2 mol of ethylene glycol and 1 mol of isophthalic acid were heated and stirred at 180 ° C., and dehydrated and condensed until the acid value was 1 or less, to give bis (2-hydroxyethyl isophthalate). ) (MBHET).

Heat 92.5 parts by weight of polyethylene glycol (PEG) (weight average molecular weight 10,000) and 5.35 parts by weight of mBHET to 120 ° C., add 4.44 parts by weight of tolylene diisocyanate (TDI), and stir the alkylene glycol / An aromatic ester / aromatic urethane polyaddition product was obtained.
The obtained polyaddition product was diluted with water to a concentration of 10% to obtain an aqueous sizing agent solution (a-28).

Example 1
A continuous bundle of carbon fibers (T700S-12K manufactured by Toray Industries, Inc.) was immersed in an aqueous solution prepared by adjusting the aqueous sizing agent solution (a-1) of Reference Example 1 to a concentration of 3.5%, and the sizing agent was adhered thereto, and a hot air dryer was used. For 1 minute at 210 ° C. The obtained carbon fiber bundle to which the sizing agent was adhered was cut into a length of 6 mm to obtain chopped fibers. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 2
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-2) of Reference Example 2 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 3
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-3) of Reference Example 3 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 4
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-4) of Reference Example 4 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 5
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-5) of Reference Example 5 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 6
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-6) of Reference Example 6 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 7
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-7) of Reference Example 7 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 8
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-8) of Reference Example 8 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 9
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-9) of Reference Example 9 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 10
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-10) of Reference Example 10 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 11
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-11) of Reference Example 11 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 12
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-12) of Reference Example 12 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 13
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-13) of Reference Example 13 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 14
Chopped fibers were obtained in the same manner as in Example 1 except that the sizing agent aqueous solution (a-10) in Reference Example 10 was adjusted to a concentration of 2.0%. The adhesion amount of the sizing agent was 1.5% by mass. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 15
A chopped fiber was obtained in the same manner as in Example 1 except that the concentration of the aqueous sizing agent solution (a-10) in Reference Example 10 was adjusted to 1.2%. The adhesion amount of the sizing agent was 0.8% by mass. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 16
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-19) of Reference Example 19 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 17
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-20) of Reference Example 20 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 18
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-21) of Reference Example 21 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 19
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-22) of Reference Example 22 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle was slightly hard, but bobbin winding was possible. Also, there was no problem with fluff. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 20
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-23) of Reference Example 23 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle was slightly hard, but bobbin winding was possible. Also, there was no problem with fluff. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 21
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-24) of Reference Example 24 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle was slightly hard, but bobbin winding was possible. Also, there was no problem with fluff. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 22
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-25) of Reference Example 25 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle was slightly hard, but bobbin winding was possible. Also, there was no problem with fluff. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 23
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-26) of Reference Example 26 was used as the sizing agent aqueous solution. Although the obtained carbon fiber bundle was hard, bobbin winding was possible. Also, there was no problem with fluff. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 24
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-27) of Reference Example 27 was used as the sizing agent aqueous solution. Although the obtained carbon fiber bundle was hard, bobbin winding was possible. Also, there was no problem with fluff. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Example 25
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-28) of Reference Example 28 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. Also, there was no problem with fluff. The properties of the obtained carbon fiber bundles are summarized in Table 1.

Comparative Example 1
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-14) of Reference Example 14 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle was slightly hard and difficult to wind up the bobbin, but could be handled. The properties of the obtained carbon fiber bundle are summarized in Table 2. Due to the absence of BHET, the openability when the bulk density of carbon fiber bundles and the concentration of carbon fiber bundles were increased was insufficient.

Comparative Example 2
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-15) of Reference Example 15 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundle are summarized in Table 2. The bulk density was insufficient because the amount of the aromatic ester unit was insufficient.

Comparative Example 3
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-16) of Reference Example 16 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in the bobbin take-up property, but fluff was observed in some parts of the fiber bundle, and the handleability was lowered. The properties of the obtained carbon fiber bundle are summarized in Table 2. The bulk density was insufficient due to the insufficient amount of the aromatic ester unit and the aromatic urethane unit.

Comparative Example 4
A chopped fiber was obtained in the same manner as in Example 1 except that the sizing agent (a-17) of Reference Example 17 was used as the sizing agent aqueous solution. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundle are summarized in Table 2. The amount of the aromatic ester unit and the aromatic urethane unit was too large, so that the opening property was lowered.

Comparative Example 5
A continuous bundle of carbon fibers (T700S manufactured by Toray Industries, Inc.) was immersed in an aqueous solution in which the aqueous sizing agent solution (a-18) of Reference Example 18 was adjusted to a concentration of 3.5%, and the sizing agent was adhered thereto, and 200 Dry at 2 ° C. for 2 minutes. The obtained sizing agent-attached carbon fiber bundle was cut into a length of 6 mm to obtain chopped fibers. At this time, the adhesion amount of the sizing agent adhered to the obtained chopped fiber was 2.2% by mass. The obtained carbon fiber bundle had no problem in bobbin winding property and fluff, and was easy to handle. The properties of the obtained carbon fiber bundle are summarized in Table 2. The resulting carbon fiber bundles were inferior in opening property, and in particular, the lack of opening at a high concentration was remarkable.

Comparative Example 6
According to Example 1 of Patent Document 4 (Japanese Patent Application Laid-Open No. 2007-231441), hydrated AP-40 (manufactured by DIC, 22.5% suspension) was used as a sizing agent, and chopped fiber in the same manner as Example 1. Got. The obtained carbon fiber bundle was quite hard, but could be handled. The properties of the obtained carbon fiber bundle are summarized in Table 2. The obtained carbon fiber bundle showed almost no opening property.

Comparative Example 7
According to Example 2 of Patent Document 4 (Japanese Patent Laid-Open No. 2007-231441), chopped in the same manner as in Comparative Example 6 except that Hydran AP-30F (manufactured by DIC, 20% suspension) was used as the sizing agent. Fiber was obtained. The obtained carbon fiber bundle was quite hard, but could be handled. The properties of the obtained carbon fiber bundle are summarized in Table 2. The obtained carbon fiber bundle showed almost no opening property.

Comparative Example 8
According to Example 3 of Patent Document 4 (Japanese Patent Laid-Open No. 2007-231441), the same procedure as in Comparative Example 6 was conducted except that Hydran AP-20 (DIC, 29.5% suspension) was used as the sizing agent. To obtain chopped fibers. The obtained carbon fiber bundle was quite hard, but could be handled. The properties of the obtained carbon fiber bundle are summarized in Table 2. The obtained carbon fiber bundle showed almost no opening property.

Comparative Example 9
According to Example 4 of Patent Document 4 (Japanese Patent Laid-Open No. 2007-231441), chopped in the same manner as in Comparative Example 6 except that Hydran HW-140SF (DIC, 25% suspension) was used as the sizing agent. Fiber was obtained. The obtained carbon fiber bundle was quite hard, but could be handled. The properties of the obtained carbon fiber bundle are summarized in Table 2. The obtained carbon fiber bundle showed almost no opening property.

Comparative Example 10
A sizing agent aqueous solution was prepared in the same manner as in Reference Example 1 except that 72.6 parts by weight of PEG (weight average molecular weight 10,000), 16.62 parts by weight of BHET, and 10.73 parts by weight of TDI were used. However, since the amount of BHET was too large, the sizing agent was not dissolved in water, the sizing agent was phase-separated, and an aqueous solution could not be prepared.

  From the examples in Table 1 and the comparative examples in Table 2, the following is clear.

  That is, the sizing agent in which the polyoxyalkylene unit, aromatic ester unit, and aromatic urethane unit shown in the examples are appropriately blended has both the bulk density of the carbon fiber bundle and the opening property, and particularly carbon. Even when the concentration of the fiber bundle is increased, good opening property is exhibited. It has also been clarified that when a carbon fiber bundle having excellent heat resistance is obtained, the bulk density is also excellent.

Claims (7)

In the carbon fiber bundle comprising carbon fiber and a sizing agent, the sizing agent is composed of 73 to 98% by mass of polyoxyalkylene units, bis (2-hydroxyethyl) terephthalate or bis (2-hydroxyethyl) isophthalate. The aromatic ester unit is 0.5 to 15% by mass and the aromatic urethane unit is 1.5 to 10% by mass, and the sizing agent adheres to the carbon fiber at a rate of 0.5 to 7% by mass. Carbon fiber bundles. The carbon fiber bundle according to claim 1, wherein the aromatic urethane unit is made of tolylene diisocyanate. The carbon fiber bundle according to claim 1 or 2, wherein the sizing agent has a thermal weight loss of 30% or less at 230 ° C for 15 minutes. The carbon fiber bundle according to any one of claims 1 to 3, wherein the polyoxyalkylene unit comprises a polyalkylene glycol having a weight average molecular weight of more than 6,000 but not more than 21,000. The carbon fiber bundle according to any one of claims 1 to 4, wherein the polyoxyalkylene unit is made of polyethylene glycol. The carbon fiber bundle according to any one of claims 1 to 5 , wherein the carbon fiber bundle is composed of 1,000 to 60,000 single fibers. The carbon fiber bundle according to any one of claims 1 to 6 , wherein the carbon fiber bundle is a chopped fiber having a fiber length of 1 to 20 mm.