CHOPPED CARBON FIBER BUNDLE AND METHOD FOR PRODUCING CHOPPED CARBON FIBER BUNDLE

Abstract

A chopped carbon fiber bundle comprising carbon fibers and a sizing agent, the sizing agent including a compound having a maleimide group, the compound having a maleimide group being liquid at 25° C. A method for producing a chopped carbon fiber bundle, the method comprising a step of applying an aqueous dispersion of a secondary sizing agent including a compound having a maleimide group to a long-length carbon fiber bundle including a primary sizing agent deposited thereon, in order to prepare a long-length carbon fiber bundle further including the aqueous dispersion of the secondary sizing agent, and a step of cutting the long-length carbon fiber bundle including the aqueous dispersion of the secondary sizing agent. A chopped carbon fiber bundle that has improved. heat resistance and. feedabli and that is capable of beng produced with high productivity is provided.

Claims

1. A carbon fiber bundle comprising: a bundle of single carbon fibers; and a sizing agent comprising a compound having a maleimide group that is liquid at 25° C., wherein a length of single carbon fibers is 1 to 50 mm.

2. A carbon fiber bundle comprising: a bundle of single carbon fibers; and a sizing agent comprising a compound having a maleimide group and an aliphatic hydrocarbon group having 2 or more carbon atoms, wherein a length of the single carbon fibers included is 1 to 50 mm.

3. The carbon fiber bundle according to claim 1, wherein a viscosity of the compound having a maleimide group is 100,000 mPa.Math.s or less at 25° C.

4. The carbon fiber bundle according to claim 2, wherein a viscosity of the compound having a maleimide group is 100,000 mPa.Math.s or less at 25° C.

5. The carbon fiber bundle according to claim 1, wherein the compound having a maleimide group is a compound represented by Formula m1 or m3 below, ##STR00010## wherein in Formula (m1), X.sup.1 represents a substituted or unsubstituted alicyclic hydrocarbon group having 5 to 8 carbon atoms, Q.sup.1 represents an aliphatic hydrocarbon group having 4 to 50 carbon atoms, and n represents 1 or 2, and ##STR00011## wherein in Formula (m3), Q.sup.3 and Q.sup.4 each independently represent an aliphatic hydrocarbon group having 6 to 100 carbon atoms, and X.sup.3 represents an alkylene group having 2 to 20 carbon atoms, a cycloalkylene group having 5 to 8 carbon atoms, a polyoxyalkylene group represented by —(C.sub.qH.sub.2qO).sub.t—(C.sub.rH.sub.2rO).sub.u—C.sub.sH.sub.2s— wherein q, r, and s each independently represent an integer of 2 to 6, t represents 0 or 1, and u represents an integer of 1 to 30, a divalent aromatic group having 6 to 12 carbon atoms, a group represented by—O—C.sub.6H.sub.4-Q.sup.6-C.sub.6H.sub.4—O— wherein Q.sup.6 represents —CH.sub.2—, —C(CH.sub.3).sub.2—, —CO—, —O—, —S—, or —SO.sub.2—, or a group formed as a result of 1 to 3 hydrogen atoms included in any of the above groups being replaced with a hydroxyl group.

6. The carbon fiber bundle according to claim 2, wherein the compound having a maleimide group is a compound represented by Formula m1 or m3 below, ##STR00012## wherein in Formula (m1), X.sup.1 represents a substituted or unsubstituted alicyclic hydrocarbon group having 5 to 8 carbon atoms, Q.sup.1 represents an aliphatic hydrocarbon group having 4 to 50 carbon atoms, and n represents 1 or 2, and ##STR00013## wherein in Formula (m3), Q.sup.3 and Q.sup.4 each independently represent an aliphatic hydrocarbon group having 6 to 100 carbon atoms, and X.sup.3 represents an alkylene group having 2 to 20 carbon atoms, a cycloalkylene group having 5 to 8 carbon atoms, a polyoxyalkylene group represented by —(C.sub.qH.sub.2qO).sub.t—(C.sub.rH.sub.2rO).sub.u—C.sub.sH.sub.2s— wherein q, r, and s each independently represent an integer of 2 to 6, t represents 0 or 1, and u represents an integer of 1 to 30, a divalent aromatic group having 6 to 12 carbon atoms, a group represented by—O—C.sub.6H.sub.4-Q.sup.6-C.sub.6H.sub.4—O— wherein Q.sup.6 represents —CH.sub.2—, —C(CH.sub.3).sub.2—, —CO—, —O—, —S—, or —SO.sub.2—, or a group formed as a result of 1 to 3 hydrogen atoms included in any of the above groups being replaced with a hydroxyl group.

7. The carbon fiber bundle according to claim 1, which has a bulk density of 200 g/L or more.

8. The carbon fiber bundle according to claim 2, which has a bulk density of 200 g/L or more.

9. The carbon fiber bundle according to claim 1, which has a bulk density of 600 g/L or less.

10. The carbon fiber bundle according to claim 2, which has a bulk density of 600 g/L or less.

11. The carbon fiber bundle according to claim 1, wherein the compound having a maleimide group has an aliphatic group having 5 or more carbon atoms.

12. The carbon fiber bundle according to claim 2, wherein the compound having a maleimide group has an aliphatic group having 5 or more carbon atoms.

13. A carbon fiber bundle comprising: a bundle of single carbon fibers; and a sizing agent comprising a compound having a maleimide group with a viscosity of 100,000 mPa.Math.s or less at 25° C., wherein a length of the single carbon fibers is 1 to 50 mm.

14. The carbon fiber bundle according to claim 13, which has a bulk density of 200 g/L or more.

15. The carbon fiber bundle according to claim 13, wherein the compound having a maleimide group has an aliphatic group having 5 or more carbon atoms.

16. A carbon fiber bundle comprising: a bundle of single carbon fibers; and greater than zero to 10% by mass of a compound having a maleimide group and an aliphatic hydrocarbon group having 2 or more carbon atoms, wherein a length of the single carbon fibers is 1 to 50 mm.

17. The carbon fiber bundle according to claim 16, which has a bulk density of 200 g/L or more.

18. The carbon fiber bundle according to claim 16, wherein the compound having a maleimide group has an aliphatic group having 5 or more carbon atoms.

19. A pellet comprising: the carbon fiber bundle according to claim 1; and a matrix resin.

20. A pellet comprising: the carbon fiber bundle according to claim 2; and a matrix resin.

Description

EXAMPLES

[0144] The present invention is described further specifically with reference to Examples below. The present invention is not limited by the description below.

[Raw Materials for Sizing Agent]

[0145] Table 1 lists the raw materials used for preparing sizing agents in Examples and Comparative Examples below.

TABLE-US-00001 TABLE 1 Category Product name Substance Available from Compound having BMI-689 Bismaleimide resin that is liquid at 25° C. Designer Molecules Inc. maleimide group BMI-1700 Bismaleimide resin that is liquid at 25° C. Designer Molecules Inc. BMI-2300 Bismaleimide resin that is solid at 25° C. Daiwa Kasei Industry Co., Ltd. Compound having jER1004 Bisphenol-A-type epoxy resin that is solid Mitsubishi Chemical epoxy group at 25° C. Corporation jER1001 Bisphenol-A-type epoxy resin that is solid Mitsubishi Chemical at 25° C. Corporation jER828 Bisphenol-A-type epoxy resin that is liquid Mitsubishi Chemical at 25° C. Corporation Surfactant ADEKA Polyoxyethylene-polyoxypropylene condensate ADEKA Corporation Pluronic F-88 (nonionic surfactant) HITENOL Polyoxyethylene polycyclic phenyl ether DKS Co. Ltd. NF-17 ammonium sulfate (anionic surfactant)

[0146] The molecular weight, viscosity, and structural formula of each of the compounds having a maleimide group which were used in Examples are described below.

<BM1-689>

[0147] Molecular weight: 689

[0148] Viscosity at 25° C.: 1500 mPa.Math.s

##STR00008##

[0149] (The aliphatic skeleton contains unsaturated bond in molecule)

<BMI-1700>

[0150] Molecular weight: 1715

[0151] Viscosity at 25° C.: 37500 mPa.Math.s

##STR00009##

[Measurement and Evaluation Methods]

(Measurement of Bulk Density)

[0152] In accordance with the method for measuring bulk density which is described above, 300 g of chopped carbon fiber bundles were charged in a 2-liter graduated cylinder. While an impact was given to the graduated cylinder, the volume of the chopped carbon fiber bundles at which the volume remained unchanged was measured. The bulk density of the chopped carbon fiber bundles was calculated on the basis of the above volume and the weight of the chopped carbon fiber bundles.

(Evaluation of Feed Property)

[0153] Into a gravimetric screw feeder including a screw having a diameter of 30 mm, 1 kg of the chopped carbon fiber bundles were charged through a hopper. While the chopped carbon fiber bundles were transported at a rate of 15 kg per hour, the feed property was determined in accordance with the following criteria.

[0154] ◯: The whole amount (1 kg) of chopped carbon fiber bundles could be transported.

[0155] Δ: The whole amount (1 kg) of chopped carbon fiber bundles could be transported, although bridging of the chopped carbon fiber bundles at the hopper was observed.

[0156] ×: Transportation failure occurred since bridging of the chopped carbon fiber bundles occurred during transportation

(Measurement of Heating Loss in Weight of Sizing Agent)

[0157] The sizing agent was subjected to a thermogravimetric analyzer Q500 (produced by TA Instruments) under the following conditions to determine a thermogravimetric curve.

[0158] Atmosphere: in nitrogen

[0159] Heating rate: 20 ° C/min

[0160] Temperature range: 30° C. to 500° C.

[0161] The mass W100 of the sizing agent at 100° C. and the mass W400 of the sizing agent at 400° C. were determined from the thermogravimetric curve. The heating loss ratio Q(%) was calculated using the following formula.

[0162] Q={(W100-W400)/W100}×100

[0163] The sizing agent used in the measurement of heating loss was a sample prepared by heating the aqueous dispersion of the secondary sizing agent prepared in each of Examples below at 110° C. for 1 hour to remove moisture. In the case where a solution of the secondary sizing agent was used, a sample prepared by performing vacuum drying at 130° C. for 1 hour to remove the solvent was used in the measurement of heating loss.

(Evaluation of Emulsifying Property)

[0164] An evaluation of “◯” was given when an aqueous dispersion of the secondary sizing agent could be prepared by phase inversion emulsification in the preparation of the aqueous dispersion in each of Examples below. An evaluation of “×” was given when the aqueous dispersion could not be prepared by phase inversion emulsification.

Production Example 1

(Preparation of Carbon Fiber Bundle on Which Primary Sizing Agent Was Deposited)

[0165] Using a homomixer, jER1001 (40 parts by mass), jER828 (40 parts by mass), ADEKA Pluronic F-88 (20 parts by mass) were stirred to form a uniform mixture while being heated at 110° C. Hereby, a primary sizing agent was prepared. While the primary sizing agent was stirred with the homomixer, ion-exchange water was added dropwise to the primary sizing agent at a rate of 20 mL per minute. After the phase inversion point had been passed, the amount of water added was increased to 100 mL per minute. Hereby, an aqueous dispersion of the primary sizing agent was prepared. The amount of the ion-exchange water added to the sizing agent was adjusted such that the concentration of the sizing agent in the dispersion liquid of the sizing agent was 30% by mass.

[0166] A long-length polyacrylonitrile carbon fiber bundle (produced by Mitsubishi Chemical Corporation, product name: PYROFIL (registered trademark) TR50S15L, number of filaments: 15000, tensile elastic modulus: 240 GPa) on which a sizing agent was not deposited was immersed in an aqueous dispersion in which the concentration of the solid component of the primary sizing agent was adjusted to 1.5% by mass and then passed through a nip roller. Subsequently, the carbon fiber bundle was brought into contact with a heating roller having a surface temperature of 140° C. for 10 seconds in order to perform drying. Hereby, a carbon fiber bundle on which the primary sizing agent had been deposited was prepared. The amount of squeezing performed by the nip roller was adjusted such that the amount of the primary sizing agent deposited was 0.2% by mass of the total mass of the primary sizing agent and the carbon fiber bundle.

Example 1

(Preparation of Aqueous Dispersion of Secondary Sizing Agent)

[0167] The raw materials listed in Table 1 were mixed with one another in the amounts (parts by mass) described in the column “Example 1” of Table 2. To the resulting mixture, 15 parts by mass of HITENOL NF-17, which is an anionic surfactant, was added. Then, stirring was performed to form a uniform mixture while heating was performed at 110° C. Hereby, a secondary sizing agent was prepared.

[0168] While the secondary sizing agent was stirred, ion-exchange water was added to the secondary sizing agent and phase inversion emulsification was performed using a homomixer. While the secondary sizing agent was stirred with the homomixer, ion-exchange water was added dropwise to the secondary sizing agent at a rate of 20 mL per minute. After the phase inversion point had been passed, the amount of water added was increased to 100 mL per minute. Hereby, a dispersion liquid of the sizing agent, which was an aqueous dispersion of the secondary sizing agent, was prepared. The amount of the ion-exchange water added to the secondary sizing agent was adjusted such that the concentration of the secondary sizing agent in the dispersion liquid of the secondary sizing agent was 30% by mass.

(Preparation of Chopped Carbon Fiber Bundle)

[0169] The carbon fiber bundle on which the primary sizing agent had been deposited was immersed in the aqueous dispersion of the secondary sizing agent, which was prepared in the above-described manner. After the carbon fiber bundle had been passed through a nip roller, the carbon fiber bundle was cut into pieces having a length of 6 mm with a roving cutter while the carbon fiber bundle was wet. The pieces of the carbon fiber bundle were dried in a hot-air drying furnace at 130° C. Hereby, chopped carbon fiber bundles were prepared. The concentration of the aqueous dispersion of the secondary sizing agent and the amount of squeezing performed by the nip roller were adjusted such that the total amount of the sizing agents deposited, that is, the total amount of the primary and secondary sizing agents deposited, was 3% by mass of the total mass of the sizing agents and the carbon fiber bundle.

[0170] Table 2 lists the results of evaluations of the secondary sizing agent and the chopped carbon fiber bundles.

Examples 2 to 5 and Comparative Example 1

[0171] An aqueous dispersion of the secondary sizing agent and chopped carbon fiber bundles were prepared as in Example 1, except that the raw materials listed in Table 1 were mixed with one another in the amounts (parts by mass) described in Table 2 to prepare a secondary sizing agent.

[0172] Table 2 lists the results of evaluations of the secondary sizing agent and the chopped carbon fiber bundles.

Reference Example 1

(Preparation of Aqueous Dispersion of Secondary Sizing Agent)

[0173] The raw materials listed in Table 1 were mixed with one another in the amounts (parts by mass) described in the column “Reference Example 1” of Table 2. To the resulting mixture, 15 parts by mass of HITENOL NF-17, which is a surfactant, was added. Then, stirring was performed while heating was performed at 110° C. Hereby, a secondary sizing agent was prepared. However, the resins and surfactant used as raw materials could not be mixed with one another.

[0174] While the secondary sizing agent was stirred with a homomixer, ion-exchange water was added dropwise to the secondary sizing agent at a rate of 20 mL per minute. However, the phase inversion point was not passed, and an aqueous dispersion could not be formed since the water and resin phases were separated from each other.

[0175] Since an aqueous dispersion could not be prepared, a solution of the secondary sizing agent was prepared in the following manner.

(Preparation of Solution of Secondary Sizing Agent)

[0176] The raw materials listed in Table 1 were mixed with one another in the amounts (parts by mass) described in the column “Reference Example 1” of Table 2 to prepare a secondary sizing agent. N-methyl-2-pyrrolidone was added to the secondary sizing agent to form a solution. Hereby, a solution of the secondary sizing agent was prepared. The amount of the N-methyl-2-pyrrolidone added to the secondary sizing agent was adjusted such that the concentration of the secondary sizing agent in the solution of the secondary sizing agent was 50% by mass.

(Preparation of Chopped Carbon Fiber Bundle)

[0177] The carbon fiber bundle on which the primary sizing agent had been deposited was immersed in the solution of the secondary sizing agent, which was prepared in the above-described manner. After the carbon fiber bundle had been passed through a nip roller, the carbon fiber bundle was cut into pieces having a length of 6 mm with a roving cutter while the carbon fiber bundle was wet. The pieces of the carbon fiber bundle were dried in a hot-air drying furnace at 180° C. Hereby, chopped carbon fiber bundles were prepared. The concentration of the solution of the secondary sizing agent and the amount of squeezing performed by the nip roller were adjusted such that the total amount of the sizing agents deposited, that is, the total amount of the primary and secondary sizing agents deposited, was 3% by mass of the total mass of the sizing agents and the carbon fiber bundle.

[0178] Table 2 lists the results of evaluations of the secondary sizing agent and the chopped carbon fiber bundles.

TABLE-US-00002 TABLE 2 Reference Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 1 Example 1 Secondary Maleimide BMI-689 15 30 45 65 sizing agent resin BMI-1700 30 (mass part) BMI-2300 30 Epoxy jER1004 70 55 40 20 55 55 50 resin jER828 35 Heating loss ratio of secondary 11.1 10.8 10.5 10.2 10.6 4.1 39.5 sizing agent, Q (%) Bulk density of chopped carbon 560 520 470 350 550 510 450 fiber bundle (g/L) Emulsifying property ◯ ◯ ◯ ◯ ◯ X ◯ Feed property ◯ ◯ ◯ Δ ◯ ◯ ◯

[0179] In any of Examples 1 to 5, the heating loss ratio Q of the sizing agent was low. Thus, it is considered that the chopped carbon fiber bundle had excellent heat resistance. In Examples 1 to 3 and 5, suitable results were obtained also in terms of feed property. In Reference Example 1, the emulsifying property was poor, although the heat resistance and feed property were good.

[0180] In Comparative Example 1, the heating loss ratio of the sizing agent was high. Thus, it is considered that heat resistance was poor.

[0181] Although the present invention has been described in detail with reference to specific aspects, it is apparent to a person skilled in the art that various alterations and modifications can be made therein without departing from the spirit and scope of the present invention.