Chopped carbon fiber bundles and method for producing chopped carbon fiber bundles

Abstract

Provided are: chopped carbon fiber bundles which have high fluidity without decreasing the dispersibility of carbon fibers and the physical properties of a molded product; and a method for producing chopped carbon fiber bundles with high productivity. Chopped carbon fiber bundles, each of which contain a carbon fiber bundle having a total fineness of from 25,000 dtex to 45,000 dtex (inclusive) and a sizing agent in an amount of from 1% by mass to 5% by mass (inclusive) relative to the total mass of the chopped carbon fiber bundle. The length (L) of each chopped carbon fiber bundle along the fiber direction of the carbon fiber bundle is from 1 mm to 50 mm (inclusive); the ratio of the longest diameter (Dmax) to the shortest diameter (Dmin) of a cross section perpendicular to the fiber direction of each chopped carbon fiber bundle, namely Dmax/Dmin is from 6.0 to 18.0 (inclusive); and the orientation parameter of the single fibers present in the surface of each chopped carbon fiber bundle is 4.0 or less.

Claims

1. A chopped carbon fiber bundle comprising: a carbon fiber bundle having a total fineness of from 25,000 dtex to 45,000 dtex; and a sizing agent in an amount of from 1% by mass to 5% by mass relative to the total mass of the chopped carbon fiber bundle, wherein a length (L) of the chopped carbon fiber bundle along the fiber direction of the carbon fiber bundle is from 1 mm to 50 mm, a ratio (Dmax/Dmin) of the longest diameter (Dmax) and the shortest diameter (Dmin) of a cross-section perpendicular to the fiber direction of the chopped carbon fiber bundle is from 6.0 to 18.0, and an orientation parameter of single fibers present at the surface of the chopped carbon fiber bundle is 4.0 or less.

2. The chopped carbon fiber bundle according to claim 1, wherein the ratio (L/Dmin) of the length (L) along the fiber direction of the chopped carbon fiber bundle and the shortest diameter (Dmin) of a cross-section perpendicular to the fiber direction of the chopped carbon fiber bundle is from 5 to 30.

3. The chopped carbon fiber bundle according to claim 1, wherein a bulk density of the chopped carbon fiber bundle is from 200 g/L to 650 g/L.

4. The chopped carbon fiber bundle according to claim 1, wherein the sizing agent comprises at least one thermoplastic resin selected from the group consisting of a urethane-based resin, a nylon-based resin, a modified olefin-based resin, a modified epoxy-based resin, and a water-soluble nylon-based resin.

5. The chopped carbon fiber bundle according to claim 3, wherein the sizing agent comprises at least one thermoplastic resin selected from the group consisting of a urethane-based resin, a nylon-based resin, a modified olefin-based resin, a modified epoxy-based resin, and a water-soluble nylon-based resin.

Description

EXAMPLES

(1) Hereinafter, embodiments of the present invention will be described in more detail by way of Examples, but the present invention is not intended to be limited by these Examples.

(2) (Measurement of Amount of Deposit of Sizing Agent)

(3) About 2 g of chopped carbon fiber bundles were collected, and the weight (W1) was measured. Subsequently, the carbon fiber bundles were left to stand for 15 minutes in a muffle furnace (manufactured by Yamato Scientific Co., Ltd., product name: FP410) set at a temperature of 450° C. in a nitrogen gas stream at 40 liters/min, and thus the sizing agent was completely thermally decomposed. Then, the carbon fiber bundles were transferred to a vessel in a dry nitrogen gas stream at 20 liters/min and cooled for 15 minutes, and then the carbon fiber bundles were weighed (W2). The amount of deposit of the sizing agent was determined by the following formula:
Amount of adhesion of sizing agent (wt %)=(W1−W2)/W1×100  (i)

(4) (Measurement of Cross-Sectional Shape of Chopped Carbon Fiber Bundle)

(5) Fifty fiber bundles were randomly selected from the chopped carbon fiber bundles thus obtained, and the lengths of the chopped carbon fiber bundles and the longest diameter of their cross-sections were measured using vernier calipers, while the shortest diameter of the cross-sections were measured using a flat face micrometer. The each average value of the measured values of the 50 bundles were calculated, and the length of the chopped carbon fiber bundle was designated as L, the longest diameter of the cross-section as Dmax, and the shortest diameter of the cross-section as Dmin.

(6) (Measurement of Bulk Density)

(7) 300 g of chopped carbon fiber bundles were filled in a 2-L graduated cylinder, and the graduated cylinder was subjected to light impacts. The volume after there was no more change in the volume of the chopped carbon fiber bundles was measured, and the bulk density was calculated using this volume and the weight of the chopped carbon fiber bundles.

(8) (Measurement of Orientation Parameter)

(9) The orientation parameter (degree of orientation) of the single fibers present at the surface of a chopped carbon fiber bundle was analyzed by the following method.

(10) A chopped carbon fiber bundle thus obtained was observed using an optical microscope (manufactured by Keyence Corp., DIGITAL MICROSCOPE VHX-500F) under reflected light at a magnification ratio of 200 times. For the observation, images (1600×1200 pixels) in which all the carbon fiber filaments were in focus in the image were taken using a high-resolution depth resolved imaging function. Meanwhile, when observation is made under reflected light, a carbon fiber filament appears white compared with a part without a filament.

(11) The images thus taken were analyzed by the following procedure using an image analysis software (manufactured by Mitani Corp., two-dimensional image analysis software, WinROOF).

(12) The images were binarized by defining pixels in which the luminance after gray scale conversion is brighter than the threshold value B, to be white, and pixels darker than the threshold value B to be black. The threshold value B of luminance was defined such that the luminance values of all the pixels included in an image were plotted into a histogram (frequency distribution), and then the sum of the frequencies of the cases of having a luminance lower than or equal to B and the sum of the number, and the sum of the frequencies of the cases of having a luminance higher than or equal to B were adjusted to have the same value.

(13) Furthermore, white lines (representing carbon fiber filaments) in a binarized image were assumed to be straight lines by a needle shape separation function of the image analysis software, and the coordinates of the starting points and the end points, (Xs, Ys) and (Xe, Ye), of all the white lines in the image were defined.

(14) The angle θ in degrees and the length L of each line segment were calculated from the coordinates of the starting points and the end points, (Xs, Ys) and (Xe, Ye), of the white lines obtained by the image analysis, using the following expression:
θ=ArcTan((Ys−Ye)/(Xs−Xe))+90
L=√([(Xs−Xe)].sup.2+[(Ys−Ye)].sup.2)

(15) For all of the white lines in the image, the angle θ and the length L of the line segments were calculated, and a frequency distribution at the angle θ ranging from 0° to 180° was produced by adding the lengths of the line segments included in the frequency for each degree.

(16) Next, for the frequency distribution thus obtained, the angle with the highest frequency was defined as θmax, and θnew was newly defined as follows for the value 0 of the original frequency axis of the frequency distribution.
θnew=θ+(90−θmax), provided that 0≦θ+(90−θmax)≦180
θnew=θ+(90−θmax)−180, provided that θ+(90−θmax)>180
θnew=θ+(90−θmax)+180, provided that θ+(90−θmax)<180

(17) In a frequency distribution which uses θnew on the horizontal axis, the angle with the highest frequency is 90°.

(18) Next, a frequency distribution which used θnew on the horizontal axis was fitted to the following Lorentz function:
f(x)=h/(1+[(x−u)].sup.2/w.sup.2)+b
(wherein x: variable, h: height of the peak, u: position of the peak, w: full width at half maximum of the peak, and b: height of the baseline)

(19) using the least squares method, and the parameter of the full width at half maximum thus obtained was defined as the degree of orientation.

(20) For one chopped carbon fiber bundle, three samples were collected, and microscopic photographs were taken at three sites for each sample. The average value of these values was defined as the orientation parameter (degree of orientation) of a single fiber present at the surface of the chopped carbon fiber bundle.

(21) (Evaluation of Feed Properties)

(22) 1 kg of the chopped carbon fiber bundles thus obtained were fed into a weight type screw feeder with a screw unit having a diameter of 30 mm, and the chopped carbon fiber bundles were conveyed at a rate of 15 kg per hour. When the entirety of 1 kg could be conveyed, the sample was considered to have satisfactory feed properties, when the chopped carbon fiber bundles caused bridging in the screw unit during conveyance and caused conveyance failure, the sample was considered to be unfeedable.

Example 1

(23) A carbon fiber bundle TRH50 60M (trade name, manufactured by Mitsubishi Rayon Co., Ltd., total fineness 33,000 dtex) in which 1.2% by mass of a low-viscosity epoxy A as a primary sizing agent was deposited, was used.

(24) The carbon fiber bundles were alternately passed through the scraping with plural fiber bundle-opening bars and a tow width regulating bar, and thereby the width of the carbon fibers per fineness was adjusted to 1/440 mm/tex. Thereafter, an aqueous urethane resin E as a secondary sizing agent was deposited to the carbon fiber bundles using an aqueous solution prepared to have a solid content concentration of the aqueous urethane resin E of 6.0% by weight (secondary sizing liquid).

(25) A portion of a touch roll was immersed in the secondary sizing liquid tank, and the secondary sizing liquid was applied on the roll surface by rotating the touch roll. Subsequently, the carbon fiber bundles were brought into continuous contact with the roll surface, and thereby the secondary sizing liquid was deposited to the carbon fiber bundles (touch roll system). At this time, the secondary sizing liquid was applied on both of the front surface and the back surface of the carbon fiber bundles using two touch rolls.

(26) Subsequently, the carbon fiber bundles were cut using a rotary cutter having an interval of cutting blades of 6 mm, before the secondary sizing liquid applied on the carbon fiber bundles dried up, that is, while the carbon fiber bundles were in a wet state. Thereafter, the cut carbon fiber bundles were dried by continuously introducing the carbon fiber bundles into a floor vibration type hot air drying furnace (drying temperature 200° C.), and thus chopped carbon fiber bundles were obtained.

(27) The amount of deposite of the sizing agent to the chopped carbon fiber bundles, the shape of the chopped carbon fiber bundles, the bulk density, and the orientation parameter were analyzed using the chopped carbon fiber bundles thus obtained. Furthermore, an evaluation of the feed properties of the same chopped carbon fiber bundles was carried out. The results are presented in Tables 1 and 2. Meanwhile, the details of the compositions of the various resins used as the sizing agent are presented in Tables 3 and 4. The same applies to the following Example 2 and other Examples.

Example 2

(28) Chopped carbon fiber bundles were obtained in the same manner as in Example 1, except that a water-soluble nylon resin F was used instead of the aqueous urethane resin E as the secondary sizing agent. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 1. In the same manner as in Example 1, the amount of deposit of the sizing agent to the chopped carbon fiber bundles, the cross-sectional shape, the bulk density, and the orientation parameter were analyzed. Furthermore, an evaluation of the feed properties of the same chopped carbon fiber bundles was carried out. The results are presented in Tables 1 and 2.

Comparative Example 1

(29) The carbon fiber bundles used in Example 1 (TRH50 60M, low viscosity epoxy A is adhered in an amount of 1.2% by mass) were subjected to twisting at a rate of 10 turns per meter. Subsequently, the carbon fiber bundles were immersed in an aqueous solution prepared by using the aqueous urethane resin E at a solid content concentration of 6.0% by weight (secondary sizing liquid), and the carbon fiber bundles were passed between nip rolls, and then were dried by bringing the carbon fiber bundles into contact with a heating roll (surface temperature 140° C.) for 10 seconds. Thus, carbon fiber bundles were obtained. The carbon fiber bundles thus obtained were cut using a rotary cutter having an interval of cutting blades of 6 mm, and thus chopped carbon fiber bundles were obtained. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 1.

Example 3

(30) Chopped carbon fiber bundles were obtained by the same method as that used in Example 2, except that the width of the carbon fibers per fineness before the secondary sizing liquid was applied to the carbon fiber bundles was adjusted to 1/230 mm/tex. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 1. The results are presented in Tables 1 and 2.

Example 4

(31) Chopped carbon fiber bundles were obtained in the same manner as in Example 3, except that a carbon fiber bundle TRW50 50L (trade name, manufactured by Mitsubishi Rayon Co., Ltd, total fiber fineness 37,000 dtex) having a low viscosity epoxy A as a primary sizing agent adhered thereto in an amount of 1.2% by mass, was used, and the aqueous urethane resin E was used as the secondary sizing agent. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 1. The results are presented in Tables 1 and 2.

Comparative Example 2

(32) Cut carbon fiber bundles were obtained were obtained by the same method as that used in Example 1, except that the width of the carbon fibers per fineness before the secondary sizing liquid was applied to the carbon fiber bundles was adjusted to 1/50 mm/tex. Subsequently, the cut carbon fiber bundles were dried by introducing the carbon fiber bundles continuously to a floor vibration type hot air drying furnace (drying temperature 200° C.), and the cut carbon fiber bundles exhibited longitudinal cracks and fluffing. Thus, intended chopped carbon fiber bundles could not be obtained.

Examples 5 to 8 and Comparative Example 3

(33) Chopped carbon fiber bundles were obtained by the same method as that used in Example 1, except that the width of the carbon fibers per fineness before the secondary sizing liquid was applied to the carbon fiber bundles was adjusted as indicated in Table 1. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 1. The results are presented in Tables 1 and 2.

Comparative Example 4

(34) The carbon fiber bundles used in Example 1 (TRH50 60M, low viscosity epoxy A is adhered in an amount of 1.2% by mass) were used. The width of the carbon fibers per fineness before the secondary sizing liquid was applied to the carbon fiber bundles was adjusted to 1/130 mm/tex, and then the aqueous urethane resin E as a secondary sizing agent was deposited to the carbon fiber bundles by the same method as that used in Example 1, using an aqueous solution prepared with the aqueous urethane resin E to obtain a solid content concentration of 6.0% by weight (secondary sizing liquid). Subsequently, the carbon fiber bundles that were in a wet state were dried in a hot air drying furnace for 2 minutes at 200° C., and then the carbon fiber bundles were cut with a rotary cutter having an interval of cutting blades of 6 mm. Thus, chopped carbon fiber bundles were obtained. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 1. The results are presented in Tables 1 and 2.

Comparative Example 5

(35) Chopped carbon fiber bundles were obtained in the same manner as in Comparative Example 4, except that the width of the carbon fibers per fineness before the secondary sizing liquid was applied to the carbon fiber bundles was adjusted to 1/410 mm/tex. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 1.

Comparative Examples 6 and 7

(36) Chopped carbon fiber bundles were obtained in the same manner as in Comparative Example 1, except that the width of the carbon fibers per fineness before the secondary sizing liquid was applied to the carbon fiber bundles was adjusted as indicated in Table 1. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 1. The results are presented in Tables 1 and 2.

Comparative Example 8

(37) Carbon fiber bundles TRH50 60M (trade name, manufactured by Mitsubishi Rayon Co., Ltd., total fiber fineness 33,000 dtex) in which a medium-viscosity urethane B as a primary sizing agent was deposited in an amount of 1.2% by mass, were cut with a rotary cutter having an interval of cutting blades of 6 mm. However, fluffing occurred to a large extent at the time of cutting, and chopped carbon fiber bundles could not be produced.

Example 9

(38) Chopped carbon fiber bundles were obtained by the same method as that used in Example 1, except that the same carbon fiber bundle used in Comparative Example 8 (TRH50 60M, medium-viscosity urethane B was adhered in an amount of 1.2% by mass) was used, and the width of the carbon fibers per fineness before the secondary sizing liquid was applied to the carbon fiber bundles was adjusted to 1/100 mm/tex. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 1. The results are presented in Tables 1 and 2.

Examples 10 and 11

(39) Chopped carbon fiber bundles were obtained by the same method as that used in Example 9, except that the width of the carbon fibers per fineness before the secondary sizing liquid was applied to the carbon fiber bundles, and the amount of deposit of the secondary sizing agent were adjusted as indicated in Table 1. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 1. The results are presented in Tables 1 and 2.

Comparative Example 9

(40) Carbon fiber bundles TRH50 60M (trade name, manufactured by Mitsubishi Rayon Co., Ltd., total fiber fineness 33,000 dtex) in which a high viscosity urethane C as a primary sizing agent was deposited in an amount of 1.2% by mass, were alternately passed through the scraping with plural fiber bundle opening bars and a tow width regulating bar in an attempt to adjust the width of the carbon fibers per fineness to 1/440 mm/tex. However, fluffing occurred due to the fiber bundle opening bars and the tow width regulating bar, and chopped carbon fiber bundles could not be produced.

Comparative Example 10

(41) Carbon fiber bundles TRH50 60M (trade name, manufactured by Mitsubishi Rayon Co., Ltd., total fiber fineness 33,000 dtex) in which a high viscosity epoxy D as a primary sizing agent was deposited in an amount of 1.2% by mass, were alternately passed through the scraping with plural fiber bundle opening bars and a tow width regulating bar in an attempt to adjust the width of the carbon fibers per fineness to 1/440 mm/tex. However, fluffing occurred due to the fiber bundle opening bars and the tow width regulating bar, and chopped carbon fiber bundles could not be produced.

Comparative Example 11

(42) Chopped carbon fiber bundles were obtained by the same method as that used in Example 1, except that the carbon fiber bundles used in Comparative Example 10 (TRH50 60M, high viscosity epoxy D was deposited in an amount of 1.2% by mass) were used, and the width of the carbon fibers per fineness before the secondary sizing liquid was applied to the carbon fiber bundles was adjusted to 1/600 mm/tex. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 1. The results are presented in Tables 1 and 2.

Example 12

(43) Chopped carbon fiber bundles were obtained in the same manner as in Example 7, except that an aqueous polyolefin resin G was used as the secondary sizing liquid. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 1. The results are presented in Tables 1 and 2.

Example 13

(44) Chopped carbon fiber bundles were obtained in the same manner as in Example 7, except that an aqueous epoxy resin H was used as the secondary sizing liquid. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 1. The results are presented in Tables 1 and 2.

(45) The chopped carbon fiber bundles of Examples had cross-sections having an appropriate flat shape, and since the single fibers that constituted the chopped carbon fiber bundles were highly oriented, even if the amount of deposit of the sizing agent was relatively low, the sizing agent was uniformly applied. Thus, chopped carbon fiber bundles having satisfactory product quality were obtained with high productivity.

(46) On the contrary, the chopped carbon fiber bundles of Comparative Example 1, Comparative Example 5, and Comparative Example 11 had cross-sections with low flatness, and since the single fibers were not oriented, the chopped carbon fiber bundles had poor handleability at the time of compound production.

(47) The chopped carbon fiber bundles of Comparative Example 3 and Comparative Example 7 had cross-sections with an appropriate flat shape; however, since the single fibers that constituted the chopped carbon fiber bundles were not oriented, fluffing easily occurred when the chopped carbon fiber bundles were rubbed with each other, and handleability was deteriorated.

(48) In the chopped carbon fiber bundles of Comparative Example 4 and Comparative Example 6, the single fibers that constituted the carbon fiber bundles were oriented; however, since the flatness of the cross-sections was low, or the flatness was excessive, the carbon fiber bundles were easily scattered and had poor handleability.

(49) The chopped carbon fiber bundles of Comparative Example 8 had cross-sections with an appropriate flat shape, and the single fibers that constituted the chopped carbon fiber bundles were oriented. However, since the amount of deposite of the sizing agent was too small, the carbon fiber bundles were easily scattered and had poor handleability.

(50) Furthermore, Comparative Example 2, Comparative Example 9, and Comparative Example 10 exhibit that if the viscosity of the primary sizing agent and the width of the carbon fiber bundles at the time of applying the sizing liquid are not adequate, chopped carbon fiber bundles cannot be produced stably.

(51) From the results described above, it was found that even if the amount of deposit of the sizing agent is relatively low, the sizing agent is uniformly applied by the present invention, and chopped carbon fiber bundles exhibiting satisfactory handleability and high productivity are obtained.

(52) TABLE-US-00001 TABLE 1 Secondary sizing agent Conditions Width of carbon fiber Amount of deposit for Raw material Primary sizing agent bundle per fineness of primary and drying carbon fiber Viscosity Amount of before application of Secondary secondary and Product (30° C., deposit secondary sizing agent sizing sizing agents cutting kind Kind Pa × s) (mass %) (mm/tex) agent (mass %) (Order) Example 1 TRH50 Low 50 1.2 1/440 Aqueous 3.2 Cut- 60M viscosity urethane ting−>hot epoxy A resin E air drying Example 2 TRH50 Low 50 1.2 1/440 Water- 3.6 Cut- 60M viscosity soluble ting−>hot epoxy A nylon air resin F drying Comparative TRH50 Low 50 1.2 1/440 Aqueous 2.6 Roll dry- Example 1 60M viscosity urethane ing−>cut- epoxy A resin E ting Example 3 TRH50 Low 50 1.2 1/230 Water- 2.5 Cut- 60M viscosity soluble ting−>hot epoxy A nylon air resin F drying Example 4 TRW50 Low 50 1.2 1/230 Aqueous 2.5 Cut- 50L viscosity urethane ting−>hot epoxy A resin E air drying Comparative TRH50 Low 50 1.2 1/50  Aqueous 2.5 Cut- Example 2 60M viscosity urethane ting−>hot epoxy A resin E air drying Example 5 TRH50 Low 50 1.2 1/100 Aqueous 2.5 Cut- 60M viscosity urethane ting−>hot epoxy A resin E air drying Example 6 TRH50 Low 50 1.2 1/130 Aqueous 2.5 Cut- 60M viscosity urethane ting−>hot epoxy A resin E air drying Example 7 TRH50 Low 50 1.2 1/230 Aqueous 2.5 Cut- 60M viscosity urethane ting−>hot epoxy A resin E air drying Example 8 TRH50 Low 50 1.2 1/400 Aqueous 2.5 Cut- 60M viscosity urethane ting−>hot epoxy A resin E air drying Comparative TRH50 Low 50 1.2 1/600 Aqueous 2.5 Cut- Example 3 60M viscosity urethane ting−>hot epoxy A resin E air drying Comparative TRH50 Low 50 1.2 1/130 Aqueous 2.5 Hot air dry- Example 4 60M viscosity urethane ing−>cut- epoxy A resin E ting Comparative TRH50 Low 50 1.2 1/400 Aqueous 2.5 Hot air dry- Example 5 60M viscosity urethane ing−>cut- epoxy A resin E ting Comparative TRH50 Low 50 1.2 1/130 Aqueous 2.5 Roll dry- Example 6 60M viscosity urethane ing−>cut- epoxy A resin E ting Comparative TRH50 Low 50 1.2 1/400 Aqueous 2.5 Roll dry- Example 7 60M viscosity urethane ing−>cut- epoxy A resin E ting Comparative TRH50 Medium 2400 0.4 No secondary sizing agent (0.4) Cut- Example 8 60M viscosity applied (1/400 mm/tex) ting−>air urethane B drying Example 9 TRH50 Medium 2400 0.4 1/100 Aqueous 1.2 Cut- 60M viscosity urethane ting−>hot urethane B resin E air drying Example 10 TRH50 Medium 2400 1.2 1/230 Aqueous 2.5 Cut- 60M viscosity urethane ting−>hot urethane B resin E air drying Example 11 TRH50 Medium 2400 1.2 1/230 Aqueous 5.0 Cut- 60M viscosity urethane ting−>hot urethane B resin E air drying Comparative TRH50 High 4000 1.2 Fiber bundle opening attempted at 1/440 — Example 9 60M viscosity mm/tex but fiber bundle opening was infeasible urethane C Comparative TRH50 High 4000 1.2 Fiber bundle opening attempted at 1/440 — Example 10 60M viscosity mm/tex but fiber bundle opening was infeasible epoxy D Comparative TRH50 High 4000 1.2 1/600 Aqueous 2.5 Cut- Example 11 60M viscosity urethane ting−>hot epoxy D resin E air drying Example 12 TRH50 Low 50 1.2 1/230 Aqueous 2.5 Cut- 60M viscosity polyolefin ting−>hot epoxy A resin G air drying Example 13 TRH50 Low 50 1.2 1/230 Aqueous 2.5 Cut- 60M viscosity epoxy ting−>hot epoxy A resin H air drying

(53) TABLE-US-00002 TABLE 2 Shape of chopped carbon fibers Longest Shortest Fiber diameter of diameter of Flatness Evaluation results length cross-section cross-section ratio of Bulk L Dmax Dmin cross-section density Orientation Feed (mm) (mm) (mm) (Dmax/Dmin) L/Dmin (g/L) parameter evaluation Example 1 6.5 5.0 0.49 10.3 13.0 250 3.8 ∘ Example 2 6.5 5.1 0.54 9.4 10.8 250 3.9 ∘ Comparative 6.6 3.2 1.4 2.3 4.6 180 4.7 x Example 1 Example 3 6.5 3.51 0.37 9.4 17.6 500 2.2 ∘ Example 4 6.2 3.70 0.39 9.6 15.9 450 2.4 ∘ Comparative Longitudinal cracks occurred in carbon fiber bundles Example 2 Example 5 6.4 3.69 0.32 11.4 20.0 550 2.2 ∘ Example 6 6.4 3.82 0.34 10.8 18.8 500 2.2 ∘ Example 7 6.4 4.01 0.36 10.3 17.8 450 2.3 ∘ Example 8 6.4 3.61 0.45 8.2 14.2 400 3.8 ∘ Comparative 6.4 2.95 0.55 6.5 11.6 400 5.3 x Example 3 Comparative 6.5 3.77 0.69 5.2 9.4 250 3.8 x Example 4 Comparative 6.5 2.60 1.00 2.5 6.5 250 4.3 x Example 5 Comparative 6.6 7.03 0.37 24.0 17.8 250 3.2 x Example 6 Comparative 6.5 6.19 0.42 15.0 15.5 250 5.0 x Example 7 Comparative Fluffing occurred upon cutting and production was infeasible Example 8 Example 9 6.4 5.31 0.35 15.0 18.3 350 3.0 ∘ Example 10 6.5 3.61 0.36 10.0 18.1 500 2.4 ∘ Example 11 6.3 3.47 0.36 9.4 17.5 520 2.2 ∘ Comparative — — — — — — — — Example 9 Comparative — — — — — — — — Example 10 Comparative 6.6 2.00 0.93 2.1 7.1 350 7.0 x Example 11 Example 12 6.5 3.51 0.37 9.5 17.6 500 2.5 ∘ Example 13 6.4 3.70 0.39 9.5 16.4 450 2.7 ∘

(54) TABLE-US-00003 TABLE 3 Name Product item Low Mixture of 50 parts by mass of 60-mol ethylene oxide viscosity adduct of bisphenol A (manufactured by Matsumoto epoxy A Yushi-Seiyaku Co., Ltd.) and 50 parts by mass of 30-mol ethylene oxide adduct of bisphenol A (manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.) (viscosity at 30° C. is 50 Pa × s) Medium N320 (manufactured by DIG Corp., epoxyurethane viscosity emulsion) (viscosity at 30° C. is 2400 Pa × s) urethane B High UWS-135 viscosity (manufactured by Sanyo Chemical Industries, Ltd., urethane C aqueous urethane emulsion) (viscosity at 30° C. is 4000 Pa × s) High Mixture of 80 parts by mass of jER157S70 viscosity (manufactured by Sanyo Chemical Industries, Ltd., epoxy epoxy D resin) and 20 parts by mass of NC-723-SF (manufactured by Nippon Nyukazai Co., Ltd., surfactant) (viscosity at 30° C. is 4000 Pa × s)

(55) TABLE-US-00004 TABLE 4 Name Product item Aqueous urethane E Hydran HW-930 (manufactured by DIG Corp., aqueous urethane resin) Water-soluble Sepolsion PA150 nylon resin F (manufactured by Sumitomo Seika Chemicals Co., Ltd., nylon emulsion) Aqueous polyolefin Aptolok BW-5550 resin G (manufactured by Mitsubishi Chemical Corp., aqueous polyolefin resin emulsion) Aqueous epoxy jER W1155R55 resin H (manufactured by Mitsubishi Chemical Corp., aqueous epoxy resin emulsion)

Example 14

(56) Carbon fiber bundles that had been adjusted to a predetermined tow width by using carbon fiber bundles TRH50 60M manufactured by Mitsubishi Rayon Co., Ltd. and having a total fineness of 32,000 dtex, and alternately passing the carbon fiber bundles through the scraping with plural fiber bundle opening bars and a tow width regulating bar, were subjected to an depositing treatment using an aqueous solution prepared with HYDRAN HW-930 (aqueous urethane resin manufactured by DIC Corp.) at a solid content concentration of 6.0% by weight (sizing liquid). The depositing treatment was carried out by a touch roll system of depositing a sizing liquid to the carbon fiber bundles by immersing a portion of a roll in the sizing liquid tank, applying the sizing liquid on the roll surface, and bringing the carbon fiber bundles into contact with the roll surface. Furthermore, the depositing treatment was carried out under the condition of 4,400 dtex/mm. Regarding the touch roll, both the front and back surfaces of the carbon fiber bundles were applied using two rolls. Cutting of the carbon fiber bundles in a wet state was carried out with a rotary cutter having an interval of cutting blades of 6 mm, and the cut carbon fiber bundles were dried at 200° C. by continuously introducing the fiber bundles into a floor vibration type hot air drying furnace, and thus chopped carbon fiber bundles were obtained.

Example 15

(57) Chopped carbon fiber bundles were obtained in the same manner as in Example 14, except that SEPOLSION PA150 (nylon emulsion manufactured by Sumitomo Seika Chemicals Co., Ltd.) was used instead of HYDRAN HW-930 as the sizing agent. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 14.

Comparative Example 12

(58) Carbon fiber bundles obtained by twisting carbon fiber bundles TRH50 60M manufactured by Mitsubishi Rayon Co., Ltd. at a rate of 10 turns per meter, were immersed in an aqueous solution prepared with HYDRAN HW-930 at a solid content concentration of 6.0% by weight (sizing liquid), and the carbon fiber bundles were passed between nip rolls. Subsequently, the carbon fiber bundles were dried by bringing the fiber bundles into contact for 10 seconds with a heating roll having the surface temperature adjusted to 140° C., and thus carbon fiber bundles were obtained. The carbon fiber bundles thus obtained were cut with a rotary cutter having an interval of cutting blades of 6 mm, and thus chopped carbon fiber bundles were obtained. The chopped carbon fiber bundles thus obtained were subjected to the same analysis as that performed in Example 14.

(59) The results of the above analyses are presented in Table 5. Since the carbon fiber bundles of Examples 14 and 15 had cross-sections having a flat shape, even if the amount of deposit of the sizing agent was relatively low, the sizing agent was applied uniformly. Thus, chopped carbon fiber bundles having satisfactory product quality could be produced with high productivity.

(60) On the other hand, the chopped carbon fiber bundles of Comparative Examples that were twisted had low flatness, and thus the chopped carbon fiber bundles had a low bulk density.

(61) TABLE-US-00005 TABLE 5 Shape of chopped fibers Raw material Sizing agent Fiber Major axis Minor axis carbon fiber Amount of length Dmax of Dmin of Bulk Product adhesion L cross-section cross-section density kind Kind (wt %) (mm) (mm) (mm) Dmax/Dmin L/Dmin (g/L) Example 14 TRH50 Urethane 3.2 6.5 5 0.5 10.3 13 250 60M Example 15 TRH50 Nylon 3.6 6.5 5.1 0.6 9.4 10.8 250 60M Comparative TRH50 Urethane 2.6 6.6 3.2 1.4 2.3 4.6 180 Example 12 60M

INDUSTRIAL APPLICABILITY

(62) The chopped carbon fiber bundle of the present invention can exhibit excellent processability and handleability in a process of compounding with a matrix resin, and when the chopped carbon fiber bundle is used, a molded product having excellent mechanical characteristics is obtained. Furthermore, since the chopped carbon fiber bundle of the present invention has a flat shape, productivity for the production of chopped carbon fiber bundles is increased to a large extent.