WO2020080238A1 - Carbon fiber bundle, carbon fiber bundle production method, and sheet molding compound production method - Google Patents

Abstract

Provided is a carbon fiber bundle for which it is possible to establish both excellent chop-ability during chopping and fiber separation and which can be used favorably particularly in production of SMC. This carbon fiber bundle comprises multiple subtows and the overlap rate P calculated by a specified formula is 5-80%.

Description

Carbon fiber bundle, method for producing carbon fiber bundle, and method for producing sheet molding compound

The present invention relates to a carbon fiber bundle, a method for producing a carbon fiber bundle, and a method for producing a sheet molding compound.
The present application claims priority based on Japanese Patent Application No. 2018-197594 filed in Japan on October 19, 2018, the contents of which are incorporated herein by reference.

▽ Carbon fiber reinforced composite material obtained by molding a molding material containing carbon fiber is widely used in various fields because of its light weight and high strength. As a molding material, a sheet molding compound using short fibers (hereinafter, also referred to as "SMC"), a prepreg using continuous fibers, and the like are known. Since SMC has excellent fluidity, it is suitable for forming a complicated shape that is difficult to form with a prepreg.

It is known that when short fibers are used, the mechanical properties of the composite material are strongly affected by the dispersion state and morphology of the short fibers in the composite material. Since carbon fiber has a relatively high manufacturing cost, a plurality of carbon fibers may be bundled to form a carbon fiber bundle. However, when the fine fiber bundles are dispersed in the composite material, the mechanical properties of the composite material are improved. Get better Therefore, it is known to use a carbon fiber bundle that includes a plurality of sub-tows and is divided and dispersed when the sub-tows are cut (cut) in the production of SMC. For example, Patent Document 1 proposes that a carbon fiber bundle obtained by winding a plurality of fiber bundles (sub-tows) on a single bobbin without aligning them and chopping them to use in the production of SMC. However, in this carbon fiber bundle, since the sub tows are not sufficiently integrated with each other, some sub tows may be separated during the production or processing of the carbon fiber bundle, and winding around a roll or the like may occur. .

By the way, a method has been proposed to improve high-order processability such as scratch resistance and chop property by attaching a sizing agent to the carbon fiber bundle. For example, Patent Document 2 proposes that a sizing agent having a specific component is applied to a carbon fiber bundle to improve high-order processability.

Japanese Patent Laid-Open No. 2010-163536 Japanese Patent Laid-Open No. 2008-274520

When bundling carbon fiber bundles containing multiple sub-tows with a sizing agent, binding the sub-tows to each other with a sizing agent that provides sufficient bundling properties allows the chopped carbon fiber bundles to be separated when the carbon fiber bundles are chopped. (Chop separation property) deteriorates, and each sub tow tends not to be divided sufficiently. On the other hand, if the amount of sizing agent attached is reduced to secure the chop separation property, or if a sizing agent with low bundling property is used, the single fiber of carbon fiber in the sub-tow will be separated and entangled with other sub-tows, resulting in chop Separation properties may decrease.

The present invention can achieve both excellent chopping properties and splitting properties at the time of chopping, and a carbon fiber bundle that can be particularly preferably used for production of SMC, and excellent chopping properties and splitting properties at the time of chopping, In particular, it is an object of the present invention to provide a method for producing a carbon fiber bundle that can be suitably used for producing SMC.

The present invention has the following configurations.

[1] A carbon fiber bundle containing a plurality of sub-tows,
A carbon fiber bundle having an overlap ratio P represented by the following formula (1) of 5 to 80%.

(In the formula, Wt represents an average value (mm) of widths of the carbon fiber bundles, Wst represents an average value (mm) of widths of the respective sub tows, and n represents the number of sub tows included in the carbon fiber bundles ( Book).)
[2] The carbon fiber bundle according to [1], wherein a plurality of the sub tows are bound with a sizing agent.
[3] The carbon fiber bundle according to [1] or [2], wherein the sub tow has a mass of 100 to 1000 mg / m.
[4] The carbon fiber bundle according to any one of [1] to [3], wherein the number of filaments of the sub tow is 500 to 15,000.
[5] The carbon fiber bundle according to any one of [1] to [4], wherein the average number of times of entanglement of each of the sub tows is 20 to 50 times / m.
[6] The carbon fiber bundle according to any one of [1] to [5], wherein each of the sub tows has an average cantilever value of 110 to 300 mm.
[7] The carbon fiber bundle according to any one of [1] to [6], wherein the total number of filaments is 1000 to 120,000.
[8] The carbon fiber bundle according to any one of [1] to [7], wherein each of the sub tows is intermittently divided from an adjacent sub tow.
[9] The carbon fiber bundle according to any one of [1] to [8], which has a splitting ratio Q defined below of 20% or more.
(Proportion Q of splitting property)
A continuous carbon fiber bundle is chopped (cut) into a length of 1 inch, and 100 chopped carbon fiber bundles that do not include undivided portions of sub tows are randomly picked up with tweezers, and the mass of each is measured. From these 100 mass measurement values, the number of chopped carbon fiber bundles corresponding to the mass of the sub tow is counted, the ratio of the number is calculated, and the ratio Q of the splitting property is defined.
[10] The carbon fiber bundle according to any one of [1] to [9], which has a bulk density calculated by the following method (I) of 60 to 400 g / L or more.
(Method (I))
(Procedure I-1) 100 g of a chopped fiber bundle for test, which is obtained by cutting a carbon fiber bundle with a rotary cutter to have a fiber length of 25 mm, is filled in a 2 L graduated cylinder (cylinder having a diameter of 88 mm and a height of 485 mm).
(Procedure I-2) A load of 500 g is uniformly applied from the upper part of the test chopped fiber bundle in the graduated cylinder, and the total volume (L) of the filled test chopped carbon fiber bundle when there is no change in volume ) Is measured and the total mass (100 g) of the test chopped fiber bundle is divided by the total volume (L) of the test chopped carbon fiber bundle to calculate the bulk density.
[11] The carbon fiber bundle according to any one of [1] to [10], which is a carbon fiber bundle for a sheet molding compound.
[12] The method for producing a carbon fiber bundle according to any one of [1] to [11], which includes the following steps (a) to (d).
(A) An aqueous dispersion containing a sizing agent is placed in a dipping tank, and a carbon fiber bundle containing a plurality of sub-tows is continuously dipped and passed through the aqueous dispersion while running.
(B) While the carbon fiber bundle pulled up from the aqueous dispersion is brought into contact with the peripheral surface of the roller, air is blown to the carbon fiber bundle to remove the excess aqueous dispersion.
(C) After the step (b), the carbon fiber bundle to which the aqueous dispersion is attached is subjected to a nip treatment, and the ratio of the mass of the aqueous dispersion to the total mass of the carbon fiber bundle and the aqueous dispersion is 40 mass. % Or less.
(D) After the step (c), the carbon fiber bundle is brought into contact with a heating roller whose peripheral surface is heated to 110 to 200 ° C. to be dried.
[13] The sizing agent contains the following components (A) and (B),
The mass ratio of the content of the component (A) to the content of the component (B) (content of the component (A) / content of the component (B)) is 1 to 20,
The method for producing a carbon fiber bundle according to [12], wherein the ratio of the total content of the component (A) and the component (B) with respect to the total amount (100 mass%) of the sizing agent is 80 mass% or more.
Component (A): An epoxy resin composition having a viscosity at 30 ° C. of 500 to 120,000 Pa · s.
Component (B): an aliphatic ester compound having a freezing point of 50 ° C. or lower.
[14] A method for producing a sheet molding compound, which comprises impregnating a resin with a fiber bundle obtained by cutting the carbon fiber bundle according to any one of [1] to [11] at intervals in a longitudinal direction.

INDUSTRIAL APPLICABILITY The carbon fiber bundle of the present invention can achieve both excellent chopping properties and splitting properties at the time of chopping, and can be particularly preferably used for production of SMC.
According to the method for producing a carbon fiber bundle of the present invention, it is possible to obtain both excellent chopping properties and splitting properties at the time of chopping, and it is possible to produce a carbon fiber bundle that can be particularly suitably used for producing SMC.

It is a schematic diagram explaining the steps 1 and 2 in the measuring method of the cantilever value of a sub toe. It is a schematic diagram explaining the procedures 3 and 4 in the measuring method of the cantilever value of a sub toe. It is a perspective view explaining the overlapping rate P of the carbon fiber bundle in the carbon fiber bundle of the present invention. It is the schematic diagram which showed an example of the manufacturing apparatus used for manufacture of the carbon fiber bundle of this invention. It is the schematic diagram which showed an example of the manufacturing apparatus used for manufacture of the carbon fiber bundle of this invention. It is the schematic diagram which showed an example of the manufacturing apparatus used for manufacture of the carbon fiber bundle of this invention.

[Carbon fiber bundle]
The carbon fiber bundle of the present invention includes a plurality of sub tows. The plurality of sub tows included in the carbon fiber bundle of the present invention may be bound with a sizing agent.

(Carbon fiber bundle)
Examples of the carbon fibers forming the carbon fiber bundle include polyacrylonitrile (PAN) -based carbon fibers, rayon-based carbon fibers, pitch-based carbon fibers, and the like.
The length of the carbon fiber bundle is not particularly limited and can be appropriately set according to the application.

The carbon fiber bundle of the present invention includes a plurality of sub tows. The carbon fiber bundle containing a plurality of sub-tows may be a plurality of sub-tows produced separately may be bundled and combined, or a large tow may be divided into a plurality of sub-tows and bundled. .
In particular, in the carbon fiber bundle of the present invention, each sub tow may be intermittently divided from the adjacent sub tows, that is, the adjacent sub tows may be intermittently divided from each other. By locally having an undivided portion between adjacent sub tows in this way, the productivity of the carbon fiber bundle and the morphological stability during processing can be further improved.

The number of sub-tows contained in the carbon fiber bundle of the present invention is not particularly limited and can be, for example, 2 to 50.
The total number of filaments of the carbon fiber bundle of the present invention is preferably about 1000 to 120,000 from the viewpoints of manufacturing cost, handleability and the like.
Since it can be preferably used as a carbon fiber bundle for a sheet molding compound, the number of filaments of the sub tow contained in the carbon fiber bundle of the present invention is preferably about 500 to 15,000.
Furthermore, if the shape of the sub tow contained in the carbon fiber bundle of the present invention is flat, the cuttability of the carbon fiber bundle and the resin impregnability into the cut carbon fiber bundle during the production of the sheet molding compound become good. It is preferable because it tends to occur.
The mass of each sub tow contained in the carbon fiber bundle of the present invention is preferably about 100 to 1000 mg / m.

The average cantilever value of each sub tow contained in the carbon fiber bundle of the present invention is 110 to 300 mm, preferably 140 to 250 mm, more preferably 160 to 220 mm.
If the average cantilever value of each sub-tow is 110 mm or more, preferably 140 mm or more, and more preferably 160 mm or more, the carbon fiber bundle is not wrapped around the roll at the time of chopping, and continuous chopping is easy (chopping is possible). Excellent). When the average cantilever value of each sub-tow is 300 mm or less, preferably 250 mm or less, more preferably 220 mm or less, the chop separation property of the carbon fiber bundle is excellent.
When the sub tows are bound with each other by the sizing agent, the cantilever value of the sub tows bound with the sizing agent is a measured value of the carbon fiber bundle with the sizing agent attached. The cantilever value of the sub tow can be adjusted by adjusting the composition and the amount of the sizing agent attached to the carbon fiber bundle.

Hereinafter, a method of measuring the cantilever value of the sub toe will be described with reference to FIGS. 1 and 2.
(Procedure 1) A 40 cm long test sub tow 100 is cut out from the carbon fiber bundle of the present invention.
(Procedure 2) As shown in FIG. 1, a test sub-toe of a measuring table 10 having a horizontal plane 12 and a slope 14 inclined downward from one end of the horizontal plane 12 and having an inclination angle of 45 degrees is provided on the horizontal plane 12. Put 100. At this time, the first end 102 in the length direction of the test sub-toe 100 is aligned with the boundary line A between the slope 14 and the horizontal surface 12. The pressing plate 200 is placed on the test sub-toe, and the end portion 202 of the pressing plate 200 is aligned with the boundary line A.
(Procedure 3) As shown in FIG. 2, when the pressing plate 200 is moved horizontally toward the slope 14 at a speed of 2 cm / sec, and the first end 102 of the test sub-toe 100 comes into contact with the slope 14. The movement of the pressing plate 200 is stopped with.
(Procedure 4) The moving distance x (mm) of the pressing plate 200 in Procedure 3 is measured.

The pressing plate 200 may have any size as long as it does not hinder the measurement, and may be, for example, a plate having a length of 400 mm × a width of 200 mm × a thickness of 5 mm.
The weight of the pressing plate 200 may be any weight that does not interfere with the measurement, and can be set to, for example, 1000 g.

The average number of times of entanglement of each sub tow contained in the carbon fiber bundle of the present invention is 20 to 50 times / m, and preferably 30 to 40 times / m.
When the entanglement of each sub-tow is 20 times / m or more, preferably 30 times / m or more, the binding force of the sub-tows becomes strong and the entanglement of the sub-tows does not occur. When the entanglement of each sub-tow is 50 times / m or less, preferably 40 times / m or less, it is possible to prevent the impregnation of the resin from being lowered due to the binding force of the sub-tows being too strong.

The number of entanglements of the sub toe is measured by the following method.
The carbon fiber bundle from which the sizing agent has been removed by heat treatment is passed through a tension applying means, the tow tension is controlled to 1.0 N, and the carbon fiber bundle divided into sub tows is wound at a running speed of 1.2 m / min. . In the meantime, the number of times the sub tow is entangled is defined as the number of times the ceramic pin of the yarn tension meter is penetrated through the sub tow immediately after passing through the tension applying means and the confounding strength of 0.5 cN or more is detected.

In the carbon fiber bundle of the present invention, the overlapping ratio P represented by the following formula (1) is 5 to 80%, preferably 10 to 60%, more preferably 15 to 50%, further preferably 20 to 40%. .
When the overlapping ratio P of the carbon fiber bundle is 5% or more, preferably 10% or more, more preferably 15% or more, still more preferably 20%, the sub tow can be wound without releasing the binding of the bobbin. If the overlapping ratio P of the carbon fiber bundle is 80% or less, preferably 60% or less, more preferably 50% or less, and further preferably 40% or less, a carbon fiber bundle having excellent chop separation property is obtained. .
The overlapping ratio is the width of the groove of the guide roller when the grooved guide roller is installed in front of the dipping flat roller in the sizing agent application step, or the number of sub-tows put into one groove, or the sizing agent. It can be adjusted by the tow tension in the coating process.

(In the formula, Wt represents the average value (mm) of the widths of the carbon fiber bundles, Wst represents the average value (mm) of the widths of the respective sub-tows, and n represents the number of the sub-tows included in the carbon fiber bundles (pieces). Is shown.)

For example, in the case of the carbon fiber bundle 30 including the five (n = 5) flat sub-tows 32 illustrated in FIG. 3, the width of the carbon fiber bundle 30 is measured at every 20 cm in the fiber longitudinal direction at five locations, and Is averaged to be Wt. Further, the width of each of the five sub tows 32 is measured, and they are averaged to obtain Wst. Then, the overlap rate P is calculated using the equation (1).

(Sizing agent)
When manufacturing the carbon fiber bundle of the present invention, a sizing agent can be appropriately used. The sizing agent used here is not particularly limited, but a sizing agent containing the component (A) and the component (B) is preferable from the viewpoint that the chop separation property is particularly excellent.

The component (A) is an epoxy resin composition having a viscosity at 30 ° C. of 500 to 120,000 Pa · s.
The viscosity of the component (A) at 30 ° C. is 500 to 120,000 Pa · s, preferably 4000 to 100000 Pa · s.
When the viscosity of the component (A) at 30 ° C. is 500 Pa · s or more, preferably 4000 Pa · s or more, excellent chopability of the carbon fiber bundle is excellent. When the viscosity of the component (A) at 30 ° C. is 120,000 Pa · s or less, preferably 100,000 Pa · s or less, the chop separation property of the carbon fiber bundle is excellent.
The viscosity is measured by the method of measuring viscosity using a cone-plate type rotational viscometer in JIS Z8803 (2011).

The viscosity of the component (A) can be adjusted by the type, combination and ratio of the epoxy resin used.
The component (A) preferably contains an epoxy resin having a softening point of 50 ° C. or higher from the viewpoint of reducing the friction resistance between carbon fibers. When an epoxy resin having a softening point of 50 ° C. or higher is used, an epoxy resin having a viscosity at 30 ° C. of 1 to 100 Pa · s is mixed to adjust the viscosity of the component (A) within the above range.
The softening point of the epoxy resin is a value measured by the ring and ball method in the JIS K 7234 (1986) epoxy resin softening point test method.

In the component (A), it is preferable to combine an epoxy resin having a softening point of 50 ° C. or higher with an epoxy resin having a viscosity at 30 ° C. of 1 to 100 Pa · s, and an epoxy resin having a softening point of 50 to 100 ° C. and 30 ° C. It is more preferable to combine an epoxy resin having a viscosity of 1 to 100 Pa · s.

Examples of the epoxy resin having a softening point of 50 ° C. or higher include bisphenol A novolac type epoxy resin, phenol novolac type epoxy resin, and dicyclopentadiene type epoxy resin. Among them, bisphenol A novolac type epoxy resin is preferable because it is a polyfunctional type epoxy resin.
Examples of the epoxy resin having a viscosity at 30 ° C. of 1 to 100 Pa · s include bisphenol F type epoxy resin and bisphenol A type epoxy resin. Among them, the bisphenol F type epoxy resin, which has a low viscosity among the aromatic epoxy resins, is preferable.
The epoxy resin used as the component (A) may be one type or two or more types.

The component (B) is an aliphatic ester compound having a freezing point of 50 ° C. or lower.
The freezing point of the aliphatic ester compound is a value measured by the method for measuring the freezing point of chemical products in JIS K0065 (1992).

The freezing point of the aliphatic ester compound is 50 ° C. or lower, preferably 30 ° C. or lower, and more preferably 15 ° C. or lower. The freezing point of the aliphatic ester compound is preferably −30 ° C. or higher, more preferably −20 ° C. or higher, even more preferably −10 ° C. or higher. Specifically, the freezing point of the aliphatic ester compound is preferably −30 to 50 ° C., more preferably −20 to 30 ° C., and even more preferably −10 to 15 ° C.
When the freezing point of the aliphatic ester compound is 50 ° C. or lower, preferably 30 ° C. or lower, more preferably 15 ° C. or lower, the chop separation property of the carbon fiber bundle is excellent. When the freezing point of the aliphatic ester compound is −30 ° C. or higher, preferably −20 ° C. or higher, more preferably −10 ° C. or higher, excellent chopability of the carbon fiber bundle is excellent.

The component (B) preferably contains an aliphatic ester compound having one or two ester bonds in the molecule. This reduces the frictional resistance between the carbon fibers.
Examples of the aliphatic ester compound having one ester bond in the molecule include 2-ethylhexyl stearate, methyl stearate, butyl stearate, isopropyl palmitate and the like.
Examples of the aliphatic ester compound having two ester bonds in the molecule include isobutyl adipate and 2-ethylhexyl adipate.

As the component (B), an aliphatic ester compound having 3 or more ester bonds in the molecule may be used. Examples thereof include 1,2,3-propanetricarboxylic acid ester and 1,3,5-cyclohexanetricarboxylic acid ester.
The aliphatic ester compound used as the component (B) is preferably an aliphatic ester compound having one ester bond in the molecule from the viewpoint of reducing the frictional resistance between carbon fibers.
The aliphatic ester compound used as the component (B) may be one type or two or more types.

The sizing agent may contain a component other than the component (A) and the component (B) in addition to the component (A) and the component (B).
Examples of other components include a surfactant, a urethane resin, a polyester resin, and a polyamide resin.
The other component may be one type or two or more types.

The ratio of the total content of the component (A) and the component (B) with respect to the total amount (100% by mass) of the sizing agent is 80% by mass or more, preferably 80 to 95% by mass, more preferably 80 to 90% by mass.
When the ratio of the total content of the component (A) and the component (B) to the total amount (100% by mass) of the sizing agent is 80% by mass or more, the carbon fiber bundle is excellent in chop goodness and chop separation property.

The mass ratio of the content of the component (A) to the content of the component (B) in the sizing agent (content of the component (A) / content of the component (B)) is 1 to 20, and 1.5 to 10 is preferable, and 3 to 5 is more preferable.
If the mass ratio of the content of the component (A) to the content of the component (B) in the sizing agent is 1 or more, preferably 1.5 or more, more preferably 3 or more, good chop of the carbon fiber bundle is obtained. Excel. When the mass ratio of the content of the component (A) to the content of the component (B) in the sizing agent is 20 or less, preferably 10 or less, more preferably 5 or less, the chop separation property of the carbon fiber bundle is excellent. .

The method for producing the sizing agent is not particularly limited, and examples thereof include a method of mixing the component (A), the component (B), and other components used as necessary by a known method.

When the sub-tows contained in the carbon fiber bundle of the present invention are bound by the sizing agent, the amount of the sizing agent attached to the total mass (100% by mass) of the carbon fiber bundle of the present invention is 0.6 to 1. 6% by mass is preferable, 0.8 to 1.4% by mass is more preferable, and 1.0 to 1.2% by mass is further preferable.
If the amount of the sizing agent attached to the total mass (100% by mass) of the carbon fiber bundle of the present invention is 0.6% by mass or more, more preferably 0.8% by mass or more, and further preferably 1.0% by mass or more. Excellent in chopping of carbon fiber bundles. If the adhesion amount of the sizing agent to the total mass (100 mass%) of the carbon fiber bundle of the present invention is 1.6 mass% or less, more preferably 1.4 mass% or less, further preferably 1.2 mass% or less. , Excellent in chop separation of carbon fiber bundles.

<Splitting ratio Q>
In addition, the carbon fiber bundle of the present invention preferably has a splitting property ratio Q defined below of 20% or more.

Separation ratio Q:
A continuous carbon fiber bundle is chopped (cut) into a length of 1 inch, and 100 chopped carbon fiber bundles that do not include undivided portions of sub tows are randomly picked up with tweezers, and the mass of each is measured. From these 100 mass measurement values, the number of chopped carbon fiber bundles corresponding to the mass of the sub tow is counted, the ratio of the number is calculated, and the ratio Q of the splitting property is defined.

Here, the chopped carbon fiber bundle does not include the undivided portion of the sub-tow, for example, a large tow to chop the carbon fiber bundle intermittently divided into a plurality of sub-tow to obtain a chopped carbon fiber bundle In this case, it means that the chopped carbon fiber bundle in which the sub tows are connected to each other due to the undivided portion is excluded from the evaluation target of the ratio Q of the splitting property.
The chopped carbon fiber bundle corresponding to the mass of the sub tow is a chopped carbon fiber bundle having a mass of 120% or less of the mass corresponding to the average fineness of the sub tow.

The higher the splitting ratio Q is, the more excellent the splitting property of the carbon fiber bundle at the time of chopping is. However, if the splitting ratio Q is 20% or more, air blowing onto the chopped carbon fiber bundle, Obtaining a sufficiently separated chopped carbon fiber bundle as a raw material for a fiber-reinforced resin molding material by adding a step of colliding a chopped carbon fiber bundle with a rotating body having a plurality of protrusions on the surface You can

20% or more is preferable, 40% or more is more preferable, 50% or more is further more preferable, and 60% or more of the ratio Q of the splitting property of a carbon fiber bundle is still more preferable. If the ratio Q of the splitting property of the carbon fiber bundle is 20% or more, preferably 40% or more, more preferably 50% or more, and still more preferably 60% or more, it has excellent chopping properties and chop splitting properties. Can be further improved.
The splitting ratio Q of the carbon fiber bundle can be set to 20% or more by binding the above sub tow with the above sizing agent.

As described above, in the carbon fiber bundle of the present invention, each sub-tow can be in a state of being intermittently divided from the adjacent sub-tows, but in this case, the length of the undivided portion between adjacent sub-tows Is preferably 1 mm or more, more preferably 3 mm or more, still more preferably 5 mm or more. The length of the undivided portion between adjacent sub tows is preferably 50 mm or less, more preferably 35 mm or less, and further preferably 25 mm or less. Specifically, the length of the undivided portion between adjacent sub tows is preferably 1 to 50 mm, more preferably 3 to 35 mm, and further preferably 5 to 25 mm.
If the length of the undivided portion between adjacent sub-tows is 1 mm or more, preferably 3 mm or more, more preferably 5 mm or more, the productivity of the carbon fiber bundle and the morphological stability during processing can be further improved, It is easy to suppress process troubles that the fiber bundle is cut and wrapped around the rotating blade or roll. If the length of the undivided portion between adjacent sub-tows is 50 mm or less, preferably 35 mm or less, more preferably 25 mm or less, it is possible to reduce the proportion of the undivided portion contained in the chopped carbon fiber bundle after cutting, The physical properties of a molded product obtained by molding the obtained molding material tend to be improved.

<Formula (1)>
Further, as described above, in the carbon fiber bundle of the present invention, adjacent sub-tows can be intermittently divided, but in this case, the intermittently divided state is represented by the following formula ( It is preferable that the condition 1) is satisfied.

0.7 ≦ a / (a + b) <1 (1)
In the formula (1), a is the length of the divided portion between adjacent sub-tows, and b is the length of the undivided portion between adjacent sub-tows.

As described above, the presence of the unseparated portion in the continuous carbon fiber bundle (that is, b> 0) suppresses the occurrence of slackness or separation of some sub-tows during the production or processing of the carbon fiber bundle. Therefore, the winding of the carbon fiber bundle around the roll or the like can be reduced.

When the value of a / (a + b) is 0.7 or more, preferably 0.8 or more, more preferably 0.9 or more, and even more preferably 0.92 or more, the ratio of chopped fiber bundles in which subtows are connected is It can be reduced. Thereby, for example, at the time of spraying onto the resin paste of the chopped carbon fiber bundle during the production of a fiber-reinforced resin molding material such as a sheet molding compound, the chopped carbon fiber bundle can be uniformly dispersed on the paste, The resin can be easily impregnated into the carbon fiber, and the quality of the molding material produced can be improved.
If the value of a / (a + b) is less than 1, the carbon fiber bundle can be stably fed to the cutting machine and chopped. The value of a / (a + b) may be 0.99 or less.

The length a of the divided portion between adjacent sub tows is preferably 1 mm or more, more preferably 10 mm or more, and further preferably 100 mm or more. The length a of the divided portion between adjacent sub tows is preferably 5000 mm or less, more preferably 3000 mm or less, and further preferably 1000 mm or less. Specifically, the length a of the divided portion between adjacent sub tows is preferably 1 to 5000 mm, more preferably 10 to 3000 mm, and further preferably 100 to 1000 mm.
When the length a of the divided portion between adjacent sub-tows is 1 mm or more, preferably 10 mm or more, more preferably 100 mm or more, the physical properties of the molded product obtained by molding the obtained molding material are further improved. If the length a of the divided portion between adjacent sub-tows is 5000 mm or less, preferably 3000 mm or less, and more preferably 1000 mm or less, the process trouble of winding around the rotary blade or the roll due to cutting or loosening of the carbon fiber bundle is prevented. Easy to control.

The length b of the undivided portion between adjacent sub tows is preferably more than 0 mm, more preferably 1 mm or more, further preferably 3 mm or more, and further preferably 5 mm or more. Further, the length b of the undivided portion between adjacent sub tows is preferably 50 mm or less, more preferably 35 mm or less, and further preferably 25 mm or less. Specifically, the length b of the undivided portion between adjacent sub-tows is preferably more than 0 mm and 50 mm or less, more preferably 1 to 50 mm, further preferably 3 to 35 mm, particularly preferably 5 to 25 mm.
If the length b of the undivided portion between adjacent sub-tows is more than 0 mm, preferably 1 mm or more, more preferably 3 mm or more, and further preferably 5 mm or more, the fiber bundle is cut and wrapped around a rotary blade or roll. Trouble is easy to control. If the length b of the undivided portion between adjacent sub-tows is 50 mm or less, preferably 35 mm or less, and more preferably 25 mm or less, the proportion of the undivided portion contained in the chopped carbon fiber bundle after cutting can be reduced. The physical properties of the molded product obtained by molding the obtained molding material are improved.

As a method of making each sub tow intermittently divided with the adjacent sub tow, a method of intermittently piercing a continuous large tow with a plurality of blades arranged in a row at a predetermined interval in the width direction of the large tow, or continuous There may be mentioned a method of intermittently spraying a fluid such as air to a plurality of positions in the width direction of the large tow.

<Formula (2), Formula (3), Formula (4)>
INDUSTRIAL APPLICABILITY The carbon fiber bundle of the present invention can be used as a raw material for a fiber-reinforced resin molding material, and is excellent in chopping property and splitting property during chopping, and thus is particularly useful as a carbon fiber bundle for SMC.

By using the carbon fiber bundle of the present invention for SMC, since SMC in which finely divided carbon fiber bundles that have been uniformly separated are obtained, variation in the quality of SMC is reduced and the carbon fiber of the present invention is also reduced. The fiber-reinforced composite material obtained by molding the SMC using the bundle has excellent mechanical properties.

When a chopped carbon fiber bundle obtained by cutting the carbon fiber bundle of the present invention is used in the production of the fiber-reinforced resin molding material, the carbon fiber bundle of the present invention may be cut so as to satisfy the condition of the following formula (2). preferable.

a / L ≦ 1000 (2)
In the formula (2), a is a length of a divided portion between adjacent sub-tows, and L is an interval at which the continuous carbon fiber bundle is cut.

a / L is 1000 or less, preferably 200 or less, more preferably 100 or less, and further preferably 50 or less.
When a / L is 1000 or less, preferably 200 or less, and more preferably 100 or less, it is easy to suppress process troubles of winding around a rotary blade or roll due to cutting or slackening of the carbon fiber bundle.

When a chopped carbon fiber bundle obtained by cutting the carbon fiber bundle of the present invention is used in the production of the fiber-reinforced resin molding material, the carbon fiber bundle of the present invention is cut so as to satisfy the condition of the following formula (3). It is preferable.

1 ≦ a / L (3)
In the formula (3), a is the length of the divided portion between adjacent sub-tows, and L is the interval at which the continuous carbon fiber bundle is cut.

a / L is 1 or more, preferably 2 or more, more preferably 3 or more, still more preferably 5 or more.
When a / L is 1 or more, preferably 2 or more, more preferably 3 or more, and further preferably 5 or more, the ratio of the undivided portion contained in the chopped carbon fiber bundle after cutting can be reduced. Therefore, the physical properties of the molded product obtained by molding the obtained molding material are improved.

Further, when a chopped carbon fiber bundle obtained by cutting the carbon fiber bundle of the present invention is used in the production of the fiber-reinforced resin molding material, the carbon fiber bundle of the present invention is cut so as to satisfy the condition of the following formula (4). It is preferable.

0 ≦ b / L <1 (4)
In the formula (4), b is the length of the undivided portion between adjacent sub-tows, and L is the interval at which the continuous carbon fiber bundle is cut.

b / L is 0 or more and less than 1, preferably 0.03 to 0.8, and more preferably 0.1 to 0.6.
When b / L is 0 or more and less than 1, preferably 0.03 to 0.8, more preferably 0.1 to 0.6, the carbon fiber bundle may be cut or loosened to cause a rotary blade, roll, etc. It is easy to suppress the process trouble of wrapping around, and the proportion of the unseparated portion contained in the chopped carbon fiber bundle after cutting can be reduced, so that the physical properties of the molded product obtained by molding the obtained molding material are improved.

The carbon fiber bundle of the present invention is particularly useful as a carbon fiber bundle for a sheet molding compound (SMC) because it has excellent chop separation properties. By using the carbon fiber bundle of the present invention for SMC, an SMC in which a fine carbon fiber bundle is dispersed can be obtained. Therefore, the carbon fiber reinforced composite material obtained by molding the SMC using the carbon fiber bundle of the present invention can be used. It has excellent mechanical properties.

[Method for producing carbon fiber bundle]
The method for producing the carbon fiber bundle of the present invention is not particularly limited. For example, a method may be mentioned in which the above sizing agent is added to water, emulsified to form an aqueous dispersion, and the aqueous dispersion is applied to a carbon fiber bundle and dried.
Further, as a method for producing the carbon fiber bundle of the present invention, a method including the following steps (a) to (d) is preferable in that the sub-tows are not bound to each other by a sizing agent as much as possible.
(A) An aqueous dispersion containing a sizing agent is placed in a dipping tank, and a carbon fiber bundle containing a plurality of sub-tows is continuously dipped and passed through the aqueous dispersion while running.
(B) While the carbon fiber bundle pulled up from the aqueous dispersion is brought into contact with the peripheral surface of the roller, air is blown to the carbon fiber bundle to remove the excess aqueous dispersion.
(C) After the step (b), the carbon fiber bundle to which the aqueous dispersion is attached is subjected to a nip treatment, and the ratio of the mass of the aqueous dispersion to the total mass of the carbon fiber bundle and the aqueous dispersion is 40 mass. % Or less.
(D) After the step (c), the carbon fiber bundle is brought into contact with a heating roller whose peripheral surface is heated to 110 to 200 ° C. to be dried.

Specifically, a method using the manufacturing apparatus 300 illustrated in FIG. 4 can be used.
The manufacturing apparatus 300 includes a dipping tank 310, a dipping flat roller 312, a pulling flat roller 314, a feed roller 316, a nip roller 318, an air blowing unit 320, and a plurality of heating rollers 322. ing.

The dipping bath 310 can accommodate the aqueous dispersion 50 containing a sizing agent.
Both the flat roller 312 and the flat roller 314 are provided so that a part thereof is immersed in the water dispersion liquid 50 contained in the immersion tank 310. The flat roller 314 is provided on the downstream side of the flat roller 312. The carbon fiber bundle 40 is immersed in the water dispersion liquid 50 stored in the dipping tank 110 while traveling by the flat roller 312, and the carbon fiber bundle 40 is pulled up from the water dispersion liquid 50 by the flat roller 314.
The feed roller 316 and the nip roller 318 are provided on the downstream side of the immersion tank 310 so as to perform a nip treatment on the carbon fiber bundle 40.
The air blowing unit 320 is provided above the flat roller 314.
The plurality of heating rollers 322 are provided on the downstream side of the feed roller 316 and the nip roller 318.

In the step (a), the aqueous dispersion 50 containing the sizing agent is stored in the dipping tank 310, and the carbon fiber bundle 40 is continuously immersed in the aqueous dispersion 50 by the flat roller 312, and then the flat roller 314 is used. Pull it up and let it pass.

The concentration of the sizing agent in the aqueous dispersion is preferably 1 to 10% by mass, more preferably 2 to 6% by mass.
When the concentration of the sizing agent in the aqueous dispersion is 1% by mass or more, more preferably 2% by mass or more, a carbon fiber bundle having excellent chop goodness can be obtained. When the concentration of the sizing agent in the aqueous dispersion is 10% by mass or less, more preferably 6% by mass or less within the above range, a carbon fiber bundle having excellent chop segmentation properties can be obtained.

In the step (b), while the carbon fiber bundle 40 pulled up from the water dispersion liquid 50 is brought into contact with the peripheral surface of the flat roller 314, air is blown to the carbon fiber bundle 40 by the air blowing means 320 to remove the excess water dispersion liquid 50. Remove.

Next, in the step (c), the feed roller 316 and the nip roller 318 perform a nip treatment while running the carbon fiber bundle 40 to which the water dispersion liquid 50 is adhered, so that the water relative to the total mass of the carbon fiber bundle 40 and the water dispersion liquid 50 is added. The mass ratio of the dispersion liquid 50 is 40 mass% or less.

The mass ratio of the aqueous dispersion to the total mass of the carbon fiber bundle and the aqueous dispersion after the nip treatment in the step (c) is preferably 40% by mass or less, more preferably 5 to 40% by mass, and 10 to 25% by mass. % Is more preferable.
When the ratio of the mass of the aqueous dispersion to the total mass of the carbon fiber bundle and the aqueous dispersion is 5% by mass or more, and more preferably 10% by mass or more, the sizing agent can be uniformly applied. When the ratio of the mass of the aqueous dispersion to the total mass of the carbon fiber bundle and the aqueous dispersion is 40% by mass or less, more preferably 25% by mass or less, the splittability between sub tows during chopping is improved.
The amount of the sizing agent attached to the carbon fiber bundle can be adjusted by the concentration of the sizing agent in the aqueous dispersion, the degree of squeezing after immersion, and the like.

In the step (d), the carbon fiber bundle 40 is brought into contact with the heating roller 322 whose peripheral surface is heated to 110 to 200 ° C. to be dried.
The temperature of the peripheral surface of the heating roller 322 when the carbon fiber bundle 40 is dried is preferably 110 to 200 ° C, more preferably 110 to 170 ° C, and further preferably 130 to 150 ° C.
When the peripheral temperature of the heating roller is 110 ° C. or higher, more preferably 130 ° C. or higher, the aqueous dispersion containing the sizing agent is sufficiently dried. When the peripheral temperature of the heating roller is 200 ° C. or lower, more preferably 170 ° C. or lower, further preferably 150 ° C. or lower, the sizing agent can be applied to the carbon fiber bundle 40 without thermal decomposition.

The method for producing the carbon fiber bundle of the present invention is not limited to the method of immersing the carbon fiber bundle in the aqueous dispersion containing the sizing agent and applying the sizing agent.

As a method of applying the sizing agent other than the dipping method, for example, a touch roll method may be adopted.
Specifically, the method for manufacturing the carbon fiber bundle of the present invention may be a method using the manufacturing apparatus 300A illustrated in FIG. 5 that are the same as those in FIG. 4 are assigned the same reference numerals and explanations thereof are omitted.

The manufacturing apparatus 300A includes an immersion tank 310, a first touch roller 324, a second touch roller 326, a feed roller 316, a nip roller 318, and a plurality of heating rollers 322. The manufacturing apparatus 300A is the same as the manufacturing apparatus 300 except that the first touch roller 324 and the second touch roller 326 are provided instead of the flat rollers 312 and 314, and the air blowing unit 320 is not provided. .

In the method using the manufacturing apparatus 300A, the water dispersion liquid 50 containing the sizing agent is stored in the dipping tank 310, and the first touch roller 324 and the second touch roller 326 cause the carbon fiber bundle 40 to travel and the water dispersion liquid. 50 is applied continuously. Next, the feed roller 316 and the nip roller 318 perform a nip treatment while the carbon fiber bundle 40 to which the water dispersion liquid 50 is attached is running, and then the carbon fiber bundle 40 is brought into contact with the heating roller 322 to be dried.

Further, the method for manufacturing the carbon fiber bundle of the present invention may be a method using the manufacturing apparatus 300B illustrated in FIG. The same parts in FIG. 6 as those in FIG.
The manufacturing apparatus 300B is the same as the manufacturing apparatus 300, except that the immersion flat roller 314A is provided instead of the pulling up flat roller 314, and the air blowing unit 320 is not provided.

The method using the manufacturing apparatus 300B is the same as the method using the manufacturing apparatus 300, except that after the aqueous dispersion 50 is applied to the carbon fiber bundle 40, air is not blown while making contact with the circumferential surface of the roller.

As described above, in the present invention, a plurality of sub-tows contained in the carbon fiber bundle are bound by a sizing agent, the average value of the cantilever value of each sub-tow, and the average of the number of confounding control within a specific range. Has been done. Thereby, when the carbon fiber bundle is chopped, excellent chopping property is obtained, and a sufficiently divided chopped carbon fiber bundle is obtained.

[Sheet molding compound (SMC)]
An SMC can be produced by impregnating a resin (matrix resin) with a fiber bundle (chopped fiber bundle) obtained by cutting the carbon fiber bundle of the present invention at intervals in the longitudinal direction.

This SMC can adopt a known aspect except that it includes a chopped fiber bundle obtained by chopping the carbon fiber bundle of the present invention.

The average fiber length of the chopped fiber bundle is not particularly limited and can be, for example, 1 to 60 mm. The average fiber length of the chopped fiber bundle is the average value of the fiber length of 100 chopped fiber bundles.

In particular, when the bulk density calculated by the following method (I) is in the range of 60 to 400 g / L, the resin impregnation property at the time of SMC production becomes good, and the fiber obtained by heating and pressing SMC is obtained. The mechanical properties of the reinforced composite material can be further improved.
(Method (I))
(Procedure I-1) 100 g of a chopped fiber bundle for test, which is obtained by cutting a carbon fiber bundle with a rotary cutter to have a fiber length of 25 mm, is filled in a 2 L graduated cylinder (cylinder having a diameter of 88 mm and a height of 485 mm).
(Procedure I-2) The total volume (L) of the filled chopped carbon fiber bundle for test when a load of 500 g is uniformly applied from the upper part of the chopped fiber bundle for test in the graduated cylinder and there is no change in volume. Is measured, and the total mass (100 g) of the test chopped fiber bundle is divided by the total volume (L) of the test chopped carbon fiber bundle to calculate the bulk density.

In the carbon fiber bundle of the present invention, the bulk density measured by the method (I) is preferably 60 to 400 g / L, more preferably 70 to 350 g / L, further preferably 80 to 320 g / L, and 100 to 280 g / L. Is particularly preferable.
If the bulk density of the carbon fiber bundle measured by the method (I) is 60 to 400 g / L, preferably 70 to 350 g / L, more preferably 80 to 320 g / L, further preferably 100 to 280 g / L, Since the chopped carbon fiber bundles are tightly entangled with each other in the SMC, a high-strength fiber-reinforced composite material can be obtained. Further, the rigidity of the chopped fiber bundle and the resin impregnating property can both be achieved, and the mechanical properties can be improved.

In the carbon fiber bundle, when the bulk density measured by the method (I) is 60 g / L or more, preferably 70 g / L or more, more preferably 80 g / L or more, further preferably 100 g / L or more, during SMC production. Since the resin impregnating property is excellent, the mechanical properties of the fiber-reinforced composite material are improved. In the carbon fiber bundle, if the bulk density measured by the method (I) is 400 g / L or less, preferably 350 g / L or less, more preferably 320 g / L or less, further preferably 280 g / L or less, in SMC. Since the chopped fiber bundles are strongly intertwined with each other, a high-strength fiber-reinforced composite material can be obtained.

A thermosetting resin or a thermoplastic resin can be used as a matrix resin when manufacturing an SMC using the carbon fiber bundle of the present invention. As the matrix resin, only the thermosetting resin may be used, only the thermoplastic resin may be used, or both the thermosetting resin and the thermoplastic resin may be used.

The thermosetting resin is not particularly limited, epoxy resin, phenol resin, unsaturated polyester resin, vinyl ester resin, phenoxy resin, alkyd resin, urethane resin, urea resin, melamine resin, maleimide resin, cyanate resin, etc. Can be mentioned.
Examples of the thermoplastic resin include polyolefin resin, polyamide resin, polyester resin, polyphenylene sulfide resin, polyether ketone resin, polyether sulfone resin, and aromatic polyamide resin.
The matrix resins may be used alone or in combination of two or more.

Matrix resins include internal mold release agents, defoamers, flame retardants, weather resistance improvers, antioxidants, heat stabilizers, UV absorbers, plasticizers, lubricants, colorants, compatibilizers, thickeners, etc. You may mix | blend the additive of.

The method for producing the SMC of the present invention is not particularly limited. For example, there is a method in which a long carbon fiber bundle of the present invention is chopped to form a chopped fiber bundle, a fiber base material including the chopped fiber bundle is formed, and a matrix resin is impregnated to obtain SMC.

[Fiber reinforced composite material]
A fiber-reinforced composite material can be obtained by placing the SMC obtained in the present invention in a mold and performing heat-press molding.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by the following description.

[material]
The raw materials used in this example are shown below.

<Component (A)>
Component (A-1): Bisphenol A novolac type epoxy resin (trade name “E157S70”, Mitsubishi Chemical Corporation, softening point: 70 ° C.).
Component (A-2): Bisphenol F type epoxy resin (trade name “jER (registered trademark, the same applies hereinafter) 807”, Mitsubishi Chemical Corporation, viscosity at 30 ° C .: 2 Pa · s).
Component (A-3): Bisphenol A type epoxy resin (trade name “jER1001”, Mitsubishi Chemical Corporation, softening point: 64 ° C.).
Component (A-4): Bisphenol A type epoxy resin (trade name “jER828”, Mitsubishi Chemical Corporation, viscosity at 30 ° C .: 10 to 15 Pa · s).

<Component (B)>
Ingredient (B-1): 2-ethylhexyl stearate (trade name “Exepearl (registered trademark) EH-S”, Kao Corporation, freezing point: 10 ° C.).

<Other ingredients>
Surfactant (C-1): polycyclic phenol ethylene oxide adduct sulfate ammonium salt (trade name "Hitenol (registered trademark) NF-17", Dai-ichi Kogyo Seiyaku Co., Ltd.).

[Cantilever value]
The cantilever value of the sub tow was measured by the following procedures 1 to 4.
(Procedure 1) A 40 cm long test subtoe was cut out from a carbon fiber bundle.
(Procedure 2) Place a test sub-toe on the horizontal plane of a measuring table having a horizontal plane and a slope having an inclination angle of 45 degrees, and incline downward from one end of the horizontal plane. The end of 1 was aligned with the boundary line between the slope and the horizontal plane. The pressing plate was placed on the test sub-toe, and the end of the pressing plate was aligned with the boundary line.
(Procedure 3) The pressing plate was moved horizontally to the slope at a speed of 2 cm / sec, and the movement of the pressing plate was stopped when the first end of the test sub-toe contacted the slope.
(Procedure 4) The moving distance x (mm) of the pressing plate in Procedure 3 was measured.

[Number of entanglements]
The number of times of subtow confounding was measured by the following method.
Before the sizing agent application step, the carbon fiber bundle to which the sizing agent has not been applied is sampled, the carbon fiber bundle is pulled up in the vertical direction, passed through the tension applying means, and the tow tension is controlled to 1.0 N, and the traveling speed is 1. It was wound up at 2 m / min. In the meantime, the number of times the entanglement strength of 0.5 cN or more was detected by penetrating the ceramic pin of the yarn tension meter to the divided sub tow immediately after passing through the tension applying means, did.

[Amount of sizing agent]
The amount of the sizing agent attached to the sizing agent-attached carbon fiber bundle obtained in each example was measured by the Soxhlet extraction method using methyl ethyl ketone. The extraction time was 1 hour.

[Evaluation of chop separation property]
A continuous carbon fiber bundle was chopped (cut) into a length of 1 inch, and 100 chopped carbon fiber bundles that did not include undivided portions of the sub tows were carefully picked up randomly with tweezers, and the mass of each was measured. From these 100 mass measurement values, the number of chopped carbon fiber bundles corresponding to the mass of the sub tow was counted, the ratio of the number was calculated, and the dispersibility ratio Q was obtained.
Specifically, a carbon fiber bundle with a sizing agent was chopped (cut) into a length of 1 inch using a rotary cutter, and the chop separation property was evaluated by the dispersibility ratio Q calculated by the above method.
Here, the chopped carbon fiber bundle corresponding to the mass of the sub tow is a chopped carbon fiber bundle having 120% or less of the average fineness of the sub tow.

The chop separation property was evaluated according to the following criteria.
A: The dispersibility ratio Q is 80% or more.
B: The dispersibility ratio Q is 60% or more and less than 80%.
C: The dispersibility ratio Q is 40% or more and less than 60%.
D: The dispersibility ratio Q is 20% or more and less than 40%.
E: Dispersibility ratio Q is less than 20%.

[Evaluation of good chop]
The adhered state of the chopped carbon fiber bundle to the rubber roll of the rotary cutter was visually confirmed, and the chop goodness was evaluated according to the following criteria.
A: Almost no sticking of the chopped carbon fiber bundle to the rubber roll was observed, and chopping could be performed continuously.
B: Some sticking of the chopped carbon fiber bundle to the rubber roll was observed, but chopping could be performed continuously.
C: The chopped carbon fiber bundles were often stuck to the rubber roll, and a chop defect occurred, which made continuous chopping difficult.

[The bulk density]
The bulk density of the carbon fiber bundle was measured by the following procedures I-1 and I-2.
(Procedure I-1) 100 g of a cut piece obtained by cutting a carbon fiber bundle with a rotary cutter to a fiber length of 25 mm was filled in a 2 L graduated cylinder (cylinder having a diameter of 88 mm and a height of 485 mm).
(Procedure I-2) A load of 500 g is uniformly applied from the upper part of the cut pieces in the graduated cylinder, and the total volume (L) of the filled cut pieces when there is no change in volume is measured. The bulk density was calculated by dividing the mass (100 g) by the total volume (L) of the cut pieces.

[Evaluation of SMC resin impregnation]
<Preparation of matrix resin composition>
100 parts by mass of a mixture of an epoxy (meth) acrylate resin and an unsaturated polyester resin (manufactured by Nippon Yupica Co., Ltd., product name: Neopol (registered trademark) 8113), 1,1-di (t-butylperoxy) cyclohexane 0.5 parts by mass of a 75 mass% solution (manufactured by NOF CORPORATION, product name: Perhexa (registered trademark) C-75 (EB)), 74 mass% solution of t-butylperoxyisopropyl carbonate (Kayaku Akzo Co., Ltd. Made by the company, product name: Kayacarboxylic (registered trademark) BIC-75) 0.5 parts by mass, internal mold release agent (phosphate ester derivative composition) (made by Accel Plastic Research Laboratory, product name: MOLD WIZ INT- 0.35 parts by mass of EQ-6), modified diphenylmethane diisocyanate (manufactured by Mitsui Chemicals, Inc., product name: Cosmonate 22.0 parts by mass of registered trademark) LL) and 0.04 parts by mass of 1,4-benzoquinone (manufactured by Seiko Chemical Co., Ltd.) are sufficiently mixed and stirred using a universal stirrer to obtain a matrix resin composition. It was

<Manufacture of SMC>
The obtained matrix resin composition was applied onto a polyethylene film (carrier film) with a doctor blade so as to have a thickness of 1.0 mm, and chopped carbon fiber bundles each having a fiber length of 25 mm were applied onto the film. The carbon fiber bundle was sprayed so that the basis weight of the bundle was substantially uniform and the direction of the carbon fiber bundle was random. The same matrix resin composition was applied onto another polyethylene carrier film to a thickness of 1.0 mm, and the matrix resin composition sides were laminated and laminated on the scattered carbon fiber bundles. Got the body The laminate was pressed between rolls to impregnate the carbon fiber bundle with the matrix resin composition to obtain an SMC precursor.
The obtained SMC precursor was allowed to stand at room temperature (23 ° C.) for 168 hours (7 days). Thereby, the matrix resin composition in the SMC precursor was sufficiently thickened to obtain SMC.

When the above SMC precursor was obtained, the resin impregnation property was confirmed visually and by touch, and evaluated according to the following evaluation criteria.
A: The chopped carbon fiber bundle is sufficiently impregnated with the matrix resin composition.
B: A portion where the matrix resin composition is not impregnated in the chopped carbon fiber bundle is slightly confirmed.
C: Many parts in which the matrix resin composition is not impregnated in the chopped carbon fiber bundle are confirmed.

[Example 1]
<Preparation of aqueous dispersion of sizing agent>
A resin composition obtained by mixing 54 parts by mass of the component (A-1) and 11 parts by mass of the component (A-2) as the component (A), 20 parts by mass of the component (B-1), and the surfactant (C-1 ) 15 parts by mass were mixed to obtain a sizing agent. Ion-exchanged water was added to the obtained sizing agent, and phase inversion emulsification was performed using a homomixer to prepare an aqueous dispersion having a sizing agent concentration of 3.3 mass%.

<Production of carbon fiber bundle with sizing agent>
The acrylonitrile-based copolymer was wet-spun to obtain a carbon fiber bundle precursor having 3000 filaments and a total fineness of 3600 tex, and 5 carbon fiber bundle precursors were wound on a bobbin. The bundled carbon fiber bundle precursor was fired to obtain a carbon fiber bundle containing 5 sub-tows (mass: 298 mg / m) and having a total number of filaments of 15,000 and a total fineness of 1000 tex. Next, the carbon fiber bundle was subjected to electrolytic oxidation treatment using ammonium hydrogen carbonate as an electrolytic solution, washed with water, and dried by a roller heated to 150 ° C.

Next, using the manufacturing apparatus 300 illustrated in FIG. 4, an aqueous dispersion of a sizing agent in which the carbon fiber bundles (carbon fiber bundles 40) that have been surface-treated by the flat rollers 312 and 314 are filled in the dipping tank 310 ( It was immersed in an aqueous dispersion 50) and passed through. While the carbon fiber bundle 40 pulled up from the water dispersion liquid 50 was brought into contact with the peripheral surface of the flat roller 314, air was blown to the carbon fiber bundle 40 by the air blowing means 320 to remove the excess water dispersion liquid 50. Next, the feed roller 316 and the nip roller 318 perform a nip treatment while running the carbon fiber bundle 40 to which the water dispersion liquid 50 is attached, so that the mass of the water dispersion liquid 50 with respect to the total mass of the carbon fiber bundle 40 and the water dispersion liquid 50 is The ratio W was set to 20% by mass. Next, the carbon fiber bundle 40 was brought into contact with the heating roller 322 whose peripheral surface was heated to 140 ° C. for 15 seconds to be dried, and the carbon fiber bundle with the sizing agent was wound on a bobbin. The amount of the sizing agent attached to the obtained carbon fiber bundle with the sizing agent was 1.2% by mass.

[Examples 2 to 7 and Examples 10 and 11]
A carbon fiber bundle with a sizing agent was produced in the same manner as in Example 1 except that the production conditions of the carbon fiber bundle with a sizing agent were changed as shown in Table 1.

[Examples 8 and 9]
A resin composition obtained by mixing 42.5 parts by mass of the component (A-3) and 42.5 parts by mass of the component (A-4) as the component (A) and 15 parts by mass of the surfactant (C-1) are mixed. Then, a sizing agent was obtained. Ion-exchanged water was added to the sizing agent, and phase inversion emulsification was performed using a homomixer to prepare an aqueous dispersion having a sizing agent concentration of 3.3 mass%. A carbon fiber bundle with a sizing agent was produced in the same manner as in Example 1 except that the obtained aqueous dispersion was used and the production conditions for the carbon fiber bundle with a sizing agent were changed as shown in Table 1.

[Example 12]
As a continuous fiber bundle, a carbon fiber bundle (trade name "TR50S 15L", manufactured by Mitsubishi Chemical Corporation) was used. The carbon fiber bundle is intermittently divided so that the length a of the divided portion between the adjacent sub-tows is 800 mm and the length b of the undivided portion between the adjacent sub-tows is 25 mm, and 9 sub-tows are included. A carbon fiber bundle having 15,000 filaments and a total fineness of 1000 tex was obtained. Then, a carbon fiber bundle with a sizing agent was manufactured in the same manner as in Example 1.

[Comparative Example 1]
A carbon fiber bundle with a sizing agent was produced in the same manner as in Example 1 except that the production conditions of the carbon fiber bundle with a sizing agent were changed as shown in Table 1.

[Comparative Example 2]
A carbon fiber bundle (trade name "TRW40 50L", manufactured by Mitsubishi Chemical Corporation) was used as a continuous fiber bundle. The carbon fiber bundle is intermittently divided so that the length a of the divided portion between the adjacent sub-tows is 800 mm and the length b of the undivided portion between the adjacent sub-tows is 25 mm, and includes 30 sub-tows. A carbon fiber bundle having 50000 filaments and a total fineness of 3750 tex was obtained. Then, a sizing agent-attached carbon fiber bundle was produced in the same manner as in Example 1 except that the production conditions for the sizing agent-attached carbon fiber bundle were changed as shown in Table 1.

Table 1 shows the evaluation results of the examples and comparative examples.

As shown in Table 1, the sizing agent-added carbon fiber bundles of Examples 1 to 9 were excellent in chop division property during chopping. In Examples 8, 9 and 12 having a low cantilever value, the chop goodness was inferior, but the level was sufficiently applicable to the production of SMC.
Further, in Example 10 in which the overlapping ratio P was high, the chop separation property was inferior, but the level was sufficiently applicable to the production of SMC. In Example 11 in which the number of entanglements was small, the chop separation property and the chop goodness were inferior, but the level was sufficiently applicable to the production of SMC.
On the other hand, in Comparative Example 1 in which the overlapping rate P was low, the chop separation property and the chop goodness were good, but troubles such as winding of the separated sub tow around the device frequently occurred during the production of SMC. did. Further, the chopped fiber bundle of Comparative Example 1 had a low resin impregnation property, and was not at a level applicable to the production of SMC.
Further, in Comparative Example 2 in which the overlapping ratio P was high, the chop splitting property was relatively good, but the chop goodness and resin impregnation were low, and it was not at a level applicable to the production of SMC.

Claims (14)

1. A carbon fiber bundle containing a plurality of sub tows,
   A carbon fiber bundle having an overlap ratio P represented by the following formula (1) of 5 to 80%.
   

   

   (In the formula, Wt represents an average value (mm) of widths of the carbon fiber bundles, Wst represents an average value (mm) of widths of the respective sub tows, and n represents the number of sub tows included in the carbon fiber bundles ( Book).)
2. The carbon fiber bundle according to claim 1, wherein a plurality of the sub tows are bound with a sizing agent.
3. The carbon fiber bundle according to claim 1 or 2, wherein the mass of the sub-tow is 100 to 1000 mg / m.
4. The carbon fiber bundle according to any one of claims 1 to 3, wherein the number of filaments of the sub tow is 500 to 15,000.
5. The carbon fiber bundle according to any one of claims 1 to 4, wherein the average number of times of entanglement of each of the sub tows is 20 to 50 times / m.
6. The carbon fiber bundle according to any one of claims 1 to 5, wherein the average cantilever value of each of the sub tows is 110 to 300 mm.
7. The carbon fiber bundle according to any one of claims 1 to 6, wherein the total number of filaments is 1000 to 120,000.
8. The carbon fiber bundle according to any one of claims 1 to 7, wherein each of the sub tows is intermittently divided from an adjacent sub tow.
9. The carbon fiber bundle according to any one of claims 1 to 8, wherein the splitting property ratio Q defined below is 20% or more.
   (Proportion Q of splitting property)
   A continuous carbon fiber bundle is chopped (cut) into a length of 1 inch, and 100 chopped carbon fiber bundles that do not include undivided portions of sub tows are randomly picked up with tweezers, and the mass of each is measured. From these 100 mass measurement values, the number of chopped carbon fiber bundles corresponding to the mass of the sub tow is counted, the ratio of the number is calculated, and the ratio Q of the splitting property is defined.
10. The carbon fiber bundle according to any one of claims 1 to 9, which has a bulk density calculated by the following method (I) of 60 to 400 g / L or more.
    (Method (I))
    (Procedure I-1) 100 g of a chopped fiber bundle for test, which is obtained by cutting a carbon fiber bundle with a rotary cutter to have a fiber length of 25 mm, is filled in a 2 L graduated cylinder (cylinder having a diameter of 88 mm and a height of 485 mm).
    (Procedure I-2) A load of 500 g is uniformly applied from the upper part of the test chopped fiber bundle in the graduated cylinder, and the total volume (L) of the filled test chopped carbon fiber bundle when there is no change in volume ) Is measured and the total mass (100 g) of the test chopped fiber bundle is divided by the total volume (L) of the test chopped carbon fiber bundle to calculate the bulk density.
11. The carbon fiber bundle according to any one of claims 1 to 10, which is a carbon fiber bundle for a sheet molding compound.
12. The method for producing a carbon fiber bundle according to any one of claims 1 to 11, which includes the following steps (a) to (d).
    (A) An aqueous dispersion containing a sizing agent is placed in a dipping tank, and a carbon fiber bundle containing a plurality of sub-tows is continuously dipped and passed through the aqueous dispersion while running.
    (B) While the carbon fiber bundle pulled up from the aqueous dispersion is brought into contact with the peripheral surface of the roller, air is blown to the carbon fiber bundle to remove the excess aqueous dispersion.
    (C) After the step (b), the carbon fiber bundle to which the aqueous dispersion is attached is subjected to a nip treatment, and the ratio of the mass of the aqueous dispersion to the total mass of the carbon fiber bundle and the aqueous dispersion is 40 mass. % Or less.
    (D) After the step (c), the carbon fiber bundle is brought into contact with a heating roller whose peripheral surface is heated to 110 to 200 ° C. to be dried.
13. The sizing agent contains the following components (A) and (B),
    The mass ratio of the content of the component (A) to the content of the component (B) (content of the component (A) / content of the component (B)) is 1 to 20,
    The method for producing a carbon fiber bundle according to claim 12, wherein the ratio of the total content of the component (A) and the component (B) with respect to the total amount (100 mass%) of the sizing agent is 80 mass% or more.
    Component (A): An epoxy resin composition having a viscosity at 30 ° C. of 500 to 120,000 Pa · s.
    Component (B): an aliphatic ester compound having a freezing point of 50 ° C. or lower.
14. A method for producing a sheet molding compound, which comprises impregnating a resin with a fiber bundle obtained by cutting the carbon fiber bundle according to any one of claims 1 to 11 at intervals in a longitudinal direction.

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