WO2024090144A1 - Method for producing partially divided carbon fiber bundle - Google Patents

Abstract

The main purpose of the present invention is to provide an improvement to a method for producing a partially divided carbon fiber bundle.　According to the method for producing a partially divided carbon fiber bundle, a carbon fiber bundle is supplied continuously from a carbon fiber production line to a partial division line connected to the carbon fiber production line, and is subjected to partial division processing in a division section provided in the partial division line. The partial division processing may include stabbing a protruding portion of a dividing jig intermittently into the carbon fiber bundle running along the longitudinal direction thereof. The protruding portion may be a needle.

Description

Method for producing partially split carbon fiber bundles

The present invention relates primarily to a method for producing a partially split carbon fiber bundle.
This application claims priority based on Japanese Patent Application No. 2022-173173 filed with the Japan Patent Office on October 28, 2022, and Japanese Patent Application No. 2023-120315 filed with the Japan Patent Office on July 24, 2023, the contents of which are incorporated herein by reference.

The mechanical properties of CFRP obtained by curing a prepreg in which a random mat type reinforcing material made of chopped carbon fiber bundles, such as SMC (sheet molding compound), is impregnated with resin, are affected by the bundle size of the chopped carbon fiber bundles, i.e., the number of carbon fiber filaments that make up the bundle. SMC using chopped carbon fiber bundles with smaller bundle size as reinforcing material can give CFRP with better mechanical properties (Patent Document 1).

On the other hand, the larger the carbon fiber bundle, the lower the production cost, so it has been proposed to partially split the carbon fiber bundle by intermittently piercing it with a plate or needle before using it to manufacture SMC (Patent Document 2).
The term "partial division" refers to partially dividing an original continuous fiber bundle into a plurality of sub-bundles.

US Patent Application Publication No. 2012/0213997 International Publication No. 2017/221655

It is an object of the present invention to provide an improvement in a method for producing partially split carbon fiber bundles. More specifically, the objects of the present invention include the following:
- To provide a technique for producing partially split carbon fiber bundles with stable quality.
- To provide partially split carbon fiber bundles suitable as raw materials for SMC.
- Prevent deterioration in the quality of the partially divided carbon fiber bundles due to problems during the partial division process.
Preventing a decrease in the production efficiency of partially divided carbon fiber bundles due to problems during the partial division process.

According to one aspect of the present invention, there is provided a method for producing partially split carbon fiber bundles, in which carbon fiber bundles are continuously supplied from a carbon fiber production line to a partial splitting line connected to the carbon fiber production line, and are subjected to a partial splitting process in a partial splitting section provided in the partial splitting line.

According to another aspect of the present invention, there is provided a method for manufacturing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial division process, the partial division process including intermittently piercing the carbon fiber bundle traveling along its own longitudinal direction with a protrusion of a division jig having a protrusion, the protrusion being formed by a needle, and the needle being inclined so as to fall downstream in the traveling direction of the carbon fiber bundle when pierced into the carbon fiber bundle.

According to yet another aspect of the present invention, there is provided a method for manufacturing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial division process, the partial division process including intermittently piercing the carbon fiber bundle traveling along its own longitudinal direction with a protrusion of a division jig having a protrusion, the protrusion being formed of a plate, and when the plate is pierced into the carbon fiber bundle, the edge of the plate facing the upstream side in the running direction of the carbon fiber bundle is inclined so as to fall toward the downstream side in the running direction of the carbon fiber bundle in the portion where the plate is pierced into the carbon fiber bundle.

According to yet another aspect of the present invention, there is provided a method for manufacturing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial division process, the partial division process including intermittently piercing the carbon fiber bundle traveling along its longitudinal direction with a protrusion of a division jig having a protrusion, the protrusion being formed of a plate, the plate-shaped protrusion having at least one convex corner with an interior angle of 90° or more but no convex corners with an interior angle of less than 90°, and the number of the convex corners of the protrusion with an interior angle of 90° or more that are pierced into the carbon fiber bundle does not exceed one in the partial division process.

According to yet another aspect of the present invention, there is provided a method for manufacturing a partially divided carbon fiber bundle by subjecting a carbon fiber bundle to a partial division process, the partial division process including intermittently piercing the carbon fiber bundle running along its longitudinal direction with a protrusion of a division jig having a protrusion, the protrusion being formed of a plate, the plate-shaped protrusion having two right-angled corners, and only one of the two right-angled corners being pierced into the carbon fiber bundle in the partial division process.

According to yet another aspect of the present invention, there is provided a method for manufacturing a partially divided carbon fiber bundle by subjecting a carbon fiber bundle to a partial division process, the partial division process including intermittently piercing the carbon fiber bundle running along its longitudinal direction with a protrusion of a division jig having a protrusion, the protrusion being formed using a rectangular plate, and in the partial division process, only one of the four right-angled corners of the rectangular plate is pierced into the carbon fiber bundle.

According to yet another aspect of the present invention, there is provided a method for manufacturing a partially divided carbon fiber bundle by subjecting a carbon fiber bundle to a partial division process, the partial division process including swinging a division jig having a protrusion to intermittently pierce the protrusion into the carbon fiber bundle traveling along its own longitudinal direction.

According to yet another aspect of the present invention, there is provided a method for manufacturing a partially divided carbon fiber bundle by subjecting a carbon fiber bundle to a partial division process, the partial division process including intermittently piercing the carbon fiber bundle traveling along its own longitudinal direction with a protrusion of a division jig having a protrusion, and blowing compressed air onto the protrusion of the division jig while the partial division process is being performed.

According to yet another aspect of the present invention, there is provided a method for manufacturing a partially divided carbon fiber bundle by subjecting a carbon fiber bundle to a partial division process, the partial division process including intermittently piercing the carbon fiber bundle running along its longitudinal direction with a protrusion of a division jig having a protrusion, the division jig having (n+1) or more protrusions, and the carbon fiber bundle being partially divided into n or (n+1) sub-bundles in the partial division process. Here, n is an integer of 2 or more.

The present invention provides an improvement in the method for producing partially split carbon fiber bundles.

FIG. 1 shows an example of a production line for partially split carbon fiber bundles including a partially splitting line. FIG. 2 shows an example of a production line for partially split carbon fiber bundles including a partially splitting line. FIG. 3 is an explanatory diagram of the x-, y- and z-directions in a partially divided section. FIG. 4 is a perspective view showing an example of a dividing jig in which the protrusions are formed by needles. FIG. 5 is a view of the dividing jig of FIG. 5 as viewed from the u direction. FIG. 6 is a view of the dividing jig of FIG. 5 as viewed from the s direction. FIG. 7 shows examples of shapes that the tapered tip of the needle may have. FIG. 8 shows an example of a method for manufacturing a dividing jig. FIG. 9 shows an example of a method for manufacturing a split jig. FIG. 10 is a perspective view showing an example of a dividing jig in which the protruding portion is formed of a plate. FIG. 11 is a view of the dividing jig of FIG. 10 as viewed from the u direction. FIG. 12 is a view of the dividing jig of FIG. 10 as viewed from the s direction. FIG. 13 shows an embodiment of a process for dividing a carbon fiber bundle into portions using a dividing jig having protruding portions formed with needles. FIG. 14 shows an embodiment of a process for dividing a carbon fiber bundle into portions using a dividing jig having protruding portions formed with needles. FIG. 15 shows an embodiment of a process for partially dividing a carbon fiber bundle using a dividing jig having protruding portions formed with needles. FIG. 16 shows an embodiment of a process for partially dividing a carbon fiber bundle using a dividing jig having protruding portions formed of plates. FIG. 17 shows an embodiment of a process for partially dividing a carbon fiber bundle using a dividing jig having protruding portions formed of plates. FIG. 18 is a plan view showing an example of a partially split carbon fiber bundle. FIG. 19 shows a situation that may occur if the position of the carbon fiber bundle in the y direction shifts while the protrusion of the dividing jig is not inserted. FIG. 20 shows a situation that may occur if the position of the carbon fiber bundle in the y direction shifts while the protrusion of the dividing jig is not inserted. FIG. 21 shows a situation that can occur if the position of the carbon fiber bundle in the y direction shifts while the protrusion of the dividing jig is not inserted. FIG. 22 is a perspective view showing an example of a slitter roll having a slit blade with a missing portion. FIG. 23 is a photograph showing the dividing jig after it has been used in the partial dividing process. FIG. 24 is a photograph showing the dividing jig after it has been used in the partial dividing process. FIG. 25 is a photograph showing the dividing jig after it has been used in the partial dividing process. FIG. 26 is a photograph showing the dividing jig after it has been used in the partial dividing process.

Below, an embodiment of the present invention will be described with reference to the drawings as appropriate. The dimensional ratios in the drawings are for the convenience of explanation and may differ from the actual ones. In addition, in the drawings, the same components are indicated by the same reference numerals, and descriptions of overlapping components may be omitted.

1. Partial Splitting Line One embodiment of the present invention relates to a method for producing a partially split carbon fiber bundle.
In a method according to an embodiment, a partial dividing line 2 having a partial dividing section 1 is provided, for example as shown in FIG.
In the partial division line 2 shown in FIG. 1 , an undivided carbon fiber bundle 3 as a starting material is unwound from a spool and supplied to a partial division section 1 .

The bundle size of the carbon fiber bundle 3, i.e., the number of carbon fiber filaments constituting the carbon fiber bundle 3, is usually 12K or more, and may be 15K or more, 24 or more, 36K or more, 48K or more, etc., and is usually 120K or less, and may be 100K or less, 80K or less, 60K or less, etc., but is not limited thereto. Here, K is a symbol meaning 1000, and for example, 12K means 12,000 and 120K means 120,000.

In the partial division section 1, the carbon fiber bundle 3 is subjected to a partial division process to become a partially divided carbon fiber bundle 4. The partial division process can be performed, for example, by intermittently piercing the carbon fiber bundle 3 running along the longitudinal direction (fiber direction) with a needle or a plate, but other tools may also be used.
In one example, the partial division process of the carbon fiber bundles 3 in the partial division section can be performed by using a slitter roll having a slit blade provided on the circumferential surface thereof with a cutout portion. An example of such a slitter roll is shown in Fig. 22. In the slitter roll 50 shown in Fig. 22, a cutout portion 53 is provided in a slit blade 52 provided on a circumferential surface 51.
The partially divided carbon fiber bundles 4 coming out of the partially divided section are wound up on another spool.

In another example, as shown in FIG. 2 , the carbon fiber production line 5 and the partial splitting line 2 are connected, and the unsplit carbon fiber bundles 3 are continuously supplied from the carbon fiber production line 5 to the partial splitting line 2 .
The carbon fiber production line 5 includes, in order from the upstream side, a calcination section 7 in which precursor fiber bundles 6 made of polyacrylonitrile are calcined to form carbon fiber bundles, a surface treatment section 8 in which surface treatment is performed to introduce functional groups onto the carbon fiber surfaces, and a sizing section 9 in which the carbon fiber bundles are sized. The calcination section 7 usually includes a flameproofing section and a carbonization section as subsections, and may further include a graphitization section.

The precursor fiber bundle 6 may be twisted, for example, at 5 to 20 turns/m. In this case, the unsplit carbon fiber bundle 3 is untwisted downstream of the baking section 7, preferably to an untwisted state. This untwisting is preferably performed before the completion of sizing, and in one example, may be performed upstream of the surface treatment section 8.

The unsplit carbon fiber bundle 3 is produced in the carbon fiber production line 5, and then supplied to the partial division line 2 without being wound around a spool, and is partially divided in the partial division section 1 of the partial division line 2 to become a partially divided carbon fiber bundle 4. The partially divided carbon fiber bundle 4 is wound around a spool.
Not winding the carbon fiber bundle produced in the carbon fiber production line onto a spool before dividing it into portions is advantageous in stabilizing the quality of the partially divided carbon fiber bundles, because the carbon fiber bundle does not develop a curl before being supplied to the partially dividing line, and therefore the posture of the carbon fiber bundle when it travels through the partially dividing section is stable.

Carbon fiber bundles are prone to curling because they have plasticity, and more specifically, because a resin containing a low molecular weight compound called a sizing agent is used to bond the carbon fibers together. Therefore, even if the carbon fiber bundle is poured into a packaging container using the method disclosed in JP 2012-188773 A, for example, instead of being wound onto a spool, the shape of the carbon fiber bundle will become curled. In general, carbon fiber bundles that have been packaged even once before being supplied to the partial division line will become curled, making their posture unstable when they run through the partial division section.

The posture of the carbon fiber bundle when it runs through the partial division section becomes particularly unstable when the carbon fiber bundle that is traverse wound around the spool is unwound and used, because in the traverse winding, the carbon fiber bundle is easily twisted locally when the moving direction of the traverse guide is reversed, and the twisted carbon fiber bundle does not completely return to its original state even after being unwound from the spool.
In the partial division process, if the twisted portion of the carbon fiber bundle is processed with a tool such as a needle or plate, many carbon fibers will be cut, resulting in a problem that the carbon fiber bundle after partial division will be severely frayed.
In contrast, when the carbon fiber production line and the partial division line are connected, a carbon fiber bundle containing almost no twisted portions can be supplied to the partial division line, so that fluffing of the carbon fiber bundle in the partial division process is also suppressed.

It is important that the carbon fiber bundles are sized before being fed to the partial division line. If the carbon fiber bundles are subjected to partial division processing without sizing, a large amount of fiber breakage will occur and the carbon fiber bundles will become significantly frayed. This is because the introduction of functional groups to the carbon fiber surface by surface treatment significantly increases the following two frictional forces. One of the two frictional forces is the frictional force acting between adjacent carbon fibers in the bundle, and the other is the frictional force acting between the carbon fibers and tools such as needles and plates used in the partial division processing. The reason why fraying associated with partial division processing is suppressed in sized carbon fiber bundles is that the sizing agent introduced into the carbon fiber bundle by sizing acts as a lubricant that reduces these frictional forces.

In the sizing section 9, the carbon fiber bundle is passed through a sizing bath and then dried. Since the carbon fibers are fixed to each other by sizing, it is desirable to apply high tension to the carbon fiber bundle in the sizing section 9 using a tensioning mechanism such as a dancer roll to sufficiently align the carbon fibers.
On the other hand, it is desirable to apply high tension to the carbon fiber bundles 3 at the partial division line 2 as well so that a tool such as a needle or plate can reliably pierce the carbon fiber bundles 3 at the partial division section 1 .
For this reason, in one example, in order to simplify the production equipment when the carbon fiber production line 5 and the partial division line 2 are connected, a single tensioning mechanism may be used as both the tensioning mechanism for the sizing section 9 and the tensioning mechanism for the partial division line 2. Furthermore, the force generated by the contraction of the precursor fiber bundle 6 due to the firing in the firing section 7 can also be used to apply tension to the carbon fiber bundles in the sizing section 9 and the partial division line 2.

2. Partial Division Processing In the method according to the embodiment, as described above, the carbon fiber bundle is divided into parts in the partial division section provided on the partial division line.
In a preferred embodiment, the subdivision process is carried out by piercing a needle or plate into the carbon fiber bundle passing through the subdivision section.
The subdivision processing method used in this preferred embodiment will now be described in detail.

The carbon fiber bundles fed to the partial division section have a flat shape, and therefore have a width direction and a thickness direction in addition to a longitudinal direction (fiber direction). The width direction and the thickness direction are each perpendicular to the longitudinal direction and perpendicular to each other.

A tension is applied to the carbon fiber bundle traveling through the partial division section so that the longitudinal direction is parallel to a first direction and the width direction is parallel to a second direction perpendicular to the first direction. In other words, the carbon fiber bundle passes through the partial division section in a state where it is stretched substantially straight along the first direction without being twisted and suspended in the air.
In this specification, the first direction is referred to as the x-direction in the sub-divided section, and the second direction is referred to as the y-direction in the sub-divided section, as shown in Figure 3. The direction perpendicular to both the x-direction and the y-direction is referred to as the z-direction.
The x-direction may be perpendicular, inclined, or parallel to the direction of gravity.
The y direction may also be perpendicular, inclined, or parallel to the direction of gravity.

It is self-evident that when a carbon fiber bundle is suspended in the air and allowed to travel, it will vibrate. Therefore, even if the longitudinal direction of the carbon fiber bundle is parallel to the x-direction when passing through the partial division section, this is not always kept strictly parallel. Similarly, the width direction and y-direction of the carbon fiber bundle traveling through the partial division section are not always strictly parallel.

A splitting jig having a protrusion formed by a needle or a plate is installed in the partial splitting section. The carbon fiber bundles fed to the partial splitting line are intermittently pierced by the protrusion of the splitting jig when passing through the partial splitting section, thereby being split into portions.

The number of protrusions that one splitting jig has is typically two or more, but may be one. The minimum number of protrusions that a splitting jig should have depends on how many sub-bundles the carbon fiber bundle should be partially divided into. How many sub-bundles the carbon fiber bundle should be partially divided into is naturally determined by the bundle size of the carbon fiber bundle that is the starting material, and the bundle size of the sub-bundles to be formed by partial division.

4, 5 and 6 show an example of a dividing jig in which the protrusions are formed by needles.
The dividing jig 20A shown in FIGS. 4, 5 and 6 has a base 21 and eight needles 22 fixed to the base 21.
The eight needles are parallel to each other and extend along the u direction shown in the figure. The eight needles are also arranged at equal intervals along the t direction perpendicular to the u direction. All eight needles have the same length, and the straight lines connecting their tips are parallel to the t direction.

The material of the needle is typically a metal, and among them, steel, such as stainless steel, is preferred, but is not limited thereto.
A needle has at least a body, which is a part having a constant cross-sectional shape and area.
The shape of the body is preferably a cylinder, but may be an elliptical cylinder, or may be a triangular prism, a square prism, a hexagonal prism, or any other prismatic prism. The cross-sectional shape of the elliptical cylinder may be an ellipse or an oval.

The tip of the needle is preferably tapered so as to facilitate piercing the carbon fiber bundle.
Examples of shapes that the tapered tip of a needle may have are shown in Figure 7. From the left, Figure 7 illustrates needles having a conical tip 22a-1, a uniplanar tapered tip 22a-2, a biplanar tapered tip 22a-3, and a hemispherical tip 22a-4.

The diameter of the needle body is preferably 1 mm or less, more preferably 0.9 mm or less, and even more preferably 0.8 mm or less. The smaller the diameter of the body, the easier it is to divide the carbon fiber bundle into sub-bundles of smaller bundle size. Therefore, it is preferable that the diameter of the body is smaller, but if it is too small, the rigidity decreases and the needle is likely to not penetrate the carbon fiber or to bend. Therefore, the diameter of the body is preferably 0.3 mm or more, more preferably 0.4 mm or more, and may be 0.5 mm or more. When the body is not cylindrical, the smallest width of the body is regarded as the diameter.

In terms of the safe handling of the splitting jig, it is preferable that the needle tip is hemispherical. In order to ensure both ease of piercing the carbon fiber bundle and safety, the tip may be tapered other than hemispherical, with a rounded end or a terminal surface perpendicular to the axial direction.

The dividing jig 20A shown in Figures 4, 5 and 6 can be manufactured by preparing a base 21 having a plurality of holes 21a formed therein, as shown in Figure 8, inserting the base of each needle 22 into each hole 21a, and then gluing and fixing the base 21 and the needles 22 together.
The dividing jig 20A shown in Figures 4, 5 and 6 is merely one example of a dividing jig having multiple needles arranged in parallel to each other and fixed to each other. There is no limitation on the method for arranging multiple needles in parallel to each other and fixing them to each other to create a dividing jig. In another example, as shown in Figure 9, a needle 22 may be sandwiched between two plates 24 and fixed with a screw 25.

10, 11 and 12 show an example of a dividing jig in which the protrusions are formed by plates.
The dividing jig 20B shown in FIGS. 10, 11 and 12 has seven spacers 31 and eight plates 32 arranged alternately and fixed to each other.
The eight plates 32 have the same length, width, and thickness, and the shape of their main surfaces (surfaces perpendicular to the thickness direction) is rectangular. The eight plates 32 are parallel to each other, and the long sides of each main surface are parallel to the u direction shown in the figure. The eight plates are arranged at equal intervals along the t direction perpendicular to the u direction.
The seven spacers 31 are stacked alternately with the eight plates 32 on the -u side of the dividing jig 20B. The +u side of each plate 32 protrudes relative to the spacers 31.

The material of the plate 32 is typically a metal, preferably steel such as stainless steel, but is not limited thereto.
There is no limitation on the method for fixing the spacer 31 and the plate 32 to each other, and for example, adhesive, clamping, screw fastening, or various other methods can be appropriately applied.

The thickness of the plate is preferably 1 mm or less, and may be 0.9 mm or less, 0.8 mm or less, 0.7 mm or less, 0.6 mm or less, 0.5 mm or less, 0.4 mm or less, 0.3 mm or less, etc. The thinner the plate, the easier it is to pierce the carbon fiber bundle and to divide the carbon fiber bundle into sub-bundles with smaller bundle sizes. From this viewpoint, it is preferable that the plate is thinner, but if it is too thin, the rigidity decreases and the plate is likely to not pierce the carbon fiber bundle or to bend. Therefore, the thickness of the plate is preferably 0.1 mm or more, more preferably 0.2 mm or more.
When the plate is too thick to easily penetrate the carbon fiber bundles, the edge of the plate may be tapered.

The dividing jig 20B shown in Figures 10, 11 and 12 shows one preferred embodiment, in which the plate 32 is rectangular, i.e., a square having four right-angled corners (90° interior corners), two of which are included in the protrusions. In a variant, the plate 32 may be a polygon other than a square, such as a triangle, pentagon or hexagon, or may be a concave polygon, or may have no corners, such as an ellipse.
From the viewpoint of keeping the manufacturing cost of the plate 32 low, the plate 32 is preferably polygonal, more preferably quadrangular, and particularly preferably rectangular.

In the partial dividing section, the partial dividing process of the carbon fiber bundle using the dividing jig is carried out as follows.
First, examples using a dividing jig in which the protrusions are formed by needles are shown in Figures 13, 14, and 15. In Figures 13, 14, and 15, the running direction of the carbon fiber bundle 11 is from left to right in the figures, and the same applies to Figures 16, 17, 19, 20, and 21 described below.
13, the dividing jig 20A is linearly reciprocated by the actuator 40, so that the needles 22 intermittently pierce the traveling carbon fiber bundle 11. The dividing jig 20A is disposed so that its t direction is parallel to the y direction.

14, the dividing jig 20A is swung about an axis 45 by an actuator (not shown), so that the needles 22 intermittently pierce the traveling carbon fiber bundle 11. The axis 45 is parallel to the y direction.
The dividing jig 20A is positioned so that its t direction is parallel to the y direction, and when a cylinder is imagined centered on the axis 45, the longitudinal direction of the needle 22 is parallel to the radial direction of the cylinder.
This example may be modified so that the splitting jig 20 rotates instead of swinging.

15, the dividing jig 20 is swung about an axis 45 by an actuator (not shown), so that the needles 22 intermittently pierce the traveling carbon fiber bundle 11. The axis 45 is parallel to the y direction.
The dividing jig 20A is positioned so that its t direction is parallel to the y direction, and when a cylinder is imagined centered on the axis 45, the longitudinal direction of the needle 22 is inclined relative to the radial direction of the cylinder.

In each of the examples shown in Figures 13, 14, and 15, both the x direction and the y direction may be horizontal, in which case the carbon fiber bundle 11 may be pierced with the needle 22 from below or from above.
13, 14, and 15, the carbon fiber bundle 11 is divided by keeping the splitting jig 20A stationary for a certain period of time with the needles 22 piercing the traveling carbon fiber bundle 11. The needles 22 piercing the carbon fiber bundle 11 are not perpendicular to the traveling direction of the carbon fiber bundle 11, but are inclined so as to fall toward the downstream side (+x direction) of the traveling direction of the carbon fiber bundle 11 (angle θ is smaller than 90°). This advantageously makes it difficult for carbon fiber waste to accumulate in the splitting jig 20.

Next, Figs. 16 and 17 show examples in which a split jig having protruding portions formed of plates is used.
In the example shown in FIG. 16, the dividing jig 20B is linearly reciprocated by the actuator 40, so that the plate 32 intermittently pierces the traveling carbon fiber bundle 11.
The dividing jig 20B is disposed so that its t direction is parallel to the y direction.
The carbon fiber bundle 11 is divided by keeping the dividing jig 20B stationary for a certain period of time with the plate 32 piercing the traveling carbon fiber bundle 11.

17, the dividing jig 20B is swung about an axis 45 by an actuator (not shown), so that the plate 32 intermittently pierces the traveling carbon fiber bundle 11. The axis 45 is parallel to the y direction.
The splitting jig 20B is positioned so that its t direction is parallel to the y direction, and the carbon fiber bundle 11 is split by keeping the splitting jig 20B stationary for a certain period of time with the plate 32 piercing the running carbon fiber bundle 11.

In both Figures 16 and 17, when the plate 32 is stuck into the carbon fiber bundle 11, the edge 32a of the plate facing the upstream side (-x direction) in the running direction of the carbon fiber bundle 11 is inclined (angle θ is smaller than 90°) so that in the part of the plate 32 that is stuck into the carbon fiber bundle 11, the edge 32a falls toward the downstream side (+x direction) in the running direction of the carbon fiber bundle 11. This advantageously makes it difficult for carbon fiber debris to accumulate in the dividing jig 20.

16 and 17, only one of the two right-angled corners that the plate 32 has in the protruding portion is pierced into the carbon fiber bundle 11. In other words, at any moment during the partial division process, the number of right-angled corners that are pierced into the carbon fiber bundle 11 among the right-angled corners that the plate 32 has in the protruding portion does not exceed one. Therefore, the protruding portion formed by the plate 32 is unlikely to get caught by the carbon fiber bundle 11 when piercing the carbon fiber bundle 11 and when coming out of the carbon fiber bundle 11.
Not limited to the case where the protruding portion is formed using a rectangular plate, when the protruding portion of the dividing jig is plate-shaped and has multiple convex corners (corners whose interior angles are convex angles), the same effect can be obtained by making the number of the multiple convex corners that are stuck into the carbon fiber bundle during the partial dividing process not exceed 1. In another aspect, in order to obtain the same effect, the number of convex corners of the plate-shaped protruding portion may be only one.
Preferably, the inner angle of the convex corner that pierces the carbon fiber bundle is set to 90° or more, so that the above effect becomes more remarkable. From the viewpoint of making it easier for the protrusion to pierce the carbon fiber bundle, the inner angle is preferably 120° or less.

Regardless of the type of protrusion, the motion of the dividing jig is preferably a reciprocating motion rather than a rotational motion. Examples of reciprocating motion include linear reciprocating motion and swinging motion. Reciprocating motion is preferred because it prevents winding when a problem occurs in which the carbon fiber bundle (all or some of the sub-bundles) breaks. If winding occurs, the production line must be stopped and recovery will take a long time.
A suitable example of an actuator for reciprocating the dividing jig is an air cylinder, but is not limited thereto, and may be an electric motor.

In the examples shown in Figures 14, 15 and 17, the dividing jig is swung so that when the protrusion is inserted into the carbon fiber bundle, it moves in the opposite direction to the running direction of the carbon fiber bundle, and when the protrusion is removed from the carbon fiber bundle, it moves in the same direction as the running direction of the carbon fiber bundle. This makes it less likely that a protrusion that has been inserted into the carbon fiber bundle will not come out, or that when the protrusion is removed from the carbon fiber bundle, the carbon fiber bundle will be pulled by the protrusion and vibrate significantly, resulting in poor insertion of the protrusion.

The carbon fiber bundle travels with the protruding portion of the dividing jig stuck therein, so that slits are formed in the carbon fiber bundle. When the protruding portion is removed from the carbon fiber bundle, the formation of the slits is interrupted. By forming slits intermittently in this manner, a partially divided carbon fiber bundle in which the carbon fiber bundle is partially divided into a plurality of sub-bundles is obtained.
As an example of the partially divided carbon fiber bundle, a partially divided carbon fiber bundle in which the divided portions into five sub-bundles are intermittently formed along the longitudinal direction is shown in Fig. 18. Fig. 18 is a plan view of the partially divided carbon fiber bundle 4 as viewed from the thickness direction.

With reference to FIG. 18, the partially divided carbon fiber bundle 4 has four slit rows formed therein, namely, a first slit row R _S1 , a second slit row R _S2 , a third slit row R _S3 and a fourth slit row R _S4 .
The first slit row R _S1 is composed of a plurality of first slits S1 arranged along the longitudinal direction of the partially split carbon fiber bundle 4.
The second slit row R _S2 is composed of a plurality of second slits S2 arranged along the longitudinal direction of the partially split carbon fiber bundle 4.
The third slit row R _S3 is composed of a plurality of third slits S3 arranged along the longitudinal direction of the partially split carbon fiber bundle 4.
The fourth slit row R _S4 is composed of a plurality of fourth slits S4 arranged along the longitudinal direction of the partially split carbon fiber bundle 4.

Since the running speed of the carbon fiber bundle is constant, the slit length Ls, which is the length of the first to fourth slits S1, S2, S3, S4, is approximately the product of the time from when the protruding portion is pierced into the carbon fiber bundle until it is pulled out and the running speed of the carbon fiber bundle. Similarly, the slit gap length L _G , which is the length of the slit gap G _S in each of the first to fourth slit rows R _S1 , R _S2 , R _S3 , R _S3 , is approximately the product of the time from when the protruding portion is pulled out of the carbon fiber bundle until it next pierces the carbon fiber bundle and the running speed of the carbon fiber bundle.
Since the motion period of the dividing jig is constant, the slit length L _S and the inter-slit gap length L _G are constant within any slit row and are common to all slit rows.

The slit length Ls is preferably 20 cm or more, more preferably 40 cm or more, and even more preferably 60 cm or more. The longer the slit length Ls, the more advantageous it is because the chopped carbon fiber bundle obtained when cutting the split carbon fiber bundle 4 to produce the SMC contains more bundles of the same size as the sub-bundles. This is because the fiber length of the chopped carbon fiber bundle is preferably 5 to 60 mm, more preferably 10 to 30 mm, and can even be 20 mm or less. From this perspective, there is no particular upper limit to the slit length Ls.

On the other hand, the larger the slit length Ls, the more likely it is that problems (e.g., winding around a roll) that occur when a sub-bundle breaks in a partial splitting line or a line that produces SMC using partially split carbon fiber bundles 4 will become serious. From this perspective, the slit length Ls is preferably 300 cm or less, more preferably 200 cm or less, and even more preferably 150 cm or less.

From the above, the slit length Ls can be set, for example, to 60 cm or more and less than 100 cm, 100 cm or more and less than 150 cm, 150 cm or more and less than 200 cm, 200 cm or more and less than 250 cm, or 250 cm or more and less than 300 cm.
The inter-slit gap length L _G is preferably 1 cm or less, more preferably 5 mm or less, further preferably 2 mm or less, and may be 1 mm or less.

The above description of the slit length _L.sub.2 and the slit gap length _L.sub.2 is not limited to the partially divided carbon fiber bundle partially divided into five sub-bundles, but also applies to the partially divided carbon fiber bundle partially divided into four or less or six or more sub-bundles.
The bundle size of the sub-bundles formed by the partial division process is not particularly limited. For example, when a carbon fiber bundle having a bundle size of 12 to 24K is partially divided, the bundle size of the sub-bundles is preferably set to 6K or less, more preferably 4K or less, even more preferably 3K or less, and even more preferably 2K or less.
The size of the sub-bundles when partially dividing a carbon fiber bundle having a bundle size of 36K to 120K is preferably set to 18K or less, and may be, for example, 15K or less, 12K or less, 9K or less, 6K or less, 4K or less, 3K or less, 2K or less, etc.
In order to suppress fluffing of the partially split carbon fiber bundle, the bundle size of the sub-bundle is preferably 0.5K or more, and more preferably 1K or more.

2.4 Number of protrusions on the dividing jig In order to divide a carbon fiber bundle partially into n sub-bundles (n is an integer of 2 or more), it is necessary to simultaneously form (n-1) slits in the carbon fiber bundle, and for this purpose, the dividing jig must have at least (n-1) protrusions. Furthermore, the dividing jig must be arranged in the partial division section so that the (n-1) protrusions can be inserted into the carbon fiber bundle simultaneously.

To divide a carbon fiber bundle into n sub-bundles using a dividing jig with exactly (n-1) protrusions, it is necessary to guide the carbon fiber bundle tightly and prevent the y-direction position of the carbon fiber bundle from shifting while traveling through the partial division section. In addition, it is necessary to precisely match the y-direction position of the dividing jig with the y-direction position of the carbon fiber bundle. Otherwise, as shown in FIG. 19, the y-direction position of the carbon fiber bundle 11 may shift significantly while the protrusion (needle 22) is not inserted, and the protrusion located at one end of the dividing jig 20 in the y direction may not insert into the carbon fiber bundle 11. If this occurs, the number of sub-bundles formed will be reduced to (n-1), and one sub-bundle with an abnormally large bundle size will be formed.

To guide the carbon fiber bundle securely, a grooved guide roller with a groove width that matches the width of the carbon fiber bundle can be used. In this case, it is desirable to set the running speed of the carbon fiber bundle relatively low, although this is disadvantageous from the standpoint of production efficiency, in order to prevent the edges of the carbon fiber bundle from folding as it passes through the grooved guide roller, narrowing the bundle width.

If a decrease in production efficiency is not desired, the idea can be changed so that, instead of dividing the carbon fiber bundle into n sub-bundles using a dividing jig with exactly (n-1) protrusions, the number of protrusions on the dividing jig can be (n+1) or more, so that the carbon fiber bundle is divided into at least n sub-bundles. In this embodiment, a certain degree of variation in the y-direction position of the carbon fiber bundle within the partial division section is tolerated so that the running speed of the carbon fiber bundle does not need to be reduced, and even if there is a variation in the y-direction position, the number of protrusions that simultaneously pierce the carbon fiber bundle does not fall below (n-1).

20 and 21 show an example in which n is 9 and the dividing jig has (n+1) or 10 needles as protrusions.
20, after the eight protrusions (needles 22) of the dividing jig 20A that had been stuck into the carbon fiber bundle 11 are pulled out, the y-direction position of the carbon fiber bundle 11 shifts slightly, so that the number of protrusions that will next be stuck into the carbon fiber bundle 11 is nine. In this case, the number of sub-bundles increases from nine to ten, but no sub-bundles with abnormally large bundle sizes are formed.

21 , the position of the carbon fiber bundle 11 in the y direction is significantly shifted after the eight protrusions (needles 22) of the dividing jig 20A that have been stuck into the carbon fiber bundle 11 are pulled out, and therefore the number of protrusions that will next be stuck into the carbon fiber bundle 11 remains at 8. In this case as well, no sub-bundles with abnormally large bundle sizes are formed.
20 and 21, the longitudinal direction of the needle 22 is parallel to the z direction when the needle 22 is inserted into the carbon fiber bundle 11, but this is not limited to this. In a preferred example, the needle 22 may be inclined so as to fall toward the downstream side in the running direction of the carbon fiber bundle 11 when the needle 22 is inserted into the carbon fiber bundle 11.

The number of protrusions of the splitting jig that simultaneously penetrate the carbon fiber bundle is set so that the bundle size of the sub-bundles formed is equal to or less than a predetermined upper limit. Therefore, if the bundle size of the carbon fiber bundle before splitting is 15K and the upper limit of the bundle size of the sub-bundles is approximately 5K, the number of protrusions of the splitting jig that simultaneously penetrate can be set to 2 or 3. If the bundle size of the carbon fiber bundle before splitting is 50K and the upper limit of the bundle size of the sub-bundles is approximately 10K, the number of protrusions of the splitting jig that simultaneously penetrate can be set to 4 or 5.

The carbon fiber bundles supplied to the partial division section may have fiber waste attached thereto, which is generated when a small portion of the carbon fibers is cut in an upstream process. The partial division process in the partial division section may also cut the carbon fibers, generating fiber waste. Such fiber waste is likely to get caught on the protruding portion of the division jig. If this fiber waste accumulates and becomes large cotton waste and adheres to the partial carbon fiber bundles, it may deteriorate the quality of the SMC manufactured using the partial carbon fiber bundles.
Therefore, in a preferred embodiment, compressed air may be blown onto the protruding portion of the dividing jig during the partial dividing process to blow off the caught fiber waste and/or cotton dust. The compressed air may be blown continuously or intermittently. More preferably, a suction nozzle is provided near the dividing jig to remove the fiber waste and/or cotton dust blown off by the compressed air, thereby preventing them from adhering to the partially divided carbon fiber bundles.

3. Summary of the Preferred Embodiments Preferred embodiments of the present invention include, but are not limited to, the following.
[Embodiment A1] A method for producing a partially split carbon fiber bundle, in which carbon fiber bundles are continuously supplied from a carbon fiber production line to a partial splitting line connected to the carbon fiber production line, and are subjected to a partial splitting process in a partial splitting section provided in the partial splitting line.
[Embodiment A2] The method according to embodiment A1, wherein the carbon fiber production line includes a sizing section, and the carbon fiber bundle is sized in the sizing section before being supplied to the portion division line.
[Embodiment A3] A method according to embodiment A2, in which a single tensioning mechanism serves as both the tensioning mechanism for the sizing section and the tensioning mechanism for the partial dividing line.
[Embodiment A4] A method according to any one of embodiments A1 to A3, in which a force generated due to the contraction of a precursor fiber bundle in the carbon fiber production line is utilized to apply tension to the carbon fiber bundle in the partial division line.
[Embodiment A5] The method according to any one of embodiments A1 to A4, wherein the partial splitting process includes intermittently piercing the carbon fiber bundle running along its longitudinal direction with a protrusion of a splitting jig having a protrusion.
[Embodiment A6] The method according to embodiment A5, wherein the protrusion is formed by a needle.
[Embodiment A7] The method according to embodiment A6, wherein the needle is inclined so as to fall toward the downstream side in the running direction of the carbon fiber bundle when the needle is pierced into the carbon fiber bundle.
[Embodiment A8] The method according to embodiment A5, wherein the protrusion is formed of a plate.
[Embodiment A9] The method according to embodiment A8, wherein in a portion of the plate-shaped protrusion that pierces the carbon fiber bundle, when the protrusion is pierced into the carbon fiber bundle, the edge of the protrusion facing the upstream side in the running direction of the carbon fiber bundle is inclined so as to fall toward the downstream side in the running direction of the carbon fiber bundle.
[Embodiment A10] The method according to embodiment A8 or A9, wherein the plate-shaped protrusion has at least one convex corner, and in the partial division process, the number of the convex corners of the protrusion that are stuck into the carbon fiber bundle does not exceed one.
[Embodiment A11] The method according to any of embodiments A8 to A10, wherein the plate-shaped protrusion has at least one convex corner with an interior angle of 90° or more but does not have any convex corners with an interior angle of less than 90°, and in the partial division process, the number of the convex corners of the protrusion that are in a state of being pierced into the carbon fiber bundle does not exceed 1.
[Embodiment A12] The method according to any one of embodiments A8 to A11, wherein the plate-shaped protrusion has two right-angled corners, and in the partial division process, only one of the two right-angled corners of the protrusion is pierced into the carbon fiber bundle.
[Embodiment A13] A method according to any one of embodiments A8 to A12, wherein the protrusion is formed using a rectangular plate, and in the partial division process, only one of the four right-angled corners of the rectangular plate penetrates the carbon fiber bundle.
[Embodiment A14] The method according to any one of embodiments A5 to A13, wherein the dividing jig is reciprocated to intermittently pierce the carbon fiber bundle with the protrusions in the partial dividing process. The reciprocating motion may be a linear reciprocating motion or a swinging motion.
[Embodiment A15] The method according to any one of embodiments A5 to A14, wherein the partial dividing process includes oscillating the dividing jig to intermittently pierce the protrusions into the carbon fiber bundle.
[Embodiment A16] The method according to embodiment A15, wherein when the protrusion penetrates the carbon fiber bundle, the protrusion moves in the opposite direction to the running direction of the carbon fiber bundle, and when the protrusion comes out of the carbon fiber bundle, the protrusion moves in the same direction as the running direction of the carbon fiber bundle.
[Embodiment A17] A method according to embodiment A15 or A16, in which the partial division section has an x direction, a y direction, and a z direction that are perpendicular to each other, and when the longitudinal direction and width direction of the carbon fiber bundle as it passes through the partial division section are parallel to the x direction and the y direction, respectively, the division jig oscillates around an axis parallel to the y direction.
[Embodiment A18] The method according to any one of embodiments A5 to A17, comprising blowing compressed air onto the protruding portion of the dividing jig while the partial dividing process is being carried out.
[Embodiment A19] The method according to any of embodiments A5 to A18, wherein the dividing jig has exactly (n-1) of the protrusions, and the partial dividing process divides the carbon fiber bundle partially into n sub-bundles, where n is an integer equal to or greater than 2.
[Embodiment A20] The method according to any one of embodiments A5 to A18, wherein the dividing jig has (n+1) or more of the protrusions, and the partial dividing process divides the carbon fiber bundle partially into n or (n+1) sub-bundles, where n is an integer of 2 or more.
[Embodiment A21] A method according to embodiment A19 or A20, wherein the bundle size of each of the sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less or 2K or less.
[Embodiment A22] The method according to any of embodiments A1 to A18, wherein the partial splitting treatment splits the carbon fiber bundle partially into a plurality of sub-bundles, and the bundle size of each of the plurality of sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less.
[Embodiment A23] The method according to any one of embodiments A1 to A22, in which, in the partial division treatment, a slit row consisting of a plurality of slits lined up along the longitudinal direction of the carbon fiber bundle is formed in the carbon fiber bundle, and the length of the plurality of slits is 20 cm or more, preferably 40 cm or more, and more preferably 60 cm or more. For example, the length may be 60 cm or more and less than 100 cm, 100 cm or more and less than 150 cm, 150 cm or more and less than 200 cm, 200 cm or more and less than 250 cm, or 250 cm or more and less than 300 cm.

[Embodiment B1] A method for producing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial dividing process, the partial dividing process including intermittently piercing the carbon fiber bundle traveling along its own longitudinal direction with a protrusion of a dividing jig having a protrusion, the protrusion being formed by a needle, and the needle being inclined so as to fall downstream in the traveling direction of the carbon fiber bundle when pierced into the carbon fiber bundle.
[Embodiment B2] A method for producing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial dividing process, the partial dividing process including intermittently piercing a protrusion of a dividing jig having a protrusion into the carbon fiber bundle running along its longitudinal direction, the protrusion being formed of a plate, and when the plate-shaped protrusion is inserted into the carbon fiber bundle, in the portion of the protrusion inserted into the carbon fiber bundle, an edge of the protrusion facing the upstream side in the running direction of the carbon fiber bundle is inclined so as to fall toward the downstream side in the running direction of the carbon fiber bundle.
[Embodiment B3] A method according to embodiment B2, in which the plate-shaped protrusion has at least one convex corner, and in the partial division process, the number of the convex corners of the protrusion that are stuck into the carbon fiber bundle does not exceed one.
[Embodiment B4] A method according to embodiment B2 or B3, in which the plate-shaped protrusion has at least one convex corner with an interior angle of 90° or more but does not have any convex corners with an interior angle of less than 90°, and in which, in the partial division process, the number of the convex corners with an interior angle of 90° or more that are in a state of being stuck into the carbon fiber bundle does not exceed one.
[Embodiment B5] A method according to any one of embodiments B2 to B4, in which the plate-shaped protrusion has two right-angled corners at the protruding end, and in the partial division process, only one of the two right-angled corners of the protrusion is pierced into the carbon fiber bundle.
[Embodiment B6] A method according to any one of embodiments B2 to B5, in which the protrusion is formed using a rectangular plate, and in the partial division process, only one of the four right-angled corners of the rectangular plate penetrates the carbon fiber bundle.
[Embodiment B7] A method for producing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial division process, the partial division process comprising intermittently piercing the carbon fiber bundle running along its longitudinal direction with a protrusion of a division jig having a protrusion, the protrusion being formed of a plate, the plate-shaped protrusion having at least one convex corner with an interior angle of 90° or more but no convex corner with an interior angle of less than 90°, and in the partial division process, the number of the convex corners with an interior angle of 90° or more that are in a state of being pierced into the carbon fiber bundle does not exceed 1.
[Embodiment B8] A method for producing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial division process, the partial division process including intermittently piercing the carbon fiber bundle running along its longitudinal direction with a protrusion of a division jig having a protrusion, the protrusion being formed of a plate, the plate-shaped protrusion having two right-angled corners, and in the partial division process, only one of the two right-angled corners is pierced into the carbon fiber bundle.
[Embodiment B9] A method for producing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial division process, the partial division process including intermittently piercing the carbon fiber bundle running along its longitudinal direction with a protrusion of a division jig having a protrusion, the protrusion being formed using a rectangular plate, and in the partial division process, only one of four right-angled corners of the rectangular plate is pierced into the carbon fiber bundle.
[Embodiment B10] The method according to any one of embodiments B1 to B9, wherein the dividing jig is reciprocated to intermittently pierce the carbon fiber bundle with the protrusions in the partial dividing process. The reciprocating motion may be a linear reciprocating motion or a swinging motion.
[Embodiment B11] A method according to any one of embodiments B1 to B10, wherein the partial dividing process includes oscillating the dividing jig to intermittently pierce the protrusions into the carbon fiber bundle.
[Embodiment B12] The method according to embodiment B11, wherein when the protrusion penetrates the carbon fiber bundle, the protrusion moves in the opposite direction to the running direction of the carbon fiber bundle, and when the protrusion comes out of the carbon fiber bundle, the protrusion moves in the same direction as the running direction of the carbon fiber bundle.
[Embodiment B13] A method according to embodiment B11 or B12, in which the space in which the partial division process is performed has an x-direction, a y-direction, and a z-direction which are perpendicular to each other, and the longitudinal direction and width direction of the carbon fiber bundle when passing through the space are parallel to the x-direction and the y-direction, respectively, and the division jig oscillates around an axis parallel to the y-direction.
[Embodiment B14] The method according to any one of embodiments B1 to B13, comprising blowing compressed air onto the protruding portion of the dividing jig while the partial dividing process is being carried out.
[Embodiment B15] The method according to any one of embodiments B1 to B14, wherein the dividing jig has exactly (n-1) of the protrusions, and the partial dividing process divides the carbon fiber bundle partially into n sub-bundles, where n is an integer equal to or greater than 2.
[Embodiment B16] The method according to any one of embodiments B1 to B14, wherein the dividing jig has (n+1) or more of the protrusions, and the partial dividing process divides the carbon fiber bundle partially into n or (n+1) sub-bundles, where n is an integer of 2 or more.
[Embodiment B17] A method according to embodiment B15 or B16, wherein the bundle size of each of the sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less or 2K or less.
[Embodiment B18] The method according to any of embodiments B1 to B14, wherein the partial splitting process splits the carbon fiber bundle partially into a plurality of sub-bundles, and the bundle size of each of the plurality of sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less.
[Embodiment B19] The method according to any one of embodiments B1 to B18, in which, in the partial division treatment, a slit row consisting of a plurality of slits lined up along the longitudinal direction of the carbon fiber bundle is formed in the carbon fiber bundle, and the length of the plurality of slits is 20 cm or more, preferably 40 cm or more, and more preferably 60 cm or more. For example, the length may be 60 cm or more and less than 100 cm, 100 cm or more and less than 150 cm, 150 cm or more and less than 200 cm, 200 cm or more and less than 250 cm, or 250 cm or more and less than 300 cm.

[Embodiment C1] A method for producing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial division process, the partial division process including swinging a division jig having a protrusion to intermittently pierce the protrusion into the carbon fiber bundle traveling along its own longitudinal direction.
[Embodiment C2] A method according to embodiment C1, wherein when the protrusion penetrates the carbon fiber bundle, the protrusion moves in the opposite direction to the running direction of the carbon fiber bundle, and when the protrusion comes out of the carbon fiber bundle, the protrusion moves in the same direction as the running direction of the carbon fiber bundle.
[Embodiment C3] A method according to embodiment C1 or C2, in which the space in which the partial division process is performed has an x-direction, a y-direction, and a z-direction which are perpendicular to each other, and the longitudinal direction and width direction of the carbon fiber bundle when passing through the space are parallel to the x-direction and the y-direction, respectively, and the division jig oscillates around an axis parallel to the y-direction.
[Embodiment C4] The method of any one of embodiments C1 to C3, wherein the protrusions are formed with needles.
[Embodiment C5] The method of any one of embodiments C1 to C3, wherein the protrusion is formed from a plate.
[Embodiment C6] The method of any one of embodiments C1 to C5, comprising blowing compressed air onto the protruding portion of the dividing jig while the partial dividing process is being performed.
[Embodiment C7] The method of any of embodiments C1 to C6, wherein the splitting jig has exactly (n-1) of the protrusions, and the partial splitting process partially splits the carbon fiber bundle into n sub-bundles, where n is an integer equal to or greater than 2.
[Embodiment C8] The method according to any one of embodiments C1 to C6, wherein the dividing jig has (n+1) or more of the protrusions, and the partial dividing process divides the carbon fiber bundle partially into n or (n+1) sub-bundles, where n is an integer of 2 or more.
[Embodiment C9] A method according to embodiment C7 or C8, wherein the bundle size of each of the sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less or 2K or less.
[Embodiment C10] The method according to any of embodiments C1 to C6, wherein the carbon fiber bundle is partially divided into a plurality of sub-bundles by the partial division treatment, and the bundle size of each of the plurality of sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less.
[Embodiment C11] The method according to any one of embodiments C1 to C10, in which, in the partial division treatment, a slit row consisting of a plurality of slits lined up along the longitudinal direction of the carbon fiber bundle is formed in the carbon fiber bundle, and the length of the plurality of slits is 20 cm or more, preferably 40 cm or more, and more preferably 60 cm or more. For example, it may be 60 cm or more and less than 100 cm, 100 cm or more and less than 150 cm, 150 cm or more and less than 200 cm, 200 cm or more and less than 250 cm, or 250 cm or more and less than 300 cm.

[Embodiment D1] A method for producing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial division process, the partial division process including intermittently piercing the carbon fiber bundle running along its own longitudinal direction with a protrusion of a dividing jig having a protrusion, and blowing compressed air onto the protrusion of the dividing jig while the partial division process is being performed.
[Embodiment D2] The method of embodiment D1, wherein the protrusion is formed by a needle.
[Embodiment D3] The method according to embodiment D1, wherein the protrusion is formed of a plate.
[Embodiment D4] The method of any of embodiments D1 to D3, wherein the splitting jig has exactly (n-1) of the protrusions, and the partial splitting process partially splits the carbon fiber bundle into n sub-bundles, where n is an integer equal to or greater than 2.
[Embodiment D5] The method according to any one of embodiments D1 to D3, wherein the dividing jig has (n+1) or more of the protrusions, and the partial dividing process divides the carbon fiber bundle partially into n or (n+1) sub-bundles, where n is an integer of 2 or more.
[Embodiment D6] A method according to embodiment D4 or D5, wherein the bundle size of each of the sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less or 2K or less.
[Embodiment D7] The method according to any of embodiments D1 to D3, wherein the partial splitting process splits the carbon fiber bundle partially into a plurality of sub-bundles, and the bundle size of each of the plurality of sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less.
[Embodiment D8] The method according to any one of embodiments D1 to D7, in which, in the partial division treatment, a slit row consisting of a plurality of slits lined up along the longitudinal direction of the carbon fiber bundle is formed in the carbon fiber bundle, and the length of the plurality of slits is 20 cm or more, preferably 40 cm or more, and more preferably 60 cm or more, and may be, for example, 60 cm or more and less than 100 cm, 100 cm or more and less than 150 cm, 150 cm or more and less than 200 cm, 200 cm or more and less than 250 cm, or 250 cm or more and less than 300 cm.

[Embodiment E1] A method for producing a partially divided carbon fiber bundle by subjecting a carbon fiber bundle to a partial division process, the partial division process comprising intermittently piercing the carbon fiber bundle running along its own longitudinal direction with a protruding portion of a division jig having a protruding portion, the division jig having (n+1) or more protruding portions, and the carbon fiber bundle is partially divided into n or (n+1) sub-bundles in the partial division process, where n is an integer of 2 or more.
[Embodiment E2] A method according to embodiment E1, wherein the bundle size of each of the sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less or 2K or less.
[Embodiment E3] The method of embodiment E1 or E2, wherein the protrusion is formed by a needle.
[Embodiment E4] The method of embodiment E1 or E2, wherein the protrusion is formed of a plate.
[Embodiment E5] The method according to any one of embodiments E1 to E4, in which, in the partial division treatment, a slit row consisting of a plurality of slits lined up along the longitudinal direction of the carbon fiber bundle is formed in the carbon fiber bundle, and the length of the plurality of slits is 20 cm or more, preferably 40 cm or more, and more preferably 60 cm or more. For example, the length may be 60 cm or more and less than 100 cm, 100 cm or more and less than 150 cm, 150 cm or more and less than 200 cm, 200 cm or more and less than 250 cm, or 250 cm or more and less than 300 cm.

4. Experimental Results The results of the experiments conducted by the present inventors are described below.

Experiment 1
By adding a partial division section to an existing carbon fiber production line which has a calcination section, surface treatment section, and sizing section, in that order from the upstream side, and a winder at the downstream end, we attempted to continuously carry out the processes from calcining precursor fiber bundles made of polyacrylonitrile to the partial division processing of the resulting carbon fiber bundles.
In the partial division section, a slitter roll having a slit blade with a notch provided on the peripheral surface was installed as a means for partial division processing.
When the partial split section was disposed between the sizing section and the winder, the partially split carbon fiber bundles could be stably produced.
On the other hand, when the partial division section was disposed between the surface treatment section and the sizing section, the carbon fiber bundles became significantly fuzzed during the partial division process, and some of the carbon fibers were unraveled to form single filaments, which could become entangled in the guide rolls.

Experiment 2
Instead of the slitter roll, a dividing jig having a plurality of needles arranged parallel to each other and fixed to each other as exemplified in Figures 4 to 6 (the same as the dividing jig used in Experiment 3 described later) was installed in the partial division section as a means for partial division treatment. The needles were intermittently pierced into the carbon fiber bundle by swinging the dividing jig around a swing axis provided parallel to the width direction of the carbon fiber bundle traveling in the partial division section.
Other than the above change, the same procedure as in Experiment 1 was followed, and an attempt was made to continuously carry out the processes from the calcination of the precursor fiber bundle made of polyacrylonitrile to the partial division of the resulting carbon fiber bundle.
The results were similar to those of Experiment 1. When the partial division section was placed between the sizing section and the winder, a partially divided carbon fiber bundle could be stably produced. However, when the partial division section was placed between the surface treatment section and the sizing section, the carbon fiber bundle became significantly frayed during the partial division process, and some of the bundle unraveled, resulting in carbon fiber in a single filament state.

Experiment 3
A partial division line as shown in FIG. 1 was prepared, and a carbon fiber bundle (TR50S15L, manufactured by Mitsubishi Chemical Co., Ltd.) having 15K filaments, which was produced in a carbon fiber production line (including a sizing section) separate from the partial division line and wound around a bobbin, was pulled out from the bobbin and an attempt was made to perform partial division processing.
In the section for dividing the specimen, a dividing jig having multiple protrusions each formed by a needle was installed as a means for dividing the specimen into portions. The needle was made of stainless steel (SUS304), had a hemispherical tip, and had a cylindrical body with a diameter of 0.8 mm.

In the dividing jig, more than 15 needles were arranged in parallel at a constant pitch of 1 mm, as in the examples shown in Figures 4 to 6. In the partially divided section, the orientation of the dividing jig was adjusted so that the straight line connecting the tips of the needles was parallel to the width direction of the traveling carbon fiber bundle. Since the width of the undivided carbon fiber bundle was approximately 7 mm, the number of needles that could be inserted into the carbon fiber bundle at the same time was approximately six.

In the partial splitting process, while the carbon fiber bundle was traveling at a constant speed of 10 m/min, the splitting jig was held still for 4.2 seconds with the needle piercing the carbon fiber bundle, and within the next 0.2 seconds, the needle was removed from the carbon fiber bundle, and the splitting jig was moved back and forth linearly so as to pierce the carbon fiber bundle again. This operation was repeated.
The direction of the reciprocating movement of the dividing jig was perpendicular to both the running direction and the width direction of the carbon fiber bundle, i.e., the dividing jig was moved parallel to the z direction in FIG.
During the rest period of 4.2 seconds, the angle (θ in the example of FIG. 13) between the longitudinal direction of the needle and the running direction of the carbon fiber bundle was kept at 90°.
As time passed, carbon fiber debris accumulated on the dividing jig as shown in FIG. 23, but this did not pose any problem to the stability of the partial dividing process.

4.4 Experiment 4
In experiment 4, the same dividing jig as that used in experiment 3 was used. However, in order to pierce the needle of the dividing jig into the carbon fiber bundle and to remove it from the carbon fiber bundle, the dividing jig was not moved back and forth linearly, but was swung around a swing axis parallel to the width direction of the traveling carbon fiber bundle (the y direction in FIG. 3 ). In this case, as in the example of FIG. 14 , when the needle was pierced into the carbon fiber bundle, it was moved in the opposite direction to the traveling direction of the carbon fiber bundle, and when the needle was removed from the carbon fiber bundle, it was moved in the same direction as the traveling direction of the carbon fiber bundle.
Furthermore, during the rest period of 4.2 seconds, the angle (θ in the example of FIG. 14 ) between the longitudinal direction of the needle and the running direction of the carbon fiber bundle was set to 45°. That is, during the rest period, the needle was inclined so as to fall at an angle of 45° downstream in the running direction of the carbon fiber bundle.
Except for the above points, partial division of the carbon fiber bundle was attempted in the same manner as in Experiment 3, and there was no problem with the stability of the partial division process. Moreover, the amount of carbon fiber scraps accumulated in the dividing jig by the partial division process for the same period of time was less than that in Experiment 3, as shown in FIG.

4.5 Experiment 5
A fiber-splitting jig was set up in the same manner as in Experiment 4, and while the carbon fiber bundle was being run, the fiber-splitting jig was stationary with a needle pierced into the carbon fiber bundle. When the jig was rotated so that the needle moved in the opposite direction to the running direction of the carbon fiber bundle, it was investigated whether the needle would come out of the carbon fiber bundle.
As a result, when the dividing jig was rotated, the carbon fiber bundle was bitten into the dividing jig, and the needle could not be removed from the carbon fiber bundle. This is thought to be because the rotation of the dividing jig caused the needle that had pierced the carbon fiber bundle to tilt toward the upstream side in the running direction of the carbon fiber bundle.

4.6. Experiment 6
In experiment 6, an attempt was made to partially divide the carbon fiber bundle in the same manner as in experiment 3, except that the dividing jig was changed.
The split jig used in Experiment 6 had multiple protrusions, each of which was formed from a rectangular plate. The rectangular plate was made of stainless steel (SUS304) and had a thickness of 0.2 mm.
In the splitting jig, more than 15 rectangular plates were arranged in parallel at a constant pitch of 0.8 mm by stacking them alternately with spacers having a thickness of 0.6 mm. In the partial splitting section, the orientation of the splitting jig was adjusted so that the straight lines connecting the corners of different rectangular plates were parallel to the width direction of the traveling carbon fiber bundle, and the position of the splitting jig during the stationary period of 4.2 seconds was adjusted so that only one corner of each rectangular plate was pierced into the carbon fiber bundle. Since the width of the unsplit carbon fiber bundle was about 7 mm, the number of rectangular plates that could be pierced into the carbon fiber bundle at the same time was approximately eight.

During the 4.2-second stationary period, the angle (θ in the example of FIG. 16 ) made by the edge of the rectangular plate facing the upstream side of the running direction of the carbon fiber bundle at the part where the rectangular plate pierced the carbon fiber bundle and the running direction was set to three different angles of 30°, 45°, and 60°. In all cases, the results showed that there was no problem with the stability of the partial division process. However, the larger the angle, the larger the amount of carbon fiber scraps accumulated in the division jig by the partial division process for the same time.
Figure 25 is a photograph of the division jig after the partial division process was performed with the angle set to 60°, and Figure 26 is a photograph of the division jig after the partial division process was performed for the same period of time with the angle set to 30°.

　The present invention has been described above with reference to specific embodiments, but each embodiment is presented as an example and does not limit the scope of the present invention. Each embodiment described in this specification can be modified in various ways within the scope of the effects of the invention, and can be combined with features described in other embodiments within the scope of feasibility.

The present invention provides an improved method for producing partially split carbon fiber bundles.

REFERENCE SIGNS LIST 1 Partial division section 2 Partial division line 3 Undivided carbon fiber bundle 4 Partially divided carbon fiber bundle 5 Carbon fiber production line 6 Precursor fiber bundle 7 Sintering section 8 Surface treatment section 9 Sizing section 11 Traveling carbon fiber bundle 20 Division jig 21 Base 22 Needle (protruding part)
22a Tip of needle 24 Plate 25 Screw 31 Spacer 32 Plate (protruding part)
32a: edge of plate 35: straight portion of plate 40: actuator 45: shaft 50: slitter roll 51: peripheral surface 52: slit blade 53: missing portion

Claims (66)

1. A method for producing a partially split carbon fiber bundle, comprising the steps of:
   The carbon fiber bundle is continuously supplied from a carbon fiber production line to a portion splitting line connected to the carbon fiber production line,
   The method comprises the steps of: dividing the part in a dividing section provided on the dividing line;
2. The method according to claim 1, wherein the carbon fiber production line includes a sizing section, and the carbon fiber bundles are sized in the sizing section before being supplied to the portion division line.
3. The method according to claim 2, in which a single tensioning mechanism serves both the tensioning mechanism for the sizing section and the tensioning mechanism for the partial dividing line.
4. The method according to any one of claims 1 to 3, wherein the force generated by the shrinkage of the precursor fiber bundle in the carbon fiber production line is utilized to apply tension to the carbon fiber bundle in the partial division line.
5. The method according to any one of claims 1 to 4, wherein the partial splitting process includes intermittently piercing the carbon fiber bundle running along its longitudinal direction with a protrusion of a splitting jig having a protrusion.
6. The method of claim 5, wherein the protrusion is formed by a needle.
7. The method according to claim 6, wherein the needle is inclined so as to fall downstream in the direction of travel of the carbon fiber bundle when it is pierced into the carbon fiber bundle.
8. The method of claim 5, wherein the protrusion is formed from a plate.
9. The method according to claim 8, wherein, in the portion of the plate-shaped protrusion that is inserted into the carbon fiber bundle, when the protrusion is inserted into the carbon fiber bundle, the edge of the protrusion facing the upstream side in the running direction of the carbon fiber bundle is inclined so as to fall toward the downstream side in the running direction of the carbon fiber bundle.
10. The method according to claim 8 or 9, wherein the plate-shaped protrusion has at least one convex corner, and in the partial division process, the number of the convex corners of the protrusion that are stuck into the carbon fiber bundle does not exceed one.
11. The method according to any one of claims 8 to 10, wherein the plate-shaped protrusion has at least one convex corner with an interior angle of 90° or more, but has no convex corners with an interior angle of less than 90°, and in the partial division process, the number of the convex corners with an interior angle of 90° or more that are stuck into the carbon fiber bundle does not exceed one.
12. The method according to any one of claims 8 to 11, wherein the plate-shaped protrusion has two right-angled corners, and in the partial division process, only one of the two right-angled corners of the protrusion is inserted into the carbon fiber bundle.
13. The method according to any one of claims 8 to 12, wherein the protrusion is formed using a rectangular plate, and in the partial division process, only one of the four right-angled corners of the rectangular plate penetrates the carbon fiber bundle.
14. The method according to any one of claims 5 to 13, wherein the partial division process involves reciprocating the division jig to intermittently pierce the protrusions into the carbon fiber bundle. The reciprocating motion may be a linear reciprocating motion or a swinging motion.
15. The method according to any one of claims 5 to 14, wherein the partial splitting process involves oscillating the splitting jig to intermittently pierce the protrusions into the carbon fiber bundle.
16. The method according to claim 15, wherein when the protrusion is inserted into the carbon fiber bundle, the protrusion moves in a direction opposite to the running direction of the carbon fiber bundle, and when the protrusion is removed from the carbon fiber bundle, the protrusion moves in the same direction as the running direction of the carbon fiber bundle.
17. The method according to claim 15 or 16, wherein the partial division section has x-, y-, and z-directions that are perpendicular to each other, and the longitudinal and width directions of the carbon fiber bundle as it passes through the partial division section are parallel to the x- and y-directions, respectively, and the division jig oscillates about an axis parallel to the y-direction.
18. The method according to any one of claims 5 to 17, comprising blowing compressed air onto the protruding portion of the splitting jig while the partial splitting process is being performed.
19. The method according to any one of claims 5 to 18, wherein the splitting jig has exactly (n-1) of the protrusions, and the partial splitting process splits the carbon fiber bundle partially into n sub-bundles, where n is an integer of 2 or more.
20. The method according to any one of claims 5 to 18, wherein the splitting jig has (n+1) or more of the protrusions, and the partial splitting process splits the carbon fiber bundle partially into n or (n+1) sub-bundles, where n is an integer of 2 or more.
21. The method of claim 19 or 20, wherein the bundle size of each of the sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less.
22. The method according to any one of claims 1 to 18, wherein the carbon fiber bundle is partially divided into a plurality of sub-bundles by the partial division process, and the bundle size of each of the plurality of sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less.
23. The method according to any one of claims 1 to 22, wherein in the partial division process, a slit row consisting of a plurality of slits aligned along the longitudinal direction of the carbon fiber bundle is formed in the carbon fiber bundle, and the length of the plurality of slits is 20 cm or more, preferably 40 cm or more, and more preferably 60 cm or more, and may be, for example, 60 cm or more and less than 100 cm, 100 cm or more and less than 150 cm, 150 cm or more and less than 200 cm, 200 cm or more and less than 250 cm, or 250 cm or more and less than 300 cm.
24. A method for producing a partially split carbon fiber bundle by subjecting a carbon fiber bundle to a partial split treatment, comprising the steps of:
    The partial division process includes intermittently piercing the carbon fiber bundle traveling along the longitudinal direction of the carbon fiber bundle with a protrusion of a division jig having a protrusion,
    The protrusion is formed of a needle,
    The method, wherein the needles are inclined so as to fall downstream in the running direction of the carbon fiber bundle when pierced into the carbon fiber bundle.
25. A method for producing a partially split carbon fiber bundle by subjecting a carbon fiber bundle to a partial split treatment, comprising the steps of:
    The partial division process includes intermittently piercing the carbon fiber bundle traveling along the longitudinal direction of the carbon fiber bundle with a protrusion of a division jig having a protrusion,
    The protrusion is formed of a plate,
    wherein, when the plate-shaped protrusion is pierced into the carbon fiber bundle, in the portion of the protrusion that has pierced the carbon fiber bundle, an edge of the protrusion facing the upstream side in the running direction of the carbon fiber bundle is inclined so as to fall toward the downstream side in the running direction of the carbon fiber bundle.
26. The method according to claim 25, wherein the plate-shaped protrusion has at least one convex corner, and the number of the convex corners of the protrusion that are stuck into the carbon fiber bundle during the partial division process does not exceed one.
27. The method according to claim 25 or 26, wherein the plate-shaped protrusion has at least one convex corner with an interior angle of 90° or more, but does not have any convex corners with an interior angle of less than 90°, and in the partial division process, the number of the convex corners with an interior angle of 90° or more that are stuck into the carbon fiber bundle does not exceed one.
28. The method according to any one of claims 25 to 27, wherein the plate-shaped protrusion has two right-angled corners at the protruding end, and only one of the two right-angled corners of the protrusion is inserted into the carbon fiber bundle during the partial division process.
29. The method according to any one of claims 25 to 28, wherein the protrusion is formed using a rectangular plate, and in the partial division process, only one of the four right-angled corners of the rectangular plate penetrates the carbon fiber bundle.
30. A method for producing a partially split carbon fiber bundle by subjecting a carbon fiber bundle to a partial split treatment, comprising the steps of:
    The partial division process includes intermittently piercing the carbon fiber bundle traveling along the longitudinal direction of the carbon fiber bundle with a protrusion of a division jig having a protrusion,
    The protrusion is formed of a plate,
    The plate-shaped protrusion has at least one convex corner with an interior angle of 90° or more, but does not have any convex corner with an interior angle of less than 90°;
    In the partial division process, the number of convex corners of the protrusion with an interior angle of 90° or more that are stuck into the carbon fiber bundle does not exceed one.
31. A method for producing a partially split carbon fiber bundle by subjecting a carbon fiber bundle to a partial split treatment, comprising the steps of:
    The partial division process includes intermittently piercing the carbon fiber bundle traveling along the longitudinal direction of the carbon fiber bundle with a protrusion of a division jig having a protrusion,
    The protrusion is formed of a plate,
    The plate-shaped protrusion has two right-angled corners;
    The method, wherein only one of the two right-angled corners penetrates the carbon fiber bundle during the partial splitting process.
32. A method for producing a partially split carbon fiber bundle by subjecting a carbon fiber bundle to a partial split treatment, comprising the steps of:
    The partial division process includes intermittently piercing the carbon fiber bundle traveling along the longitudinal direction of the carbon fiber bundle with a protrusion of a division jig having a protrusion,
    The protrusion is formed using a rectangular plate;
    The method, wherein in the partial division process, only one of the four right-angled corners of the rectangular plate penetrates the carbon fiber bundle.
33. The method according to any one of claims 24 to 32, wherein the partial division process involves reciprocating the division jig to intermittently pierce the protrusions into the carbon fiber bundle. The reciprocating motion may be a linear reciprocating motion or an oscillating motion.
34. The method according to any one of claims 24 to 33, wherein the partial splitting process involves oscillating the splitting jig to intermittently pierce the protrusions into the carbon fiber bundle.
35. The method according to claim 34, wherein when the protrusion is inserted into the carbon fiber bundle, the protrusion moves in a direction opposite to the running direction of the carbon fiber bundle, and when the protrusion is removed from the carbon fiber bundle, the protrusion moves in the same direction as the running direction of the carbon fiber bundle.
36. The method according to claim 34 or 35, wherein the space in which the partial division process is performed has x, y, and z directions that are perpendicular to each other, and when the longitudinal direction and width direction of the carbon fiber bundle when passing through the space are parallel to the x and y directions, respectively, the division jig oscillates around an axis parallel to the y direction.
37. The method according to any one of claims 24 to 36, comprising blowing compressed air onto the protruding portion of the splitting jig while the partial splitting process is being performed.
38. The method according to any one of claims 24 to 37, wherein the splitting jig has exactly (n-1) of the protrusions, and the partial splitting process splits the carbon fiber bundle partially into n sub-bundles, where n is an integer of 2 or more.
39. The method according to any one of claims 24 to 37, wherein the splitting jig has (n+1) or more of the protrusions, and the partial splitting process splits the carbon fiber bundle partially into n or (n+1) sub-bundles, where n is an integer of 2 or more.
40. The method of claim 38 or 39, wherein the bundle size of each of the sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less.
41. The method according to any one of claims 24 to 37, wherein the partial division process divides the carbon fiber bundle into a plurality of sub-bundles, and the bundle size of each of the plurality of sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, and even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less.
42. The method according to any one of claims 24 to 41, wherein in the partial division process, a slit row consisting of a plurality of slits aligned along the longitudinal direction of the carbon fiber bundle is formed in the carbon fiber bundle, and the length of the plurality of slits is 20 cm or more, preferably 40 cm or more, and more preferably 60 cm or more, and may be, for example, 60 cm or more and less than 100 cm, 100 cm or more and less than 150 cm, 150 cm or more and less than 200 cm, 200 cm or more and less than 250 cm, or 250 cm or more and less than 300 cm.
43. A method for producing a partially split carbon fiber bundle by subjecting a carbon fiber bundle to a partial split treatment, comprising the steps of:
    The partial division process includes swinging a division jig having protrusions to intermittently pierce the carbon fiber bundle traveling along its longitudinal direction with the protrusions.
44. The method according to claim 43, wherein when the protrusion is inserted into the carbon fiber bundle, the protrusion moves in a direction opposite to the running direction of the carbon fiber bundle, and when the protrusion is removed from the carbon fiber bundle, the protrusion moves in the same direction as the running direction of the carbon fiber bundle.
45. The method according to claim 43 or 44, wherein the space in which the partial division process is performed has x, y, and z directions that are perpendicular to each other, and when the longitudinal direction and width direction of the carbon fiber bundle when passing through the space are parallel to the x and y directions, respectively, the division jig oscillates around an axis parallel to the y direction.
46. The method according to any one of claims 43 to 45, wherein the protrusion is formed by a needle.
47. The method according to any one of claims 43 to 45, wherein the protrusion is formed of a plate.
48. The method according to any one of claims 43 to 47, comprising blowing compressed air onto the protruding portion of the splitting jig while the partial splitting process is being performed.
49. The method according to any one of claims 43 to 48, wherein the splitting jig has exactly (n-1) of the protrusions, and the partial splitting process splits the carbon fiber bundle partially into n sub-bundles, where n is an integer of 2 or more.
50. The method according to any one of claims 43 to 48, wherein the splitting jig has (n+1) or more of the protrusions, and the partial splitting process splits the carbon fiber bundle partially into n or (n+1) sub-bundles, where n is an integer of 2 or more.
51. The method of claim 49 or 50, wherein the bundle size of each of the sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less.
52. The method according to any one of claims 43 to 48, wherein the carbon fiber bundle is partially divided into a plurality of sub-bundles by the partial division process, and the bundle size of each of the plurality of sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less.
53. The method according to any one of claims 43 to 52, wherein in the partial division process, a slit row consisting of a plurality of slits aligned along the longitudinal direction of the carbon fiber bundle is formed in the carbon fiber bundle, and the length of the plurality of slits is 20 cm or more, preferably 40 cm or more, more preferably 60 cm or more, and may be, for example, 60 cm or more and less than 100 cm, 100 cm or more and less than 150 cm, 150 cm or more and less than 200 cm, 200 cm or more and less than 250 cm, or 250 cm or more and less than 300 cm.
54. A method for producing a partially split carbon fiber bundle by subjecting a carbon fiber bundle to a partial split treatment, comprising the steps of:
    The partial division process includes intermittently piercing the carbon fiber bundle traveling along the longitudinal direction of the carbon fiber bundle with a protrusion of a division jig having a protrusion,
    A method comprising blowing compressed air onto the protruding portion of the dividing jig while the partial dividing process is being performed.
55. The method of claim 54, wherein the protrusion is formed by a needle.
56. The method of claim 54, wherein the protrusion is formed from a plate.
57. The method according to any one of claims 54 to 56, wherein the splitting jig has exactly (n-1) of the protrusions, and the partial splitting process splits the carbon fiber bundle partially into n sub-bundles, where n is an integer of 2 or more.
58. The method according to any one of claims 54 to 56, wherein the splitting jig has (n+1) or more of the protrusions, and the partial splitting process splits the carbon fiber bundle partially into n or (n+1) sub-bundles, where n is an integer of 2 or more.
59. The method of claim 57 or 58, wherein the bundle size of each of the sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less.
60. The method according to any one of claims 54 to 56, wherein the carbon fiber bundle is partially divided into a plurality of sub-bundles by the partial division process, and the bundle size of each of the plurality of sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, and even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less.
61. The method according to any one of claims 54 to 60, wherein in the partial division process, a slit row consisting of a plurality of slits aligned along the longitudinal direction of the carbon fiber bundle is formed in the carbon fiber bundle, and the length of the plurality of slits is 20 cm or more, preferably 40 cm or more, more preferably 60 cm or more, and may be, for example, 60 cm or more and less than 100 cm, 100 cm or more and less than 150 cm, 150 cm or more and less than 200 cm, 200 cm or more and less than 250 cm, or 250 cm or more and less than 300 cm.
62. A method for producing a partially split carbon fiber bundle by subjecting a carbon fiber bundle to a partial split treatment, comprising the steps of:
    The partial division process includes intermittently piercing the carbon fiber bundle traveling along the longitudinal direction of the carbon fiber bundle with a protrusion of a division jig having a protrusion,
    The dividing jig has (n+1) or more of the protrusions,
    The method, wherein the partial division process partially divides the carbon fiber bundle into n or (n+1) sub-bundles, where n is an integer of 2 or more.
63. The method of claim 62, wherein the bundle size of each of the sub-bundles is 18K or less, preferably 15K or less, more preferably 12K or less, even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less.
64. The method of claim 62 or 63, wherein the protrusion is formed by a needle.
65. The method of claim 62 or 63, wherein the protrusion is formed from a plate.
66. The method according to any one of claims 62 to 65, wherein in the partial division process, a slit row consisting of a plurality of slits aligned along the longitudinal direction of the carbon fiber bundle is formed in the carbon fiber bundle, and the length of the plurality of slits is 20 cm or more, preferably 40 cm or more, and more preferably 60 cm or more, and may be, for example, 60 cm or more and less than 100 cm, 100 cm or more and less than 150 cm, 150 cm or more and less than 200 cm, 200 cm or more and less than 250 cm, or 250 cm or more and less than 300 cm.

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