Method for producing partially divided carbon fiber bundle

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

[0001] The present invention relates primarily to a method for producing a partially split carbon fiber bundle. This application claims priority to 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.

[0002] 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 constituting the bundle. SMC using chopped carbon fiber bundles with smaller bundle size as reinforcing material can provide CFRP with better mechanical properties (Patent Document 1).

[0003] On the other hand, the larger the carbon fiber bundle size, the lower the production cost. Therefore, it has been proposed to partially split the carbon fiber bundle by intermittently piercing it with a plate or needle before using it in the production of SMC (Patent Document 2). Partial splitting refers to partially splitting an original single continuous fiber bundle into multiple sub-bundles.

[0004] US Patent Application Publication No. 2012 / 0213997 International Patent Application Publication No. 2017 / 221655

[0005] An object of the present invention is to provide an improvement in a method for producing a partially split carbon fiber bundle. More specifically, the objects of the present invention include the following: - To provide a technique for producing a partially split carbon fiber bundle with stable quality. - To provide a partially split carbon fiber bundle suitable as a raw material for SMC. - To prevent a decrease in the quality of the partially split carbon fiber bundle caused by problems during the partial splitting process. - To prevent a decrease in the production efficiency of the partially split carbon fiber bundle caused by problems during the partial splitting process.

[0006] According to one aspect of the present invention, there is provided 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.

[0007] 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 dividing process, wherein the partial dividing process includes intermittently piercing the carbon fiber bundle running along its longitudinal direction with a protrusion of a dividing jig having a protrusion, the protrusion being formed by a needle, and the needle is inclined so as to fall downstream in the running direction of the carbon fiber bundle when pierced into the carbon fiber bundle.

[0008] 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 dividing process, wherein the partial dividing process includes intermittently piercing the carbon fiber bundle running along its longitudinal direction with a protrusion of a dividing jig having a protrusion, the protrusion being formed by a plate, and when the plate is pierced into the carbon fiber bundle, at the portion where 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.

[0009] 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 dividing treatment, wherein the partial dividing treatment includes intermittently piercing the carbon fiber bundle running along its longitudinal direction with protrusions of a dividing jig having protrusions, the protrusions being formed of plates, the plate-shaped protrusions 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 in the partial dividing treatment, 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 one.

[0010] 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 dividing process, wherein the partial dividing process includes intermittently piercing the carbon fiber bundle running along its longitudinal direction with protrusions of a dividing jig having protrusions, the protrusions being formed of plates, the plate-shaped protrusions having two right-angled corners, and only one of the two right-angled corners being pierced into the carbon fiber bundle in the partial dividing process.

[0011] 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 dividing process, wherein the partial dividing process includes intermittently piercing the carbon fiber bundle running along its longitudinal direction with protrusions of a dividing jig having protrusions, the protrusions being formed using a rectangular plate, and in the partial dividing process, only one of four right-angled corners of the rectangular plate is pierced into the carbon fiber bundle.

[0012] 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 dividing process, wherein the partial dividing process includes swinging a dividing jig having protrusions to intermittently pierce the protrusions into the carbon fiber bundle running along the longitudinal direction of the carbon fiber bundle.

[0013] 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, wherein the partial division process includes intermittently piercing the carbon fiber bundle traveling along its longitudinal direction with protrusions of a dividing jig having protrusions, and the method includes blowing compressed air onto the protrusions of the dividing jig while the partial division process is being performed.

[0014] 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 dividing treatment, wherein the partial dividing treatment includes intermittently piercing the carbon fiber bundle traveling along its longitudinal direction with protrusions of a dividing jig having protrusions, the dividing jig having (n+1) or more protrusions, and the carbon fiber bundle is partially divided into n or (n+1) sub-bundles in the partial dividing treatment, where n is an integer of 2 or more.

[0015] In accordance with the present invention, an improvement in the method for producing partially split carbon fiber bundles is provided.

[0016] FIG. 1 shows an example of a production line for partially divided carbon fiber bundles including a partial dividing line. FIG. 2 shows an example of a production line for partially divided carbon fiber bundles including a partial dividing line. FIG. 3 is an explanatory diagram of the x, y, and z directions in a partial dividing section. FIG. 4 is a perspective view showing an example of a dividing jig in which protrusions are formed with needles. FIG. 5 is a view of the dividing jig of FIG. 5 as seen from the u direction. FIG. 6 is a view of the dividing jig of FIG. 5 as seen from the s direction. FIG. 7 shows examples of shapes that the tapered tips of the needles 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 dividing jig. FIG. 10 is a perspective view showing an example of a dividing jig in which protrusions are formed with plates. FIG. 11 is a view of the dividing jig of FIG. 10 as seen from the u direction. FIG. 12 is a view of the dividing jig of FIG. 10 as seen from the s direction. FIG. 13 shows one embodiment of a process for partially dividing a carbon fiber bundle using a dividing jig in which protrusions are formed with needles. FIG. 14 shows an embodiment of partial division processing of a carbon fiber bundle using a dividing jig having protruding portions formed with needles. FIG. 15 shows an embodiment of partial division processing of a carbon fiber bundle using a dividing jig having protruding portions formed with needles. FIG. 16 shows an embodiment of partial division processing of a carbon fiber bundle using a dividing jig having protruding portions formed with plates. FIG. 17 shows an embodiment of partial division processing of a carbon fiber bundle using a dividing jig having protruding portions formed with plates. FIG. 18 is a plan view showing an example of a partially divided carbon fiber bundle. FIG. 19 shows a situation that may occur when the y-direction position of the carbon fiber bundle is shifted while the protruding portions of the dividing jig are not inserted. FIG. 20 shows a situation that may occur when the y-direction position of the carbon fiber bundle is shifted while the protruding portions of the dividing jig are not inserted. FIG. 21 shows a situation that may occur when the y-direction position of the carbon fiber bundle is shifted while the protruding portions of the dividing jig are not inserted. FIG. 22 is a perspective view showing an example of a slitter roll having a missing portion provided in the slit blade. Fig. 23 is a photograph showing the dividing jig after use in the partial dividing process. Fig. 24 is a photograph showing the dividing jig after use in the partial dividing process. Fig. 25 is a photograph showing the dividing jig after use in the partial dividing process. Fig. 26 is a photograph showing the dividing jig after use in the partial dividing process.

[0017] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 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.

[0018] 1. Partial Dividing Line One embodiment of the present invention relates to a method for producing a partially divided carbon fiber bundle. In the method according to the embodiment, a partial dividing line 2 having a partial dividing section 1 is prepared, for example, as shown in Fig. 1. In the partial dividing line 2 shown in Fig. 1, an undivided carbon fiber bundle 3, which is a starting material, is unwound from a spool and supplied to the partial dividing section 1.

[0019] 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.

[0020] In the partial division section 1, the carbon fiber bundles 3 are subjected to partial division processing to become partially divided carbon fiber bundles 4. The partial division processing can be performed, for example, by intermittently piercing the carbon fiber bundles 3 traveling 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 processing of the carbon fiber bundles 3 in the partial division section can be performed using a slitter roll having a cutout portion on a slit blade provided on the circumferential surface. 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 on a slit blade 52 provided on a circumferential surface 51. The partially divided carbon fiber bundles 4 that have left the partial division section are taken up on another spool.

[0021] 2, a carbon fiber production line 5 and a partial splitting line 2 are connected, and 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 flame retardant section and a carbonization section as subsections, and may further include a graphitization section.

[0022] The precursor fiber bundle 6 may be twisted at, for example, 5 to 20 turns / m. In this case, the unsplit carbon fiber bundle 3 is untwisted downstream of the baking section 7 so that it is preferably in an untwisted state. This untwisting is preferably carried out before the sizing is completed, and may be carried out upstream of the surface treatment section 8, for example.

[0023] After being produced in the carbon fiber production line 5, the undivided carbon fiber bundle 3 is 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 the 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 around a spool before being partially divided is advantageous in terms of stabilizing the quality of the partially divided carbon fiber bundle. This is because the carbon fiber bundle does not develop a curl before being supplied to the partial division line, and therefore the posture of the carbon fiber bundle when it runs through the partial division section is stable.

[0024] 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 bundles are thrown into a packaging container using, for example, the method disclosed in Japanese Patent Application Laid-Open No. 2012-188773 instead of being wound onto a spool, the shape of the carbon fiber bundles will also become curled. In general, carbon fiber bundles that have been packaged even once before being supplied to the partial division line will become curled, and their posture will become unstable when they run through the partial division section.

[0025] The posture of the carbon fiber bundle traveling through the partial division section becomes particularly unstable when a carbon fiber bundle that has been traverse wound around a spool is unwound and used. This is because, with traverse winding, the carbon fiber bundle is prone to localized twisting when the moving direction of the traverse guide is reversed, and the twist of the carbon fiber bundle does not completely return to its original state even after being unwound from the spool. In the partial division step, if the twisted portion of the carbon fiber bundle is processed with a tool such as a needle or plate, many carbon fibers are cut, which can cause the problem of severe fuzzing of the carbon fiber bundle after partial division. In contrast, when the carbon fiber production line and the partial division line are connected, a carbon fiber bundle that contains almost no twisted portions can be supplied to the partial division line, and fuzzing of the carbon fiber bundle in the partial division step is also suppressed.

[0026] It is important to size the carbon fiber bundle before feeding it to the partial division line. If the carbon fiber bundle is subjected to partial division without sizing, a large amount of fiber breakage will occur, and the carbon fiber bundle will become significantly fuzzed. This is because the introduction of functional groups onto the carbon fiber surface by surface treatment significantly increases both of the following two frictional forces: one is the frictional force acting between adjacent carbon fibers in the bundle, and the other is the frictional force acting between the carbon fiber and tools such as needles and plates used in the partial division process. The reason why fuzzing associated with the partial division process 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.

[0027] In the sizing section 9, the carbon fiber bundle is passed through a sizing bath and then dried. Because 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 also desirable to apply high tension to the carbon fiber bundle 3 in the partial division line 2 so that a tool such as a needle or plate can reliably pierce the carbon fiber bundle 3 in the partial division section 1. For this reason, in one example, to simplify the manufacturing 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 shrinkage of the precursor fiber bundle 6 due to baking in the baking section 7 can be used to apply tension to the carbon fiber bundle in the sizing section 9 and the partial division line 2.

[0028] 2. Partial Division Treatment In the method according to the embodiment, as described above, the carbon fiber bundle is partially divided in the partial division section provided in the partial division line. In a preferred embodiment, the partial division treatment is performed by piercing the carbon fiber bundle passing through the partial division section with a needle or a plate. Here, the method of partial division treatment used in this preferred embodiment will be described in detail.

[0029] 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 thickness direction are each perpendicular to the longitudinal direction and are also perpendicular to each other.

[0030] A tension is applied to the carbon fiber bundle traveling through the partially divided section so that its longitudinal direction is parallel to a first direction and its width direction is parallel to a second direction perpendicular to the first direction. In other words, the carbon fiber bundle passes through the partially divided section in a suspended state, stretched substantially straight along the first direction without being twisted. In this specification, as shown in FIG. 3 , the first direction is referred to as the x-direction in the partially divided section, and the second direction is referred to as the y-direction in the partially divided section. A 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.

[0031] It is obvious that a carbon fiber bundle vibrates when it is suspended in the air and travels. Therefore, even if the longitudinal direction of the carbon fiber bundle is parallel to the x-direction when it passes through the partial division section, this parallelism is not always maintained. Similarly, the width direction and y-direction of the carbon fiber bundle traveling through the partial division section are not always strictly parallel.

[0032] 2.2 Dividing Jig A dividing jig having protrusions formed by needles or plates is installed in the dividing section. The carbon fiber bundles fed to the dividing line are intermittently pierced by the protrusions of the dividing jig as they pass through the dividing section, thereby being divided into portions.

[0033] The number of protrusions that one dividing jig has is typically two or more, but may be one. The minimum number of protrusions that the dividing jig should have varies depending on how many sub-bundles the carbon fiber bundle should be partially divided into. The number of sub-bundles that 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.

[0034] Figures 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 Figures 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 figures. The eight needles are also arranged at equal intervals along the t direction, which is perpendicular to the u direction. All eight needles have the same length, and the straight line connecting their tips is parallel to the t direction.

[0035] The needle is typically made of a metal. Among these, steel, such as stainless steel, is preferred, but is not limited thereto. The needle has at least a body. The body is a part with a constant cross-sectional shape and area. The body is preferably cylindrical, but may also be an elliptical cylinder, or may be a triangular prism, a square prism, a hexagonal prism, or any other rectangular prism. The cross-sectional shape of the elliptical cylinder may be an ellipse or an oval.

[0036] The tip of the needle is preferably tapered so that it can be easily pierced into the carbon fiber bundle. Figure 7 shows examples of shapes that the tapered tip of the needle may have. Figure 7 illustrates, from left to right, 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.

[0037] 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, a smaller diameter of the body is preferable, but if it is too small, the rigidity decreases, and the needle may not pierce the carbon fiber or may be easily bent. 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 considered to be the diameter.

[0038] In terms of safe handling of the dividing jig, it is preferable that the needle tip is hemispherical. In order to obtain both ease of piercing the carbon fiber bundle and safety, the tapered tip other than hemispherical may have a rounded end or may have a terminal surface perpendicular to the axial direction.

[0039] The dividing jig 20A shown in Figures 4, 5, and 6 can be produced by preparing a base 21 having a plurality of holes 21a, inserting the base of each needle 22 into each hole 21a, and then gluing and fixing the needles 22 to the base 21, as shown in Figure 8. The dividing jig 20A shown in Figures 4, 5, and 6 is merely one example of a dividing jig having a plurality of needles arranged parallel to each other and fixed to each other. There is no limitation on the method for arranging a plurality of needles parallel to each other and fixing them to each other to produce a dividing jig. In another example, as shown in Figure 9, the needles 22 may be sandwiched between two plates 24 and fixed with screws 25.

[0040] Figures 10, 11, and 12 show an example of a dividing jig in which protrusions are formed from plates. The dividing jig 20B shown in Figures 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 their main surfaces (surfaces perpendicular to the thickness direction) are 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 figures. 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.

[0041] The plate 32 is typically made of a metal, preferably steel such as stainless steel, but not limited thereto. The method for fixing the spacer 31 and the plate 32 to each other is not limited, and various methods such as adhesive, clamping, screw fastening, and the like may be used as appropriate.

[0042] 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 bundles and to divide the carbon fiber bundles into sub-bundles with smaller bundle sizes. From this perspective, a thinner plate is preferable, but if it is too thin, the rigidity decreases and the plate may not pierce the carbon fiber bundles or may bend easily. 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 and difficult to pierce the carbon fiber bundles, the edge of the plate may be tapered.

[0043] The dividing jig 20B shown in Figures 10, 11, and 12 shows one preferred example, in which the plate 32 is rectangular, i.e., a quadrangle having four right-angle 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 quadrangle, 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.

[0044] 2.3. Partial Division In the partial division section, partial division of the carbon fiber bundle using a dividing jig is performed as follows. First, FIGS. 13, 14, and 15 show examples using a dividing jig with protrusions formed by needles. In FIGS. 13, 14, and 15, the running direction of the carbon fiber bundle 11 is from left to right in the figures, and this also applies to FIGS. 16, 17, 19, 20, and 21 described below. In the example shown in FIG. 13, the dividing jig 20A is linearly reciprocated by the actuator 40, so that the needles 22 intermittently pierce the running carbon fiber bundle 11. The dividing jig 20A is arranged so that its t direction is parallel to the y direction.

[0045] 14, the needles 22 intermittently pierce the traveling carbon fiber bundle 11 by swinging the dividing jig 20A around an axis 45 by an actuator (not shown). The axis 45 is parallel to the y direction. The dividing jig 20A is arranged so that its t direction is parallel to the y direction and, when a cylinder is imagined with the axis 45 as its center, the longitudinal direction of the needles 22 is parallel to the radial direction of the cylinder. This example can be modified so that the dividing jig 20A rotates instead of swinging.

[0046] 15 also shows an example in which the needles 22 intermittently pierce the running carbon fiber bundle 11 by swinging the dividing jig 20 about an axis 45 by an actuator (not shown). The axis 45 is parallel to the y direction. The dividing jig 20A is arranged so that its t direction is parallel to the y direction and so that, when a cylinder is imagined with the axis 45 as its center, the longitudinal direction of the needles 22 is inclined with respect to the radial direction of the cylinder.

[0047] 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 needles 22 from below or from above. In each of the examples shown in Figures 13, 14, and 15, the carbon fiber bundle 11 is split by keeping the splitting jig 20A stationary for a certain period of time with the needles 22 pierced into the traveling carbon fiber bundle 11. The needles 22 pierced into 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 of the traveling direction of the carbon fiber bundle 11 (+x direction) (angle θ is less than 90°). This advantageously makes it difficult for carbon fiber debris to accumulate in the splitting jig 20.

[0048] 16 and 17 show examples using a dividing jig in which the protruding portion is formed of a plate. In the example shown in Fig. 16, the dividing jig 20B is linearly reciprocated by the actuator 40, whereby the plate 32 intermittently pierces the traveling carbon fiber bundle 11. The dividing jig 20B is positioned 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.

[0049] 17 , the dividing jig 20B is swung around an axis 45 by an actuator (not shown), thereby intermittently piercing the plate 32 into the traveling carbon fiber bundle 11. The axis 45 is parallel to the y direction. The dividing jig 20B is arranged so that its t direction is parallel to the y direction, and 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.

[0050] 16 and 17 , when the plate 32 is pierced into the carbon fiber bundle 11, the edge 32 a of the plate facing the upstream side (−x direction) in the running direction of the carbon fiber bundle 11 is inclined so as to tilt toward the downstream side (+x direction) in the running direction of the carbon fiber bundle 11 (angle θ is smaller than 90°) in the part of the plate 32 that is pierced into the carbon fiber bundle 11. This advantageously makes it difficult for carbon fiber debris to accumulate in the dividing jig 20.

[0051] Furthermore, in each example shown in FIGS. 16 and 17 , only one of the two right-angled corners of the protruding portion of the plate 32 penetrates the carbon fiber bundle 11. In other words, at any moment during the partial division process, the number of right-angled corners of the protruding portion of the plate 32 that penetrates the carbon fiber bundle 11 does not exceed one. Therefore, the protruding portion formed by the plate 32 is unlikely to get caught on the carbon fiber bundle 11 when it penetrates the carbon fiber bundle 11 or when it is removed from the carbon fiber bundle 11. This is not limited to cases where the protruding portion is formed using a rectangular plate, but when the protruding portion of the dividing jig is plate-shaped and has multiple convex corners (corners with convex interior angles), the same effect can be achieved by ensuring that the number of the multiple convex corners that penetrates the carbon fiber bundle does not exceed one during the partial division process. In another aspect, the number of convex corners of the plate-shaped protruding portion may be only one to achieve the same effect. Preferably, the interior angle of the convex corner that pierces the carbon fiber bundle is set to 90° or more, so that the above effect becomes more pronounced. From the viewpoint of making it easier for the protrusion to pierce the carbon fiber bundle, the interior angle is preferably 120° or less.

[0052] Regardless of the type of protrusion, it is preferable that the motion of the dividing jig be reciprocating rather than rotating. Examples of reciprocating include linear reciprocating and swinging. Reciprocating is preferable 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. An example of an actuator for reciprocating the dividing jig is an air cylinder, but this is not limited to this and an electric motor may also be used.

[0053] 14, 15, and 17, the dividing jig is swung so that when the protrusions pierce the carbon fiber bundle, they move in the opposite direction to the running direction of the carbon fiber bundle, and when the protrusions come out of the carbon fiber bundle, they move in the same direction as the running direction of the carbon fiber bundle. Therefore, problems such as the protrusions that have pierced the carbon fiber bundle not being able to be removed, or the carbon fiber bundle being pulled by the protrusions and vibrating greatly when the protrusions come out of the carbon fiber bundle, which makes it difficult for the protrusions to be pierced properly thereafter, are less likely to occur.

[0054] As the carbon fiber bundle travels with the protruding parts of the dividing jig stuck in it, slits are formed in the carbon fiber bundle. When the protruding parts are 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 is obtained in which the carbon fiber bundle is partially divided into a plurality of sub-bundles. As an example of a partially divided carbon fiber bundle, FIG. 18 shows a partially divided carbon fiber bundle in which the divided parts into five sub-bundles are formed intermittently along the longitudinal direction. FIG. 18 is a plan view of a partially divided carbon fiber bundle 4 as viewed from the thickness direction.

[0055] Referring to FIG. 18, the partially split carbon fiber bundle 4 has a first slit row R Ｓ１ , second slit row R Ｓ２ , third slit row R Ｓ３ and the fourth slit row R Ｓ４ Four slit rows are formed. Ｓ１ The second slit row R is made up of a plurality of first slits S1 arranged along the longitudinal direction of the partially split carbon fiber bundle 4. Ｓ２ The third slit row R is made up of a plurality of second slits S2 arranged along the longitudinal direction of the partially split carbon fiber bundle 4. Ｓ３ The fourth slit row R is made up of a plurality of third slits S3 arranged along the longitudinal direction of the partially split carbon fiber bundle 4. Ｓ４ consists of a plurality of fourth slits S4 arranged along the longitudinal direction of the partially split carbon fiber bundle 4.

[0056] 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, and S4, is roughly the product of the time from when the protrusions pierce the carbon fiber bundle until when they are pulled out and the running speed of the carbon fiber bundle. Ｓ１ , R Ｓ２ , R Ｓ３ , R Ｓ３ The gap G between the slits at each Ｓ The gap length between the slits is L Ｇ is roughly the product of the time from when the protrusion is pulled out of the carbon fiber bundle until it is next stuck into the carbon fiber bundle and the running speed of the carbon fiber bundle. Ｓ and the gap length between the slits L Ｇ is constant within any slit row and is common among all slit rows.

[0057] The slit length Ls is preferably 20 cm or more, more preferably 40 cm or more, and even more preferably 60 cm or more. A larger slit length Ls is advantageous because the chopped carbon fiber bundles obtained when the split carbon fiber bundles 4 are cut to produce an SMC contain a larger number of fibers having the same bundle size as the sub-bundles. This is because the fiber length of the chopped carbon fiber bundles is preferably 5 to 60 mm, more preferably 10 to 30 mm, and can even be 20 mm or less. From this viewpoint, there is no particular upper limit to the slit length Ls.

[0058] On the other hand, the longer the slit length Ls, the more likely it is that problems (for example, winding around a roll) that occur when a sub-bundle breaks in a partial dividing line or a line for producing an SMC using the partially divided carbon fiber bundles 4 will become serious. From this viewpoint, the slit length Ls is preferably 300 cm or less, more preferably 200 cm or less, and even more preferably 150 cm or less.

[0059] From the above, the slit length Ls can be set to, 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. Ｇis preferably 1 cm or less, more preferably 5 mm or less, even more preferably 2 mm or less, and may be 1 mm or less.

[0060] Slit length L Ｓ and the gap length L between the slits Ｇ The above description of the partially divided carbon fiber bundles applies not only to partially divided carbon fiber bundles partially divided into five sub-bundles, but also to partially divided carbon fiber bundles partially divided into four or less or six or more sub-bundles. The bundle size of the sub-bundles formed by the partially dividing treatment is not particularly limited. For example, when a carbon fiber bundle having a bundle size of 12 to 24K is divided into a partial dividing treatment, 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. When a carbon fiber bundle having a bundle size of 36K to 120K is divided into a partial dividing treatment, the size of the sub-bundles 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 fuzzing of the partially divided carbon fiber bundles, the bundle size of the sub-bundles is preferably 0.5K or more, more preferably 1K or more.

[0061] 2.4 Number of protrusions on the dividing jig 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 simultaneously pierce the carbon fiber bundle.

[0062] To partially divide a carbon fiber bundle into n sub-bundles using a dividing jig having exactly (n-1) protrusions, it is necessary to firmly guide the carbon fiber bundle so that the position of the carbon fiber bundle in the y direction does not shift 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 position of the carbon fiber bundle 11 in the y direction may shift significantly while the protrusions (needles 22) are not piercing the carbon fiber bundle 11, resulting in a situation where the protrusions located at one end of the dividing jig 20 in the y direction do not pierce 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.

[0063] To firmly guide the carbon fiber bundle, a grooved guide roller having a groove width that matches the width of the carbon fiber bundle may be used. In this case, in order to prevent the edges of the carbon fiber bundle from being folded when passing through the grooved guide roller and the bundle width from becoming narrower, it is desirable to set the running speed of the carbon fiber bundle relatively low, although this is disadvantageous from the viewpoint of production efficiency.

[0064] If a decrease in production efficiency is not desired, the idea can be changed so that, instead of dividing a carbon fiber bundle into n sub-bundles using a dividing jig having exactly (n-1) protrusions, the number of protrusions that the dividing jig has may be (n+1) or more, so that the carbon fiber bundle is partially divided into at least n sub-bundles. In this embodiment, to avoid the need to reduce the running speed of the carbon fiber bundle, fluctuations in the y-direction position of the carbon fiber bundle within the partially divided section are allowed to a certain extent, and even if there is a fluctuation in the y-direction position, the number of protrusions that simultaneously pierce the carbon fiber bundle is set to not fall below (n-1).

[0065] 20 and 21 show an example in which n is 9 and the dividing jig has (n+1) or 10 needles as protrusions. In the example shown in Fig. 20, after the eight protrusions (needles 22) of the dividing jig 20A that had been stuck in the carbon fiber bundle 11 are removed, the position of the carbon fiber bundle 11 in the y direction shifts slightly, so that the number of protrusions that will next be stuck in 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.

[0066] In the example shown in Figure 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 had been stuck in the carbon fiber bundle 11 are removed, and as a result, the number of protrusions that will next be stuck in the carbon fiber bundle 11 remains at eight. In this case, too, sub-bundles with abnormally large bundle sizes are not formed. In the examples shown in Figures 20 and 21, the longitudinal direction of the needles 22 when stuck in the carbon fiber bundle 11 is parallel to the z direction, but this is not limited to this. In a preferred example, the needles 22 may be inclined so as to fall downstream in the traveling direction of the carbon fiber bundle 11 when stuck in the carbon fiber bundle 11.

[0067] The number of protrusions of the dividing jig that simultaneously pierce the carbon fiber bundle is set so that the bundle size of the formed sub-bundles is equal to or less than a predetermined upper limit. Therefore, if the bundle size of the carbon fiber bundle before the dividing process is 15K and the upper limit of the bundle size of the sub-bundles is approximately 5K, the number of protrusions of the dividing jig that simultaneously pierce the carbon fiber bundle may be set to 2 or 3. If the bundle size of the carbon fiber bundle before the dividing process is 50K and the upper limit of the bundle size of the sub-bundles is approximately 10K, the number of protrusions of the dividing jig that simultaneously pierce the carbon fiber bundle may be set to 4 or 5.

[0068] The carbon fiber bundles supplied to the partial dividing section may have fiber waste attached thereto, which is generated when a small portion of the carbon fibers is cut in an upstream process. Furthermore, the partial dividing process in the partial dividing section may also cut the carbon fibers, generating fiber waste. Such fiber waste is likely to get caught on the protruding portion of the dividing jig. If this fiber waste accumulates and becomes large cotton waste, and adheres to the partially divided carbon fiber bundles, there is a risk of deteriorating the quality of the SMC manufactured using the partially divided carbon fiber bundles. Therefore, in a preferred example, compressed air may be blown onto the protruding portion of the dividing jig during the partial dividing process to blow away the caught fiber waste and / or cotton waste. The blowing of compressed air may be continuous or intermittent. More preferably, a suction nozzle is installed near the dividing jig to remove the fiber waste and / or cotton waste blown away by the compressed air, thereby preventing them from adhering to the partially divided carbon fiber bundles.

[0069] 3. Summary of Embodiments Preferred embodiments of the present invention include, but are not limited to, the following. [Embodiment A1] A method for producing a partially divided carbon fiber bundle, wherein a carbon fiber bundle is continuously supplied from a carbon fiber production line to a partial division line connected to the carbon fiber production line, and is subjected to a partial division process in a partial division section provided in the partial division 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 partial division line. [Embodiment A3] The method according to Embodiment A2, wherein a single tensioning mechanism serves as both a tensioning mechanism for the sizing section and a tensioning mechanism for the partial division line. [Embodiment A4] The method according to any one of Embodiments A1 to A3, wherein a force generated due to contraction of a precursor fiber bundle in the carbon fiber production line is used 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 dividing treatment includes intermittently piercing the carbon fiber bundle traveling along its longitudinal direction with protrusions of a dividing jig having protrusions. [Embodiment A6] The method according to Embodiment A5, wherein the protrusions are formed by needles. [Embodiment A7] The method according to Embodiment A6, wherein the needles are inclined so as to fall toward the downstream side in the traveling direction of the carbon fiber bundle when pierced into the carbon fiber bundle. [Embodiment A8] The method according to Embodiment A5, wherein the protrusions are formed by plates. [Embodiment A9] The method according to Embodiment A8, wherein, at a portion of the plate-shaped protrusions that pierces the carbon fiber bundle, an edge of the protrusion facing the upstream side in the traveling direction of the carbon fiber bundle when the protrusions pierce the carbon fiber bundle is inclined so as to fall toward the downstream side in the traveling direction of the carbon fiber bundle when the protrusions pierce the carbon fiber bundle. [Embodiment A10] A 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 convex corners of the protrusion that are stuck into the carbon fiber bundle does not exceed one.[Embodiment A11] The method according to any one 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 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 the protrusion has that are in a state of piercing 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 that the protrusion has is pierced into the carbon fiber bundle. [Embodiment A13] The 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 that the rectangular plate has is pierced into the carbon fiber bundle. [Embodiment A14] The method according to any one of Embodiments A5 to A13, wherein the partial dividing process involves reciprocating the dividing jig to intermittently pierce the carbon fiber bundle with the protruding portions. The reciprocating motion may be linear or may be swinging. [Embodiment A15] The method according to any one of Embodiments A5 to A14, wherein the partial dividing process involves swinging the dividing jig to intermittently pierce the carbon fiber bundle with the protruding portions. [Embodiment A16] The method according to Embodiment A15, wherein the protruding portions move in the opposite direction to the running direction of the carbon fiber bundle when they pierce the carbon fiber bundle, and move in the same direction as the running direction of the carbon fiber bundle when they come out of the carbon fiber bundle. [Embodiment A17] The method according to embodiment A15 or A16, wherein the partial division section has x, y, and z directions that are orthogonal to one another, and the longitudinal direction and width direction of the carbon fiber bundle when passing through the partial division section are parallel to the x and y directions, respectively, and the dividing jig oscillates around an axis parallel to the y direction. [Embodiment A18] The method according to any of embodiments A5 to A17, comprising blowing compressed air to the protruding portions of the dividing jig while the partial division process is being performed. [Embodiment A19] The method according to any of embodiments A5 to A18, wherein the dividing jig has exactly (n-1) protruding portions, and the carbon fiber bundle is partially divided into n sub-bundles in the partial division process.Here, n is an integer of 2 or more. [Embodiment A20] The method according to any one of Embodiments A5 to A18, wherein the dividing jig has (n+1) or more protrusions, and the carbon fiber bundle is partially divided into n or (n+1) sub-bundles in the partial dividing process. Here, n is an integer of 2 or more. [Embodiment A21] The 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 one of Embodiments A1 to A18, wherein the carbon fiber bundle is partially divided into a plurality of sub-bundles by the partial dividing 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. [Embodiment A23] The method according to any one of Embodiments A1 to A22, wherein 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.

[0070] [Embodiment B1] A method for producing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial division treatment, wherein the partial division treatment comprises intermittently piercing the carbon fiber bundle running along its longitudinal direction with protrusions of a dividing jig having protrusions, the protrusions being formed by needles, and the needles being inclined so as to lean toward the downstream side in the running 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 division treatment, wherein the partial division treatment comprises intermittently piercing the carbon fiber bundle running along its longitudinal direction with protrusions of a dividing jig having protrusions, the protrusions being formed by plates, and when the plate-shaped protrusions are 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 lean toward the downstream side in the running direction of the carbon fiber bundle when the plate-shaped protrusions are pierced into the carbon fiber bundle. [Embodiment B3] The method according to embodiment B2, 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 1. [Embodiment B4] The method according to embodiment B2 or B3, 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 stuck into the carbon fiber bundle does not exceed 1. [Embodiment B5] The method according to any of embodiments B2 to B4, wherein the plate-shaped protrusion has two right-angled corners at the end in the protruding direction, and in the partial division process, only one of the two right-angled corners of the protrusion is stuck 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 dividing treatment, wherein the partial dividing treatment comprises intermittently piercing the carbon fiber bundle running along its longitudinal direction with protruding portions of a dividing jig having protrusions, the protruding portions being formed of plates, the plate-shaped protruding portions 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 wherein, in the partial dividing treatment, the number of convex corners having an interior angle of 90° or more of the protruding portions that are stuck 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 dividing treatment, wherein the partial dividing treatment comprises intermittently piercing the carbon fiber bundle running along its longitudinal direction with protruding portions of a dividing jig having protrusions, the protruding portions being formed of plates, the plate-shaped protruding portions having two right-angled corners, and only one of the two right-angled corners piercing the carbon fiber bundle in the partial dividing treatment. [Embodiment B9] A method for producing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial division treatment, the partial division treatment comprising intermittently piercing the carbon fiber bundle traveling along its longitudinal direction with protrusions of a dividing jig having protrusions, the protrusions being formed using a rectangular plate, and the partial division treatment piercing the carbon fiber bundle at only one of four right-angled corners of the rectangular plate. [Embodiment B10] The method according to any of Embodiments B1 to B9, wherein the partial division treatment involves reciprocating the dividing jig to intermittently pierce the carbon fiber bundle with the protrusions. The reciprocating motion may be linear or may be swinging. [Embodiment B11] The method according to any of Embodiments B1 to B10, wherein the partial division treatment involves swinging the dividing jig to intermittently pierce the carbon fiber bundle with the protrusions. [Embodiment B12] The method according to embodiment B11, wherein when the protrusion pierces 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] The method according to embodiment B11 or B12, wherein the space in which the partial division treatment is performed has x, y, and z directions that are orthogonal 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 and y directions, respectively, and the dividing jig oscillates around an axis parallel to the y direction. [Embodiment B14] The method according to any of embodiments B1 to B13, comprising blowing compressed air to the protruding portions of the dividing jig while the partial division treatment is being performed. [Embodiment B15] The method according to any of embodiments B1 to B14, wherein the dividing jig has exactly (n-1) protruding portions, and the carbon fiber bundle is partially divided into n sub-bundles in the partial division treatment, where n is an integer of 2 or greater. [Embodiment B16] The method according to any of embodiments B1 to B14, wherein the dividing jig has (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 treatment. wherein n is an integer of 2 or greater. [Embodiment B17] The 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 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 B19] The method according to any one of embodiments B1 to B18, wherein 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.

[0071] [Embodiment C1] A method for producing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial division treatment, the partial division treatment comprising swinging a dividing jig having protrusions to intermittently pierce the carbon fiber bundle traveling along its longitudinal direction with the protrusions. [Embodiment C2] The method according to Embodiment C1, wherein the protrusions move in the opposite direction to the traveling direction of the carbon fiber bundle when piercing the carbon fiber bundle, and move in the same direction as the traveling direction of the carbon fiber bundle when removing the carbon fiber bundle. [Embodiment C3] The method according to Embodiment C1 or C2, wherein the space in which the partial division treatment is performed has x, y, and z directions that are orthogonal 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 and y directions, respectively, and the dividing jig swings about an axis parallel to the y direction. [Embodiment C4] The method according to any of Embodiments C1 to C3, wherein the protrusions are formed by needles. [Embodiment C5] The method according to any one of Embodiments C1 to C3, wherein the protrusions are formed by plates. [Embodiment C6] The method according to any one of Embodiments C1 to C5, comprising blowing compressed air onto the protrusions of the dividing jig while the partial division process is being performed. [Embodiment C7] The method according to any one of Embodiments C1 to C6, wherein the dividing jig has exactly (n-1) protrusions, and the carbon fiber bundle is partially divided into n sub-bundles in the partial division process, where n is an integer of 2 or greater. [Embodiment C8] The method according to any one of Embodiments C1 to C6, wherein the dividing jig has (n+1) or more protrusions, 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 greater. [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 one of Embodiments C1 to C6, wherein the partial division treatment partially 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. [Embodiment C11] The method according to any one of Embodiments C1 to C10, wherein the partial division treatment forms a slit row in the carbon fiber bundle, the slit row consisting of a plurality of slits lined up along the longitudinal direction of 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.

[0072] [Embodiment D1] A method for producing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial dividing treatment, the partial dividing treatment comprising intermittently piercing the carbon fiber bundle traveling along its longitudinal direction with protrusions of a dividing jig having protrusions, and blowing compressed air onto the protrusions of the dividing jig while the partial dividing treatment is being performed. [Embodiment D2] The method according to Embodiment D1, in which the protrusions are formed by needles. [Embodiment D3] The method according to Embodiment D1, in which the protrusions are formed by plates. [Embodiment D4] The method according to any one of Embodiments D1 to D3, in which the dividing jig has exactly (n-1) protrusions, and in the partial dividing treatment, the carbon fiber bundle is partially divided into n sub-bundles, where n is an integer of 2 or greater. [Embodiment D5] The method according to any one of Embodiments D1 to D3, in which the dividing jig has (n+1) or more protrusions, and in the partial dividing treatment, the carbon fiber bundle is partially divided into n or (n+1) sub-bundles. wherein n is an integer of 2 or greater. [Embodiment D6] The 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 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 D8] The method according to any one of embodiments D1 to D7, wherein 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.

[0073] [Embodiment E1] A method for producing partially divided carbon fiber bundles by subjecting a carbon fiber bundle to a partial division treatment, the partial division treatment comprising intermittently piercing the carbon fiber bundle traveling along its longitudinal direction with protrusions of a dividing jig having protrusions, the dividing 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 treatment. Here, n is an integer of 2 or more. [Embodiment E2] The 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 according to embodiment E1 or E2, wherein the protrusions are formed by needles. [Embodiment E4] The method according to embodiment E1 or E2, wherein the protrusions are formed by plates. [Embodiment E5] The method according to any one of embodiments E1 to E4, wherein 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.

[0074] 4. Experimental Results The results of the experiments conducted by the present inventors are described below.

[0075] 4.1. Experiment 1 In an existing carbon fiber production line equipped with a baking section, a surface treatment section, and a sizing section, in that order from the upstream side, and a winder at the downstream end, a partial division section was added to attempt to continuously perform processes from baking a precursor fiber bundle made of polyacrylonitrile to partial division of the resulting carbon fiber bundles. A slitter roll with a missing slit blade on its peripheral surface was installed in the partial division section as a means for partial division. When the partial division section was placed between the sizing section and the winder, partially divided carbon fiber bundles could be stably produced. In contrast, when the partial division section was placed between the surface treatment section and the sizing section, the carbon fiber bundles became significantly fluffy during the partial division process, and some of the fibers unraveled, resulting in single-filament carbon fibers. These single-filament carbon fibers were at risk of becoming entangled around the guide rolls.

[0076] 4.2. Experiment 2 Instead of the slitter roll, a dividing jig (the same as the dividing jig used in Experiment 3 described below) having multiple needles arranged parallel to and fixed to each other, as illustrated in Figures 4 to 6, was installed in the partial division section as a means for partial division treatment. The dividing jig was swung around a swing axis provided parallel to the width direction of the carbon fiber bundle traveling through the partial division section, thereby intermittently piercing the carbon fiber bundle with the needles. Except for this change, an attempt was made to continuously perform the processes from the calcination of the precursor fiber bundle made of polyacrylonitrile to the partial division treatment of the resulting carbon fiber bundle in the same manner as in Experiment 1. The results were similar to those of Experiment 1. When the partial division section was placed between the sizing section and the winder, partially divided carbon fiber bundles 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 fuzzed during the partial division treatment, and a portion of the bundle unraveled, resulting in the production of carbon fibers in a single filament state.

[0077] 4.3 Experiment 3: A partial division line as shown in Figure 1 was prepared, and a carbon fiber bundle (Mitsubishi Chemical's TR50S15L) with 15,000 filaments wound on a bobbin, which had been produced in a carbon fiber production line (including a sizing section) separate from the partial division line, was unwound from the bobbin and subjected to partial division processing. A dividing jig with multiple protrusions, each formed by a needle, was installed in the partial division section as a means for partial division processing. The needles were made of stainless steel (SUS304), had hemispherical tips, and cylindrical bodies with a diameter of 0.8 mm.

[0078] 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 partial dividing section, the orientation of the dividing jig was adjusted so that the line formed by 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 about 7 mm, the number of needles that could simultaneously pierce the carbon fiber bundle was approximately six.

[0079] In the partial division process, the carbon fiber bundle was run at a constant speed of 10 m / min, and the dividing jig was stopped for 4.2 seconds with the needle pierced into the carbon fiber bundle. Then, within the next 0.2 seconds, the needle was removed from the carbon fiber bundle and the dividing jig was linearly reciprocated so as to pierce the carbon fiber bundle again. This operation was repeated. The direction of reciprocation of the dividing jig was perpendicular to both the running direction and width direction of the carbon fiber bundle. That is, the dividing jig was moved parallel to the z direction shown in FIG. 3. During the 4.2-second stationary period, the angle between the longitudinal direction of the needle and the running direction of the carbon fiber bundle (θ in the example of FIG. 13) was 90°. Over time, carbon fiber debris accumulated on the dividing jig as shown in FIG. 23, but this did not result in any problems with the stability of the partial division process.

[0080] 4.4. Experiment 4 In Experiment 4, the same dividing jig as used in Experiment 3 was used. However, to pierce the needles of the dividing jig into the carbon fiber bundle and remove them from the carbon fiber bundle, the dividing jig was not linearly reciprocated, but was swung around a swing axis parallel to the width direction of the running carbon fiber bundle (the y direction in Figure 3 ). As shown in the example of Figure 14 , when piercing the carbon fiber bundle with the needles, the needles were moved in the opposite direction to the running direction of the carbon fiber bundle, and when removing the needles from the carbon fiber bundle, the needles were moved in the same direction as the running direction of the carbon fiber bundle. Furthermore, during the rest period of 4.2 seconds, the angle between the longitudinal direction of the needle and the running direction of the carbon fiber bundle (θ in the example of Figure 14 ) was set to 45°. That is, during the rest period, the needles were tilted so as to tilt at an angle of 45° downstream of 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 no problems were found with the stability of the partial division process. Furthermore, the amount of carbon fiber waste accumulated in the dividing jig by the partial dividing process for the same period of time was less than that in Experiment 3, as shown in FIG.

[0081] 4.5. Experiment 5 A splitting jig was set up in the same manner as in Experiment 4, and while a carbon fiber bundle was being run, the splitting jig was stationary with the 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 splitting jig was rotated, the carbon fiber bundle bit into the splitting jig, and the needle did not come out of the carbon fiber bundle. This is thought to be because the rotation of the splitting jig caused the needle pierced into the carbon fiber bundle to tilt so that it fell upstream in the running direction of the carbon fiber bundle.

[0082] 4.6. Experiment 6 In Experiment 6, partial division of a carbon fiber bundle was attempted in the same manner as in Experiment 3, except that the dividing jig was changed. The dividing jig used in Experiment 6 had multiple protrusions, each formed by a rectangular plate. The rectangular plates were made of stainless steel (SUS304) and had a thickness of 0.2 mm. In the dividing jig, more than 15 rectangular plates were stacked alternately with 0.6 mm thick spacers, arranging them in parallel at a constant pitch of 0.8 mm. In the partial division section, the orientation of the dividing jig was adjusted so that the lines connecting the corners of different rectangular plates were parallel to the width direction of the traveling carbon fiber bundle. The position of the dividing jig during the 4.2-second stationary period was also adjusted so that only one corner of each rectangular plate pierced the carbon fiber bundle. Since the width of the undivided carbon fiber bundle was approximately 7 mm, the number of rectangular plates that could simultaneously pierce the carbon fiber bundle was approximately eight.

[0083] During the 4.2-second stationary period, the angle (θ in the example of Figure 16) formed by the edge of the rectangular plate facing upstream in the running direction of the carbon fiber bundle at the part where the rectangular plate pierced the carbon fiber bundle was set to three angles: 30°, 45°, and 60°. In all cases, there were no problems with the stability of the partial division process. However, the larger the angle, the greater the amount of carbon fiber debris accumulated in the dividing jig after the same period of partial division. Figure 25 is a photograph of the dividing jig after partial division with the angle set to 60°. Figure 26 is a photograph of the dividing jig after partial division with the same period of partial division with the angle set to 30°.

[0084] While the present invention has been described above with reference to specific embodiments, these embodiments are presented as examples and do 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.

[0085] According to the present invention, an improved method for producing partially split carbon fiber bundles is provided.

[0086] 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 Burning section 8 Surface treatment section 9 Sizing section 11 Running carbon fiber bundle 20 Division jig 21 Base 22 Needle (protruding portion) 22a Needle tip 24 Plate 25 Screw 31 Spacer 32 Plate (protruding portion) 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

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 partial division process is performed in a partial division section provided on the partial division line, The method, 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.

2. The method according to claim 1 , wherein the carbon fiber production line comprises a sizing section, and the carbon fiber bundles are sized in the sizing section before being supplied to the portion splitting line.

3. The method according to claim 2 , wherein a single tensioning mechanism serves as both the tensioning mechanism for the sizing section and the tensioning mechanism for the partial dividing line.

4. The method according to claim 1 , wherein a force generated due to contraction of a precursor fiber bundle in the carbon fiber production line is utilized to apply tension to the carbon fiber bundle in the portion division line.

5. The method according to claim 1 , wherein the partial division process includes intermittently piercing the carbon fiber bundle running along its longitudinal direction with a protrusion of a division jig having the protrusion.

6. The method of claim 5 , wherein the protrusions are formed with needles.

7. The method according to claim 6 , wherein the needles are inclined so as to fall toward a downstream side in a running direction of the carbon fiber bundle when the needles are pierced into the carbon fiber bundle.

8. The method of claim 5 , wherein the protrusions are formed from a plate.

9. 9. The method according to claim 8, wherein, in a portion of the plate-shaped protrusion that pierces the carbon fiber bundle, when the protrusion pierces 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.

10. The method according to claim 8, 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 in a state of being pierced into the carbon fiber bundle does not exceed one.

11. 9. The method according to claim 8, 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 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 stuck into the carbon fiber bundle does not exceed one.

12. The method according to claim 8, 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 penetrates into the carbon fiber bundle.

13. 9. The method of claim 8, wherein the protrusion is formed using a rectangular plate, and in the partial division process, only one of four right-angled corners of the rectangular plate penetrates the carbon fiber bundle.

14. The method according to claim 5 , wherein the partial dividing process comprises reciprocating the dividing jig to intermittently pierce the carbon fiber bundle with the protrusions. The reciprocating motion may be a linear reciprocating motion or a swinging motion.

15. The method according to claim 5 , wherein the dividing jig is swung to intermittently pierce the carbon fiber bundle with the protrusions in the partial dividing process.

16. The method according to claim 15, wherein when the protrusion penetrates the carbon fiber bundle, the protrusion moves in a direction opposite 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.

17. 16. The method according to claim 15, wherein the partial division section has an x-direction, a y-direction, and a z-direction which are perpendicular to each other, and when the longitudinal direction and the width direction of the carbon fiber bundle when passing through the partial division section are parallel to the x-direction and the y-direction, respectively, the dividing jig oscillates about an axis parallel to the y-direction.

18. The method of claim 5 , further comprising blowing compressed air onto the protruding portion of the dividing jig while the portion dividing process is taking place.

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 partially splits the carbon fiber bundle into n sub-bundles, where n is an integer equal to or greater than 2.

20. The method according to any one of claims 5 to 18, wherein the dividing jig has (n+1) or more of the protrusions, and the carbon fiber bundle is divided partially into n or (n+1) sub-bundles in the partial dividing process, where n is an integer of 2 or more.

21. 20. The method of claim 19, wherein the bundle size of each of the sub-bundles is 18K 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 each of the plurality of sub-bundles has a bundle size of 18K or less.