Method for producing partially divided carbon fiber bundles

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

[Technical Field]

[0001] 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, and the contents thereof are incorporated herein by reference. [Background technology]

[0002] The mechanical properties of CFRP obtained by curing a prepreg impregnated with resin and reinforced with a random mat-type reinforcing material consisting of chopped carbon fiber bundles, such as SMC (Sheet Molding Compound), are influenced by the bundle size of the chopped carbon fiber bundles, that is, the number of carbon fiber filaments that make up the bundle. SMC using chopped carbon fiber bundles with smaller bundle sizes as reinforcement can yield CFRP with better mechanical properties (Patent Document 1).

[0003] On the other hand, the larger the size of the carbon fiber bundle, 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 manufacture of SMC (Patent Document 2). Partial division refers to the process of dividing a single continuous fiber bundle into multiple sub-bundles. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2012 / 0213997 [Patent Document 2] International Publication No. 2017 / 221655 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The object of the present invention is to provide improvements in a method for producing partially divided carbon fiber bundles. More specifically, the object of the present invention includes the following: To provide a technique for producing partially divided carbon fiber bundles with stable quality. To provide partially divided carbon fiber bundles suitable as raw materials for SMC. To prevent a decrease in the quality of partially divided carbon fiber bundles caused by problems during the partial division process. To prevent a decrease in the manufacturing efficiency of partially divided carbon fiber bundles caused by problems during the partial division process. [Means for solving the problem]

[0006] According to one aspect of the present invention, a method for producing a partially divided carbon fiber bundle is provided, wherein the carbon fiber bundle is continuously supplied from a carbon fiber manufacturing line to a partially divided line connected to the carbon fiber manufacturing line, and is partially divided in a partially divided section provided in the partially divided line.

[0007] According to another aspect of the present invention, a method is provided for producing a partially divided carbon fiber bundle by partially dividing a carbon fiber bundle, the partially dividing process comprising intermittently piercing the carbon fiber bundle, which is running along its longitudinal direction, with the projections of a dividing jig having projections, wherein the projections are formed of needles and are inclined to fall downstream in the direction of travel of the carbon fiber bundle when pierced.

[0008] According to yet another aspect of the present invention, a method is provided for producing a partially divided carbon fiber bundle by partially dividing a carbon fiber bundle, wherein the partial division process includes intermittently piercing the carbon fiber bundle, which is running along its longitudinal direction, with the projections of a dividing jig having projections, the projections being formed of plates, and when the plates are 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 to tilt downstream in the running direction of the carbon fiber bundle at the portion where the plates are pierced into the carbon fiber bundle.

[0009] According to yet another aspect of the present invention, a method is provided for producing a partially divided carbon fiber bundle by partially dividing a carbon fiber bundle, wherein the partial division process includes intermittently piercing the carbon fiber bundle, which runs along its longitudinal direction, with the 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 internal angle of 90° or more but no convex corners with an internal angle of less than 90°, and in the partial division process, the number of convex corners of the protrusion with an internal angle of 90° or more that are pierced into the carbon fiber bundle does not exceed one.

[0010] A method for producing a partially divided carbon fiber bundle by partially dividing a carbon fiber bundle is provided, the partially divided process comprising intermittently piercing the carbon fiber bundle, which runs along its longitudinal direction, with a projection of a dividing jig having a projection, wherein the projection is formed of a plate, the plate-shaped projection has two right-angle corners, and in the partially divided process only one of the two right-angle corners pierces the carbon fiber bundle.

[0011] According to still another aspect of the present invention, there is provided 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 including intermittently piercing the carbon fiber bundle traveling along its longitudinal direction with the protruding portion of a dividing jig having a protruding portion, the protruding portion being formed using a rectangular plate, and in the partial division process, only one of the four right-angled corners of the rectangular plate pierces the carbon fiber bundle.

[0012] According to still another aspect of the present invention, there is provided 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 including swinging a dividing jig having a protruding portion and intermittently piercing the carbon fiber bundle traveling along its longitudinal direction with the protruding portion.

[0013] According to still another aspect of the present invention, there is provided 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 including intermittently piercing the carbon fiber bundle traveling along its longitudinal direction with the protruding portion of a dividing jig having a protruding portion, and blowing compressed air onto the protruding portion of the dividing jig when the partial division process is being performed.

[0014] According to still another aspect of the present invention, there is provided 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 including intermittently piercing the carbon fiber bundle traveling along its longitudinal direction with the protruding portion of a dividing jig having a protruding portion, the dividing jig having (n + 1) or more of the protruding portions, and in the partial division process, the carbon fiber bundle being partially divided into n or (n + 1) sub-bundles. Here, n is an integer of 2 or more.

Advantages of the Invention

[0015] According to the present invention, an improvement in a method for producing a partially divided carbon fiber bundle is provided.

Brief Description of the Drawings

[0016] [Figure 1] Figure 1 shows an example of a production line of a partially divided carbon fiber bundle including a partial division line. [Figure 2] Figure 2 shows an example of a production line of a partially divided carbon fiber bundle including a partial division line. [Figure 3] Figure 3 is an explanatory diagram of the x, y, and z directions in the partial division section. [Figure 4] Figure 4 is a perspective view showing an example of a dividing jig in which the protrusion is formed by a needle. [Figure 5] Figure 5 is a view of the dividing jig of Figure 5 seen from the u direction. [Figure 6] Figure 6 is a view of the dividing jig of Figure 5 seen from the s direction. [Figure 7] Figure 7 shows an example of the shape that the tapered tip of the needle can have. [Figure 8] Figure 8 shows an example of a manufacturing method of the dividing jig. [Figure 9] Figure 9 shows an example of a manufacturing method of the dividing jig. [Figure 10] Figure 10 is a perspective view showing an example of a dividing jig in which the protrusion is formed by a plate. [Figure 11] Figure 11 is a view of the dividing jig of Figure 10 seen from the u direction. [Figure 12] Figure 12 is a view of the dividing jig of Figure 10 seen from the s direction. [Figure 13] Figure 13 shows an aspect of the partial division process of the carbon fiber bundle using a dividing jig in which the protrusion is formed by a needle. [Figure 14] Figure 14 shows an aspect of the partial division process of the carbon fiber bundle using a dividing jig in which the protrusion is formed by a needle. [Figure 15] Figure 15 shows an aspect of the partial division process of the carbon fiber bundle using a dividing jig in which the protrusion is formed by a needle. [Figure 16] Figure 16 shows an aspect of the partial division process of the carbon fiber bundle using a dividing jig in which the protrusion is formed by a plate. [Figure 17]Figure 17 shows one embodiment of partial division of a carbon fiber bundle using a division jig in which the protruding portion is formed from a plate. [Figure 18] Figure 18 is a plan view showing an example of a partially divided carbon fiber bundle. [Figure 19] Figure 19 illustrates what can happen if the y-direction position of the carbon fiber bundle shifts while the protrusion of the splitting jig is not inserted. [Figure 20] Figure 20 illustrates what can happen if the y-direction position of the carbon fiber bundle shifts while the protrusion of the splitting jig is not inserted. [Figure 21] Figure 21 illustrates what can happen if the y-direction position of the carbon fiber bundle shifts while the protrusion of the splitting jig is not inserted. [Figure 22] Figure 22 is a perspective view showing an example of a slitter roll with a defect in the slitting blade. [Figure 23] Figure 23 is a photograph showing the division jig after it has been used for partial division. [Figure 24] Figure 24 is a photograph showing the division jig after it has been used for partial division. [Figure 25] Figure 25 is a photograph showing the division jig after it has been used for partial division. [Figure 26] Figure 26 is a photograph showing the division jig after it has been used for partial division. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described below with reference to the drawings as appropriate. The dimensional ratios in the drawings are for illustrative purposes only and may differ from those in reality. In addition, identical components are indicated by the same reference numerals in the drawings, and descriptions of redundant components may be omitted.

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

[0019] The bundle size of carbon fiber bundle 3, that is, the number of carbon fiber filaments constituting carbon fiber bundle 3, is usually 12K or more, but may be 15K or more, 24 or more, 36K or more, 48K or more, etc., and is usually 120K or less, but may be 100K or less, 80K or less, 60K or less, etc., but is not limited to these values. Here, K is a symbol meaning 1000, for example, 12K means 12,000, and 120K means 120,000.

[0020] In partial division section 1, the carbon fiber bundle 3 is partially divided 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 plate, but other tools may also be used. In one example, the partial division of the carbon fiber bundle 3 in the partially divided section can be performed using a slitter roll with a defect in the slitting blade provided on its circumferential surface. An example of such a slitter roll is shown in Figure 22. In the slitter roll 50 shown in Figure 22, a defect 53 is provided in the slitting blade 52 provided on the circumferential surface 51. The partially divided carbon fiber bundles 4 that have exited the partially divided section are wound onto another spool.

[0021] In another example, as shown in Figure 2, the carbon fiber manufacturing line 5 and the partial division line 2 are connected, and undivided carbon fiber bundles 3 are continuously supplied from the carbon fiber manufacturing line 5 to the partial division line 2. The carbon fiber manufacturing line 5 includes, in order from upstream, a firing section 7 for firing precursor fiber bundles 6 made of polyacrylonitrile to form carbon fiber bundles, a surface treatment section 8 for surface treatment to introduce functional groups to the carbon fiber surface, and a sizing section 9 for sizing the carbon fiber bundles. The firing section 7 typically includes a flame-retardant section and a carbonization section as subsections, and may also include a graphitization section.

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

[0023] The undivided carbon fiber bundles 3 are manufactured in the carbon fiber manufacturing line 5 and then supplied to the partial division line 2 without being wound onto a spool. There, they are partially divided in the partial division section 1 of the partial division line 2 to become partially divided carbon fiber bundles 4. The partially divided carbon fiber bundles 4 are then wound onto a spool. Not winding carbon fiber bundles onto spools before partial splitting in a carbon fiber manufacturing line is advantageous in stabilizing the quality of the partially split carbon fiber bundles. This is because the absence of coiling before being supplied to the partial splitting line ensures a stable posture as the carbon fiber bundles travel through the partial splitting sections.

[0024] Carbon fiber bundles are prone to developing a curl due to their plasticity, or more specifically, because a resin containing low-molecular-weight compounds called a sizing agent is used to bind the carbon fibers together. Therefore, even when carbon fiber bundles are sprinkled into a packaging container using a method disclosed in, for example, Japanese Patent Publication No. 2012-188773, instead of being wound onto a spool, the shape of the carbon fiber bundles will still develop a curl. Generally speaking, carbon fiber bundles that have been packaged even once before being supplied to a partial division line will develop a curl, resulting in an unstable posture when running through the partial division section.

[0025] The orientation of the carbon fiber bundle when it travels through a divided section becomes particularly unstable when the carbon fiber bundle is unwound from a spool that has been traversed. This is because, in traversed winding, the carbon fiber bundle is prone to localized twisting when the direction of movement of the traverse guide is reversed, and this twisting does not completely return to its original state even after being unwound from the spool. In the partial splitting process, if the twisted portion of the carbon fiber bundle is processed with a tool such as a needle or plate, a large number of carbon fibers are cut, which can lead to the problem of the carbon fiber bundle becoming severely frayed after partial splitting. In contrast, when the carbon fiber manufacturing line and the partial splitting line are connected, carbon fiber bundles containing almost no twisted portions can be supplied to the partial splitting line, thus suppressing the fuzzing of the carbon fiber bundles during the partial splitting process.

[0026] It is important that carbon fiber bundles are sized before being supplied to the partial splitting line. If carbon fiber bundles are partially split 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 on the carbon fiber surface through surface treatment greatly increases both of the following frictional forces. One of these 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 the tools, such as needles or plates, used in the partial splitting process. The fraying associated with partial splitting is suppressed in sized carbon fiber bundles because the sizing agent introduced into the carbon fiber bundles acts as a lubricant that reduces these frictional forces.

[0027] In sizing section 9, the carbon fiber bundles are passed through a sizing bath and then dried. Since sizing fixes the carbon fibers together, it is desirable in sizing section 9 to apply high tension to the carbon fiber bundles using a tension-applying mechanism such as a Dansaroll to ensure that the carbon fibers are properly aligned. On the other hand, in the partial division section 1, it is desirable to apply high tension to the carbon fiber bundle 3 in the partial division line 2 as well, so that a tool such as a needle or plate can be reliably inserted into the carbon fiber bundle 3. Therefore, in one example, to simplify the manufacturing equipment when connecting the carbon fiber manufacturing line 5 and the partial division line 2, the tension-applying mechanism for the sizing section 9 and the tension-applying mechanism for the partial division line 2 may be combined into a single tension-applying mechanism. Furthermore, the force generated by the shrinkage of the precursor fiber bundle 6 due to 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.

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

[0029] 2.1. Partial Section The carbon fiber bundles supplied to the partial division section have a flattened shape and therefore have a width direction and a thickness direction in addition to the 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] Tension is applied to the carbon fiber bundles running through the segmented sections such that their longitudinal direction is parallel to a first direction and their width direction is parallel to a second direction perpendicular to the first direction. In other words, the carbon fiber bundles are stretched almost straight along the first direction without twisting and pass through the segmented sections while suspended in mid-air. In this specification, as shown in Figure 3, the first direction described above is referred to as the x-direction in the subdivision section, and the second direction described above is referred to as the y-direction in the subdivision section. 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 in which gravity acts. The y-direction may also be perpendicular, inclined, or parallel to the direction in which gravity acts.

[0031] It is obvious that a bundle of carbon fibers will vibrate when suspended in mid-air. Therefore, even if the longitudinal direction of the carbon fiber bundle is parallel to the x-direction when passing through a segmented section, it is not always kept strictly parallel. Similarly, the width and y directions of the carbon fiber bundle as it travels through a segmented section are not always strictly parallel.

[0032] 2.2. Split Jig A splitting jig having projections formed of needles or plates is installed in the partial splitting section. As the carbon fiber bundle supplied to the partial splitting line passes through the partial splitting section, it is intermittently pierced by the projections of the splitting jig, thereby being partially split.

[0033] A splitting jig typically has two or more protrusions, but it may also have one. The minimum number of protrusions a splitting jig should have depends on how many sub-bundles the carbon fiber bundle should be partially divided into. The number of sub-bundles to which the carbon fiber bundle should be partially divided is naturally determined by the bundle size of the starting material carbon fiber bundle and the bundle size of the sub-bundles to be formed by the partial division.

[0034] Figures 4, 5, and 6 show an example of a splitting 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 figure. The eight needles are also arranged at equal intervals along the t-direction, which is perpendicular to the u-direction. All eight needles are of the same length, and the line formed by connecting their tips is parallel to the t-direction.

[0035] The needle material is typically metal. While steel, such as stainless steel, is preferred, it is not limited to this material. A needle has at least a body. The body is a portion with a constant cross-sectional shape and area. The shape of the body is preferably cylindrical, but it may also be an elliptical prism, or a triangular prism, quadrangular prism, hexagonal prism, or other type of prism. The cross-sectional shape of the elliptical prism may be elliptical or oblong.

[0036] Preferably, the tip of the needle is tapered to facilitate penetration into the carbon fiber bundle. Figure 7 shows examples of possible shapes for the tapered tip of a needle. From left to right, Figure 7 illustrates needles with a conical tip 22a-1, a single-plane tapered tip 22a-2, a double-plane 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 smaller sub-bundles. Therefore, a smaller diameter of the body is preferable, but if it is too small, the rigidity decreases, making it easier for the needle to fail to 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 minimum width of the body is considered the diameter.

[0038] In terms of safely handling the splitting jig, a hemispherical tip of the needle is preferable. To achieve both ease of penetration into carbon fiber bundles and safety, a tapered tip other than a hemispherical shape may be rounded at the end, or an end surface perpendicular to the axial direction may be provided.

[0039] The splitting jig 20A shown in Figures 4, 5, and 6 can be manufactured by preparing a base 21 with multiple holes 21a, inserting the base of one needle 22 into each hole 21a, and then gluing the base 21 and the needles 22 together, 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 multiple needles arranged parallel to each other and fixed to one another. There are no limitations on the method for creating a dividing jig by arranging multiple needles parallel to each other and fixing them to one another. 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 the protruding portion is formed from a plate. The dividing jig 20B shown in Figures 10, 11, and 12 has seven spacers 31 and eight plates 32 that are 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 furthermore, the longer side of each main surface is parallel to the u direction shown in the figure. The eight plates are arranged at equal intervals along the t direction, which is perpendicular to the u direction. The seven spacers 31 are stacked alternately with the eight plates 32 on the -u side of the splitting jig 20B. The +u side of each plate 32 protrudes relative to the spacers 31.

[0041] The material of plate 32 is typically metal. Steel, such as stainless steel, is preferred, but is not limited to it. There are no limitations on the method of fixing the spacer 31 and the plate 32 to each other; for example, adhesive, clamping, screwing, and various other methods can be applied as appropriate.

[0042] The plate thickness 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 penetrate the carbon fiber bundle, and the easier it is to divide the carbon fiber bundle into smaller sub-bundles. From this viewpoint, a thinner plate is preferable, but if it is too thin, the rigidity decreases, and the plate is more likely to fail to penetrate the carbon fiber bundle or to bend. Therefore, the plate thickness is preferably 0.1 mm or more, more preferably 0.2 mm or more. If the plate is too thick and difficult to insert into the carbon fiber bundle, the edges of the plate may be tapered.

[0043] The dividing jig 20B shown in Figures 10, 11, and 12 represents one preferred example, in which the plate 32 is rectangular, that is, a quadrilateral with four right-angle corners (corners with an interior angle of 90°), and two of these four right-angle corners are included in the protruding portion. In modified examples, the plate 32 may be a polygon other than a quadrilateral, such as a triangle, pentagon, or hexagon, or it may be a concave polygon, or it may be a shape without 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 quadrilateral, and particularly preferably rectangular.

[0044] 2.3. Partial division In the partial division section, the partial division of carbon fiber bundles using a division jig is performed as follows. First, Figures 13, 14, and 15 show examples using a splitting jig with protrusions formed by needles. In Figures 13, 14, and 15, the 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, which will be described later. In the example shown in Figure 13, the splitting jig 20A is moved linearly back and forth by the actuator 40, thereby intermittently piercing the moving carbon fiber bundle 11 with the needle 22. The splitting jig 20A is positioned so that its t-direction is parallel to the y-direction.

[0045] In the example shown in Figure 14, the splitting jig 20A is oscillated around the axis 45 by an actuator (not shown), thereby intermittently piercing the moving carbon fiber bundle 11 with the needle 22. The axis 45 is parallel to the y-direction. The dividing jig 20A is positioned such that its t-direction is parallel to the y-direction, and that when a cylinder is imagined with the axis 45 as its center, the longitudinal direction of the needle 22 is parallel to the radial direction of the cylinder. This example can be modified so that the split jig 20 is rotated instead of oscillating.

[0046] In the example shown in Figure 15, the splitting jig 20 is oscillated around the axis 45 by an actuator (not shown), thereby intermittently piercing the moving carbon fiber bundle 11 with the needle 22. The axis 45 is parallel to the y-direction. The dividing jig 20A is positioned such that its t-direction is parallel to the y-direction, and that when a cylinder is imagined with the axis 45 as its center, the longitudinal direction of the needle 22 is inclined with respect to the radial direction of the cylinder.

[0047] In the examples shown in Figures 13, 14, and 15, both the x and y directions may be horizontal, in which case the carbon fiber bundle 11 may be pierced by the needle 22 from below or from above. In the examples shown in Figures 13, 14, and 15, the carbon fiber bundle 11 is divided by keeping the dividing jig 20A stationary for a certain period of time with the needle 22 embedded in the moving carbon fiber bundle 11. The needle 22, which is embedded in the carbon fiber bundle 11, is not perpendicular to the direction of travel of the carbon fiber bundle 11, but is tilted so as to fall downstream (towards the +x direction) of the direction of travel of the carbon fiber bundle 11 (angle θ is less than 90°). Conveniently, this makes it difficult for carbon fiber debris to accumulate in the dividing jig 20.

[0048] Next, Figures 16 and 17 show examples using a split jig in which the protruding portion is formed from a plate. In the example shown in Figure 16, the actuator 40 causes the split jig 20B to reciprocate linearly, thereby intermittently piercing the moving carbon fiber bundle 11 with the plate 32. The split 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 while the plate 32 is embedded in the carbon fiber bundle 11 on which it is running.

[0049] In the example shown in Figure 17, the split jig 20B is oscillated around the axis 45 by an actuator (not shown), thereby intermittently piercing the moving carbon fiber bundle 11 with the plate 32. 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 splitting of the carbon fiber bundle 11 is performed by keeping the splitting jig 20B stationary for a certain period of time with the plate 32 embedded in the carbon fiber bundle 11 on which it is running.

[0050] In both Figures 16 and 17, when the plate 32 is embedded in the carbon fiber bundle 11, the portion of the plate 32 embedded in the carbon fiber bundle 11 has an edge 32a of the plate facing the upstream side (-x direction) of the carbon fiber bundle 11's direction of travel tilted toward the downstream side (+x direction) of the carbon fiber bundle 11's direction of travel (angle θ is less than 90°). Conveniently, this makes it less likely for carbon fiber debris to accumulate in the splitting jig 20.

[0051] Furthermore, in the examples shown in Figures 16 and 17, only one of the two right-angle corners that the plate 32 has within the protrusion penetrates the carbon fiber bundle 11. In other words, at any given moment during the partial division process, the number of right-angle corners that the plate 32 has in the protrusion that are penetrated by the carbon fiber bundle 11 does not exceed one. Therefore, the protrusion formed by the plate 32 is less likely to get caught on the carbon fiber bundle 11, both when penetrating it and when withdrawing from it. Not limited to cases where the protrusion is formed using a rectangular plate, if the protrusion of the dividing jig is plate-shaped and has multiple convex corners (corners with convex interior angles), the same effect can be obtained by ensuring that the number of these convex corners that are embedded in the carbon fiber bundle during the partial division process does not exceed one. In another embodiment, to obtain the same effect, the number of convex corners on the plate-shaped protrusion may be limited to just one. Preferably, the above effect becomes more pronounced by making the inner angle of the protruding corner that penetrates the carbon fiber bundle 90° or more. From the viewpoint of making it easier for the protrusion to penetrate the carbon fiber bundle, it is preferable that the inner angle is 120° or less.

[0052] Regardless of the type of protrusion, the motion of the splitting jig is preferably reciprocating rather than rotational. Examples of reciprocating motion include linear reciprocating and oscillating motion. Reciprocating motion is preferred because it prevents entanglement when a problem occurs in which the carbon fiber bundle (all or some sub-bundles) breaks. If entanglement occurs, the manufacturing line needs to be stopped, and recovery takes a long time. A preferred actuator for reciprocating the split jig is an air cylinder, but it is not limited to that, and an electric motor may also be used.

[0053] In the examples shown in Figures 14, 15, and 17, the splitting jig is oscillated so that when a protrusion penetrates a carbon fiber bundle, it moves in the opposite direction to the direction of the carbon fiber bundle's movement, and when a protrusion withdraws from the carbon fiber bundle, it moves in the same direction as the direction of the carbon fiber bundle's movement. Therefore, problems such as a protrusion becoming stuck in a carbon fiber bundle and not being able to be removed, or the carbon fiber bundle vibrating violently when a protrusion withdraws from it, causing subsequent penetration of the protrusion to be unsuccessful, are less likely to occur.

[0054] As the carbon fiber bundle travels with the protrusions of the splitting jig inserted, slits are formed in the carbon fiber bundle. When the protrusions are removed from the carbon fiber bundle, slit formation is interrupted. By forming slits intermittently in this way, a partially split carbon fiber bundle is obtained in which the carbon fiber bundle is partially divided into multiple sub-bundles. As an example of a partially divided carbon fiber bundle, Figure 18 shows a partially divided carbon fiber bundle in which five sub-bundles are intermittently formed along the longitudinal direction. Figure 18 is a plan view of the partially divided carbon fiber bundle 4 as seen from the thickness direction.

[0055] Referring to Figure 18, the partially divided 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 rows of slits are formed. First slit row R S1 It consists of a plurality of first slits S1 arranged along the longitudinal direction of the partially divided carbon fiber bundle 4. Second slit row R S2 It consists of multiple second slits S2 arranged along the longitudinal direction of the partially divided carbon fiber bundle 4. Third slit row R S3 It consists of a plurality of third slits S3 arranged along the longitudinal direction of the partially divided carbon fiber bundle 4. Fourth slit row R S4 It consists of multiple fourth slits S4 arranged along the longitudinal direction of the partially divided 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 generally the product of the time from when the protrusion pierces the carbon fiber bundle until it is removed and the running speed of the carbon fiber bundle. Similarly, the first to fourth slit rows R S1 , R S2 , R S3 , R S3 In each of, the slit gap G S The slit gap length L G is generally the product of the time from when the protrusion is removed from the carbon fiber bundle until it pierces the carbon fiber bundle next 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 slit gap length L G are constant within any slit row and are common among all slit rows.

[0057] The slit length Ls is preferably 20 cm or more, more preferably 40 cm or more, and still more preferably 60 cm or more. The larger the slit length Ls, the more advantageous it is because the chopped carbon fiber bundle obtained when cutting the divided carbon fiber bundle 4 to manufacture SMC contains many with a bundle size equivalent to that of 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 be further 20 mm or less. From this perspective, there is no particular upper limit for the slit length Ls.

[0058] On the other hand, the larger the slit length Ls, the more likely problems (such as winding around the roll) that occur when the sub-bundle breaks become serious in the line for manufacturing SMC using the partial division line or the partial division carbon fiber bundle 4. From this perspective, the slit length Ls is preferably 300 cm or less, more preferably 200 cm or less, and still more preferably 150 cm or less.

[0059] Based on the above, the slit length Ls can be set to, for example, 60 cm or more but less than 100 cm, 100 cm or more but less than 150 cm, 150 cm or more but less than 200 cm, 200 cm or more but less than 250 cm, or 250 cm or more but 300 cm or less. Slit gap length L G It is 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 points apply not only to partially divided carbon fiber bundles that are partially divided into five sub-bundles, but also to partially divided carbon fiber bundles that are partially divided into four or fewer sub-bundles or six or more sub-bundles. The bundle size of the sub-bundles formed by the partial splitting process is not particularly limited. For example, when a carbon fiber bundle with a bundle size of 12 to 24K is subjected to partial splitting, 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 partially dividing a carbon fiber bundle with a bundle size of 36K to 120K, the size of the sub-bundle 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. To suppress the fluffing of the partially divided carbon fiber bundles, the bundle size of the sub-bundles is preferably 0.5K or larger, and more preferably 1K or larger.

[0061] 2.4. Number of protrusions on the splitting jig To partially divide a carbon fiber bundle into n sub-bundles (where n is an integer greater than or equal to 2), it is necessary to simultaneously form (n-1) slits in the carbon fiber bundle. Therefore, the dividing jig must have at least (n-1) protrusions. Furthermore, the dividing jig must be positioned in the partial division section such that (n-1) protrusions can simultaneously penetrate 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 and prevent its y-direction position from shifting while it is moving through the dividing section. In addition, it is necessary to precisely match the y-direction position of the dividing jig with that of the carbon fiber bundle. Otherwise, as shown in Figure 19, the y-direction position of the carbon fiber bundle 11 may shift significantly while the protrusions (needles 22) are not piercing it, 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 decrease to (n-1), and one sub-bundle with an abnormally large bundle size will be formed.

[0063] To properly guide the carbon fiber bundles, grooved guide rollers with groove widths matching the width of the carbon fiber bundles should be used. In this case, although it is disadvantageous from the standpoint of production efficiency, it is desirable to set the running speed of the carbon fiber bundles low to prevent the edges of the bundles from folding and narrowing the bundle width as they pass through the grooved guide rollers.

[0064] If a decrease in production efficiency is undesirable, one can change the approach and, instead of using a dividing jig with exactly (n-1) protrusions to divide the carbon fiber bundle into n sub-bundles, the number of protrusions on the dividing jig 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 reducing the running speed of the carbon fiber bundle, some variation in the y-direction position of the carbon fiber bundle within the partial division section is permitted, and even with variations in the y-direction position, the number of protrusions simultaneously piercing the carbon fiber bundle does not fall below (n-1).

[0065] Figures 20 and 21 show an example where n is 9 and the splitting jig has (n+1) needles, or 10 needles, as protrusions. In the example shown in Figure 20, after the eight protrusions (needles 22) of the splitting jig 20A that were inserted into the carbon fiber bundle 11 were removed, the position of the carbon fiber bundle 11 in the y-direction shifted slightly, resulting in nine protrusions being inserted into the carbon fiber bundle 11 next. 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, after the eight protrusions (needles 22) of the splitting jig 20A that were inserted into the carbon fiber bundle 11 are removed, the y-direction position of the carbon fiber bundle 11 is significantly shifted. As a result, the number of protrusions that will next insert into the carbon fiber bundle 11 remains at eight. In this case as well, no sub-bundles with abnormally large bundle sizes are formed. In the examples shown in Figures 20 and 21, the longitudinal direction of the needle 22 when it is inserted into the carbon fiber bundle 11 is parallel to the z-direction, but this is not limited to this configuration. In a preferred example, the needle 22 may be inclined to tilt downstream in the direction of travel of the carbon fiber bundle 11 when it is inserted into the carbon fiber bundle 11.

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

[0068] Carbon fiber bundles supplied to the partial splitting section may have fiber debris attached to them, which is generated when a small portion of the carbon fibers are cut in the upstream process. Furthermore, the partial splitting process in the partial splitting section can also cut carbon fibers, generating fiber debris. Such fiber debris easily gets caught on the protrusions of the splitting jig. If this fiber debris accumulates and forms large cotton-like particles that adhere to the partially split carbon fiber bundles, it may degrade the quality of the SMC (Steel Molding Co., Ltd.) manufactured using those bundles. Therefore, in a preferred example, compressed air may be blown onto the protruding part of the splitting jig during the partial splitting process to blow away any trapped fiber debris and / or cotton lint. The blowing of compressed air may be continuous or intermittent. More preferably, a suction nozzle is installed near the splitting jig to remove the fiber debris and / or cotton lint blown away by the compressed air, thereby preventing them from adhering to the partially split 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 manufacturing a partially divided carbon fiber bundle, wherein the carbon fiber bundle is continuously supplied from a carbon fiber manufacturing line to a partially divided line connected to the carbon fiber manufacturing line, and is partially divided in a partially divided section provided in the partially divided line. [Embodiment A2] The method according to Embodiment A1, wherein the carbon fiber manufacturing line includes a sizing section, and the carbon fiber bundle is sized in the sizing section and then supplied to the partial division line. [Embodiment A3] A method according to Embodiment A2, wherein the tension-applying mechanism for the sizing section and the tension-applying mechanism for the partial division line are combined into a single tension-applying mechanism. [Embodiment A4] A method according to any one of Embodiments A1 to A3, wherein the force generated due to the shrinkage of the precursor fiber bundle in the carbon fiber manufacturing line is used to apply tension to the carbon fiber bundle in the partial division line. [Embodiment A5] The partial division process is a method according to any one of embodiments A1 to A4, which includes intermittently piercing the carbon fiber bundle, which runs along its longitudinal direction, with the protrusions of a division jig having protrusions. [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 to fall downstream in the direction of travel of the carbon fiber bundle when it is pierced into the carbon fiber bundle. [Embodiment A8] The method according to Embodiment A5, wherein the protruding portion is formed of a plate. [Embodiment A9] The method according to Embodiment A8, wherein, in the portion of the plate-shaped projection that pierces the carbon fiber bundle, when the projection is pierced into the carbon fiber bundle, the edge of the projection facing the upstream side in the direction of travel of the carbon fiber bundle is inclined to tilt toward the downstream side in the direction of travel of the carbon fiber bundle. [Embodiment A10] A method according to embodiment A8 or A9, wherein the plate-shaped projection has at least one convex corner, and in the partial division process, the number of convex corners of the projection that are piercing the carbon fiber bundle does not exceed one. [Embodiment A11] A method according to any of Embodiments A8 to A10, wherein the plate-shaped protrusion has at least one convex corner with an internal angle of 90° or more, but no convex corners with an internal angle of less than 90°, and in the partial division process, the number of convex corners with an internal angle of 90° or more that are embedded in the carbon fiber bundle does not exceed 1. [Embodiment A12] A method according to any of Embodiments A8 to A11, wherein the plate-shaped projection has two right-angle corners, and in the partial division process, only one of the two right-angle corners of the projection penetrates the carbon fiber bundle. [Embodiment A13] A method according to any of embodiments A8 to A12, wherein the protruding portion is formed using a rectangular plate, and in the partial division process, only one of the four right-angle corners of the rectangular plate penetrates the carbon fiber bundle. [Embodiment A14] The partial division process is a method according to any of embodiments A5 to A13, wherein the division jig is reciprocated to intermittently pierce the carbon fiber bundle with the protrusions. The reciprocating motion may be linear or oscillating. [Embodiment A15] A method according to any of Embodiments A5 to A14, wherein the partial division process involves oscillating the division jig to intermittently insert the protruding portion into the carbon fiber bundle. [Embodiment A16] A method according to Embodiment A15, wherein when the protrusion is inserted into the carbon fiber bundle, the protrusion moves in the opposite direction to the direction of travel of the carbon fiber bundle, and when the protrusion is withdrawn from the carbon fiber bundle, the protrusion moves in the same direction as the direction of travel of the carbon fiber bundle. [Embodiment A17] A method according to Embodiment A15 or A16, wherein the dividing sections have mutually orthogonal x, y, and z directions, and the longitudinal and width directions of the carbon fiber bundle as it passes through the dividing sections are parallel to the x and y directions, respectively, the dividing jig swings about an axis parallel to the y direction. [Embodiment A18] A method according to any one of embodiments A5 to A17, which includes blowing compressed air onto the protruding portion of the dividing jig while the partial division process is being performed. [Embodiment A19] A method according to any of Embodiments A5 to A18, wherein the dividing jig has exactly (n-1) protrusions, and in the partial dividing process, the carbon fiber bundle is partially divided into n sub-bundles, where n is an integer of 2 or more. [Embodiment A20] A method according to any of Embodiments A5 to A18, wherein the dividing jig has (n+1) or more protrusions, and in the partial dividing process, the carbon fiber bundle is partially divided into n or (n+1) sub-bundles, where 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, and even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less. [Embodiment A22] A method according to any of Embodiments A1 to A18, 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. [Embodiment A23] In the partial division process, a row of slits consisting of a plurality of slits arranged 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, 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 300 cm or less, according to any of Embodiments A1 to A22.

[0070] [Embodiment B1] A method for producing a partially divided carbon fiber bundle by partially dividing a carbon fiber bundle, wherein the partial division process includes intermittently piercing the carbon fiber bundle, which is running along its longitudinal direction, with the projections of a dividing jig having projections, the projections being formed of needles, and the needles being inclined to tilt downstream in the direction of travel of the carbon fiber bundle when pierced by the carbon fiber bundle. [Embodiment B2] A method for producing a partially divided carbon fiber bundle by partially dividing a carbon fiber bundle, wherein the partial division process includes intermittently inserting the protrusions of a dividing jig having protrusions into the carbon fiber bundle which is running along its longitudinal direction, the protrusions being formed of a plate, and when the plate-shaped protrusions are inserted into the carbon fiber bundle, the portion of the protrusions that is inserted into the carbon fiber bundle is inclined such that the edge of the protrusion facing the upstream side in the running direction of the carbon fiber bundle tilts toward the downstream side in the running direction of the carbon fiber bundle. [Embodiment B3] The method according to Embodiment B2, wherein the plate-shaped projection has at least one convex corner, and in the partial division process, the number of convex corners of the projection that are piercing the carbon fiber bundle does not exceed one. [Embodiment B4] A method according to Embodiment B2 or B3, wherein the plate-shaped projection has at least one convex corner with an internal angle of 90° or more, but no convex corners with an internal angle of less than 90°, and in the partial division process, the number of convex corners with an internal angle of 90° or more that are embedded in the carbon fiber bundle does not exceed 1. [Embodiment B5] A method according to any of Embodiments B2 to B4, wherein the plate-shaped protrusion has two right-angle corners at its protruding end, and in the partial division process, only one of the two right-angle corners of the protrusion penetrates the carbon fiber bundle. [Embodiment B6] A method according to any of Embodiments B2 to B5, wherein the protruding portion is formed using a rectangular plate, and in the partial division process, only one of the four right-angle corners of the rectangular plate penetrates the carbon fiber bundle. [Embodiment B7] A method for producing a partially divided carbon fiber bundle by partially dividing a carbon fiber bundle, wherein the partial division process includes intermittently piercing the carbon fiber bundle, which runs along its longitudinal direction, with the protrusions of a dividing jig having protrusions, wherein the protrusions are formed of plates, and the plate-shaped protrusions have at least one convex corner with an internal angle of 90° or more, but no convex corners with an internal angle of less than 90°, and in the partial division process, the number of convex corners of the protrusions with an internal angle of 90° or more that are pierced into the carbon fiber bundle does not exceed one. [Embodiment B8] A method for producing a partially divided carbon fiber bundle by partially dividing a carbon fiber bundle, wherein the partial division process includes intermittently piercing the carbon fiber bundle, which is running along its longitudinal direction, with the projection of a dividing jig having a projection, wherein the projection is formed of a plate, the plate-shaped projection has two right-angle corners, and in the partial division process, only one of the two right-angle corners pierces the carbon fiber bundle. [Embodiment B9] A method for producing a partially divided carbon fiber bundle by partially dividing a carbon fiber bundle, wherein the partial division process includes intermittently piercing the carbon fiber bundle, which runs along its longitudinal direction, with the projection of a dividing jig having a projection, wherein the projection is formed using a rectangular plate, and in the partial division process, only one of the four right-angle corners of the rectangular plate pierces the carbon fiber bundle. [Embodiment B10] A method according to any of Embodiments B1 to B9, wherein the partial division process involves reciprocating the division jig to intermittently insert the protrusions into the carbon fiber bundle. The reciprocating motion may be linear or oscillating. [Embodiment B11] A method according to any of Embodiments B1 to B10, wherein the partial division process involves oscillating the division jig to intermittently insert the protruding portion into the carbon fiber bundle. [Embodiment B12] The method according to Embodiment B11, wherein when the protrusion is inserted into the carbon fiber bundle, the protrusion moves in the opposite direction to the direction of travel of the carbon fiber bundle, and when the protrusion is withdrawn from the carbon fiber bundle, the protrusion moves in the same direction as the direction of travel of the carbon fiber bundle. [Embodiment B13] A method according to Embodiment B11 or B12, wherein the space in which the partial division process is performed has mutually orthogonal x, y, and z directions, and the longitudinal and width directions of the carbon fiber bundle as it passes through the space are parallel to the x and y directions, respectively, the division jig swings about an axis parallel to the y direction. [Embodiment B14] A method according to any one of Embodiments B1 to B13, which includes blowing compressed air onto the protruding portion of the dividing jig while the partial division process is being performed. [Embodiment B15] A method according to any of Embodiments B1 to B14, wherein the dividing jig has exactly (n-1) protrusions, and in the partial dividing process, the carbon fiber bundle is partially divided into n sub-bundles, where n is an integer of 2 or more. [Embodiment B16] A method according to any of Embodiments B1 to B14, wherein the dividing jig has (n+1) or more of the protrusions, and in the partial dividing process, the carbon fiber bundle is partially divided into n or (n+1) sub-bundles, where n is an integer of 2 or more. [Embodiment B17] The method according to Embodiment B15 or B16, wherein the bundle size of each sub-bundle 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 B18] A 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 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. [Embodiment B19] In the partial division process, a row of slits consisting of a plurality of slits arranged 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, 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 300 cm or less, according to any of Embodiments B1 to B18.

[0071] [Embodiment C1] A method for producing a partially divided carbon fiber bundle by partially dividing a carbon fiber bundle, wherein the partially divided process includes oscillating a dividing jig having protrusions to intermittently pierce the carbon fiber bundle, which is traveling along its longitudinal direction, with the protrusions. [Embodiment C2] The method according to Embodiment C1, wherein when the protrusion is inserted into the carbon fiber bundle, the protrusion moves in the opposite direction to the direction of travel of the carbon fiber bundle, and when the protrusion is withdrawn from the carbon fiber bundle, the protrusion moves in the same direction as the direction of travel of the carbon fiber bundle. [Embodiment C3] A method according to Embodiment C1 or C2, wherein the space in which the partial division process is performed has mutually orthogonal x, y, and z directions, and when the carbon fiber bundle passes through the space, the longitudinal direction and width direction are parallel to the x direction and the y direction, respectively, the division jig swings about an axis parallel to the y direction. [Embodiment C4] A method according to any one of embodiments C1 to C3, wherein the protruding portion is formed by a needle. [Embodiment C5] A method according to any of Embodiments C1 to C3, wherein the protruding portion is formed of a plate. [Embodiment C6] A method according to any one of embodiments C1 to C5, which includes blowing compressed air onto the protruding portion of the dividing jig while the partial division process is being performed. [Embodiment C7] A method according to any of Embodiments C1 to C6, wherein the dividing jig has exactly (n-1) protrusions, and in the partial dividing process, the carbon fiber bundle is partially divided into n sub-bundles, where n is an integer of 2 or more. [Embodiment C8] A method according to any of Embodiments C1 to C6, wherein the dividing jig has (n+1) or more protrusions, and in the partial dividing process, the carbon fiber bundle is partially divided into n or (n+1) sub-bundles, where n is an integer of 2 or more. [Embodiment C9] The 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, and even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less. [Embodiment C10] A 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 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. [Embodiment C11] In the partial division process, a row of slits consisting of a plurality of slits arranged 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, 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 300 cm or less, according to any of Embodiments C1 to C10.

[0072] [Embodiment D1] A method for producing a partially divided carbon fiber bundle by partially dividing a carbon fiber bundle, wherein the partial division process includes intermittently piercing the carbon fiber bundle, which is running along its longitudinal direction, with the protrusions of a dividing jig having protrusions, and blowing compressed air onto the protrusions of the dividing jig while the partial division process is being performed. [Embodiment D2] The method according to Embodiment D1, wherein the protrusion is formed by a needle. [Embodiment D3] The method according to Embodiment D1, wherein the protruding portion is formed of a plate. [Embodiment D4] A method according to any of Embodiments D1 to D3, wherein the dividing jig has exactly (n-1) protrusions, and in the partial dividing process, the carbon fiber bundle is partially divided into n sub-bundles, where n is an integer of 2 or more. [Embodiment D5] A method according to any of Embodiments D1 to D3, wherein the dividing jig has (n+1) or more protrusions, and in the partial dividing process, the carbon fiber bundle is partially divided into n or (n+1) sub-bundles, where n is an integer of 2 or more. [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, and even more preferably 9K or less, and may be 6K or less, 4K or less, 3K or less, or 2K or less. [Embodiment D7] A 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 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. [Embodiment D8] In the partial division process, a row of slits consisting of a plurality of slits arranged 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, 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 300 cm or less, according to any of Embodiments D1 to D7.

[0073] [Embodiment E1] A method for producing a partially divided carbon fiber bundle by partially dividing a carbon fiber bundle, wherein the partial division process includes intermittently inserting the protrusions of a dividing jig having protrusions into the carbon fiber bundle running along its longitudinal direction, the dividing jig having (n+1) or more protrusions, and 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. [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, and 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 protrusion is formed by a needle. [Embodiment E4] The method according to embodiment E1 or E2, wherein the protruding portion is formed of a plate. [Embodiment E5] In the partial division process, a row of slits consisting of a plurality of slits arranged 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, 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 300 cm or less, according to any of Embodiments E1 to E4.

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

[0075] 4.1. Experiment 1 We attempted to continuously perform the process from firing a precursor fiber bundle made of polyacrylonitrile to the subsequent partial division of the resulting carbon fiber bundle by adding a partial division section to an existing carbon fiber manufacturing line that has a firing section, a surface treatment section, and a sizing section in that order from the upstream side, and a winder at the downstream end. In the partially divided section, a slitter roll was installed as a means of partial division, with a slitting blade on its circumferential surface having a defect. When the partially divided sections were placed between the sizing section and the winder, it was possible to stably manufacture partially divided carbon fiber bundles. In contrast, when a partial division section was placed between the surface treatment section and the sizing section, the carbon fiber bundles became significantly fuzzy during the partial division process, and some of them unraveled, resulting in the formation of single-filament carbon fibers. These single-filament carbon fibers were at risk of becoming entangled in the guide roll.

[0076] 4.2. Experiment 2 Instead of the slitter roll described above, a splitting jig (the same as the one used in Experiment 3 described later) having multiple needles arranged parallel to each other and fixed to each other, as illustrated in Figures 4-6, was installed in the partial splitting section as a means of partial splitting. By swinging the splitting jig around a pivot axis set parallel to the width direction of the carbon fiber bundle running through the partial splitting section, the needles were intermittently pierced into the carbon fiber bundle. Aside from the aforementioned modification, we attempted to continuously perform the process from calcining a precursor fiber bundle made of polyacrylonitrile to the partial splitting 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, the partial division 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 bundles became significantly fuzzy during the partial division process, and some of them dissolved, resulting in the generation of carbon fibers in a single filament state.

[0077] 4.3. Experiment 3 We prepared a partial splitting line as shown in Figure 1, and attempted to partially split a 15K carbon fiber bundle (TR50S15L from Mitsubishi Chemical) that was manufactured on a separate carbon fiber manufacturing line (including a sizing section) and wound onto a bobbin. In the partially divided section, a dividing jig was installed as a means of partial division, each having multiple protrusions formed by needles. The needles were made of stainless steel (SUS304), with hemispherical tips and cylindrical bodies with a diameter of 0.8 mm.

[0078] In the splitting jig, more than 15 needles were arranged parallel to each other at a constant pitch of 1 mm, as shown in the examples in Figures 4-6. In the partial splitting section, the orientation of the splitting jig was adjusted so that the straight line formed by connecting the tips of the needles was parallel to the width direction of the running carbon fiber bundle. Since the width of the unsplit carbon fiber bundle was approximately 7 mm, the number of needles that could simultaneously penetrate the carbon fiber bundle was approximately 6.

[0079] In the partial splitting process, the carbon fiber bundle was moved at a constant speed of 10 m / min, the splitting jig was held still for 4.2 seconds with the needle embedded in the carbon fiber bundle, and then the splitting jig was moved back and forth linearly for the next 0.2 seconds so that the needle would be withdrawn from the carbon fiber bundle and then embedded again. This process was repeated. The reciprocating motion of the splitting jig was perpendicular to both the running direction and the width direction of the carbon fiber bundle. In other words, the splitting jig was moved parallel to the z-direction shown in Figure 3. During the 4.2-second stationary period, the angle between the longitudinal direction of the needle and the direction of the carbon fiber bundle (θ in the example in Figure 13) was set to 90°. As time passed, carbon fiber debris accumulated in the splitting jig, as shown in Figure 23, but the results indicated that there were no problems with the stability of the partial splitting process.

[0080] 4.4. Experiment 4 In Experiment 4, the same splitting jig used in Experiment 3 was used. However, instead of reciprocating the splitting jig linearly to insert the needle into the carbon fiber bundle and withdraw it, the jig was oscillated around an axis of motion parallel to the width direction of the moving carbon fiber bundle (the y-direction in Figure 3). In this case, as shown in the example in Figure 14, when inserting the needle into the carbon fiber bundle, the needle was moved in the opposite direction to the direction of movement of the carbon fiber bundle, and when withdrawing the needle from the carbon fiber bundle, the needle was moved in the same direction as the direction of movement of the carbon fiber bundle. Furthermore, during the 4.2-second resting period, the angle between the longitudinal direction of the needle and the direction of travel of the carbon fiber bundle (θ in the example in Figure 14) was set to 45°. That is, during the resting period, the needle was tilted at an angle of 45° to the downstream side in the direction of travel of the carbon fiber bundle. Aside from the points mentioned above, when we attempted to partially split the carbon fiber bundle in the same manner as in Experiment 3, there were no problems with the stability of the partial splitting process. Furthermore, the amount of carbon fiber waste accumulated in the splitting jig after the same amount of partial splitting time was less than in Experiment 3, as shown in Figure 24.

[0081] 4.5. Experiment 5 In the same manner as in Experiment 4, a fiber splitting jig was set up, and while a carbon fiber bundle was being moved, the splitting jig, which was stationary with a needle embedded in the carbon fiber bundle, was rotated so that the needle moved in the opposite direction to the direction of movement of the carbon fiber bundle. The question was then asked whether the needle would come out of the carbon fiber bundle. As a result, when the splitting jig was rotated, the carbon fiber bundle became embedded in the jig, and the needle could not be removed from the carbon fiber bundle. The cause is thought to be that the rotation of the splitting jig caused the needle, which had pierced the carbon fiber bundle, to tilt toward the upstream side in the direction of the carbon fiber bundle's movement.

[0082] 4.6. Experiment 6 In Experiment 6, we attempted to partially divide the carbon fiber bundle in the same manner as in Experiment 3, except that we changed the division jig. The dividing jig used in Experiment 6 had multiple protrusions, each formed from a rectangular plate. The rectangular plates were made of stainless steel (SUS304) and had a thickness of 0.2 mm. In the splitting 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 splitting section, the orientation of the splitting jig was adjusted so that the straight lines formed by connecting the corners between different rectangular plates were parallel to the width direction of the moving carbon fiber bundle. The position of the splitting 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 unsplit carbon fiber bundle was approximately 7 mm, the number of rectangular plates that could pierce the carbon fiber bundle simultaneously was approximately 8.

[0083] During the 4.2-second stationary period, the angle (θ in the example in Figure 16) between the edge of the rectangular plate facing the upstream direction of the carbon fiber bundle at the point where the rectangular plate penetrates the carbon fiber bundle was set to 30°, 45°, and 60°. In all cases, the stability of the partial division process was found to be without problems. However, the larger the angle, the greater the amount of carbon fiber waste accumulated in the division jig during the same period of partial division. Figure 25 is a photograph of the division jig after partial division processing with the angle set to 60°. Figure 26 is a photograph of the division jig after the same partial division processing is performed with the angle set to 30°.

[0084] Although the present invention has been described above with reference to specific embodiments, each embodiment is presented as an example and does not limit the scope of the present invention. Each embodiment described herein can be modified in various ways within the scope in which the effects of the invention are achieved, and can be combined with features described in other embodiments to the extent that is feasible. [Industrial applicability]

[0085] The present invention provides an improved method for manufacturing partially divided carbon fiber bundles. [Explanation of Symbols]

[0086] 1. Partial division section 2 Partial division lines 3. Undivided carbon fiber bundles 4 Partially divided carbon fiber bundles 5. Carbon Fiber Manufacturing Line 6 Precursor fiber bundle 7. Firing Section 8. Surface treatment section 9. Sizing Section 11. Moving carbon fiber bundles 20-segment jig 21 base 22 needles (protrusion) 22a Tip of the needle 24 plates 25 screws 31 Spacers 32 Plate (protruding part) 32a Plate edge 35 Straight section of the plate 40 Actuators 45 axis 50 Slitter Roll 51 Peripheral surface 52 Slit blades 53. Defective area

Claims

1. A method for producing a partially divided carbon fiber bundle, A bundle of carbon fibers is continuously supplied from the carbon fiber manufacturing line to a partial division line connected to the carbon fiber manufacturing line. In the partial division section provided on the aforementioned partial division line, a partial division process is performed. In the aforementioned partial division process, a row of slits consisting of multiple slits arranged along the longitudinal direction of the carbon fiber bundle is formed in the carbon fiber bundle, and the length of the multiple slits is 20 cm or more.

2. The method according to claim 1, wherein the carbon fiber manufacturing line includes a sizing section, and the carbon fiber bundle is sized in the sizing section and then supplied to the partial division line.

3. The method according to claim 2, wherein the tensioning mechanism for the sizing section and the tensioning mechanism for the partial division line are combined into a single tensioning mechanism.

4. The method according to claim 1, wherein the force generated due to the shrinkage of the precursor fiber bundle in the carbon fiber manufacturing line is used to apply tension to the carbon fiber bundle in the partial division line.

5. The method according to claim 1, wherein the partial division process includes intermittently inserting the protrusions of a division jig having protrusions into the carbon fiber bundles running along their longitudinal direction.

6. The method according to claim 5, wherein the protruding portion is formed by a needle.

7. The method according to claim 6, wherein the needle is inclined 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 according to claim 5, wherein the protruding portion is formed of a plate.

9. The method according to claim 8, wherein, in the portion of the plate-shaped projection that pierces the carbon fiber bundle, when the projection is pierced into the carbon fiber bundle, the edge of the projection facing the upstream side in the direction of travel of the carbon fiber bundle is inclined to tilt downstream in the direction of travel of the carbon fiber bundle.

10. The method according to claim 8, wherein the plate-shaped projection has at least one convex corner, and in the partial division process, the number of convex corners of the projection that are piercing the carbon fiber bundle does not exceed one.

11. The method according to claim 8, wherein the plate-shaped projection has at least one convex corner with an internal angle of 90° or more, but no convex corners with an internal angle of less than 90°, and in the partial division process, the number of convex corners with an internal angle of 90° or more that are embedded in the carbon fiber bundle does not exceed one.

12. The method according to claim 8, wherein the plate-shaped projection has two right-angle corners, and in the partial division process, only one of the two right-angle corners of the projection penetrates the carbon fiber bundle.

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

14. The method according to claim 5, wherein in the partial division process, the division jig is reciprocated to intermittently insert the protrusions into the carbon fiber bundle. The aforementioned reciprocating motion may be a linear reciprocating motion or an oscillating motion.

15. The method according to claim 5, wherein in the partial division process, the division jig is oscillated to intermittently insert 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 the opposite direction to the direction of travel of the carbon fiber bundle, and when the protrusion is withdrawn from the carbon fiber bundle, the protrusion moves in the same direction as the direction of travel of the carbon fiber bundle.

17. The method according to claim 15, wherein the partial division sections have mutually orthogonal x, y, and z directions, and when the carbon fiber bundle passes through the partial division sections, the longitudinal and width directions are parallel to the x and y directions, respectively, the division jig swings about an axis parallel to the y direction.

18. The method according to claim 5, further comprising blowing compressed air onto the protruding portion of the dividing jig while the partial division process is being performed.

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

21. The method according to 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 the bundle size of each of the plurality of sub-bundles is 18K or less.

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