JP4822528B2 - Sheet-like carbon fiber knitted fabric and method for producing the same - Google Patents

Description

  The present invention relates to a sheet-like carbon fiber knitted fabric used for molding a fiber reinforced plastic (hereinafter sometimes abbreviated as FRP) and a method for producing the same.

  Composite materials using carbon fibers as reinforced fibers, especially FRP, have characteristics such as light weight, high strength, and high rigidity, and their use in many fields has become widespread. For example, aerospace It is used for civil engineering and sports. As a typical form of the reinforcing fiber fabric, a unidirectional reinforcing fiber material (for example, Patent Document 1) in which a woven fabric, a reinforcing fiber bundle is held by a knitting yarn, and a reinforcing fiber bundle are arranged in parallel in one direction and heat in a B stage state. There is a sheet material such as a unidirectional prepreg bonded with a curable resin. Although these reinforced fiber fabrics can satisfy the demands for excellent mechanical properties and weight reduction when the composite material is made as described above, the carbon fiber bundles are linearly arranged. Although it has excellent mechanical properties, it has the following anisotropy because it has a form of extreme anisotropy in which the mechanical properties suddenly decrease with distance from the fiber axis.

  For example, when trying to form a quasi-isotropic molded product having a three-dimensional complex curved surface, the conventional reinforced fiber fabric and prepreg form are inferior in stretchability and draping properties, so that deep drawing is difficult. there were. In addition, since it is a material having extreme anisotropy, it is necessary to cut these sheet materials into small pieces and laminate them while shaping each one so that the fiber axes are different, which makes the molding operation very complicated. there were. In addition, since the breaking elongation of the carbon fibers is small and the carbon fiber bundles are linearly arranged, there is a problem that when a strong impact is applied to the molded product, the carbon fiber is broken with a relatively low impact force.

  In order to solve the above problems, the industry has tried to process carbon fiber into a knitted form, but fluff and yarn breaks occur frequently during knitting, and the current situation is that satisfactory products are not yet obtained. It is.

On the other hand, a method for producing a carbon fiber knitted fabric by knitting a precursor of polyacrylonitrile fiber and then infusibilizing (flameproofing) and carbonizing the precursor has been proposed (Patent Document 2). In addition, the precursor is significantly shrunk due to carbonization treatment, the width of the fabric becomes unstable, and not only becomes a carbon fiber knitted fabric with non-uniform fiber weight, but also because of carbonization treatment under no tension, high strength, high elastic modulus, There was a problem that a so-called high-performance carbon fiber knitted fabric could not be obtained.
JP 2004-360106 A JP-A-9-176939

  Accordingly, an object of the present invention is to provide a high-performance sheet-like carbon fiber knitted fabric having high elasticity and high elastic modulus that is rich in stretchability and drape and can be shaped even on complex curved surfaces, and the high-performance sheet-like carbon fiber. An object of the present invention is to provide a method for producing a sheet-like carbon fiber knitted fabric that can suppress the generation of fuzz and can be knitted without breaking the yarn.

In order to solve the above problems, a sheet-like carbon fiber knitted fabric according to the present invention is a sheet-like carbon fiber knitted fabric comprising a continuous carbon fiber bundle produced by carbonizing under tension using polyacrylonitrile fiber as a precursor , The carbon fiber bundle has a tensile strength of 3 to 10 GPa and a tensile modulus of 200 to 600 GPa, and a knitting yarn made of the carbon fiber bundle forms a continuous loop in the warp direction. The number of filaments in the bundle is 6,000 or less, the fineness of the carbon fiber bundle is 60 to 400 tex, and the basis weight of carbon fiber per square meter is 100 to 700 g . Thus, by using a carbon fiber bundle having an appropriate number of filaments and fineness, particularly a continuous carbon fiber bundle, loop formation and the like can be performed relatively easily, and knitting into a knitted fabric becomes possible. Since it is a knitted fabric, a sheet-like carbon fiber knitted fabric that is far more stretchable and draped than a woven fabric, unidirectional reinforcing fiber material, etc., and can be easily shaped even on complex curved surfaces can be realized.

In particular, in the sheet-like carbon fiber knitted fabric according to the present invention, the number of filaments of the carbon fiber bundle is 6,000 or less and the fineness of the carbon fiber bundle is 60 to 400 tex , and the carbon fiber basis weight per square meter is 100~700g Ru der. By adjusting to such an appropriate range, it is possible to realize a sheet-like carbon fiber knitted fabric that is excellent in formability and capable of expressing desired mechanical properties in a pseudo-isotropic manner.

Further, as shown in the embodiments described later, the knitting yarn made of carbon fiber bundles forms a loop that is continuous in the warp direction . In other words, the insertion yarn composed of a plurality of carbon fiber bundles is sequentially knitted by a loop composed of carbon fiber bundles arranged in the vertical direction.

In addition, in order to enable the sheet-like carbon fiber knitted fabric as described above to be manufactured reliably and easily, the present invention wraps a chain knitting yarn of a carbon fiber bundle around a guide of a Russell knitting machine in a spiral manner, and performs pseudo twisting. The carbon fiber bundle is converged by the above, and the knitting operation is repeated while suppressing the return of the carbon fiber bundle in the direction opposite to the supply direction due to friction between the carbon fiber bundle and the guide, or the carbon fiber A method for producing a sheet-like carbon fiber knitted fabric, characterized in that a bundle of carbon fiber bundles is fed while being bundled by passing a bundled chain knitting yarn through a pipe guide narrowed at the bottom of the Russell knitting machine, and the knitting operation is repeated. Also provide.

  Such a method for producing a sheet-like carbon fiber knitted fabric according to the present invention can be carried out by knitting using a Russell knitting machine equipped with a needle, a guide and a sinker, or a Russell knitting machine equipped with a needle and a guide.

  According to the sheet-like carbon fiber knitted fabric according to the present invention, because it is excellent in drape and can be deep-drawn, the molding operation when molding a composite material is very simple. Excellent. This is a sheet composed of continuous carbon fiber bundles manufactured using polyacrylonitrile fiber as a precursor, and is an effect brought about by a loop structure in a knitted form.

  Moreover, according to the manufacturing method of the sheet-like carbon fiber knitted fabric according to the present invention, it is possible to prevent generation of fluff and yarn breakage during knitting of the sheet-like carbon fiber knitted fabric, and a knitted fabric with uniform quality can be obtained. In particular, the target sheet-like carbon fiber knitted fabric can be easily obtained by winding the carbon fiber bundle spirally around the guide or by feeding it through a pipe guide while converging and repeating the knitting operation. Can be organized.

Hereinafter, the present invention will be described in detail together with preferred embodiments with reference to the drawings.
FIG. 1: has shown the elements on larger scale for demonstrating the sheet-like carbon fiber knitted fabric 1 of this invention, especially the sheet-like carbon fiber warp knitted fabric 1. A plurality of knitting yarns 2 made of carbon fiber bundles are arranged in parallel while forming a continuous loop in the warp direction (sheet length direction), and a plurality of insertion yarns 3 made of carbon fiber bundles are knitted into the loop. It is. In the present embodiment, the insertion yarn 3 intersects every three knitting yarns 2 and the direction is reversed (the guide is shaken by three stitches for each course) to form a warp knitted fabric.

  In the sheet-like carbon fiber knitted fabric 1 (sheet material) of the present invention, the carbon fiber bundle of the knitting yarn 2 forms a loop, and the insertion yarn 3 is knitted and integrated into the loop. When pulled in the length direction, the loop expands, and the arrangement angle of the insertion thread 3 changes accordingly. Therefore, the sheet material is easily stretched and stretchable, and also has a good drape. This drape is a complex curved surface. Greatly governs the formability of Since the knitted fabric is excellent in stretchability and drape as described above, it can be shaped even on complicated curved surfaces.

  In the knitted fabric, the carbon fiber bundle (knitting yarn 2) forms a loop, and the insertion yarn 3 is also arranged in two directions in a folded form, and the fibers are arranged in multiple directions as a whole. It does not show extreme anisotropy like the form of unidirectional material or fabric. Therefore, even if the sheets are shaped one by one so that the fiber axes are different from each other, even if a large number of sheets are laminated in the same direction, a quasi-isotropic characteristic can be obtained, and the molding operation becomes extremely simple.

  As for the knitting structure in the sheet-like carbon fiber knitted fabric of the present invention, the knitting yarn 2 forms a loop in the warp direction as in the embodiment of FIG. 1, and the insertion yarn 3 is knitted into the loop and integrated. Therefore, the form is stable and the fiber orientation is not disturbed during the laminating operation, which is preferable, but is not limited thereto. In addition, there are tissues such as denbi, tulle, marquisette, etc. Also, the insert yarn has the effect of preventing the ear part from curling the ear part, for example, the presence or absence of knitting structure or insert yarn, etc. There are many combinations of. These may be appropriately designed depending on the intended use and usage pattern.

  As the carbon fiber yarn, a spun yarn obtained by spinning a short fiber is also known, but since the spun yarn is formed by strong twisting, the converging property is strong and the cross-sectional shape of the yarn is close to a circle. A knitted fabric knitted using such a knitting yarn has many voids, the surface of the knitted fabric is uneven, and the bending of the knitting yarn increases. In addition, since the yarn is formed by spinning short fibers, the strength expression in the FRP is also low, and therefore in the present invention, a continuous carbon fiber bundle in which a large number of continuous filaments are bundled is used.

  The carbon fiber used in the present invention is produced by oxidizing and flameproofing a fiber bundle of polyacrylonitrile by heating it in an oxygen atmosphere and carbonizing it in a high temperature inert gas under tension. The Therefore, although it depends on the processing conditions, it becomes a high-performance carbon fiber having a high strength and a high elastic modulus with a tensile strength of 3 to 10 GPa and a tensile elastic modulus of 200 to 600 GPa, and has uniform characteristics with little variation.

The number of filaments and fineness of the continuous carbon fiber bundle used in the present invention may be about 12,000 and 800 tex, for example , but if the carbon fiber bundle is too thick, the knitting yarn and the insertion yarn intersect. On the other hand, there are voids (locations B in FIG. 1) in which the carbon fiber does not exist in the knitted structure, so that the voids B are filled when formed into FRP. Since the resin shrinks when cured, the FRP has large irregularities. In addition, voids are likely to occur in large voids. Therefore, in the present invention, the following number of filaments 6,000 (e.g., a range of 1,000 to 6,000 lines) a and fineness of the carbon fiber bundle 400 tex or less, in particular, is in the range of 60 to 400 tex ing.

  In addition, since the resin filled in the voids B has vibration absorption performance, depending on the application, the voids can be used, the number and size can be appropriately designed, and the resin can be optimized to absorb vibration. It can also be used to actively have sexual functions.

Further, the carbon fiber basis weight per square meter of carbon fiber knit according to the present invention is Ru 100~700g der. When surface smoothness is required for an FRP molded product, 100 to 300 g / m ² using a thin carbon fiber bundle, mechanical properties are required for the FRP molded product, or a thick FRP molded product is required. In that case, it is preferable to use a thick carbon fiber bundle to have a basis weight of 300 to 700 g / m ² . Further, if the basis weight is less than 100 g / m ² , the knitted fabric becomes a large knitted fabric, and the voids increase and the unevenness of the FRP molded product increases, and if it exceeds 700 g / m ² , Since the bending (crimp) of the carbon fiber bundle becomes large and the mechanical properties of the FRP molded product are deteriorated due to stress concentration, it is not preferable.

  In the FRP in which the sheet-like carbon fiber knitted fabric according to the present invention is laminated, when an impact force is applied, the carbon fiber is bent, so that a large load is immediately applied to the carbon fiber like a unidirectional material in which the carbon fibers are arranged straight. However, since the FRP matrix resin first breaks and absorbs impact energy, and then the carbon fiber breaks, an FRP molded product having high impact resistance is obtained.

  In order to further improve the impact resistance of FRP, it is preferable to use a resin having a high elongation at break in order to increase the impact absorption energy at the resin portion. In the case of thermoplastic resins, polyamide resins, polyetherimide resins, and polyether ether ketone resins are used. In the case of thermosetting resins such as epoxy resins and vinyl ester resins, high elongation at break is 4 to 10%. An elongation resin is preferred.

  As shown in FIG. 1, the sheet-like carbon fiber knitted fabric according to the present invention is not so large in stitches, the surface unevenness of the knitted fabric is also moderate, and can be formed into a sheet shape. Thus, FRP having a large fiber volume content can be obtained.

  Further, when FRP is formed, a known woven fabric, a unidirectional reinforcing fiber material in which a reinforcing fiber bundle is held by a knitting yarn, or a sheet material such as a unidirectional prepreg may be laminated and molded as appropriate. In other words, it is possible to use a sheet-like carbon fiber knitted fabric according to the present invention on at least a part, particularly on the side of shaping to a curved surface, etc., and to combine the known reinforcing fiber sheet material with the remaining part. is there.

  Since the sheet-like carbon fiber knitted fabric according to the present invention is a knitted fabric using carbon fiber bundles that have already been carbonized, it becomes a fabric having a stable width as compared with a carbon fiber knitted fabric obtained by carbonizing a knitted fabric made of a precursor, and has a fiber weight per unit area. A uniform carbon fiber knitted fabric, and a so-called high performance carbon fiber knitted fabric having high strength and high elastic modulus.

  Next, the manufacturing method of the sheet-like carbon fiber knitted fabric of this invention is demonstrated. When the sheet-like carbon fiber knitted fabric of the present invention is knitted, the explanation will be made focusing on the loop knitting in which the knitting yarn has problems such as generation of fuzz and yarn breakage.

  First, each step of a normal loop knitting operation on the Russell knitting machine will be described with reference to FIGS. In each figure, F indicates the front of the Russell knitting machine, and B indicates the rear of the Russell knitting machine. FIG. 2 shows a state at the time of starting, in which the needle 4 is at the lowest position, the sinker 6 moves to the front F side of the Russell knitting machine, and the guide 7 remains at the front position. Next, as shown in FIG. 3, the needle 4 rises, and the hook 9 closed by the tongue 5 opens. The sinker 6 moves to the front position, stays at that point, presses the knitted fabric 8 that rises as the needle 4 rises, and the loop on the hook 9 slides downward in the hook 9. . At this time, the guide 7 starts backswing. Subsequently, as shown in FIG. 4, the needle 4 continues to rise and reaches the highest point, and the loop that has been slid by the hook 9 falls to the bottom of the needle 4. The guide 7 backswings toward the rear B side of the needle hook 9, and the sinker 6 starts to retract from the needle 4. Next, as shown in FIG. 5, the guide 7 that has finished the backswing is overlapped by jogging left or right to form a loop, and the guide 7 starts the front swing and the knitting yarn 2 that becomes a loop becomes the needle 4. When the needle 4 is lowered as shown in FIG. 6, the knitting yarn wound around the needle 4 slides into the hook 9. When the needle 4 is lowered, the hook 9 is closed by the tongue 5, and the knitting yarn sliding into the hook 9 is held as a new loop. Further, since the needle 4 descends, the loop that has fallen below the needle 4 becomes an old loop and slides on the tongue 5 that closes the hook 9. At this time, the sinker 6 is in the retracted position. Next, as shown in FIG. 7, the needle 4 reaches the lowest position (knockover position), the old loop comes off from the needle 4, and the new loop and the old loop in the hook 9 are entangled. A series of operations from the starting position to the knockover position is taken as one course, and these operations are repeated.

  Next, referring to FIGS. 8 and 9, an example of a method for producing a sheet-like carbon fiber warp knitted fabric according to the present invention is compared with the case of producing a sheet-like carbon fiber warp knitted fabric by the conventional method shown in FIGS. While explaining. The supplied carbon fiber bundle 10 is spirally wound around the guide 7 and passed through the guide hole 11. Conventionally, the supplied yarn is passed through the guide 7 from the left to the right as it is. However, when the supplied yarn is a carbon fiber bundle, there are the following problems.

  FIGS. 10 and 11 show a case where a carbon fiber warp knitted fabric is produced by a conventional method, and FIG. 12 shows a warp tension balance device existing above the guide block 12 of FIGS. Usually, as shown in FIG. 10, the carbon fiber bundle 10 is passed through the guide hole 11 without being wound around the guide 7. When the carbon fiber bundle 10 is applied to the hook 9 of the needle 4 and the needle 4 is lowered, the carbon fiber bundle 10 is pulled to increase the tension. This tension is absorbed by the tension rail 13, and even when the tension is weakened when the needle 4 is raised, the tension rail 13 is adjusted so that the thread can be supplied with a constant tension. However, the tension is actually completely absorbed. The tension that cannot be absorbed by the tension rail 13 is applied to the knitting yarn to be supplied.

  When the knitting yarn is a synthetic fiber, the synthetic fiber is stretchable, and the yarn loosens even when the needle 4 is lowered and the tension is applied from the state where the needle 4 is lowered and the tension applied to the knitting yarn is weakened. The going is absorbed by the shrinkage of the thread. Therefore, although there is a bending through the guide hole 11 from the left to the right, the yarn path does not swell and is almost linear and stable.

  However, when the knitting yarn is the carbon fiber bundle 10, as shown in FIG. 10, the tension is applied to the carbon fiber bundle 10 when the needle 4 is lowered. At this time, since the carbon fiber bundle 10 is under tension, the filaments converge. However, as shown in FIG. 11, when the needle 4 is raised, the tension applied to the carbon fiber bundle 10 is weakened, the yarn is loosened, and the bundling is gradually released. Since the yarn path is bent, the filament meanders due to the difference in the path between the inner peripheral side and the outer peripheral side, causing the yarn to crack. Since the carbon fiber has a large elastic modulus, when the deformation is applied, the restoring force that tries to return to the original works to eliminate the meandering of the filament, so that the yarn path of the carbon fiber bundle 10 swells greatly at the a ′ portion. .

  When this happens, the needle 4 rises, the guide 7 swings forward and the needle 4 passes by the side of the guide 7, rubbing the carbon fibers swollen at the a ′ portion, the number of rotations of the needle and guide of the knitting machine, That is, since the movement speed is 5 to 10 times higher than that of a loom or the like, fluff is generated. Here, reinforcing fibers such as glass fibers and aramid fibers have a lower elastic modulus and higher elongation at break than carbon fibers, so even if they are rubbed slightly with a needle, they are less likely to fluff than carbon fibers, but carbon fibers have an elastic modulus. Because it is large and has low knot strength, fluff is likely to occur. In addition, if the tension of the carbon fiber bundle 10 is weakened when the needle 4 is raised, the carbon fiber bundle 10 returns to the direction opposite to the direction in which the yarn is supplied, and the carbon fiber bundle 10 repeatedly advances and retreats as the needle 4 moves up and down. The guide hole 11 is rubbed many times and fluff is likely to occur. As described above, when the fluff is generated and the carbon fiber is damaged, the yarn breaks when the portion is pulled by the hook 9 of the needle 4. Even if the yarn is not broken, there are many fluffs, and the knitted fabric is not formed cleanly when knitting. Further, when a high tension was applied to the carbon fiber in order to prevent swelling at the a 'portion, the carbon fiber was refracted at the hook 9 or the guide hole 11, and the carbon fiber was broken as it was, so that the knitting was very difficult.

  Therefore, in the present invention, as shown in FIGS. 8 and 9, the carbon fiber bundle 10 is spirally wound around the guide 7 and then passed through the guide hole 11. As shown in FIG. 8, when the carbon fiber bundle 10 is hooked on the hook 9 of the needle 4 and the needle 4 is lowered, the carbon fiber bundle 10 is pulled and tension is applied, and the filament of the carbon fiber bundle 10 is pulled by this tension. Focus. As shown in FIG. 9, when the needle 4 is raised, the tension applied to the carbon fiber bundle 10 is weakened and the yarn is loosened, the filaments meander to attempt to break the yarn. Since the guide 7 is spirally wound and then passed through the guide hole 11, the carbon fiber bundle 10 is twisted to create a pseudo twisted state, and the carbon fiber bundle 10 is converged. For this reason, the yarn path a portion corresponding to the a ′ portion described above does not bulge out greatly.

  Therefore, when the needle 4 passes by the side of the guide 7, the needle 4 does not rub against the carbon fiber and no fluff is generated. In addition, since the carbon fiber bundle 10 is spirally wound around the guide 7, a contact is made between the carbon fiber bundle 10 and the guide 7, and a small frictional force is generated, and the needle 4 is raised to raise the carbon fiber bundle. Even if the tension of 10 is weakened, the return in the direction opposite to the supply direction of the carbon fiber bundle 10 can be reduced, and the advancement and retreat of the yarn can be suppressed, so that the damage of the carbon fiber bundle can be reduced. Here, the portion of the guide 7 around which the carbon fiber bundle 10 is wound has a smaller curvature than that of the guide hole 11, and fluff does not occur when the portion is in contact. Further, since the return of the carbon fiber in the reverse direction is reduced, the carbon fiber bundle between the needle 4 and the guide hole 11 is slightly loosened, and even if the needle 4 is lowered and the carbon fiber bundle 10 is pulled, the knitting is performed. Since the carbon fiber bundle 10 has a slight looseness in the vicinity of the locating, it is possible to prevent a sudden strong tension from being applied, and it is possible to prevent yarn breakage.

  In the above embodiment, the guide 7 having the guide hole 11 is used as a member for guiding the carbon fiber bundle as the knitting yarn when forming the loop. For example, as shown in FIG. May be. In the case of the pipe guide 15, the supplied yarn can be passed linearly, and since it passes through the pipe, it is restrained in the pipe and the yarn path is stable, and the lower portion of the pipe guide 15 is narrowed down. It is preferable because the yarn can be supplied in a state where the filaments are converged.

  Here, in order to prevent as much tension as possible when the needle 4 is lowered, it is preferable to use a thin tension leaf spring 14 (shown in FIG. 12). In addition, the tension of the knitting yarn is applied to the knot portion of the loop applied to the needle 4, and when the knitted fabric is wound with a strong tension, the winding force is also applied to the loop knot portion, which is very strong. The load is applied, and the carbon fiber breaks due to low knot strength. Therefore, the winding tension should be such that the knitted fabric can be wound lightly without being pulled strongly.

  Furthermore, in order to supply the carbon fiber bundle 10 to the needle 4 without fuzzing, it is preferable to remove the sinker 6 and perform knitting. In normal knitting, the knitted fabric can be knitted by the loop formed when the needle 4 is raised falling from the hook 9 to the lower part of the needle 4. The loop may not fall to the bottom of the needle 4. In this case, the knitted fabric cannot be knitted. Therefore, as shown in FIG. 3, when the needle 4 is lifted by holding the knitted fabric with the sinker 6, the loop is prevented from rising together with the needle 4. Try to fall to the bottom. Subsequently, as shown in FIG. 6, when the needle 4 descends, the sinker 6 moves away from the needle 4 to a position retracted. The sinker 6 repeats the back-and-forth movement so that when the needle 4 is lowered, the sinker 6 moves forward in preparation for the needle 4 rising.

  When a knitted fabric is knitted with a thick fiber bundle such as carbon fiber, the fiber bundle supplied by the forward / backward movement of the sinker 6 is easily pierced and fuzzed easily. When it is pulled, the thread breaks easily.

  Therefore, the occurrence of fluff can be prevented by removing the sinker 6 and knitting. Here, the loop does not fall below the needle 4 without the sinker 6 and it is difficult to knit the knitted fabric. However, the synthetic fiber has a lower elastic modulus than the carbon fiber. Therefore, the loop becomes thin and wraps around the needle 4, and the loop is less likely to fall below the needle 4. However, since carbon fiber is highly elastic, when a loop is formed, the loop takes a circular shape and the needle 4 easily passes through the loop, and the loop falls to the bottom of the needle 4 without the sinker 6. The loop is easy to come off from the needle 4 and the knitted fabric is easily knitted.

The carbon fiber bundle used in the present invention preferably has a smaller number of filaments from the viewpoint of suppressing fluff generation due to rubbing of the carbon fiber bundle with the needle during knitting and preventing the sinker from sticking into the carbon fiber bundle. The number is 6,000 or less . Moreover, it is better that the carbon fiber bundle is imparted with a sizing agent using a sizing agent, and the sizing agent adhesion amount is preferably about 0.2 to 1.5% by weight. Moreover, since twisting of the carbon fiber bundle is also effective for imparting convergence, it is desirable to apply a slight twist of about 5 to 15 times per meter, for example.

  In the description of the above embodiment, a compound needle is illustrated as the needle 4, but a latch needle may be used in place of the needle 4 and the tongue 5.

  As described above, the sheet-like carbon fiber warp knitted fabric according to the present invention described above is excellent in drape and can be deep-drawn and shaped, so the molding operation is very simple. Excellent shock resistance. This is a sheet composed of continuous carbon fiber bundles manufactured using polyacrylonitrile fiber as a precursor, and is an effect brought about by a loop structure in a knitted form.

  Moreover, according to the manufacturing method of the sheet-like carbon fiber warp knitted fabric according to the present invention described above, generation of fluff and yarn breakage during knitting of carbon fibers can be prevented, and a knitted fabric with uniform quality can be obtained. This is an effect obtained by repeating the knitting operation by winding the carbon fiber bundle around the guide in a spiral manner or by feeding it through a pipe guide while converging it.

  The sheet-like carbon fiber knitted fabric according to the present invention and the method for producing the same are particularly suitable for use in molding FRP having a complicated shape such as a curved surface.

It is a partial top view of the sheet-like carbon fiber knitted fabric which concerns on one Embodiment of this invention. It is a schematic partial perspective view for demonstrating one step of normal loop knitting operation in a Russell knitting machine. FIG. 3 is a schematic partial perspective view for explaining a next step of FIG. 2. FIG. 4 is a schematic partial perspective view for explaining a next step of FIG. 3. FIG. 5 is a schematic partial perspective view for explaining a next step of FIG. 4. FIG. 6 is a schematic partial perspective view for explaining the next step of FIG. 5. FIG. 7 is a schematic partial perspective view for explaining a next step of FIG. 6. It is a general | schematic fragmentary perspective view of the Russell knitting machine which shows the yarn path in the manufacturing method of the sheet-like carbon fiber knitted fabric which concerns on one Embodiment of this invention. FIG. 9 is a schematic partial perspective view for explaining a next step of FIG. 8. It is a general | schematic fragmentary perspective view of the Russell knitting machine which shows the yarn path in the case of manufacturing a sheet-like carbon fiber knitted fabric by the conventional method. FIG. 11 is a schematic partial perspective view for explaining a next step of FIG. 10. It is a schematic perspective view of the warp tension balance device of a Russell knitting machine. It is a general | schematic fragmentary perspective view of the Russell knitting machine which shows the yarn path in the manufacturing method of the sheet-like carbon fiber knitted fabric which concerns on another embodiment of this invention.

Explanation of symbols

B: Location where the knitting yarn and the insertion yarn intersect B: Cavity where no carbon fiber exists 1: Sheet-like carbon fiber knitted fabric 2: Knitting yarn 3: Insertion yarn 4: Needle 5: Tong 6: Sinker 7: Guide 8 : Fabric 9: Hook 10: Carbon fiber bundle 11: Guide hole 12: Guide block 13: Tension rail 14: Tension leaf spring 15: Pipe guide a: Yarn portion near guide hole according to the present invention a ': Guide by conventional method Thread path near the hole F: Russell knitting machine front B: Russell knitting machine rear

Claims (3)

A sheet-like carbon fiber knitted fabric made of a continuous carbon fiber bundle produced by carbonizing under tension using polyacrylonitrile fiber as a precursor, and the tensile strength of the carbon fiber in the carbon fiber bundle is 3 to 10 GPa and the tensile elastic modulus is 200 to 600 GPa, a knitting yarn composed of the carbon fiber bundle is formed into a continuous loop in the warp direction, the number of filaments of the carbon fiber bundle is 6,000 or less, and the fineness of the carbon fiber bundle is 60 A sheet-like carbon fiber knitted fabric characterized by being -400 tex and having a carbon fiber basis weight per square meter of 100-700 g . The chain knitting yarn of the carbon fiber bundle is spirally wound around the guide of the Russell knitting machine, the carbon fiber bundle is focused by pseudo twisting, and the carbon fiber bundle is reversed in the direction of supply by the friction force between the carbon fiber bundle and the guide. while suppressing a return direction, and repeating the knitting operations, the method for manufacturing a sheet-like carbon fiber or knitted fabric according to claim 1. By passing the chain stitch yarn of carbon fiber bundle to a pipe guide the lower is narrowed Russell knitting machine, supplies while focusing the carbon fiber bundle, and repeating the knitting operations, according to claim 1 Manufacturing method of sheet-like carbon fiber knitted fabric.

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