Manufacturing method of composite yarn

Abstract

To produce a composite yarn having a relatively high physical strength in which a core fiber layer and a sheath fiber of a core-sheath structure are relatively strongly bonded to each other. The present invention provides a method for producing a yarn having a core-sheath structure by winding a sheath fiber made of a thermoplastic resin around a core fiber; a step of heating the obtained core-sheath structure yarn to a temperature equal to or higher than the melting point of the thermoplastic resin; The method of the present invention allows the production of composite yarns with higher adhesion between the core fiber layer and the sheath fiber layer. Furthermore, by combining different types of core fiber and sheath fiber, composite yarns of various qualities can be produced.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a composite yarn. [Background technology]

[0002] By combining two or more different types of fibers, it may be possible to produce a yarn with higher performance, for example, a yarn that combines rigidity and flexibility. Various methods for producing such yarns that combine two or more different types of fibers have been studied. For example, Patent Document 1 discloses a core-sheath type composite fiber containing a core component and a sheath component, in which the core component and the sheath component are arranged substantially concentrically, and the sheath component has a density of 0.90 g / cm 3 More than 0.93g / cm 3 Patent Document 1 discloses a sheath-core conjugate fiber which contains 60% by mass or more of a linear low-density polyethylene having a melting point of 100°C or more and 130°C or less, and the core component contains 60% by mass or more of a polyester resin having a melting point 50°C or more higher than the melting point of the linear low-density polyethylene, and the sheath-core conjugate fiber has a dry heat shrinkage rate at 140°C of 5.0% or less. Patent Document 1 discloses the effect that the invention provides a fiber assembly which is resistant to heat shrinkage and has improved dimensional stability. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-147878 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the composite fiber obtained by the method of the invention disclosed in Patent Document 1 is produced by melt spinning using a concentric core-sheath composite nozzle. Such core-sheath composite fibers produced by melt spinning or pultrusion have a problem in that the strength of the fiber decreases with use. Therefore, a technology that can solve the above problem has been desired. [Means for solving the problem]

[0005] As a result of extensive research, the present inventors have found that the above problems can be solved by a specific manufacturing method, and have arrived at the present invention. That is, the present invention provides: [1] A process for producing a core-sheath yarn by winding a sheath fiber made of a thermoplastic resin around a core fiber; and a step of heating the obtained core-sheath structure yarn to a temperature equal to or higher than the melting point of the thermoplastic resin; a method for producing a composite yarn, comprising: [2] The manufacturing method according to [1], wherein the core fiber is a fiber having a strength of 2 GPa or more and an elastic modulus of 50 GPa or more. [3] The step of producing the core-sheath yarn comprises: at least one core fiber bundle providing the core fiber; at least one sheath fiber bundle providing sheath fibers; a twisting mechanism including a traveler or flyer; and a bobbin for winding a core-sheath yarn in which a sheath fiber is wound around a core fiber by the twisting mechanism, The manufacturing method according to [1], which is carried out using a twisting machine including at least two guides between the core fiber bundle and sheath fiber bundle and the twisting mechanism, which adjust the traveling direction of the core fibers supplied from the core fiber bundle to be substantially the same as the central axis direction of the bobbin; [4] The step of producing the core-sheath yarn comprises: at least one core fiber bundle providing the core fiber; at least one sheath fiber bundle providing sheath fibers; a twisting mechanism including a traveler or flyer; and a bobbin for winding a core-sheath yarn in which a sheath fiber is wound around a core fiber by the twisting mechanism, The manufacturing method according to [1], further comprising: a twisting machine including a guide between the core fiber bundle and the sheath fiber bundle and the twisting mechanism, the guide having holes for passing the core fiber and the sheath fiber separately, the holes for passing the sheath fiber being positioned on an imaginary circle having the hole for passing the core fiber as the center; Regarding. [Effects of the Invention]

[0006] The method of the present invention makes it possible to produce a composite yarn having a higher strength in which the core fiber layer and the sheath fiber are bonded relatively strongly. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a perspective view of a twisting machine that can be used with the method of the present invention; [Figure 2] FIG. 2 is a perspective view showing a twisting machine having a different configuration from that shown in FIG. [Figure 3] 2A is a side view of the guide, the twisting mechanism, and the bobbin in the twisting machine of FIG. 1 as viewed from the right, and FIG. 2B is a front view. [Figure 4] 4A is a right side view and FIG. 4B is a front view when the angle of the bobbin in FIG. 3 is changed. [Figure 5] (A) is a front view of the guide, (B) is a side view of the guide of (A), (C) is a front view of a guide different from (A), and (D) is a side view of (C). [Figure 6] (A) Front view of the guide, (B) Side view of the guide of (A), (C) Plan view of a guide different from (A), (D) AB cross section of (C), (E) Plan view of a guide different from (A) and (C), (F) Plan view of a guide different from (A), (C) and (E), and (G) Side view of the guide of (F). [Figure 7] FIG. 3 is a perspective view showing a twisting machine of a different configuration from that of FIGS. 1 and 2. [Figure 8] FIG. 8 is a perspective view showing a twisting machine having a configuration different from those shown in FIGS. [Figure 9] 2 is an enlarged schematic view of the vicinity of a guide for explaining the state when yarn is twisted by the yarn twisting machine of FIG. 1. FIG. [Figure 10] 9 is an enlarged schematic view of the vicinity of a guide for explaining the state when yarn is twisted by the yarn twisting machine of FIG. 8. FIG. [Figure 11] 1 is an enlarged photograph of a core-sheath structure yarn obtained by the method of the present invention (part of the sheath fiber is unwound). [Figure 12] 1 is a photograph in which the color analysis results obtained by an X-ray CT device of the composite yarn obtained by the method of the present invention are converted into gray. [Figure 13] This is a photograph in which the color analysis results obtained by an X-ray CT device for a comparative composite yarn are converted into gray. DETAILED DESCRIPTION OF THE INVENTION

[0008] Preferred embodiments of the present invention will be described with reference to the drawings. It goes without saying that the present invention is not limited to the following embodiments and aspects, and various modifications are possible within the technical scope of the present invention. In addition, the terms "up and down," "front and back," and "left and right" in the text refer to the directions shown in the drawings.

[0009] As described above, the method of the present invention comprises: A step of winding a sheath fiber made of a thermoplastic resin around a core fiber to produce a core-sheath yarn (hereinafter referred to as the "first step"); and a step of heating the obtained core-sheath structure yarn to a temperature equal to or higher than the melting point of the thermoplastic resin (hereinafter referred to as the "second step"); Each step will be described in detail below. In the following description, "sheath-core yarn" means a yarn produced in the first step that has a sheath-core structure but in which the sheath fibers are not melted, and "composite yarn" means a yarn that has a sheath-core structure and in which at least the sheath fibers are melted and fused together.

[0010] 1.First step As described above, the first step is a step of producing a core-sheath yarn by winding a sheath fiber made of a thermoplastic resin around a core fiber. Here, the core fiber and sheath fiber used in the present invention may be short fibers or long fibers. These fibers may be raw yarns (fibers in the state before twisting) or twisted yarns.

[0011] The core fiber can be made of any material used in yarn production, without any particular limitations. Examples of such materials include natural fiber materials such as cotton, linen, silk, and wool; regenerated fiber materials such as rayon, polynosic, and cupra; synthetic fiber materials such as aramid, polyethylene, polyarylate, polyparaphenylenebenzoxazole (PBO), polyester, nylon, acrylic, and polyurethane; and semi-synthetic fiber materials such as acetate, triacetate, and promix. These materials may be used alone or in combination of two or more. Among these, it is particularly preferable to select a fiber having a strength of 2 GPa or more and a modulus of elasticity of 50 GPa or more as the core fiber. The use of such fibers allows for the production of composite yarns with higher strength. A typical example of a fiber having a strength of 2 GPa or more and a modulus of elasticity of 50 GPa or more is a fiber known as a "super fiber," which has high strength and modulus. Examples of such fibers include para-aramid resins (e.g., Technora (registered trademark), Twaron (registered trademark), and Kevlar (registered trademark)), ultra-high molecular weight polyethylene fibers (e.g., Dyneema (registered trademark)), polyarylate fibers (e.g., Vectran (registered trademark)), liquid crystal polyester resins (e.g., Sivelas (registered trademark)), and PBO resins (e.g., Zylon (registered trademark)). The thickness of the core fiber can be adjusted appropriately based on the thickness required for the composite yarn to be finally obtained. Specific examples of thickness are, for example, about 50 to 2500 μm.

[0012] The material constituting the sheath fiber can be any material used in yarn production, provided that it is a thermoplastic resin. By using such a thermoplastic resin, the sheath fibers arranged around the core fiber melt and fuse to each other during heating in the second step described below, forming a sheath fiber layer, thereby obtaining a composite yarn in which the core fiber layer and the sheath fiber layer are more firmly bonded. Examples of such thermoplastic resins include polyethylene, polypropylene, nylon, and polyester. These materials may be used alone or in combination of two or more. The thickness of the sheath fiber can be adjusted appropriately based on the thickness and other factors required for the final composite yarn. A specific example of the thickness is, for example, approximately 50 to 1,000 μm.

[0013] The core fiber material and the sheath fiber material can be combined without any particular restrictions. Various types of composite yarns can be produced by combining the core fiber material and the sheath fiber material in various ways. For example, by setting the melting point of the core fiber material higher than that of the sheath fiber material and setting the heating temperature in the second step (described later) higher than the melting point of the sheath fiber but lower than the melting point of the core fiber, or by using a highly heat-resistant fiber such as the super fiber described above as the core fiber, a composite yarn can be produced in which the sheath fibers are fused together but the core fibers are not fused together, and air is trapped in the core fiber layer.

[0014] Regarding the method for winding the sheath fiber around the core fiber, any method conventionally used in producing yarn, particularly yarn with a sheath-core structure, can be used. For example, methods using a ring twister, a flyer twister, an Italian twister, a braiding machine, etc. can be used. In the present invention, when the sheath fiber is wound around the core fiber, it is preferable that the sheath fiber cover 90% or more, preferably 95% or more, and more preferably 99% or more of the surface of the core fiber.

[0015] The sheath fibers may be wound around the core fibers using a twisting machine such as the following: A twisting machine that can be used in the method of the present invention includes at least one core fiber bundle 2 that supplies the core fibers, at least one sheath fiber bundle 3 that supplies the sheath fibers, a twisting mechanism 4 including a traveler or flyer, and a bobbin 5 for winding a core-sheath yarn in which the sheath fibers have been wound around the core fibers by the twisting mechanism 4, and the twisting machine 1 includes at least two guides 6 between the core fiber bundle 2 and sheath fiber bundle 3 and the twisting mechanism 4 to adjust the traveling direction of at least the core fibers supplied from the core fiber bundle 2 to be substantially the same as the central axis direction of the bobbin 5; or A twisting machine 1 includes at least one core fiber bundle 2 that supplies core fibers, at least one sheath fiber bundle 3 that supplies sheath fibers, a twisting mechanism 4 including a traveler or flyer, and a bobbin 5 for winding a core-sheath yarn in which the sheath fiber is wound around the core fiber by the twisting mechanism 4, and includes a guide 6 between the core fiber bundle 2 and the sheath fiber bundle 3 and the twisting mechanism 4, the guide 6 having holes for passing the core fiber and the sheath fiber separately, the holes for passing the sheath fiber being positioned on an imaginary circle centered on the hole for passing the core fiber. These twisting machines will be described in detail below.

[0016] (1) Structure of twisting machine that can be used in the first process FIG. 1 shows one embodiment of a ring twisting machine including a twisting mechanism 4 including a traveler, as a specific example of a twisting machine 1 that can be used in the first step. The twisting machine 1 in FIG. 1 is provided with one core fiber bundle 2 that supplies the core fiber CF described above. Two or more core fiber bundles 2 can be provided as needed. For example, when bundling two or more core fibers CF of the same type, or when bundling two or more different types of core fibers CF, the number of core fiber bundles 2 can be increased depending on the number of core fibers CF used. Specific examples of the core fiber bundle 2 include a bobbin around which the core fiber CF is wound, a cone around which the core fiber CF is wound, etc.

[0017] The twisting machine 1 in FIG. 1 is provided with four sheath fiber bundles 3 (sheath fiber bundles 3', 3", 3'" and 3"") for supplying the sheath fibers SF as described above. Note that one or more sheath fiber bundles 3 may be provided as necessary. For example, when only one sheath fiber SF of one type is wound around the core fiber CF, only one sheath fiber bundle 3 may be provided. On the other hand, when two or more sheath fibers of only one type or two or more sheath fibers of different types are wound around the core fiber CF, two or more sheath fiber bundles 3 may be provided. Note that specific forms of the sheath fiber bundle 3 include a bobbin around which the sheath fiber SF is wound and a cone around which the sheath fiber is wound.

[0018] The twisting machine 1 is equipped with a roller 21 for conveying the core fibers CF supplied from the core fiber bundle 2 and a roller 31 (rollers 31′, 31″, 31′″, and 31″″ in FIG. 1 ) for conveying the sheath fibers SF supplied from the sheath fiber bundle 3. By rotating the rollers 21 and 31 using power such as a motor, the core fibers CF and sheath fibers SF wound around the core fiber bundle 2 and sheath fiber bundle 3 can be sent out toward the twisting mechanism 4. The rollers 21 and 31 can be the same roller, or, as shown in FIG. 1 , the rollers 21 and 31 can be separate rollers. By making the rollers 21 and 31 separate rollers, the rotation speed of each roller can be adjusted individually. When producing a yarn with a core-sheath structure, the sheath fibers SF must be wound around the core fibers CF, so the supply amount of the sheath fibers SF per unit time may need to be greater than the supply amount of the core fibers CF. As described above, by using roller 21 and roller 31 as separate rollers and adjusting the rotation speed of each roller per unit time, it is possible to more easily control the optimal supply amount of sheath fibers relative to the core fibers CF.

[0019] The twisting machine 1 includes a twisting mechanism 4 including a traveler or flyer. This type of twisting mechanism 4 is generally used in twisting machines called ring twisters or flyer twisters. The twisting machine 1 shown in Figure 1 includes a twisting mechanism 4 including a traveler 43. The twisting mechanism 4 in Figure 1 is initially equipped with a ballooning control ring 41 that centers the upper part of a bobbin 5 (described later) and a traveler ring 42 that centers the lower part of the bobbin 5. A traveler 43, which is a ring-shaped member, is provided at an arbitrary position on the traveler ring 42. The core fibers CF supplied from the core fiber bundle 2 and the sheath fibers SF supplied from the sheath fiber bundle 3 pass inside the ballooning control ring 41 and through the loop of the traveler 43 to be wound onto the rotating bobbin 5.

[0020] On the other hand, Figure 2 shows a case where a twisting mechanism 4 including a flyer is used as the twisting mechanism 4. In Figure 2, parts that are assigned the same numbers as in Figure 1 are explained the same as in Figure 1 unless otherwise specified. The twisting mechanism 4 in Figure 2 is equipped with a flyer 44 that is rotatably held around a bobbin 5, which will be described later. The flyer 44 is equipped with a loop 45 for passing each fiber. The core fibers CF supplied from the core fiber bundle 2 and the sheath fibers SF supplied from the sheath fiber bundle 3 are passed through the loop 45 of the flyer 44, and are wound onto the bobbin 5 as the flyer 44 rotates around the bobbin 5.

[0021] The yarn twisting machine 1 includes a bobbin 5. As described above, when the yarn twisting machine 1 includes the twisting mechanism 4 including the traveler 43, the bobbin 5 is provided inside the ballooning control ring 41 and the traveler ring 42, and when the yarn twisting machine 1 includes the twisting mechanism 4 including the flyer 44, the bobbin 5 is provided inside the flyer 44. Furthermore, the bobbin 5 is held so as to be movable up and down in the axial direction of the bobbin 5 as necessary in order to uniformly wind the yarn having a sheath-core structure around the bobbin 5.

[0022] The twisting machine 1 may include at least two guides 6 between the core fiber bundle 2 and sheath fiber bundle 3 and the twisting mechanism 4, which adjust the traveling direction of at least the yarn supplied from the core fiber bundle 2 to be substantially the same as the central axial direction of the bobbin 5. The twisting machine 1 in FIGS. 1 and 2 is provided with two guides 6, guide 6U and guide 6L. Guide 6U is provided after rollers 21 and 31. Another guide 6L is provided next to guide 6U and before the twisting mechanism 4. Guide 6L is preferably positioned so that the core fibers CF and sheath fibers SF that have passed through guide 6L are directly supplied to the twisting mechanism 4. Here, the positional relationship between guide 6U and guide 6L is such that, as described above, the traveling direction of at least the core fibers CF supplied from the core fiber bundle 2 is adjusted to be substantially the same as the central axial direction of the bobbin 5. Here, "at least the traveling direction of the core fiber CF" means that, as long as the traveling direction of the core fiber CF is approximately the same as the central axis direction of the bobbin 5, the traveling direction of the sheath fiber may or may not be approximately the same as the central axis direction of the bobbin 5. Figure 3 is a diagram explaining the positional relationship between the guide 6U, the guide 6L, and the bobbin 5 in the twisting machine 1 of Figure 1. In Figures 3(A) and (B), the bobbin 5 is installed so that its central axis (in other words, the rotation axis of the bobbin 5) is vertical. The direction of the central axis of the bobbin 5 is the direction of the dotted line α.

[0023] Meanwhile, the core fiber CF supplied from the roller 21 is supplied to the guide 6L via the guide 6U. The direction of travel of the core fiber CF from the guide 6U to the guide 6L is the direction of the dotted line β in FIG. 3(A). The positional relationship between the guides 6U and 6L in the present invention is such that the direction of the α and the direction of the β are substantially identical when viewed from the front-rear and left-right directions. Here, when the guide L has a hole through which the core fiber CF passes, such as the hole 6L2 shown in FIG. 6(A) or the hole 6L4 shown in FIG. 6(C), the direction of travel β of the core fiber CF is defined as the direction when the core fiber CF supplied from the guide 6U passes through the center of the hole. Furthermore, "the direction of the α and the direction of the β are substantially the same" not only includes the case where the directions of the α and the β are exactly the same, but also includes an angle where the α and the β are not exactly the same but allow the sheath fiber SF to be wound around the core fiber CF with as small a gap as possible. Specifically, the difference between the angles α and β includes an error of about ±10°. By making α and β approximately equal, it is possible to suppress positional deviation of the core fiber CF and the sheath fibers SF', SF'', SF''', and SF'''' due to ballooning or the like caused by the twisting mechanism 4. Furthermore, the sheath fibers SF are wound around the core fiber CF with as small a gap as possible, preferably without any gaps, resulting in a higher-quality sheath-core yarn. As described above, it is sufficient for α and β to be approximately equal, and the angles α and β themselves can be freely changed. For example, as shown in Figures 4(A) and (B), if the angle at which the bobbin 5 is installed is not perpendicular to the ground, the position of the guide 6, particularly the guide 6L, can be adjusted to make the traveling direction β of the core fiber CF approximately the same as the direction α of the central axis of the bobbin 5.

[0024] Furthermore, it is more preferable that the guides 6U and 6L position at least the axis of the core fiber CF, which is adjusted by these guides, on an extension of the central axis of the bobbin 5 (in other words, the axis of the rotation shaft of the bobbin 5). That is, in the example of FIG. 3 , when viewed from the front-rear and left-right directions, it is more preferable that the central axis α of the bobbin 5, when extended, coincides with the axis of the core fiber CF, in other words, the axis of the central axis in the traveling direction of the core fiber CF. By aligning the central axis α of the bobbin 5 with the axis β of the core fiber CF in this way, positional deviation of the core fiber CF and the sheath fibers SF', SF'', SF''', and SF'''' due to ballooning or the like caused by the twisting mechanism 4 can be further suppressed. Furthermore, the sheath fiber SF is wound around the core fiber CF with as small a gap as possible, preferably without any gaps, resulting in a higher-quality sheath-core yarn. Note that the term "aligned" not only includes perfect alignment but also includes an error that allows the sheath fiber SF to be wound around the core fiber CF with as small a gap as possible. Specifically, for example, there may be a case where the angle of the line extending from the central axis α of the bobbin 5 and the angle of the axis of the core fiber CF have a difference of about ±10°.

[0025] Here, the guide 6 is not particularly limited in terms of its shape or material, provided that it can at least adjust the traveling direction of the core fiber CF as described above. For example, FIG. 5 shows a specific example of the form of the guide 6U. FIGS. 5(A) and 5(B) show a ring-shaped guide 6U, which is a ring 6U1 having a hole 6U2 at its center. The core fiber CF and sheath fiber SF pass through the hole 6U2 to reach the guide 6L. The size of the hole 6U2 can be adjusted appropriately based on the type and thickness of the core fiber CF and sheath fiber SF used. The specific size of the hole 6U2 is, for example, approximately 1 to 15 times the combined thickness of the core fiber CF and sheath fiber SF passing through the hole 6U2.

[0026] 5(C) and (D) show another example of the guide 6U. In the example of FIGS. 5(C) and (D), the guide 6U includes a plurality of disk-shaped wall portions 6U3 and a connecting portion 6U4 that has a smaller radius than the wall portions 6U3 and connects the wall portions 6U3. When the guide 6U is viewed from the side, a hole 6U5 is formed that penetrates the wall portions 6U3 and the connecting portion 6U4. A shaft can be inserted into the hole 6U5, and the shaft is rotatably held on the housing of the yarn twisting machine 1 or the like. The core fibers CF and sheath fibers SF supplied from the core fiber bundle 2 and sheath fiber bundle 3 are wound in an area surrounded by two walls 6U3. For example, when one core fiber CF and four sheath fibers SF are passed through the guide 6U, the core fiber CF can be passed through the area of ​​joint portion 6U4" in FIG. 5(C) and the remaining four sheath fibers SF can be passed through the areas of joint portions 6U4, 6U4', 6U4'" and 6U4'" in FIG. 5(C). By passing the core fiber CF and the sheath fiber SF through different areas of the guide 6U in this way, the arrangement of the core fiber CF and the sheath fiber SF is made clear, and the sheath fiber SF is wound around the core fiber CF with as small a gap as possible, preferably without any gaps, resulting in a higher quality sheath-core yarn.

[0027] 6 shows a specific example of the guide 6L. FIGS. 6(A) and 6(B) show a ring-shaped guide 6L, which is a ring 6L1 having a hole 6L2 in the center. The core fiber CF and sheath fiber SF pass through the hole 6L2 to reach the twisting mechanism 4. The size of the hole 6L2 can be adjusted appropriately based on the types and thicknesses of the core fiber CF and sheath fiber SF used. The specific size of the hole 6L2 is, for example, about 1 to 15 times the combined thickness of the core fiber CF and sheath fiber SF that pass through the hole 6L2.

[0028] Figures 6(C) and (D) show another example of the guide 6L. The guide 6L shown in Figures 6(C) and (D) has a flat main body 6L3 with a hole 6L4 penetrating vertically and multiple holes 6L4' (four in Figure 6(C)) around the hole 6L4. Each of these holes 6L4 and 6L4' allows the core fiber CF and sheath fiber SF to pass through separately. By providing holes that allow the core fiber CF and sheath fiber SF to pass through separately, the arrangement of the core fiber CF and sheath fiber SF is clearly defined, and the sheath fiber SF is wound around the core fiber CF with as small a gap as possible, preferably without any gaps, resulting in a higher-quality core-sheath yarn. The size of the holes 6L4 and 6L4' can be adjusted appropriately based on the type and thickness of the core fiber CF and sheath fiber SF used. Specifically, the size of the holes 6L4 and 6L4' is, for example, about 1 to 15 times the thickness of the core fiber CF and sheath fiber SF that pass through the holes 6L4 and 6L4'.

[0029] Furthermore, when the guide 6L has holes through which the core fiber CF and the sheath fiber SF are separately passed, it is more preferable that the holes through which the sheath fiber SF are passed lie on an imaginary circle centered on the hole through which the core fiber CF is passed. Here, "the holes through which the sheath fiber SF are passed lie on an imaginary circle centered on the hole through which the core fiber CF is passed" means, for example, that in FIG. 6C, when the hole through which the core fiber CF is passed is hole 6L4 and the hole through which the sheath fiber SF is passed is hole 6L4', the center of each hole 6L4' lies on an imaginary circle (dotted circle θ in FIG. 6C) drawn with the center of hole 6L4 at its center. By adjusting the positions of the holes through which the sheath fiber SF is passed and the holes through which the core fiber CF is passed as described above, the arrangement of the core fiber CF and the sheath fiber SF is clearly defined, and the sheath fiber SF is wound around the core fiber CF with as small a gap as possible, preferably without any gaps, resulting in a higher-quality sheath-core yarn. Note that the imaginary circle may be more than one. For example, when four sheath fibers SF are used to produce a core-sheath yarn, four opposing holes 6L4' may be arranged on an imaginary circle θ1, and the other two opposing holes 6L4' may be arranged on an imaginary circle θ2, as shown in Fig. 6(E). Note that the distance between the holes 6L4 and 6L4', in other words, the radius of the imaginary circle θ, can be adjusted appropriately based on the materials, number, and thickness of the core fibers and sheath fibers used, as well as the target thickness of the composite yarn to be finally obtained.

[0030] 6(C) and 6(D), the guide 6L is shown as a plate-shaped member, but is not limited to this. For example, as shown in FIGS. 6(F) and 6(G), the guide 6L may be configured to have multiple pipes connected to it, specifically, multiple pipes 6L5 for passing the core fibers CF and multiple pipes 6L6 for passing the sheath fibers SF arranged around the pipes 6L5. Note that the number of holes 6L4' and pipes 6L6 for passing the sheath fibers SF may be one or more.

[0031] The guides 6U and 6L can be made of any material conventionally used in the manufacture of twisting machine guides. Examples of such materials include metals such as iron, steel, and aluminum; resins such as acrylic, polycarbonate, and polyvinyl chloride; glass; and rubbers such as natural and synthetic rubbers. If the guides 6U and 6L have holes through which the fibers pass, providing an elastic material such as rubber at the contact points between the edges of the holes and the fibers can reduce friction as the fibers pass through and further reduce the possibility of the fibers being cut due to frictional heat or the like. If the guides 6U and 6L have holes, the shape of the holes may be circular, as shown in the drawings, or polygonal, such as triangular, rectangular, pentagonal, or hexagonal.

[0032] Figure 7 shows yet another example of the twisting machine 1. In Figure 7, parts that are assigned the same numbers as in Figures 1 and 2 are the same as those in Figures 1 and 2 unless otherwise specified. The twisting machine 1 in Figure 7 has only one guide 6L, and the guide 6L has one hole 6L4 through which the core fiber CF passes and four holes 6L4' arranged on an imaginary circle centered on the hole 6L4 through which the sheath fibers SF pass, as shown in Figures 6(C) and 6(D). The provision of such a guide reduces the effects of ballooning of the core fiber CF and sheath fiber SF that occurs when the twisting mechanism 4 rotates. Furthermore, by clarifying the positional relationship between the core fiber CF and the sheath fiber SF, the sheath fiber SF is wound around the core fiber CF with as small a gap as possible, preferably without any gaps, resulting in a higher-quality sheath-core yarn.

[0033] FIG. 8 shows yet another example of the twisting machine 1. In FIG. 8, parts that are assigned the same numbers as in FIGS. 1, 2, and 7 are the same as those in FIGS. 1, 2, and 7 unless otherwise specified. The twisting machine 1 in FIG. 8 is the same as the twisting machine 1 in FIG. 1, except that instead of the ring-shaped guide 6L in the twisting machine 1 in FIG. 1, a guide 6L having a configuration as shown in FIGS. 6(C) and 6(D) is used. In the twisting machine 1 in FIG. 8, the guide 6L has one hole 6L4 through which the core fiber CF passes and four holes 6L4' through which the sheath fibers SF arranged on a virtual circle centered on the hole 6L4, as shown in FIGS. 6(C) and 6(D). The guides 6U and 6L are adjusted so that at least the traveling direction of the core fiber CF is substantially the same as the direction of the central axis of the bobbin 5, and so that when the central axis of the bobbin 5 is extended, they coincide with the axis of the core fiber CF, in other words, the central axis in the traveling direction of the core fiber CF. By using the guide 6L as described above and adjusting at least the axis of the core fiber CF as described above, the effects of ballooning can be further suppressed, and the sheath fiber SF is wound around the core fiber CF with as small a gap as possible, preferably without any gap, resulting in a yarn with a sheath-core structure of higher quality. The effects of ballooning can be suppressed by providing the guide 6L as shown in Figure 7, but the effects of ballooning can be further suppressed by controlling the traveling direction of at least the core fiber CF with the guides 6U and 6L.

[0034] (2) Carrying out the first step using the twisting machine A method for producing a sheath-core yarn CY using the twisting machine 1 shown in Figure 1 will be described. In the example of Figure 1, one core fiber bundle 2 and four sheath fiber bundles 3 (3', 3'', 3''', and 3'''') are provided. The core fiber bundle 2 and the sheath fiber bundle 3 are wound with a core fiber CF and a sheath fiber SF (sheath fibers SF', SF'', SF''', and SF''''), respectively. Because the twisting machine 1 has the above-mentioned structure, it can efficiently produce a sheath-core yarn CY even when using twisted yarns. Driving the twisting machine 1 rotates rollers 21, 31', 31'', 31''', and 31'''', and bobbin 5. The core fiber CF wound around the core fiber bundle 2 is fed out by roller 21 that has started to rotate. Furthermore, the sheath fibers SF', SF'', SF''' and SF'''' wound around the sheath fiber bundles 3', 3'', 3''', and 3'''' are respectively fed out by rollers 31', 31'', 31''', and 31'''', which have started to rotate. Here, as described above, by using separate rollers to feed out the core fibers CF and the sheath fibers SF, it becomes easier to adjust the speed of each roller. For example, by making the speed of rollers 31', 31'', 31''', and 31'''' faster than the speed of roller 21, the feed speed of each fiber can be adjusted, and preferably the sheath fibers SF can be wound more efficiently around the core fibers CF without any gaps.

[0035] The core fiber CF and sheath fibers SF', SF'', SF''', and SF'''' fed by the rollers pass through guide U. In the example of Figure 1, guide 6U has a shape as shown in Figures 5(C) and (D). In the twisting machine 1 of Figure 1, the guide 6U is rotatably held by a rotation shaft passing through a hole 6U5. The fed core fiber CF passes through the central region surrounded by wall portion 6U3 of guide 6U, i.e., the region of joint portion 6U4'' in Figure 5(C). Furthermore, the fed sheath fiber SF passes through the region surrounded by wall portion 6U3 other than the region through which the sheath fiber CF passes, i.e., the regions of joint portions 6U4, 6U4', 6U4''', and 6U4'''' in Figure 5(C).

[0036] The core fiber CF and sheath fiber SF (SF', SF'', SF''', and SF'''') that have passed through the guide 6U then pass through the guide 6L. As described above, the positions of the guides 6U and 6L are adjusted so that at least the traveling direction of the core fiber CF is approximately the same as the central axis of the bobbin 5, i.e., the direction of the rotation axis of the bobbin 5. The traveling direction of the sheath fiber SF may be the same as or different from the direction of the central axis of the bobbin 5. By adjusting the guides in this way, it is possible to more efficiently produce a yarn CY with a core-sheath structure in which the sheath fiber SF is uniformly wound around the core fiber CF. Furthermore, by adjusting the guides 6U and 6L so that at least the direction of travel of the core fiber CF is approximately the same as the direction of the central axis of the bobbin 5, and so that when the central axis of the bobbin 5 is extended, it coincides with the axis of the core fiber CF, in other words, the central axis in the direction of travel of the core fiber CF, it is possible to further suppress positional deviation of the core fiber CF and the sheath fibers SF', SF'', SF''', and SF'''' due to ballooning, etc., caused by the twisting mechanism 4, and the sheath fiber SF is wound around the core fiber CF with as small a gap as possible, preferably without any gaps, thereby obtaining a yarn with a core-sheath structure of higher quality.

[0037] In the twisting machine 1 of Fig. 1, the guide 6L is a ring-shaped guide as shown in Figs. 6(A) and (B). The core fiber CF and sheath fiber SF that have passed through the guide 6U pass through a hole 6L2 in the guide 6L. The core fiber CF and sheath fiber SF that have passed through the hole 6L2 are wound onto the rotating bobbin 5 and twisted together by the rotation of the bobbin 5 (see Fig. 9). Even if ballooning occurs due to the rotation of the bobbin, the use of the ring-shaped guide 6L can keep the deviation due to ballooning within the size of the hole 6L2 in the guide 6L (for example, the deviation of each fiber indicated by the solid line in Fig. 9 is suppressed to the point indicated by the dotted line), thereby further suppressing deviations in the quality of the core-sheath yarn CY that is produced. During the twisting, the traveling direction of at least the core fiber CF is substantially the same as the direction of the central axis of the bobbin 5, so that the sheath fiber SF is reliably wound around the core fiber CF, resulting in a sheath-core yarn CY in which the sheath fiber SF is neatly wound. The sheath-core yarn CY obtained by winding is wound onto the rotating bobbin 5. When a specified length of sheath-core yarn CY has been wound onto the bobbin 5, for example, the twisting machine 1 may be stopped, the bobbin on which the yarn is wound may be replaced with a bobbin on which no yarn is wound, and twisting may be resumed. The twisting machine 1 may also be equipped with two or more of the above-mentioned mechanisms.

[0038] Next, a method for producing a sheath-core yarn CY using the twisting machine 1 shown in Figure 2 will be described. Note that in the following explanation, explanations of operations that are performed in the same way as when using the twisting machine 1 of Figure 1 will be omitted. The twisting machine 1 of Figure 2 is equipped with a flyer 44 instead of a traveler 43. The twisting machine 1 of Figure 2 is similar to the twisting machine 1 of Figure 1 except that, while the bobbin 5 rotates in the twisting machine 1 of Figure 1, the bobbin 5 does not rotate in the twisting machine 1 of Figure 2, but the flyer 44 does, and a sheath-core yarn CY can be produced in the same way as when using the twisting machine 1 of Figure 1.

[0039] Next, a method for producing a core-sheath yarn using the twisting machine 1 shown in Figure 7 will be described. Note that in the following explanation, explanations of operations that are performed in the same way as when using the twisting machine 1 of Figures 1 and 2 will be omitted. The core fiber CF and sheath fibers SF', SF'', SF''', and SF'''' supplied from the core fiber bundle 2 and the sheath fiber bundles 3', 3'', 3''', and 3'''' reach the guide 6L. The core fiber CF that has passed through the hole 6L4 in the guide 6L and the sheath fibers SF', SF'', SF''', and SF'''' that have passed through the holes 6L4', 6L4', 6L4', and 6L4' are wound onto the rotating bobbin 5 and twisted together by the rotation of the bobbin 5 (see Figure 10). By using a guide 6L having the above-described shape, the positions of the core fiber CF and the sheath fibers SF', SF'', SF''', and SF'''' do not shift significantly due to ballooning, etc. (for example, the deviation of each fiber depicted by a solid line in Figure 10 is suppressed up to the position of the dotted line), and the sheath fiber SF is wound around the core fiber CF with as small a gap as possible, preferably without any gaps, resulting in a higher-quality core-sheath yarn CY.

[0040] Next, a method for producing a core-sheath yarn CY using the twisting machine 1 shown in Figure 8 will be described. Note that in the following explanation, explanations of operations that are performed in the same way as when using the twisting machine 1 of Figures 1, 2, and 7 will be omitted. The core fiber CF and sheath fibers SF', SF'', SF''', and SF'''' supplied from the core fiber bundle 2 and the sheath fiber bundles 3', 3'', 3''', and 3'''' pass through guide 6U and then reach guide 6L. The core fiber CF that passes through hole 6L4 in guide 6L and the sheath fibers SF', SF'', SF''', and SF'''' that pass through holes 6L4', 6L4', 6L4', and 6L4' are wound onto the rotating bobbin 5 and twisted together by the rotation of the bobbin 5. By using a guide 6L having the above-described shape, at least the direction of travel of the core fiber CF is approximately the same as the direction of the central axis of the bobbin 5, and by extending the central axis of the bobbin 5, it is possible to align it with the axis of the core fiber CF, in other words, the central axis in the direction of travel of the core fiber CF, and by using a guide 6L having the above-described shape, it is possible to further suppress positional deviation of the core fiber CF and the sheath fibers SF', SF'', SF''' and SF'''' due to ballooning, etc., and the sheath fiber SF is wound around the core fiber CF with as small a gap as possible, preferably without any gaps, thereby obtaining a higher quality core-sheath structure yarn.

[0041] 2.Second process As described above, the second step is a step of heating the sheath-core yarn obtained in the first step to a temperature equal to or higher than the melting point of the thermoplastic resin.

[0042] Any equipment commonly used for heating yarns can be used to heat sheath-core yarns. Specific examples of such equipment include continuous heat-circulating dry heat ovens. When using a continuous heat-circulating dry heat oven to heat sheath-core yarns, the temperature inside the dry heat oven is preferably set to a temperature equal to or higher than the melting point of the thermoplastic resin that forms the sheath fiber, specifically, a temperature preferably 0 to 50°C, more preferably 0 to 30°C, and even more preferably 0 to 20°C higher than the melting point. Furthermore, if melting of the core fiber is not desired, in other words, if air is to be retained in the core fiber layer, it is preferable to set the temperature inside the dry heat oven to a temperature equal to or higher than the melting point of the sheath fiber material but lower than the melting point of the core fiber material, as described above.

[0043] The heating time for the sheath-core yarn can be adjusted as appropriate based on the equipment used for heating, the types of core and sheath fibers used, their thicknesses, the heating temperature, the state of the composite yarn finally obtained, and other factors. Specifically, when a continuous heat-circulating dry heat bath is used, the time for which the sheath-core yarn passes through the dry heat bath is preferably 30 to 300 seconds, more preferably 45 to 200 seconds, and even more preferably 60 to 100 seconds. By heating, at least the surfaces of the sheath fibers are melted to fuse the sheath fibers together, and preferably the entire sheath fibers are melted to form a single sheath fiber layer. After heating, the composite yarn having a sheath-core structure is obtained by cooling.

[0044] 3. Obtained composite yarn The composite yarn obtained by the method of the present invention is produced by the above-described method, and therefore the core fiber layer and sheath fiber layer are relatively tightly adhered to each other. Therefore, compared to composite yarns with a core-sheath structure obtained by conventional methods, such as melt spinning using a core-sheath die or pultrusion molding, the core-sheath structure is less likely to collapse even when subjected to physical stimuli. Furthermore, for example, when a so-called super fiber is used as the core fiber and a flexible material, such as nylon 6, is used as the sheath fiber, it is possible to obtain a yarn that has the high strength of the super fiber and the high surface friction resistance due to the flexibility of the sheath fiber. Furthermore, by adjusting the material of the core fiber layer or the heating temperature in the second step, it is possible to produce a composite yarn in which air is incorporated into the core fiber layer.

[0045] 4. Uses of composite yarn The composite yarn obtained by the method of the present invention can be used for any application for which composite yarn has conventionally been used. Examples of such applications include fishing line, tennis strings, and threads used in nets for preventing damage caused by birds and animals. The materials of the core fiber and sheath fiber can be appropriately selected and combined depending on the application.

[0046] The present invention will be described in more detail below with reference to examples, although it goes without saying that the examples do not affect the scope of the present invention. [Example]

[0047] 1. Equipment used (1) Twisting machine: A twisting machine shown in Figure 8 equipped with one core fiber bundle and four sheath fiber bundles was used. (2) Heating device Uniplus Co., Ltd. heat circulation type dry heat tank (model number: BDS-500-4000) (3) Measuring instrument: Bruker Japan Co., Ltd. nanofocus X-ray CT system for high-performance materials (model number: SKYSCAN1272) (measurement conditions: pixel resolution: 1 μm, X-ray tube voltage: 40 kV, exposure time: 1350 ms, rotation step (movement angle per measurement): 0.2°, sample measurement: 360°, number of accumulations: 2)

[0048] 2. Fibers used Core fiber: One strand of aromatic polyamide resin (product name: Kevlar (registered trademark) 1670T, fiber diameter equivalent to 300 μm) manufactured by Toray DuPont Co., Ltd. Sheath fiber: 4 strands of Toray Industries, Inc.'s 6 nylon (product name: Amilan, 940 dtex (equivalent to a fiber diameter of 150 μm), melting point 225°C)

[0049] 3. Manufacturing of composite yarn Using the twisting machine, a sheath-core yarn was produced in which the sheath fiber was wound around the core fiber (first step). A photograph of the sheath-core yarn produced in the first step is shown in Figure 11. The photograph in Figure 11 shows the sheath-core yarn in a state where the sheath fiber has been partially unwound. As is clear from Figure 11, the sheath fiber is wound so as to completely cover the white core fiber. Next, the sheath-core yarn produced in the first step was heated in the dry heat oven. The temperature inside the dry heat oven was set to 240°C, and the time the sheath-core yarn passed through the dry heat oven was set to 85 seconds. After cooling by air for 60 seconds, the composite yarn of the example was obtained.

[0050] FIG. 12 shows a photograph of the composite yarn of the example obtained above, analyzed using the X-ray CT scanner. The photograph in FIG. 12 is a photograph in which the color analysis results obtained using the X-ray CT scanner have been converted into gray. In FIG. 12, the region marked with SL is the sheath fiber layer region, and the central region marked with CL is the core fiber layer region. The core fiber layer CL contains an air layer (AL) as an element other than the fibers that make up the core fiber layer (note that the air layer is shown in red in the color analysis results). However, as is clear from the photograph in FIG. 12, there is almost no air layer (AL) between the sheath fiber layer and the core fiber layer, and it was found that the sheath fiber layer and the core fiber layer are in close contact with each other. Note that in the color analysis results before conversion to gray, the core fiber layer and the sheath fiber layer each have different color tones and shades of color due to differences in the densities of the core fiber and the sheath fiber.

[0051] On the other hand, as a comparative example, a composite yarn with a core-sheath structure produced by the pultrusion method (FRP rod Compose Tension Member manufactured by Ube Exsymo Co., Ltd. (core layer: Kevlar (registered trademark) 1670 dtex, sheath layer: unsaturated polyester)) was analyzed using the X-ray CT scanner in the same manner as above, and the results are shown in Figure 13. Note that, like Figure 12, the photograph in Figure 13 is a photograph in which the color analysis results obtained by the X-ray CT scanner have been converted into gray. As is clear from the photograph in Figure 13, it was found that there are many continuous air layers AL (areas shown in red in the color analysis results) between the sheath fiber layer SL and the core fiber layer CL. [Industrial Applicability]

[0052] The twisting machine of the present invention and the method for producing a composite yarn using the twisting machine can produce a composite yarn in which the core fiber layer and the sheath fiber layer are more closely attached. By combining various types of core fiber and sheath fiber, such a composite yarn can be made into a composite yarn suitable for a variety of applications. [Explanation of symbols]

[0053] 1: Yarn twisting machine 2: core fiber bundle, 21: roller 3: sheath fiber bundle, 31: roller 4: twisting mechanism, 41: ballooning control ring, 42: traveler ring, 43: traveler, 44: flyer 5: Bobbin 6: Guide 6U: Upper guide, 6U1: Ring, 6U2: Hole, 6U3: Wall, 6U4: Connection, 6U5: Hole 6L: Lower guide, 6L1: Ring, 6L2: Hole, 6L3: Main body, 6L4: Hole, 6L5: Pipe, 6L6: Pipe CF: Core fiber SF: sheath fiber CY: Core-sheath structure thread

Claims

1. A step of winding a sheath fiber made of a thermoplastic resin around a core fiber to produce a core-sheath structure yarn; a step of heating the obtained core-sheath structure yarn to a temperature equal to or higher than the melting point of the thermoplastic resin; A method for producing a composite yarn, including [a specific component].

2. The manufacturing method according to claim 1 , wherein the core fiber has a strength of 2 GPa or more and an elastic modulus of 50 GPa or more.

3. The step of producing the core-sheath yarn comprises: at least one core fiber bundle providing the core fiber; at least one sheath fiber bundle providing sheath fibers; a twisting mechanism including a traveler or flyer; and a bobbin for winding a core-sheath yarn in which a sheath fiber is wound around a core fiber by the twisting mechanism, The manufacturing method according to claim 1, further comprising a twisting machine that includes at least two guides between the core fiber bundle and the sheath fiber bundle and the twisting mechanism, which adjust the direction of travel of the core fibers supplied from the core fiber bundle to be substantially the same as the direction of the central axis of the bobbin.

4. The step of producing the core-sheath yarn comprises: at least one core fiber bundle providing the core fiber; at least one sheath fiber bundle providing sheath fibers; a twisting mechanism including a traveler or flyer; and a bobbin for winding a core-sheath yarn in which a sheath fiber is wound around a core fiber by the twisting mechanism, The manufacturing method according to claim 1, further comprising a twisting machine that includes a guide between the core fiber bundle and the sheath fiber bundle and the twisting mechanism, the guide having holes for passing the core fibers and sheath fibers separately, wherein the position of the hole for passing the sheath fibers lies on a virtual circle centered on the hole for passing the core fibers.

Images