Composite spun yarn for fiber-reinforced thermoplastics

Abstract

The object of the present invention is to provide a composite spun yarn for fiber-reinforced thermoplastics that makes it possible to obtain molded articles in which the disordering of the continuous reinforcing fibers is sufficiently suppressed during FRP production, and that allows molten thermoplastic resin to easily penetrate between the single fibers of the reinforcing long fibers (continuous reinforcing fibers) that make up the core when producing the molded article, making it easy to mold, and that results in molded articles that are strong. The composite spun yarn (1) for fiber-reinforced thermoplastics of the present invention is characterized in that a spun yarn (C) (5) made of thermoplastic staple fibers is wound around a substantially untwisted fiber bundle (4) formed from a core (A) containing at least continuous reinforcing fibers (a1) (2) and a sheath (B) made of thermoplastic staple fibers (3).

Description

[Technical Field]

[0001] The present invention relates to a composite spun yarn for fiber-reinforced thermoplastics, which is composed of continuous reinforcing fibers and thermoplastic fibers. [Background technology]

[0002] Metal has traditionally been used as a constituent material for items requiring light weight and strength, such as automobiles, airplanes, and prosthetic limbs, but recently metal has been replaced by fiber-reinforced plastics (FRPs) that incorporate carbon fiber and glass fiber, which are particularly excellent in terms of light weight, high rigidity, high strength, and durability. The reinforcing fibers used in FRPs come in the form of long fiber, short fiber, whiskers, etc., and thermosetting resins such as epoxy resins are the mainstream for matrix resins, although thermoplastic resins such as polyamide and polyphenylene ether are also used in some cases.

[0003] When a thermoplastic resin is used as the matrix, short fibers are mainly used as reinforcing fibers and the product is manufactured by injection molding. However, because the reinforcing fibers are short, the rigidity and strength are low, and to compensate for this, the product must be thickened, resulting in a heavy weight.

[0004] In recent years, mixed yarns containing continuous reinforcing fibers and thermoplastic long fibers have been developed. Because mixed yarns are not final processed products and the continuous reinforcing fibers are not impregnated with thermoplastic resins, they have excellent flexibility and processability. For example, the resulting mixed yarns can be woven alone or with other fibers to form intermediate materials called fabric preforms, or braided into hollow pipe-shaped preforms. Patent Document 1 describes a mixed yarn obtained by aligning opened continuous reinforcing fibers and thermoplastic long fibers and entangling them with compressed air. Patent Document 2 describes a covered yarn developed in which thermoplastic long fibers are spirally wrapped around continuous reinforcing fibers. However, when these mixed yarns are heated and melted to form FRP, the shrinkage of the thermoplastic long fibers causes the orientation of the continuous reinforcing fibers to become disordered. As a result, the resulting molded articles cannot fully utilize the inherent capabilities of the continuous reinforcing fibers, resulting in poor molded article strength.

[0005] In response to these problems with the prior art, the applicant proposed a conjugate spun yarn with excellent resin impregnation and processability in Patent Document 3, which is made by blending continuous reinforcing fibers and thermoplastic short fibers and wrapping them with thermoplastic long fibers to bind them. In Patent Document 3, by using thermoplastic short fibers as the majority of the thermoplastic fibers used, the disorder in the orientation of the continuous reinforcing fibers caused by shrinkage of the thermoplastic fibers when heated and melted was improved, and the strength of the resulting molded body was also excellent, but the disorder in the orientation caused by the shrinkage of the thermoplastic fibers was not completely resolved, and it was difficult to say that the inherent capabilities of the continuous reinforcing fibers were fully exhibited. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-237945 [Patent Document 2] Japanese Patent Publication No. 2021-066974 [Patent Document 3] Patent application No. 2023-064679 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention was devised to solve the problems of the prior art described above, and its purpose is to provide a composite spun yarn for fiber-reinforced thermoplastics that makes it possible to obtain molded articles in which the disordering of the continuous reinforcing fibers is sufficiently suppressed during FRP production, and that allows molten thermoplastic resin to easily penetrate between the single fibers of the reinforcing long fibers (continuous reinforcing fibers) that make up the core when producing the molded article, making it easy to mold, and that results in molded articles that are strong. [Means for solving the problem]

[0008] As a result of intensive research into achieving the above-mentioned object, the present inventors have found that by forming a composite spun yarn in which a spun yarn made of thermoplastic staple fibers is wound around a fiber bundle having a core-sheath structure formed from a core containing continuous reinforcing fibers and a sheath made of thermoplastic staple fibers, when the composite spun yarn obtained is filled into a mold and the thermoplastic staple fibers are heated and melted, a molded product can be obtained without being affected by the shrinkage of the thermoplastic fibers during molding and without disrupting the orientation of the continuous reinforcing fibers, and further, the thermoplastic resin of the staple fibers in the sheath can be sufficiently infiltrated between the single continuous reinforcing fibers in the core of the fiber bundle, resulting in a molded product with uniform physical properties that are excellent in moldability and strength, which led to the completion of the present invention.

[0009] That is, the present invention has the following features (1) to (11). (1) A conjugated spun yarn for fiber-reinforced thermoplastics, characterized in that a spun yarn (C) made of thermoplastic staple fibers is wound around a substantially untwisted fiber bundle formed from a core (A) containing at least continuous reinforcing fibers (a1) and a sheath (B) made of thermoplastic staple fibers. (2) The conjugated spun yarn for fiber-reinforced thermoplastics according to (1), characterized in that the core (A) is composed only of continuous reinforcing fibers (a1). (3) A composite spun yarn for fiber-reinforced thermoplastics according to (1), characterized in that the core (A) is composed of a spun yarn (a2) made of a thermoplastic staple fiber and a continuous reinforcing fiber (a1) arranged so as to cover the spun yarn (a2). (4) The composite spun yarn for fiber-reinforced thermoplastics according to (1), characterized in that the core (A) is composed of a mixture of continuous reinforcing fibers (a1) and thermoplastic short fibers (a3). (5) A composite spun yarn for fiber-reinforced thermoplastics according to (1), characterized in that the continuous reinforcing fiber (a1) is at least one type of fiber selected from the group consisting of carbon fiber, glass fiber, basalt fiber, PBO fiber, and aramid fiber, and the blending ratio of the continuous reinforcing fiber (a1) in the composite spun yarn is 20 to 80 mass%. (6) A composite spun yarn for fiber-reinforced thermoplastics according to (1), characterized in that the thermoplastic staple fibers constituting the sheath portion (B) and the thermoplastic staple fibers constituting the spun yarn (C) each comprise at least one thermoplastic resin selected from the group consisting of polyamide, copolymerized polyamide, polypropylene, polyphenylene sulfide, polyetherimide, polycarbonate, polyaryletherketone, polyetheretherketone, polyimide, and polyhydroxyether. (7) A composite spun yarn for fiber-reinforced thermoplastics according to (3), characterized in that the thermoplastic short fibers constituting the spun yarn (a2) are made of at least one thermoplastic resin selected from the group consisting of polyamide, copolymerized polyamide, polypropylene, polyphenylene sulfide, polyetherimide, polycarbonate, polyaryletherketone, polyetheretherketone, polyimide, and polyhydroxyether. (8) A composite spun yarn for fiber-reinforced thermoplastics according to (3), characterized in that the mass ratio ((a2):(B)+(C)) of the spun yarn (a2) to the sheath portion (B) and the spun yarn (C) is 70:30 to 30:70. (9) The composite spun yarn for fiber-reinforced thermoplastics according to (4), characterized in that the thermoplastic short fiber (a3) ​​is made of at least one thermoplastic resin selected from the group consisting of polyamide, copolymerized polyamide, polypropylene, polyphenylene sulfide, polyetherimide, polycarbonate, polyaryletherketone, polyetheretherketone, polyimide, and polyhydroxyether. (10) The composite spun yarn for fiber-reinforced thermoplastics according to (4), characterized in that the mass ratio ((a3):((B)+(C))) of the thermoplastic short fiber (a3) ​​to the sheath portion (B) and the spun yarn (C) is 70:30 to 30:70. (11) A conjugate spun yarn for fiber-reinforced thermoplastics according to any one of (1) to (10), characterized in that the conjugate spun yarn has a total fineness of 500 to 50,000 dtex. [Effects of the Invention]

[0010] In the conjugate spun yarn for fiber-reinforced thermoplastics of the present invention, all of the thermoplastic fibers used are short fibers, which suppresses thermal shrinkage of the thermoplastic fibers when heated to a temperature higher than the melting point of the thermoplastic resin that forms the thermoplastic fibers. Therefore, even when the conjugate spun yarn is made into a fiber-reinforced plastic molded article, no disturbance occurs in the orientation of the continuous reinforcing fibers, and as a result, the strength of the finished fiber-reinforced plastic molded article can be uniformly increased.

[0011] Furthermore, the composite spun yarn for fiber-reinforced thermoplastics of the present invention is a fiber bundle with a double core-sheath structure in which thermoplastic short fibers, which become the matrix resin when made into a fiber-reinforced thermoplastic (FRTP), are directly arranged in the inner and outer layers of the continuous reinforcing fibers. Furthermore, spun yarns made of thermoplastic short fibers are wrapped around and bound to this fiber bundle. This increases the contact area between the continuous reinforcing fibers and the surrounding thermoplastic short fibers, and also reduces the distance between the continuous reinforcing fiber layer and the thermoplastic fiber layer. Therefore, when heated to a temperature higher than the melting point of the thermoplastic resin forming the thermoplastic fibers, the molten thermoplastic resin penetrates sufficiently quickly between the individual fibers of the continuous reinforcing fibers, allowing for uniform integration of the continuous reinforcing fibers and the thermoplastic resin. As a result, fiber-reinforced thermoplastic plastic molded articles with good moldability, high strength, and uniform physical properties can be easily obtained.

[0012] Furthermore, in the composite spun yarn for fiber-reinforced thermoplastics of the present invention, the thermoplastic short fibers that become the matrix resin when made into FRTP are used as a fiber bundle with a double core-sheath structure, in which the thermoplastic short fibers are arranged directly in the inner and outer layers of the continuous reinforcing fibers.This means that when heated to a temperature higher than the melting point of the thermoplastic resin that forms the thermoplastic fibers, the thermoplastic resin penetrates into the continuous reinforcing fiber layer from two directions, and the continuous reinforcing fibers flow at the single fiber level in accordance with the penetration of the thermoplastic resin.As a result, a fiber-reinforced thermoplastic plastic molded article in which the continuous reinforcing fibers are uniformly dispersed can be easily obtained. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic perspective view of an example of the composite spun yarn for fiber-reinforced thermoplastics of the present invention. [Figure 2] FIG. 2 is a detailed schematic perspective view of an example of the composite spun yarn for fiber-reinforced thermoplastics of the present invention. [Figure 3] FIG. 3 is an example of a cross-sectional photograph of the composite spun yarn for fiber-reinforced thermoplastics shown in FIG. [Figure 4] FIG. 4 is a schematic diagram of an example of an apparatus for producing a composite spun yarn for fiber-reinforced thermoplastics according to the present invention. [Figure 5] FIG. 5 is a photograph of a unidirectional molded article made of the composite spun yarn of Example 5. [Figure 6] FIG. 6 is a photograph of a unidirectional material formed from the composite spun yarn of Comparative Example 1. [Figure 7] FIG. 7 is a cross-sectional photograph showing the state of impregnation of the thermoplastic resin in the composite spun yarn of Example 5. [Figure 8] FIG. 8 is a cross-sectional photograph showing the state of impregnation of the thermoplastic resin in the composite spun yarn of Example 4. [Figure 9] FIG. 9 is a cross-sectional photograph showing the state of impregnation of the thermoplastic resin in the composite spun yarn of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] The conjugate spun yarn for fiber-reinforced thermoplastics of the present invention is characterized by being constructed by wrapping a spun yarn (C) made of thermoplastic staple fibers around a fiber bundle with a substantially untwisted core-sheath structure formed from a core (A) containing continuous reinforcing fibers (a1) and a sheath (B) made of thermoplastic staple fibers. In the conjugate spun yarn of the present invention, the core (A) containing continuous reinforcing fibers (a1) is directly surrounded by the thermoplastic staple fibers (B). This allows the resin derived from the molten thermoplastic staple fibers to easily penetrate between the filaments of the continuous reinforcing fibers that make up the core when heated and melted. Furthermore, by using only staple thermoplastic fibers, the thermal shrinkage of the spun yarn (C) when heated and melted is suppressed, which in turn suppresses the thermal shrinkage of the conjugate spun yarn and prevents the orientation of the continuous reinforcing fibers from becoming distorted. Specifically, thermoplastic fibers undergo large dimensional changes (shrinkage) upon heat treatment, and the dimensional change of thermoplastic long fibers in particular is much larger than that of spun yarns. Since continuous reinforcing fibers do not shrink as much as thermoplastic fibers, in the case of composite yarns that use thermoplastic long fibers as hold-down yarns and combine them with continuous reinforcing fibers, the difference in shrinkage behavior between them and the thermoplastic long fibers and the continuous reinforcing fibers is large, and the thermoplastic long fibers undergo thermal shrinkage during heat treatment, resulting in shrinkage of the composite spun yarn and disruption of the orientation of the continuous reinforcing fibers in the fiber axial direction. In the present invention, all thermoplastic fibers are short fibers, so the aforementioned shrinkage of the composite spun yarn is suppressed and the orientation of the continuous reinforcing fibers is maintained.

[0015] The continuous reinforcing fiber (a1) used in the conjugate spun yarn of the present invention is a reinforcing fiber that extends continuously in the longitudinal direction and is synonymous with "long reinforcing fiber." The continuous reinforcing fiber used in the conjugate spun yarn of the present invention is preferably a high-strength fiber having a tensile strength of 1000 MPa or more and a tensile modulus of elasticity of 30 GPa or more. Because such high-strength fibers are very difficult to bend, it is difficult to consistently produce uniform spun yarns using conventional spinning methods. However, the conjugate spun yarn of the present invention can be produced without any problems. Examples of the continuous reinforcing fiber (a1) include carbon fiber, glass fiber, aramid fiber, polyparaphenylene benzobisoxazole fiber (PBO fiber), phenol fiber, metal fiber, aramid fiber, and ceramic fiber. In the present invention, it is preferable to use at least one fiber selected from the group consisting of carbon fiber, glass fiber, basalt fiber, PBO fiber, and aramid fiber. Carbon fiber, glass fiber, and aramid fiber are more preferred, and carbon fiber and glass fiber are even more preferred.

[0016] The blending ratio of the continuous reinforcing fiber (a1) in the conjugated spun yarn of the present invention is preferably 20 to 80% by mass, more preferably 25 to 75% by mass. If the blending ratio is less than the above range, the strength-improving effect of the reinforcing fiber is likely to decrease. If the blending ratio exceeds the above range, the coverage of the thermoplastic fiber becomes too low, and voids are likely to occur.

[0017] The single filament fineness (single fiber fineness) of the continuous reinforcing fibers (a1) is preferably 0.3 to 10 dtex, more preferably 0.5 to 5 dtex. The total fineness of the continuous reinforcing fibers (a1) is preferably 500 to 50,000 dtex, more preferably 650 to 40,000 dtex. The number of filaments is preferably 700 to 70,000, more preferably 900 to 60,000. A fineness within this range makes it easy to handle as a reinforcing fiber for FRTP. The continuous reinforcing fibers (a1) are preferably substantially untwisted, and even if there is a small amount of twist, the number of twists is preferably 10 times / inch or less, more preferably 5 times / inch or less. If the number of twists exceeds the above range, the permeability of the thermoplastic resin that serves as the matrix is ​​likely to decrease.

[0018] The strength of the continuous reinforcing fibers (a1) is preferably 1000 to 8000 MPa, and more preferably 2000 MPa or more. If the strength is below the above range, it becomes difficult for the molded FRTP to maintain sufficient strength. If the strength exceeds the above range, it becomes difficult to stably produce a composite spun yarn.

[0019] The thermoplastic staple fibers used in the conjugated spun yarn of the present invention are preferably made of a thermoplastic resin typically used as a matrix resin in FRTP and having a melting point lower than the decomposition temperature of the continuous reinforcing fibers. For example, when carbon fibers are used as the continuous reinforcing fibers, the thermoplastic staple fibers are preferably made of a resin having a melting point or glass transition temperature of 400°C or lower. The thermoplastic staple fibers are preferably made of at least one thermoplastic resin selected from the group consisting of polyamide, copolymerized polyamide, polypropylene, polyphenylene sulfide, polyetherimide, polyethersulfone, polyketone, polycarbonate, polysulfone, polyphenylene ether, polyimide, polyamideimide, polyaryletherketone, polyetheretherketone, and polyhydroxyether. In particular, the thermoplastic staple fibers are preferably made of at least one thermoplastic resin selected from the group consisting of polyamide, copolymerized polyamide, polypropylene, polyphenylene sulfide, polyetherimide, polycarbonate, polyetheretherketone, and polyimide.

[0020] The single filament fineness of the thermoplastic staple fiber is preferably 0.3 to 20 dtex, more preferably 0.5 to 15 dtex, and even more preferably 0.8 to 10 dtex. If the single filament fineness is smaller than the above range, spinnability tends to decrease. If it is larger than the above range, the fiber bundle becomes too stiff, making it difficult to stably produce a composite spun yarn. The fiber length of the thermoplastic staple fiber is preferably 25 to 70 mm, more preferably 30 to 60 mm, and even more preferably 32 to 55 mm. If the fiber length is outside the above range, uniform spinning becomes difficult.

[0021] The composite spun yarn of the present invention is in the form of a fiber bundle in which continuous reinforcing fibers (a1) and thermoplastic staple fibers are mixed substantially without twist, and has a core-sheath structure in which a core (A) containing the continuous reinforcing fibers (a1) is present on the inside of the cross section of the fiber bundle, and a sheath (B) consisting of a group of thermoplastic staple fibers is present on the outer periphery of the cross section of the fiber bundle. In this core-sheath structure, the thermoplastic staple fibers are always present on the outer periphery of the cross section of the fiber bundle, but it is sufficient for the thermoplastic staple fibers to cover most of the continuous reinforcing fibers (a1) of the core (A), and they do not have to cover them completely.

[0022] By forming a fiber bundle with a core-sheath structure that is substantially untwisted, the continuous reinforcing fibers (a1) are sufficiently coated with the thermoplastic short fibers. When the thermoplastic short fibers are melted by heating to form a matrix resin, the matrix resin can be sufficiently and uniformly impregnated into the continuous reinforcing fibers, thereby suppressing the occurrence of voids and reducing variations in strength. In the present invention, "substantially untwisted" means that the twist is so loose that the convergence of the fiber bundle cannot be maintained when the spun yarn (C) used as the presser yarn is removed from the composite spun yarn. Specifically, when the composite fiber is attached to a twist detector and both ends of the composite spun yarn are grasped, the spun yarn (C) used as the presser yarn is removed to leave only the fiber bundle. Then, when the center of the fiber bundle is pinched with tweezers and squeezed in the fiber axial direction, the thermoplastic short fibers in the sheath portion (B) of the fiber bundle come out of the core portion (A) of the fiber bundle, making it impossible to maintain the fiber bundle.

[0023] The content of continuous reinforcing fibers (a1) in the fiber bundle is preferably 20 to 80% by mass, more preferably 25 to 75% by mass. If the content of continuous reinforcing fibers is less than the above range, the strength-improving effect of the reinforcing fibers is likely to decrease. If the content exceeds the above range, the coverage of the thermoplastic fibers becomes too low, and voids are likely to occur.

[0024] In the composite spun yarn of the present invention, the sheath-core structure is made of fiber bundles that are substantially untwisted, allowing for stable spinning. If the fiber bundles of the sheath-core structure are twisted, the continuous reinforcing fiber bundles are exposed to the surface of the composite spun yarn, reducing coverage, and the rigidity of the continuous reinforcing fibers can cause untwisting of the composite spun yarn, making it difficult to stabilize spinning and producing a composite spun yarn with stable quality. In contrast, the composite spun yarn of the present invention has a sheath-core structure made of fiber bundles that are substantially untwisted, so the above-mentioned problems do not occur and spinning is more likely to be stable.

[0025] The core (A) of the composite spun yarn of the present invention may be configured, for example, as follows: (i) a spun yarn (a2) made of thermoplastic staple fibers and continuous reinforcing fibers (a1) arranged to cover the spun yarn (a2); or (ii) a mixture of continuous reinforcing fibers (a1) and thermoplastic staple fibers (a3). These configurations (i) and (ii) bring the thermoplastic fibers and the continuous reinforcing fibers into close proximity, increasing the contact area. Therefore, when the composite spun yarn is heated and melted, the thermoplastic resin penetrates the continuous reinforcing fiber layer from two directions. In particular, the thermoplastic staple fibers arranged inside the continuous reinforcing fibers pass through the continuous reinforcing fiber layer and attempt to flow out. Therefore, the continuous reinforcing fibers diffuse at the single fiber level in accordance with the diffusion and penetration of the thermoplastic resin. As a result, the continuous reinforcing fibers are uniformly dispersed in the resulting fiber-reinforced plastic molding. In the case of the structure (i), the spun yarn (a2) does not need to be completely disposed at the center of the core (A) as long as most of it is covered with the continuous reinforcing fiber (a1).In the case of the structure (ii), the continuous reinforcing fiber (a1) and the thermoplastic short fiber (a3) ​​do not need to be completely uniformly mixed as long as most of them are mixed with each other.

[0026] The thermoplastic staple fibers constituting the core (A) of the conjugate spun yarn of the present invention are preferably made of a thermoplastic resin typically used as a matrix resin in FRTP and have a melting point lower than the decomposition temperature of the continuous reinforcing fibers. For example, when carbon fibers are used as the continuous reinforcing fibers, the thermoplastic staple fibers are preferably made of a resin having a melting point or glass transition temperature of 400°C or lower. The thermoplastic staple fibers constituting the core (A) are preferably made of at least one thermoplastic resin selected from the group consisting of polyamide, copolymer polyamide, polypropylene, polyphenylene sulfide, polyetherimide, polyethersulfone, polyketone, polycarbonate, polysulfone, polyphenylene ether, polyimide, polyamideimide, polyaryletherketone, polyetheretherketone, and polyhydroxyether. In particular, the thermoplastic staple fibers constituting the core (A) are preferably made of at least one thermoplastic resin selected from the group consisting of polyamide, copolymer polyamide, polypropylene, polyphenylene sulfide, polyetherimide, polycarbonate, polyetheretherketone, and polyimide. The thermoplastic staple fibers that may form part of the core (A), the thermoplastic staple fibers that form the sheath (B), and the thermoplastic staple fibers that form the spun yarn (C) can be made of different types of thermoplastic resins, but when recycling FRTP, they are preferably made of the same type of thermoplastic resin. Here, the shrinkage percentage of the spun yarn made of the thermoplastic staple fibers (a2) of the core (A) in configuration (i) is preferably 3.5% or less, and more preferably 3% or less. If the shrinkage percentage exceeds the above range, the orientation of the continuous reinforcing fibers may be disrupted due to the influence of thermal shrinkage during heating and melting.

[0027] In the conjugated spun yarn of the present invention, when the above configuration (i) is used, the mass ratio ((a2):((B)+(C))) of the thermoplastic staple fiber (a2) constituting the core (A) to the sheath portion (B) and spun yarn (C) is preferably 70:30 to 30:70. More preferably, it is 65:35 to 35:65. If the mass ratio of the sheath portion (B) and spun yarn (C) to the thermoplastic staple fiber (a2) constituting the core (A) exceeds the above range, the coverage of the outer periphery of the cross section of the fiber bundle with the thermoplastic staple fiber decreases, making voids more likely to occur. If the mass ratio of the sheath portion (B) and spun yarn (C) to the thermoplastic staple fiber (a2) constituting the core (A) is less than the above range, resin outflow from the core is reduced, making voids more likely to occur.

[0028] In the conjugated spun yarn of the present invention, when the above configuration (ii) is used, the mass ratio ((a3):((B)+(C))) of the thermoplastic staple fiber (a3) ​​to the sheath portion (B) and spun yarn (C) is preferably 70:30 to 30:70. More preferably, it is 65:35 to 35:65. If the mass ratio of the sheath portion (B) and spun yarn (C) to the thermoplastic staple fiber (a2) constituting the core portion (A) exceeds the above range, the coverage of the outer periphery of the cross section of the fiber bundle by the thermoplastic staple fiber decreases, and voids tend to occur. If the mass ratio of the sheath portion (B) and spun yarn (C) to the thermoplastic staple fiber (a2) constituting the core portion (A) is less than the above range, resin outflow from the core is reduced, and voids tend to occur.

[0029] Here, impregnation means replacing the air between and within the fiber bundles with the thermoplastic resin, and the distance the resin needs to travel for this purpose is defined as the impregnation distance. In the present invention, the thickness direction distance (L1) of the thickest point of the continuous reinforcing fiber layer in the cross section of the composite spun yarn is measured using a measurement function, and half of this value (L1 / 2) is defined as the impregnation distance. The impregnation distance is preferably 200 μm or less, more preferably 180 μm or less. If the impregnation distance exceeds the above value, the distance between the continuous reinforcing fiber and the thermoplastic fiber in the cross section of the composite yarn becomes large, making it more likely that voids will occur during heat melting. If the impregnation distance is within the above value, the thermoplastic resin will quickly penetrate the continuous reinforcing fiber bundle as the thermoplastic short fiber is heat melted, making it easier to obtain a molded product with high physical properties. To achieve the above-mentioned impregnation distance, the core (A) may be composed of only continuous reinforcing fiber (a1) when the fineness of the continuous reinforcing fiber used is in the range of 500 to 2000 dtex, and when the fineness of the continuous reinforcing fiber used is in the range of more than 2000 dtex, it is preferable to use the configuration (i) or (ii) in which the core (A) is composed of a combination of continuous reinforcing fiber (a1) and thermoplastic short fiber (a2 or a3).

[0030] The fiber bundle of the composite spun yarn of the present invention is essentially untwisted and therefore prone to unraveling. Therefore, in the present invention, a spun yarn (C) made of thermoplastic staple fibers is wound around the fiber bundle as a presser thread (a thread that binds the fiber bundle), thereby preventing the fiber bundle from unraveling. By using the spun yarn (C) as the presser thread, although the staple fibers themselves shrink due to heat, the fibers are not physically continuous, so the thermal shrinkage of the spun yarn is smaller than that of thermoplastic long fibers, and the continuous reinforcing fibers are less susceptible to the thermal shrinkage of the thermoplastic fibers. The shrinkage percentage of the spun yarn (C) used as the presser thread is preferably 3.5% or less, more preferably 3% or less. If the shrinkage percentage exceeds the above range, the orientation of the continuous reinforcing fibers may be disrupted due to the thermal shrinkage during heating and melting. The spun yarn (C) made of thermoplastic staple fibers is preferably made of a thermoplastic resin typically used as a matrix resin for FRTP, and is preferably made from a resin having a melting point or glass transition temperature lower than the decomposition temperature of the continuous reinforcing fibers. For example, when carbon fibers are used as the continuous reinforcing fibers, the thermoplastic staple fibers constituting the spun yarn (C) are preferably thermoplastic fibers made of a resin having a melting point or glass transition temperature of 400°C or lower. The thermoplastic staple fibers constituting the spun yarn (C) are preferably staple fibers made of at least one thermoplastic resin selected from the group consisting of polyamide, copolymer polyamide, polypropylene, polyphenylene sulfide, polyetherimide, polyethersulfone, polyketone, polycarbonate, polysulfone, polyphenylene ether, polyimide, polyamideimide, polyaryletherketone, polyetheretherketone, and polyhydroxyether. In particular, the thermoplastic staple fibers constituting the spun yarn (C) are preferably staple fibers made of at least one thermoplastic resin selected from the group consisting of polyamide, copolymer polyamide, polypropylene, polyphenylene sulfide, polyetherimide, polycarbonate, polyaryletherketone, polyetheretherketone, polyimide, and polyhydroxyether.The thermoplastic staple fibers constituting the spun yarn (C), the thermoplastic staple fibers constituting the sheath (B), and the thermoplastic staple fibers that may constitute part of the core (A) may be made of different types of thermoplastic resins, but when recycling FRTP, it is preferable that they be made of the same type of thermoplastic resin.

[0031] The total fineness of the spun yarn (C) is preferably 10 to 1,000 dtex, more preferably 50 to 800 dtex. If the total fineness is smaller than the above range, the binding of the composite spun yarn may be weak, making it prone to fuzzing, or the spun yarn may break due to friction, resulting in the yarn being pulled out. If the total fineness is larger than the above range, the fiber bundle may be twisted when binding a fiber bundle consisting of the continuous reinforcing fiber (a1) and the thermoplastic staple fiber with the spun yarn (C) consisting of the thermoplastic staple fiber, making stable production difficult. The single fiber fineness of the thermoplastic staple fiber used in the spun yarn (C) is preferably 0.3 to 20 dtex, more preferably 0.5 to 15 dtex, and even more preferably 0.8 to 10 dtex. If the single fiber fineness is smaller than the above range, spinnability may be reduced. If the total fineness is larger than the above range, the fiber bundle may be too stiff, making it difficult to stably produce the composite spun yarn. The fiber length of the thermoplastic short fibers constituting the spun yarn (C) is preferably 25 to 70 mm, more preferably 30 to 60 mm, and even more preferably 32 to 55 mm. If the fiber length is outside the above range, uniform spinning becomes difficult.

[0032] The bundling twist number of the spun yarn (C) is preferably 1 to 1000 T / m, more preferably 30 to 800 T / m, and even more preferably 50 to 500 T / m. If the bundling twist number is below the above range, the bundling strength is weak and the fiber bundle is likely to come loose. If it exceeds the above range, the fiber bundle is overly tightened, making it difficult to stably produce a composite yarn. The twist direction when winding the fiber bundle may be either the S direction or the Z direction.

[0033] The total fineness of the composite spun yarn of the present invention is preferably 500 to 50,000 dtex, more preferably 800 to 48,000 dtex, and even more preferably 1,000 to 45,000 dtex. If the total fineness is below the above range, it tends to be difficult to produce a uniform spun yarn. If it exceeds the above range, special equipment is required to produce the composite yarn of the present invention, which may increase production costs.

[0034] Next, the conjugate spun yarn of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of an example of the conjugate spun yarn of the present invention. As can be seen from FIG. 1, the conjugate spun yarn 1 of FIG. 1 has a structure in which a spun yarn 5 made of a thermoplastic staple fiber is wound around a fiber bundle 4 having a core-sheath structure composed of a continuous reinforcing fiber 2 that forms the core and a thermoplastic staple fiber 3 that covers the continuous reinforcing fiber 2 and forms the sheath. FIG. 1 shows an example in which the spun yarn 5 is wound around the fiber bundle 4 with an S twist. The thermoplastic staple fiber 3 and the spun yarn 5 are melted by heating when forming the FRTP and become a matrix resin. FIG. 2 is a perspective view of an example of the conjugate spun yarn of the present invention in an embodiment different from that of FIG. 1. As can be seen from FIG. 2, the conjugate spun yarn 6 in FIG. 2 has a configuration in which a spun yarn 5 made of thermoplastic staple fibers is wound around a fiber bundle 8 having a double core-sheath structure, the double core-sheath structure consisting of a core made of a spun yarn 7 made of thermoplastic staple fibers and continuous reinforcing fibers 2 arranged to cover the spun yarn 7, and a sheath made of thermoplastic staple fibers 3 covering the continuous reinforcing fibers 2. FIG. 3 is a cross-sectional photograph of an example of the conjugate spun yarn 6 shown in FIG. 2. In FIG. 3, 2 is the continuous reinforcing fiber that forms part of the core, 3 is the group of thermoplastic staple fibers that form the sheath, 5 is the spun yarn made of thermoplastic staple fibers that serve as the presser thread, 7 is the spun yarn made of thermoplastic staple fibers that form part of the core, and 8 is the fiber bundle with a double core-sheath structure. In FIG. 3, it is sufficient that the spun yarn 7 that forms part of the core is mostly covered by the continuous reinforcing fibers 2, but it does not have to be completely covered. It is also sufficient that the core is mostly covered by the group of thermoplastic staple fibers 3 that form the sheath, but it does not have to be completely covered.

[0035] Next, an example of a method for producing a conjugate spun yarn of the present invention will be described with reference to FIG. 4. FIG. 4 is a schematic diagram of an example of an apparatus for producing a conjugate spun yarn of the present invention. As can be seen from FIG. 4, first, continuous reinforcing fiber 2 is supplied as a core yarn. Thermoplastic short fibers 3 that will form the sheath portion are drafted by a draft device 9 and then supplied. Next, the core continuous reinforcing fiber 2 and the drafted thermoplastic short fibers 3 are combined through a guide 10 to form a fiber bundle 4 with a core-sheath structure. This fiber bundle 4 is substantially untwisted. Thereafter, the fiber bundle 4 is wound with a spun yarn 5 made of thermoplastic short fibers drawn from a hollow bobbin 11, thereby bundling the fiber bundles and producing a conjugate spun yarn 1. The conjugate spun yarn 1 passes through feed rollers 12 and is wound onto a winding package to produce a conjugate spun yarn cheese 13.

[0036] When the composite spun yarn of the present invention has the above-mentioned configuration (i), a spun yarn 7 made of thermoplastic staple fibers is supplied simultaneously with the continuous reinforcing fibers 2, and the drafted thermoplastic staple fibers 3 are combined through a guide 10 to form a fiber bundle 8 with a core-sheath structure. Here, by supplying the spun yarn 7 positioned in the center of the continuous reinforcing fibers 2 in the fiber width direction, a double core structure as shown in Figure 3 is formed. Then, the fiber bundle 8 is wound with a spun yarn 5 made of thermoplastic staple fibers drawn from a hollow bobbin 11, thereby bundling the fiber bundles and producing a composite spun yarn 6. The composite spun yarn 6 passes through a feed roller 12 and is wound onto a winding package, completing a composite spun yarn cheese 13.

[0037] When the conjugate spun yarn of the present invention has the above-mentioned configuration (ii), the continuous reinforcing fibers 2 are passed through a roller and spread. The thermoplastic staple fibers 14 are arranged and fed so as to overlap with the spread continuous reinforcing fibers 2 at approximately the same width, and the drafted thermoplastic staple fibers 3 are combined through a guide 10 to form a fiber bundle 15 with a core-sheath structure. The spread continuous reinforcing fibers 2 and the thermoplastic staple fibers 14 are then converged and mixed by the spun yarn 5 made of thermoplastic staple fibers and the winding tension of the feed roller 12. This fiber bundle 15 is substantially untwisted. The fiber bundle 15 is then wound around the spun yarn 5 drawn from the hollow bobbin 11, thereby binding the fiber bundles and producing the conjugate spun yarn 16. The conjugate spun yarn 16 passes through the feed roller 12 and is wound onto a winding package to produce the conjugate spun yarn cheese 13.

[0038] The strength of the core of the fiber bundle in the composite spun yarn of the present invention is preferably 500 to 8000 MPa, more preferably 1300 to 7000 MPa. The strength of the core depends on the physical properties of the continuous reinforcing fibers, but in the present invention, the continuous reinforcing fibers are substantially untwisted and converged, resulting in a yarn form that makes it easy for the continuous reinforcing fibers to exhibit their inherent strength.

[0039] The composite spun yarn of the present invention can be used as an intermediate for fiber reinforced resin by paralleling the yarn itself using a roving method or the like to form an FRTP, or by forming it into a woven fabric, knitted fabric, multiaxial insertion warp knitted fabric, or braided fabric. These intermediates can also be made into prepregs for use in final molded products. Paralleling the composite spun yarn, woven fabric, knitted fabric, and multiaxial insertion warp knitted fabric can be molded into a sheet or tape shape for use, and braided fabrics can be molded into a pipe shape for use. Any known structure can be used for the woven and knitted fabrics.

[0040] Such a molded article can be produced by filling a mold with the conjugated spun yarn of the present invention and heating the mold to a temperature higher than the higher melting point of the thermoplastic staple fiber and the spun yarn made of the thermoplastic staple fiber (or the glass transition temperature in the case of a resin without a melting point) to melt the thermoplastic staple fiber. The heating temperature is preferably lower than the decomposition temperature of the continuous reinforcing fiber. Considering the permeability of the thermoplastic resin into the continuous reinforcing fiber, it is preferable to heat and melt the thermoplastic staple fiber at a temperature 15°C to 300°C higher than the melting point of the thermoplastic staple fiber for molding. For example, when polyamide 6 fiber is used as the thermoplastic staple fiber, the mold temperature is preferably about 220 to 300°C. The mold filling rate is preferably 100 to 350%, more preferably 105 to 200%.

[0041] The molded article can be produced by a conventionally known molding method, such as a hot stamping method, a prepreg molding method, an SMC molding method, etc. Alternatively, the molded article may be formed by a film stacking method in which a thermoplastic resin film is melted and compressed.

[0042] The conjugated spun yarn of the present invention can also be wound around a metal frame and hot-pressed to form a prepreg or molded article. Fig. 5 shows a photograph of a unidirectional molded article produced by winding the conjugated spun yarn of the present invention (Example 5) around a metal frame, filling it directly into a mold, and pressing it. Fig. 6 shows a photograph of a unidirectional molded article produced by winding a conjugated yarn (Comparative Example 1) in which the pressure yarn, which is not the conjugated spun yarn of the present invention, is a thermoplastic continuous fiber, around a metal frame, filling it directly into a mold, and pressing it.

[0043] Molded articles made with the conjugated spun yarn of the present invention can have a uniform and excellent appearance. That is, with the conjugated spun yarn of the present invention, there is no disorder of the continuous reinforcing fibers due to the flow of the resin during molding, as shown in Figure 5. On the other hand, in an example where the presser thread is made of a thermoplastic continuous fiber, which is not the conjugated spun yarn of the present invention, the orientation of the continuous reinforcing fibers is disturbed due to the influence of shrinkage when the presser thread is heated and melted, as shown in Figure 6. The surface of conventionally molded prepregs tends to be of poor quality, with many irregularities caused by voids in areas where the matrix resin is not sufficiently infiltrated. However, when the conjugated spun yarn of the present invention is used, the matrix resin is sufficiently and uniformly infiltrated, with few voids, resulting in a smooth prepreg surface.

[0044] In a preferred embodiment, the molded article produced as described above from the composite spun yarn of the present invention is a unidirectional molded article that can achieve a tensile strength of 700 to 2000 MPa, or even 800 to 2000 MPa, a tensile modulus of 50 to 150 GPa, or even 70 to 150 GPa, a flexural strength of 500 to 2000 MPa, or even 800 to 2000 MPa, and a flexural modulus of 40 to 130 GPa, or even 70 to 150 GPa.

[0045] The molded article produced as described above from the composite spun yarn of the present invention has a high fiber volume content (Vf) but a small void ratio, which is an index of the amount of voids. Specifically, the Vf is 30 to 70%, or even 44 to 70%, and the void ratio of the cross section of the woven fabric is 1.0% or less, or even 0.8% or less, and it is even possible to completely eliminate the generation of voids. [Example]

[0046] The effects of the present invention will be specifically described below based on examples, but the present invention is not limited to these. The methods for measuring the respective characteristic values ​​in the present invention are as follows.

[0047] (1) Single fiber fineness of short fibers The single yarn fineness (single fiber fineness) was determined based on JIS-L1015-8.5.1 Correct Fineness Method A.

[0048] (2) Measurement of total fineness of spun yarn The total fineness of the core spun yarn (a2) and the presser yarn (C) was measured in accordance with JIS L 1095 9.4.2.

[0049] (3) Confirmation that the fiber bundle is substantially untwisted The composite spun yarn was attached to a twist detector and both ends of the composite spun yarn were grasped. A needle was then inserted between the fiber bundle and the presser thread (C). The presser thread (C) was untwisted just enough to loosen it, while the presser thread (C) was carefully removed using tweezers and scissors. The fiber bundle was then twisted by the amount of untwist. When the center of this fiber bundle was pinched with tweezers and squeezed in the fiber axial direction, if the thermoplastic short fibers moved from the fiber bundle in accordance with the movement of the tweezers, it was judged to be essentially untwisted. This is a state in which the fiber bundle cannot be maintained.

[0050] (4) Measurement of shrinkage rate of spun yarn The shrinkage rates of the core spun yarn (a2), the presser yarn (C), and the composite spun yarn were measured in accordance with JIS L 1013 8.18.2 a) (2010) dry heat dimensional change rate %. The dryer temperature was set to 130°C.

[0051] (5) Number of twists of the presser thread wrapped around the fiber bundle The number of twists was determined in accordance with JIS-L1095-9.15.1 Method A. Specifically, after the composite spun yarn was attached to a twist detector, a needle was inserted between the fiber bundle and the presser thread (C) to untwist it, and the number of twists at which the fiber bundle and the presser thread separated was taken as the bundle twist.

[0052] (6) Measurement of the blend ratio of each raw material in composite spun yarn JIS L1030-2 Test method for blend ratio of textile products - Part 2: Fiber blend ratio 4. Measured in accordance with the unraveling method.

[0053] (7) Volume fraction of continuous reinforcing fibers in composite spun yarn (Vf') The volume content Vf' (%) of the continuous reinforcing fibers in the composite spun yarn was calculated using the following formula. Vf'=(Tf / ρf) / (Tf / ρf+Tr / ρr)×100 Tf: Fineness of continuous reinforcing fiber (dtex) Tr: Thermoplastic fiber (short fiber + spun yarn) fineness (dtex) ρf: specific gravity of continuous reinforcing fiber (g / cm 3 ) ρr: Specific gravity of thermoplastic fiber (short fiber + spun yarn) (g / cm 3 )

[0054] (8) Total fineness measurement of composite spun yarn Measurement was carried out in accordance with JIS L 1095 9.4.2.

[0055] (9) Measurement of the impregnation distance of composite spun yarn A 10 mm diameter hole was drilled in a commercially available polypropylene plate (3 mm thick). The composite spun yarn was wrapped in a colored fiber bundle, passed through the hole, and fixed. The sample was then cut with a microtome to prepare an observation sample. The sample was photographed using a VHX-7000 digital microscope. The magnification was set to 150x so that the entire cross section of the composite spun yarn could be observed. The thickness direction distance (L1) of the thickest point of the continuous reinforcing fiber layer was measured using the measurement function, and half of this value (L1 / 2) was used as the impregnation distance.

[0056] (10) Fiber orientation of molded body The orientation of the continuous reinforcing fibers was evaluated from the appearance of the unidirectional molded body. The results were judged as follows, by comparing with Figures 5 and 6. 1: As shown in Figure 6, the orientation of the continuous reinforcing fibers is disturbed. 2: As shown in Figure 5, there is no visible disorder in the orientation of the continuous reinforcing fibers. If the rating is 1, the molded product has poor physical properties, and if it is 2, the molded product has excellent physical properties.

[0057] (11) Dispersibility of continuous reinforcing fibers The thickness direction cross section of the molded body was observed as follows. A sample was prepared by cutting the molded body into 15 mm x 15 mm so that the cut edge was aligned with the continuous reinforcing fiber direction, and embedded in epoxy resin. The sample was polished until the thickness direction cross section of the molded body could be clearly observed. The polished sample was photographed using a high-end inverted metallurgical microscope GX71 / DP73 microscope digital camera (manufactured by Olympus). Images taken within a photographed range of 1.5 mm in the thickness direction of the molded body x 15 mm in the fiber arrangement direction were superimposed to form a single continuous image. The degree of dispersion of the continuous reinforcing fibers over the entire observation surface was evaluated using the following index. In Figures 7 to 9, the white granular dots represent the continuous reinforcing fibers, and the black areas represent the thermoplastic resin. 1: As shown in Figure 9, the cross section of the molded body clearly shows traces of reinforcing fiber bundles and there are resin pools. 2: As shown in Figure 8, no trace of reinforcing fiber bundles is visible in the cross section of the molded body, but resin pools are present. 3: As shown in Figure 7, no trace of reinforcing fiber bundles is visible in the cross section of the molded body, and no resin pools are present. If the evaluation result is 1, the molded product will have poor physical properties, if it is 2, it will exhibit excellent physical properties, and if it is 3, it will exhibit even better physical properties.

[0058] (12) Fiber volume content of molded body (Vf) The weight content of continuous reinforcing fibers (Wf) was measured with reference to JIS K 7052. A cleaned and dried porcelain crucible was weighed accurately to the nearest 0.1 mg using an electronic balance (M1). Test pieces, 1.5 mm thick and 150 mm square, were cut from any position on the molded body and placed in a porcelain crucible. They were then dried in a dryer at 105°C until the mass was constant. They were then cooled in a desiccator and weighed accurately to the nearest 0.1 mg using an electronic balance (M2). They were then heated in an electric furnace at an ambient temperature of 420°C for 8 hours. The porcelain crucible and calcined ash were transferred to a desiccator, cooled to room temperature, and weighed to the nearest 0.1 mg (M3). Using these values, the weight content of continuous reinforcing fibers (Wf) was calculated using the following equation: Wf = (M3 - M1) / (M2 - M1) x 100 Wf: Weight content of continuous reinforcing fibers (%) M1: Dry mass of porcelain (g) M2: Mass of the crucible and sample before firing (g) M3: Mass of crucible and sample after firing (g) Using the weight content (Wf) of the continuous reinforcing fibers obtained above, the volume content (Vf) of the continuous reinforcing fibers was calculated according to the following formula. Vf=Wf / ρf / (Wf / ρf+(1-Wf) / ρr)×100

[0059] (13) Void ratio of the green body (Vv) The thickness direction cross section of the molded body was observed as follows. The molded body was cut into 15 mm x 15 mm samples with the cut edges aligned with the direction of the continuous reinforcing fibers, and embedded in epoxy resin. The samples were polished until the thickness direction cross section of the molded body could be clearly observed. The polished samples were photographed using a VHX-7000 digital microscope. The images were taken at a magnification of 300x. In the photographed images, the area of ​​the entire observation surface and the area of ​​the voids were determined, and the void ratio was calculated using the following formula. The average of the calculated values ​​for five locations was used as the void ratio. Cavity rate (%) = 100 × (total area of ​​cavity) / (total area of ​​observation surface)

[0060] (14) Bending strength and bending modulus of molded product Measurements were carried out in accordance with the test piece dimensions and test method specified in JIS-K7074. (i) Preparation of test specimens A test piece measuring 100 mm in length and 15 mm in width was cut out from the obtained molded body in the direction parallel to the fiber direction (0°). (ii) Measurement of bending strength and bending modulus Using the cut specimens, a three-point bending test was performed at 23°C and 50% humidity, with a support distance of 80 mm and a speed of 5 mm / min, to measure strength and modulus of elasticity. The testing machine used was the Shimadzu Autograph AG-X plus 100 kN. The average values ​​obtained from three measurements were used as the bending strength and modulus of elasticity.

[0061] (15) Tensile strength and tensile modulus of molded body Measurements were carried out in accordance with the test piece dimensions and test method specified in JIS-K7165. (i) Preparation of test specimens Test pieces measuring 200 mm in length and 1.25 mm in width were cut out from the obtained molded body in a direction parallel to the fiber direction (0°). Both ends of the test pieces were reinforced with tabs. The tabs were made of a composite material of glass fiber woven fabric and epoxy resin, and were 50 mm in length and 1.25 mm in width. CN adhesive (general-purpose) manufactured by Tokyo Measuring Instruments Research Institute Co., Ltd. was used as the adhesive for the tabs. After the tabs were attached to the test pieces, they were left to stand overnight in an environment of 23°C and 50% humidity. (ii) Measurement of tensile strength and tensile modulus Using the test specimens prepared above, a tensile test was conducted at a gripping distance of 100 mm and a speed of 2 mm / min under an environment of 23°C and 50% humidity to measure the tensile strength and tensile modulus. The testing machine used was the Shimadzu Autograph AG-X plus 100kN. A Kyowa Electronics KFRPB-5-120-C1-3 L3M2R strain gauge was attached. The average values ​​of three measurements were used as the tensile strength and tensile modulus.

[0062] Example 1 The raw fibers for producing the composite spun yarn were prepared as follows. (continuous reinforcing fiber) As the continuous reinforcing fiber (a1), PAN-based carbon fiber manufactured by Toray Industries, Inc. ("Torayca T700SC-12000" total fineness 8000 dtex, 12000 filaments, single fiber fineness 0.66 dtex, tensile strength 4900 MPa, density 1.80 g / cm) was used. 3 The decomposition temperature of this continuous reinforcing fiber is 500°C or higher in an oxygen atmosphere.

[0063] (Making thermoplastic staple fibers and spun yarns) Polyamide 6 polymer (PA6) was spun to produce 1100 dtex / 500 filament long fibers (single fiber fineness 2.2 dtex, density 1.13 g / cm 3) was obtained. A large number of these long fibers were collected and cut to a length of 51 mm using a guillotine cutter to obtain staple fibers. 100% of the polyamide 6 staple fibers were mixed and beaten using a cotton blender manufactured by Ohara Iron Works. Subsequently, a carded sliver was made using a carding machine manufactured by Howa, and passed through a drafting frame manufactured by Hara Loom Works to obtain a sliver of 371.2 grains / 6 yds. Next, a roving frame manufactured by Toyota Industries Corporation was used to apply a draft of 7.9 times, and a roving yarn of 124 grains / 15 yds of thermoplastic staple fibers was spun. This roving yarn was used as the thermoplastic staple fiber to become the sheath portion (B). The aforementioned roving yarn was used in a spinning frame manufactured by Toyota Industries Corporation to apply a draft of 24.9 times, and a spun yarn (C) to become the presser yarn was spun at 30 / 1. The melting point of this thermoplastic staple fiber was 225°C.

[0064] (Making composite yarn) A composite spun yarn with a total fineness of 12,943 dtex was produced using a Trispin spinning machine (ON-2000H) manufactured by Koseki Noboru Shoten Co., Ltd. Specifically, the aforementioned continuous reinforcing fiber was supplied as the core yarn 2 in Figure 4, and six of the aforementioned thermoplastic staple fiber rovings were supplied as the sheath yarn 3. The aforementioned thermoplastic staple fiber roving 3 was subjected to a 6.2x draft in a draft device 9 and overlapped with the continuous reinforcing fiber 2 to form a substantially untwisted core-sheath fiber bundle 4. The aforementioned spun yarn was then wound around the core-sheath fiber bundle 4 with an S-twist at a spindle rotation speed of 1,420 rpm on a bobbin 8 as a presser yarn 5 to bind the fiber bundles, producing composite spun yarn 1, which was then wound around a cheese 13. Details of the obtained composite spun yarn and its evaluation results are shown in Table 1.

[0065] (Production of unidirectionally molded body) Using a wrap reel winder, the composite yarn was wound around a metal frame 400 mm long and 220 mm wide at a winding pitch of 1.5 mm to a width of 150 mm. This was then subjected to heat compression molding using a press molding machine manufactured by Asano Co., Ltd. at a mold temperature of 265°C and a pressure of 3 MPa for 10 minutes to produce one unidirectionally molded product. The details and evaluation results of this molded product are shown in Table 1.

[0066] Example 2 As the continuous reinforcing fiber (a1), PAN-based carbon fiber manufactured by Toray Industries, Inc. ("Torayca T300B-1000" total fineness 660 dtex, 1000 filaments, single yarn fineness 0.66 dtex, tensile strength 3530 MPa, density 1.78 g / cm) was used. 3 ) was used. The decomposition temperature of this continuous reinforcing fiber is 500°C or higher in an oxygen atmosphere. The same sheath part (B) and spun yarn (C) used as the presser yarn were used as in Example 1, and the same equipment was used to produce the same conjugate spun yarn as in Example 1. However, in Example 1, when overlapping the thermoplastic short fiber roving with the continuous reinforcing fiber, a draft of 6.2 times was applied to six rovings, but in Example 2, a draft of 21.3 times was applied after overlapping one roving with the continuous reinforcing fiber bundle, thereby producing a conjugate spun yarn with a total fineness of 1084 dtex. Details of the obtained conjugate spun yarn and its evaluation results are shown in Table 1.

[0067] This composite spun yarn was used to produce one unidirectionally molded article using the same device as in Example 1. Details of this molded article and the evaluation results are shown in Table 1.

[0068] Example 3 The continuous reinforcing fiber (a1), sheath (B), and spun yarn (C) used as the holddown yarn were the same as in Example 1. The spun yarn (a2) constituting part of the core (A) was made by using two 124 grain / 15 yd rovings described in Example 1, drafted at 16.6 times, and spun at 10 / 1. A composite spun yarn was produced in the same manner as in Example 1 using the same apparatus as in Example 1. However, four 10 / 1 spun yarns were arranged so as to be positioned inside the continuous reinforcing fiber (a1), and the mass ratio of the spun yarn (a2) constituting part of the core (A) to the sheath (B) and spun yarn (C) was (a2):((B) + (C)) = 47:53. In Example 1, when the thermoplastic staple fiber rovings were layered with the continuous reinforcing fiber, six rovings were subjected to a draft of 6.2 times, but in Example 3, four rovings were layered with the continuous reinforcing fiber bundle and then subjected to a draft of 8.3 times, thereby producing a conjugated spun yarn with a total fineness of 12,978 dtex. Details of the obtained conjugated spun yarn and the evaluation results are shown in Table 1.

[0069] This composite spun yarn was used to produce one unidirectionally molded article using the same device as in Example 1. Details of this molded article and the evaluation results are shown in Table 1.

[0070] Example 4 The continuous reinforcing fiber (a1) was a PAN-based carbon fiber "Torayca T700SC-6000" manufactured by Toray Industries, Inc., with a total fineness of 4000 dtex, 6000 filaments, a single yarn fineness of 0.66 dtex, a tensile strength of 4900 MPa, and a density of 1.80 g / cm. 3 ) was used. The decomposition temperature of this continuous reinforcing fiber is 500°C or higher in an oxygen atmosphere. The sheath portion (B), the spun yarn (C) used as the holddown yarn, and the spun yarn (a2) constituting part of the core portion (A) were the same as in Example 3, and the same equipment as in Example 1 was used to produce the same composite spun yarn as in Example 3. However, two 10 / 1 spun yarns were arranged inside the continuous reinforcing fiber, and the mass ratio of the spun yarn (a2) constituting part of the core portion (A) to the sheath portion (B) and the spun yarn (C) was (a2):((B) + (C)) = 47:53. In Example 3, when the thermoplastic short fiber roving was layered with the continuous reinforcing fiber, a draft of 8.3 times was applied to four rovings. In Example 4, however, a draft of 8.7 times was applied after layering two rovings with the continuous reinforcing fiber bundle, thereby producing a composite spun yarn with a total fineness of 6511 dtex. Details of the obtained composite spun yarn and its evaluation results are shown in Table 1.

[0071] This composite spun yarn was used to produce one unidirectionally molded article using the same equipment as in Example 1. Details of this molded article and the evaluation results are shown in Table 1. The state of impregnation of the thermoplastic resin in the composite spun yarn is shown in the cross-sectional photograph of Figure 8.

[0072] Example 5 The continuous reinforcing fibers (a1) were the same as those used in Example 1. To prepare the thermoplastic short fibers, polypropylene polymer (PP) was spun to produce 1100 dtex / 500 filament long fibers (single filament fineness 2.2 dtex, density 0.91 g / cm). 3), and a large number of these long fibers were collected and cut to a length of 51 mm using a guillotine cutter to obtain staple fibers. 100% of the polypropylene staple fibers were blended and beaten using a cotton blending machine manufactured by Ohara Iron Works. Then, a carded sliver was made using a carding machine manufactured by Toyowa, and passed through a loom-made drawing frame to obtain a sliver of 370.0 grains / 6 yds. Next, a roving frame manufactured by Toyota Industries Corporation was used to apply a draft of 7.7 times, and a roving yarn of 120 grains / 15 yds of thermoplastic staple fibers was spun. This roving yarn was used as the thermoplastic staple fiber (B) that would form the sheath. The aforementioned roving yarn was also used to apply a draft of 16.1 times using a spinning frame manufactured by Toyota Industries Corporation, and spun at a ratio of 20 / 1 to form the spun yarn (C) that would serve as the presser yarn and the spun yarn (a2) that would form part of the core (A). The melting point of this thermoplastic staple fiber was 168°C. A composite spun yarn was produced in the same manner as in Example 3 using the same apparatus as in Example 1. However, six 20 / 1 spun yarns were arranged so as to be positioned inside the continuous reinforcing fiber, and the mass ratio of the spun yarn (a2) constituting part of the core (A) to the sheath (B) and spun yarn (C) was (a2):((B)+(C))=44:56. In Example 3, a draft of 8.3 times was applied to four rovings when overlapping the thermoplastic short fiber roving with the continuous reinforcing fiber. In Example 5, however, a draft of 9.3 times was applied to the four rovings after overlapping them with the continuous reinforcing fiber bundle, thereby producing a composite spun yarn with a total fineness of 12,000 dtex. Details of the obtained composite spun yarn and evaluation results are shown in Table 1.

[0073] This composite spun yarn was used to produce one unidirectionally molded article using the same equipment as in Example 1. Details of this molded article and the evaluation results are shown in Table 1. The state of impregnation of the thermoplastic resin in the composite spun yarn is shown in the cross-sectional photograph of Figure 7.

[0074] Example 6 The continuous reinforcing fibers (a1) were the same as those used in Example 1. To prepare the thermoplastic short fibers, polycarbonate polymer (PC) was spun to produce 1540 dtex / 200 filament long fibers (single filament fineness 7.7 dtex, density 1.2 g / cm). 3) was obtained, and a large number of these long fibers were collected and cut to a length of 51 mm using a guillotine cutter to obtain staple fibers. 100% of the polycarbonate staple fibers were blended and beaten using a cotton blending machine manufactured by Ohara Iron Works. Subsequently, a carded sliver was made using a carding machine manufactured by Howa, and passed through a loom-made drawing frame to obtain a sliver of 375 grains / 6 yds. Next, a roving frame manufactured by Toyota Industries Corporation was used to apply a draft of 7.8 times, and a roving yarn of 120 grains / 15 yds of thermoplastic staple fibers was spun. This roving yarn was used as the thermoplastic staple fiber to form the sheath portion (B). Furthermore, two of the aforementioned roving yarns were used to apply a draft of 16.0 times using a spinning frame manufactured by Toyota Industries Corporation, and spun at a ratio of 10 / 1 to form the spun yarn (C) used as the presser yarn and the spun yarn (a2) constituting part of the core portion (A). The glass transition temperature of this thermoplastic staple fiber was 149°C. A composite spun yarn was produced in the same manner as in Example 3 using the same apparatus as in Example 1. However, four 10 / 1 spun yarns were arranged so as to be positioned inside the continuous reinforcing fiber, and the mass ratio of the spun yarn (a2) constituting part of the core (A) to the sheath (B) and spun yarn (C) was (a2):((B)+(C))=44:56. In Example 3, a draft of 8.3 times was applied to the four rovings when overlapping the thermoplastic staple fiber roving with the continuous reinforcing fiber. In Example 6, however, a draft of 8.0 times was applied to the four rovings after overlapping them with the continuous reinforcing fiber bundle, thereby producing a composite spun yarn with a total fineness of 13,333 dtex. Details of the obtained composite spun yarn and its evaluation results are shown in Table 1.

[0075] This composite spun yarn was used to produce one unidirectionally molded article using the same device as in Example 1. Details of this molded article and the evaluation results are shown in Table 1.

[0076] Example 7 The continuous reinforcing fibers (a1) were the same as those used in Example 1. To prepare the thermoplastic short fibers, polyphenylene sulfide polymer (PPS) was spun to produce 1100 dtex / 500 filament long fibers (single filament fineness 2.2 dtex, density 1.35 g / cm). 3), and a large number of these long fibers were collected and cut to a length of 51 mm using a guillotine cutter to obtain staple fibers. 100% of the polyphenylene sulfide staple fibers were blended and beaten using a cotton blending machine manufactured by Ohara Iron Works. Then, a carded sliver was made using a carding machine manufactured by Howa, and passed through a drafting frame manufactured by Hara Loom Works to obtain a sliver of 371 grains / 6 yds. Next, a roving frame manufactured by Toyota Industries Corporation was used to apply a draft of 7.4 times, and a roving yarn of 125 grains / 15 yds of thermoplastic staple fibers was spun. This roving yarn was used as the thermoplastic staple fiber to form the sheath portion (B). Furthermore, two of the aforementioned roving yarns were used in a spinning frame manufactured by Toyota Industries Corporation to apply a draft of 33.4 times, and spun at a ratio of 20 / 1 to form the spun yarn (C) used as the presser yarn and the spun yarn (a2) constituting part of the core portion (A). The melting point of this thermoplastic staple fiber was 277°C. A composite spun yarn was produced in the same manner as in Example 3 using the same apparatus as in Example 1. However, nine 20 / 1 spun yarns were arranged so as to be positioned inside the continuous reinforcing fiber, and the mass ratio of the spun yarn (a2) constituting part of the core (A) to the sheath (B) and spun yarn (C) was (a2):((B)+(C))=44:56. In Example 3, a draft of 8.3 times was applied to four rovings when overlapping the thermoplastic short fiber roving with the continuous reinforcing fiber. In Example 7, however, a draft of 6.4 times was applied to the four rovings after overlapping them with the continuous reinforcing fiber bundle, thereby producing a composite spun yarn with a total fineness of 14,000 dtex. Details of the obtained composite spun yarn and the evaluation results are shown in Table 1.

[0077] This composite spun yarn was used to produce one unidirectionally molded article using the same device as in Example 1. Details of this molded article and the evaluation results are shown in Table 1.

[0078] Example 8 The continuous reinforcing fibers (a1) were the same as those used in Example 1. To prepare the thermoplastic short fibers, polyimide polymer (PI) was spun to produce 1100 dtex / 500 filament long fibers (single fiber fineness 2.2 dtex, density 1.4 g / cm). 3) was obtained, and a large number of these long fibers were collected and cut to a length of 51 mm using a guillotine cutter to obtain staple fibers. 100% of the polyimide staple fibers were blended and beaten using a cotton blending machine manufactured by Ohara Iron Works. Subsequently, a carded sliver was made using a carding machine manufactured by Howa, and passed through a drafting frame manufactured by Hara Loom Co., Ltd. to obtain a sliver of 369.0 grains / 6 yds. Next, a roving frame manufactured by Toyota Industries Corporation was used to apply a draft of 7.4 times, and a roving yarn of 125 grains / 15 yds of thermoplastic staple fibers was spun. This roving yarn was used as the thermoplastic staple fiber to form the sheath portion (B). Furthermore, two of the aforementioned roving yarns were used in a spinning frame manufactured by Toyota Industries Corporation to apply a draft of 33.4 times, and spun at a ratio of 20 / 1 to form the spun yarn (C) to serve as the presser yarn and the spun yarn (a2) to form part of the core portion (A). The melting point of this thermoplastic staple fiber was 277°C. A composite spun yarn was produced in the same manner as in Example 3 using the same apparatus as in Example 1. However, nine 20 / 1 spun yarns were arranged so as to be positioned inside the continuous reinforcing fiber, and the mass ratio of the spun yarn (a2) constituting part of the core (A) to the sheath (B) and spun yarn (C) was (a2):((B)+(C))=43:57. In Example 3, a draft of 8.3 times was applied to four rovings when overlapping the thermoplastic short fiber roving with the continuous reinforcing fiber. In Example 8, however, a draft of 6.1 times was applied to the four rovings after overlapping them with the continuous reinforcing fiber bundle, thereby producing a composite spun yarn with a total fineness of 14,198 dtex. Details of the obtained composite spun yarn and its evaluation results are shown in Table 1.

[0079] This composite spun yarn was used to produce one unidirectionally molded article using the same device as in Example 1. Details of this molded article and the evaluation results are shown in Table 1.

[0080] Example 9 The continuous reinforcing fiber (a1), sheath (B), spun yarn (C) serving as a holddown yarn, and spun yarn (a2) constituting part of the core (A) were the same as in Example 6, and a conjugate spun yarn was produced in the same manner as in Example 3 using the same equipment as in Example 1. However, six 10 / 1 spun yarns were arranged inside the continuous reinforcing fiber, and the mass ratio of the spun yarn (a2) inside the continuous reinforcing fiber core to the sheath (B) and spun yarn (C) was (a2):((B) + (C)) = 67:33. In Example 3, a draft of 8.3 times was applied to four rovings when overlapping the thermoplastic staple fiber roving with the continuous reinforcing fiber. In Example 9, however, a draft of 7.9 times was applied after overlapping two rovings with the continuous reinforcing fiber bundle, producing a conjugate spun yarn with a total fineness of 13,333 dtex. Details of the resulting conjugate spun yarn and its evaluation results are shown in Table 1.

[0081] This composite spun yarn was used to produce one unidirectionally molded article using the same device as in Example 1. Details of this molded article and the evaluation results are shown in Table 1.

[0082] Example 10 As the continuous reinforcing fiber (a1), TORAY PAN-based carbon fiber "TORAYCA T700SC-24000" manufactured by Toray Industries, Inc., with a total fineness of 16,500 dtex, 24,000 filaments, a single yarn fineness of 0.66 dtex, a tensile strength of 4,900 MPa, and a density of 1.80 g / cm 3) was used. The decomposition temperature of this continuous reinforcing fiber is 500°C or higher in an oxygen atmosphere. The sheath portion (B), the spun yarn (C) used as the holddown yarn, and the spun yarn (a2) constituting part of the core portion (A) were the same as in Example 6, and a conjugate spun yarn was produced in the same manner as in Example 3 using the same equipment as in Example 1. However, 20 spun yarns at a 10 / 1 ratio were arranged inside the continuous reinforcing fiber, and the mass ratio of the spun yarn (a2) constituting part of the core portion (A) to the sheath portion (B) and the spun yarn (C) was a2:(B+C) = 46:54. In Example 3, when the thermoplastic short fiber roving was layered with the continuous reinforcing fiber, a draft of 8.3 times was applied to four rovings. In Example 10, however, a draft of 3.7 times was applied after layering 10 rovings with the continuous reinforcing fiber bundle, thereby producing a conjugate spun yarn with a total fineness of 42,167 dtex. Details of the obtained conjugate spun yarn and its evaluation results are shown in Table 1.

[0083] This composite spun yarn was used to produce one unidirectionally molded article using the same device as in Example 1. Details of this molded article and the evaluation results are shown in Table 1.

[0084] Example 11 The continuous reinforcing fiber (a1) was Nippon Sheet Glass's glass roving (high strength, high modulus glass fiber) "RMR060X-RW370K-C," with a total fineness of 6000 dtex, 1750 filaments, a fiber diameter of 13 μm, a tensile strength of 4300 MPa, and a density of 2.58 g / cm. 3) was used. The decomposition temperature of this continuous reinforcing fiber is 500°C or higher in an oxygen atmosphere. The sheath portion (B), the spun yarn (C) used as the holddown yarn, and the spun yarn (a2) constituting part of the core portion (A) were the same as in Example 5, and a conjugate spun yarn was produced in the same manner as in Example 3 using the same apparatus as in Example 1. However, three 20 / 1 spun yarns were arranged so as to be disposed inside the continuous reinforcing fiber, and the mass ratio of the spun yarn (a2) constituting part of the core portion (A) to the sheath portion (B) and the spun yarn (C) was (a2):((B) + (C)) = 42:58. In Example 3, when the thermoplastic short fiber roving was layered with the continuous reinforcing fiber, a draft of 8.3 times was applied to four rovings. In Example 11, however, a draft of 10.4 times was applied after layering two rovings with the continuous reinforcing fiber bundle, thereby producing a conjugate spun yarn with a total fineness of 8093 dtex. Details of the obtained composite spun yarn and the evaluation results are shown in Table 1.

[0085] This composite spun yarn was used to produce one unidirectionally molded article using the same device as in Example 1. Details of this molded article and the evaluation results are shown in Table 1.

[0086] Example 12 The continuous reinforcing fibers (a1), sheath (B), and spun yarn (C) used as the presser yarn were the same as in Example 1. The thermoplastic staple fibers to be blended with the continuous reinforcing fibers were a 371.2 grain / 6 yd sliver described in Example 1, which was subjected to a draft of 11.6 times using a Toyota Industries Corporation roving frame to produce a roving of 80 grain / 15 yd. A composite spun yarn was produced in the same manner as in Example 3 using the same equipment as in Example 1. However, the continuous reinforcing fibers were passed through a 1 cm diameter roller four times and combined with the thermoplastic staple fibers (a3), which were bundled by the tension during spinning, and the core was blended. The mass ratio of the thermoplastic staple fibers (a3) ​​blended with the continuous reinforcing fibers to the sheath (B) and spun yarn (C) was (a3):((B) + (C)) = 42:58. In Example 3, when the thermoplastic short fiber rovings were layered with the continuous reinforcing fiber, four rovings were subjected to a draft of 8.3 times, but in Example 12, six rovings were layered with the continuous reinforcing fiber bundle and then subjected to a draft of 6.8 times, thereby producing a conjugated spun yarn with a total fineness of 15,533 dtex. Details of the obtained conjugated spun yarn and the evaluation results are shown in Table 1.

[0087] This composite spun yarn was used to produce one unidirectionally molded article using the same device as in Example 1. Details of this molded article and the evaluation results are shown in Table 1.

[0088] (Comparative Example 1) Comparative Example 1 is an example in which thermoplastic continuous fibers are used as the presser threads. The continuous reinforcing fibers (a1) and sheath (B) were the same as those used in Example 1. The thermoplastic long fibers were 222 dtex, 24 filaments (single filament fineness 9.3 dtex, density 1.13 g / cm). 3) Commercially available semi-dull polyamide 6 (PA6) filaments (raw silk) were used. The melting point of this thermoplastic filament was 225°C. A conjugate spun yarn was produced in the same manner as in Example 1 using the same apparatus. However, in Example 1, a 6.2-fold draft was applied to the rovings of thermoplastic staple fibers when they were layered with the continuous reinforcing fibers. In Comparative Example 1, however, a 5.9-fold draft was applied to the six rovings after they were layered with the continuous reinforcing fiber bundles, thereby producing a conjugate spun yarn with a total fineness of 13,022 dtex. Details of the obtained conjugate spun yarn and its evaluation results are shown in Table 1.

[0089] This composite spun yarn was used to produce one unidirectionally molded article using the same device as in Example 1. Details of this molded article and the evaluation results are shown in Table 1. The state of impregnation of the thermoplastic resin in the composite spun yarn is shown in the cross-sectional photograph of Figure 9.

[0090] [Table 1]

[0091] As can be seen from Table 1, the conjugate spun yarns of Examples 1 to 12, which satisfied the conditions of the present invention, had excellent fiber orientation in the molded body. In particular, the conjugate spun yarns of Examples 3 to 12, which had a core composed of thermoplastic short fibers and continuous reinforcing fibers, had excellent dispersion of the continuous reinforcing fibers in the cross section of the molded body. Furthermore, the molded bodies made from the conjugate spun yarns of Examples 1 to 12 achieved satisfactory results in all aspects, including appearance, void ratio, strength, and elastic modulus. In contrast, Comparative Example 1, in which the presser yarn was a thermoplastic long fiber, had poor orientation of the continuous reinforcing fibers in the molded body, and the inherent strength of the continuous reinforcing fibers could not be fully demonstrated. [Industrial Applicability]

[0092] The conjugate spun yarn of the present invention has excellent strength and spinnability, and when it is heated and melted to form a fiber-reinforced plastic molding, it can provide a product with excellent moldability, strength, and uniformity of physical properties. [Explanation of symbols]

[0093] 1. Composite spun yarn 2 Continuous reinforcing fibers 3. Thermoplastic short fibers 4. Sheath-core fiber bundle 5. Spun yarn 6. Composite spun yarn 7. Spun Yarn 8 Double core-sheath fiber bundle 9 Draft device 10 Guide 11 Hollow bobbin 12 Feed roller 13. Cheese 14 Thermoplastic short fibers 15 Sheath-core fiber bundle 16. Composite spun yarn

Claims

1. A composite spun yarn for fiber-reinforced thermoplastic plastics, characterized in that a spun yarn (C) made of thermoplastic staple fibers is wound around a substantially untwisted fiber bundle formed from a core (A) containing at least continuous reinforcing fibers (a1) and a sheath (B) made of thermoplastic staple fibers.

2. 2. The fiber-reinforced conjugate spun yarn for thermoplastics according to claim 1, wherein the core (A) is composed only of continuous reinforcing fibers (a1).

3. 2. The composite spun yarn for fiber-reinforced thermoplastics according to claim 1, characterized in that the core (A) is composed of a spun yarn (a2) made of a thermoplastic short fiber and a continuous reinforcing fiber (a1) arranged so as to cover the spun yarn (a2).

4. 2. The fiber-reinforced conjugate spun yarn for thermoplastics according to claim 1, wherein the core (A) is composed of a mixture of continuous reinforcing fibers (a1) and thermoplastic short fibers (a3).

5. 2. The conjugate spun yarn for fiber-reinforced thermoplastics according to claim 1, characterized in that the continuous reinforcing fiber (a1) is at least one type of fiber selected from the group consisting of carbon fiber, glass fiber, basalt fiber, PBO fiber, and aramid fiber, and the mixing ratio of the continuous reinforcing fiber (a1) in the conjugate spun yarn is 20 to 80 mass%.

6. 2. The fiber-reinforced conjugate spun yarn for thermoplastics according to claim 1, wherein the thermoplastic staple fibers constituting the sheath portion (B) and the thermoplastic staple fibers constituting the spun yarn (C) each comprise at least one thermoplastic resin selected from the group consisting of polyamide, copolymerized polyamide, polypropylene, polyphenylene sulfide, polyetherimide, polycarbonate, polyaryletherketone, polyetheretherketone, polyimide, and polyhydroxyether.

7. 4. The composite spun yarn for fiber-reinforced thermoplastic plastics according to claim 3, characterized in that the thermoplastic short fibers constituting the spun yarn (a2) are made of at least one thermoplastic resin selected from the group consisting of polyamide, copolymerized polyamide, polypropylene, polyphenylene sulfide, polyetherimide, polycarbonate, polyaryletherketone, polyetheretherketone, polyimide, and polyhydroxyether.

8. The composite spun yarn for fiber reinforced thermoplastics according to claim 3, characterized in that the mass ratio ((a2):(B)+(C)) of the spun yarn (a2) to the sheath portion (B) and the spun yarn (C) is 70:30 to 30:

70.

9. 5. The fiber-reinforced conjugate spun yarn for thermoplastics according to claim 4, characterized in that the thermoplastic short fibers (a3) ​​are made of at least one thermoplastic resin selected from the group consisting of polyamide, copolymerized polyamide, polypropylene, polyphenylene sulfide, polyetherimide, polycarbonate, polyaryletherketone, polyetheretherketone, polyimide, and polyhydroxyether.

10. The composite spun yarn for fiber-reinforced thermoplastics according to claim 4, characterized in that the mass ratio ((a3):((B) + (C))) of the thermoplastic short fiber (a3) ​​to the sheath portion (B) and the spun yarn (C) is 70:30 to 30:

70.

11. The composite spun yarn for fiber-reinforced thermoplastics according to any one of claims 1 to 10, characterized in that the composite spun yarn has a total fineness of 500 to 50,000 dtex.

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