Carbon fiber reinforced thermoplastic resin strand containing blended yarn of recycled carbon fiber and thermoplastic resin fiber

Abstract

To provide a carbon fiber reinforced thermoplastic resin strand that can be stably produced using recycled carbon fiber obtained by a method of heat treatment and decomposition and a thermoplastic resin as raw materials, and is particularly suitable for producing a three-dimensional object with excellent mechanical properties.SOLUTION: There is provided a carbon fiber reinforced thermoplastic resin strand formed of blended yarn containing recycled carbon fiber and thermoplastic resin fiber, wherein the recycled carbon fiber has a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, and the recycled carbon fiber contains a residual carbon component, and a content of the residual carbon component is more than 0 wt.% and 5.0 wt.% or less based on an amount of the recycled carbon fiber.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a carbon fiber reinforced thermoplastic resin strand containing a blended yarn of recycled carbon fiber and a thermoplastic resin fiber suitable for three-dimensional shaping. The present invention also relates to a method for manufacturing the same.

Background Art

[0002] Conventionally, a technique is known in which three-dimensional shaping is performed by sequentially laminating a resin for each cross-section obtained by cutting an object to be shaped with a plurality of parallel planes, and a shaped object serving as a three-dimensional model of the object to be shaped is generated. Such a technique is called three-dimensional shaping and can be used for component prototyping and product manufacturing. Examples of three-dimensional shaping methods include a stereolithography method using a photocurable resin, a powder lamination method using a powder of metal or resin, a fused deposition method in which a resin is melted and deposited, a thin plate lamination method in which paper, a resin sheet, or a thin metal plate is laminated, and an inkjet method in which a liquid or powder resin or metal is ejected.

[0003] As an example of the fused deposition method, a fused deposition method using a thermoplastic polymer material is disclosed in Patent Document 1. In this technique, a solid thermoplastic polymer material is supplied to a discharge head, and in the discharge head, the polymer material is melted, and the melted polymer material is discharged from the discharge head and repeatedly deposited in layers. Examples of thermoplastic polymers that can be used in this technique include polyether sulfone, polyether imide, polyphenyl sulfone, polyphenylene, polycarbonate, high-impact polystyrene, polysulfone, polystyrene, acrylic resin, amorphous polyamide, polyester, nylon, PEEK, and ABS. In particular, this method is preferably used for polylactic acid, which is a plant-derived thermoplastic polyester, because it can be melted and discharged at a relatively low temperature and has the advantage of a small environmental load.

[0004] In addition, fiber-reinforced resin compositions (FRP molded products) containing fibers in a resin are lightweight and have excellent mechanical properties, so they are used in a wide range of fields from aerospace applications to sports applications. In the above-described melt lamination method, a technique is also known in which a fiber resin material in which a molten thermoplastic resin and fibers are integrated is laminated on a profile, and a fiber resin material is further laminated on the laminated fiber resin material. (Patent Document 2)

[0005] Furthermore, in recent years, the demand for recycled carbon fibers recovered from used carbon fiber-containing products and the like has been increasing. Most of the recycled carbon fibers are discontinuously cut carbon fibers. In order to handle them in the same way as unused continuous carbon fibers as raw materials for carbon fiber-containing products such as carbon fiber-reinforced resin composites, methods for manufacturing spun yarns from recycled carbon fibers have been studied.

[0006] Patent Document 3 describes a method for manufacturing a spun yarn in which a carbide containing recycled carbon fibers obtained by heat-treating scrap of a carbon fiber-reinforced resin composite at a temperature of 900 °C or higher is blended with thermoplastic resin fibers.

[0007] Patent Document 4 describes a method of utilizing a spun yarn in which cut unused discontinuous carbon fibers are blended with synthetic fibers, imitating recycled carbon fibers that do not contain carbides and are recovered by heat-treating a carbon fiber-reinforced resin composite.

[0008] Patent Document 5 describes a method for manufacturing a spun yarn using only carbon fibers or recycled carbon fibers without blending them with thermoplastic resin fibers.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0010] As methods for decomposing used carbon fiber reinforced resin composite materials to obtain recycled carbon fibers, there are methods of decomposing the resin component by heat treatment, methods of dissolving and removing it using a solvent, methods of electrolysis, etc. Among the methods that have been widely popularized conventionally, the method of decomposing by heat treatment can be mentioned.

[0011] However, when producing a blended yarn with a thermoplastic resin fiber using the recycled carbon fiber obtained by the method of decomposing by heat treatment as a raw material, the resin in the carbon fiber reinforced resin composite material may not be completely decomposed, residual carbide may be generated, making it difficult to produce the blended yarn, or the mechanical properties of the fiber obtained after decomposition, especially the strength of the fiber, may decrease compared to the fiber before decomposition, and the strength of the molded body of the fiber reinforced composite material using this fiber may also be low.

[0012] An object of the present disclosure is to provide a carbon fiber reinforced thermoplastic resin strand that can be stably produced using recycled carbon fiber obtained by the method of decomposing by heat treatment and a thermoplastic resin as raw materials, and is particularly suitable for producing a three-dimensional shaped article having excellent mechanical properties.

Means for Solving the Problems

[0013] According to the following aspects of the present disclosure, the above problems can be solved: <Aspect 1> A carbon fiber reinforced thermoplastic resin strand containing a blended yarn containing recycled carbon fiber and a thermoplastic resin fiber, wherein the recycled carbon fiber has a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, and The recycled carbon fiber contains a residual carbon component, and the content of the residual carbon component is more than 0% by weight and 5.0% by weight or less based on the recycled carbon fiber. A carbon fiber reinforced thermoplastic resin strand, characterized by the above. <Aspect 2> The carbon fiber reinforced thermoplastic resin strand according to Aspect 1, wherein the content of the recycled carbon fiber is more than 50% by weight and 98% by weight or less based on the blended yarn. <Aspect 3> The carbon fiber reinforced thermoplastic resin strand according to Aspect 1 or 2, wherein the average lengths of the recycled carbon fiber and the thermoplastic resin fiber are each 20 mm or more and 80 mm or less. <Aspect 4> The carbon fiber reinforced thermoplastic resin strand according to any one of Aspects 1 to 3, wherein the thermoplastic resin fiber is selected from polyolefin resin fibers, polyester resin fibers, polyamide resin fibers, polyether ketone resin fibers, polycarbonate resin fibers, phenoxy resin fibers, and polyphenylene sulfide resin fibers, and mixtures thereof. <Aspect 5> It has a core-sheath structure, the blended yarn is the core component, and the thermoplastic resin is the sheath component, The carbon fiber reinforced thermoplastic resin strand according to any one of Aspects 1 to 4, characterized by the above. <Aspect 6> The carbon fiber reinforced thermoplastic resin strand according to Aspect 5, wherein the melting point T0 (°C) of the thermoplastic resin as the sheath component is lower than the melting point T1 (°C) of the thermoplastic resin fiber contained in the blended yarn, and T1 - T0 > 10 is satisfied. <Aspect 7> Decomposing the plastic component contained in the carbon fiber-containing plastic product by a semiconductor thermal activation method to produce recycled carbon fiber, and producing a blended yarn by blending the recycled carbon fiber and the thermoplastic resin fiber A method for producing a carbon fiber reinforced thermoplastic resin strand according to any one of Aspects 1 to 6, including the above. <Aspect 8> A method for manufacturing a three-dimensional object by a fused deposition method using the carbon fiber reinforced thermoplastic resin strand according to any one of Aspects 1 to 6.

Advantages of the Invention

[0014] According to the present invention, it is possible to stably manufacture using, as raw materials, recycled carbon fibers obtained by a method of heat-treating and decomposing and thermoplastic resin fibers, and in particular, it is possible to provide a carbon fiber reinforced thermoplastic resin strand suitable for manufacturing a three-dimensional object having excellent mechanical properties.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0016] The carbon fiber reinforced thermoplastic resin strand according to the present disclosure has a blended yarn containing recycled carbon fibers and thermoplastic resin fibers. This blended yarn of recycled carbon fibers and thermoplastic resin fibers is such that the recycled carbon fibers have a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, and the recycled carbon fibers contain a residual carbon component, and the content of the residual carbon component is more than 0% by weight and 5.0% by weight or less with respect to the recycled carbon fibers, It is characterized by.

[0017] In one embodiment according to the present disclosure, the carbon fiber reinforced thermoplastic resin strand is composed of the above-mentioned blended yarn.

[0018] The blended yarn according to the present disclosure is manufactured by a general spinning method and may include processes such as carding, roving, and slubbing. Here, the carding process may be a process of separating and loosening the aggregates of discontinuous fibers, opening the fibers, and aligning the mixed single fibers in one direction to produce a thick sliver. The roving process may be a process of combining several slivers, doubling them, and further improving the fiber orientation degree while stretching. The slubbing process may be a process of further stretching this sliver, twisting it, and winding up the blended yarn.

[0019] Since the tensile strength of the sliver is provided by the frictional force due to the contact or entanglement between single fibers, the tensile strength is improved by each fiber being well opened and the contact area or entanglement between single fibers increasing. Also, by suppressing single fiber breakage and not increasing the joints between single fibers, a decrease in tensile strength can be suppressed. By increasing the twist, the contact area between single fibers increases, so the tensile strength is improved. To supplement the frictional force, an oil agent may be applied to each fiber or the sliver as necessary.

[0020] Generally, carbon fibers have no crimpability and high surface smoothness, so the entanglement between single fibers is weak. Furthermore, due to their high elastic modulus, low elongation, and hardness, they are relatively brittle and easy to break. The thermoplastic resin fiber blended with recycled carbon fiber has the effect of enhancing the entanglement between single fibers. Even by blending a small amount of thermoplastic resin fiber, the tensile strength of the sliver is greatly improved.

[0021] Although not intended to be limited by theory, the blended yarn according to the present disclosure has a high Weibull shape factor in the single fiber tensile strength of recycled carbon fibers, so the variation in tensile strength is small. Compared with general unused carbon fibers having the same tensile strength, there are few single fibers with low tensile strength, so it is considered that single fiber breakage of recycled carbon fibers is relatively suppressed.

[0022] In addition, as general characteristics of the recycled carbon fiber obtained by the method of heat treatment and decomposition, the tensile strength is likely to decrease due to the generation of oxidation defects in the recycled carbon fiber, and the carbide of the resin component may be contained in the recycled carbon fiber as a residual carbon component. The residual carbon component may firmly bond the single fibers of the recycled carbon fiber together. In the production of spun yarn, the residual carbon component is considered to prevent fiber opening in the carding process and entanglement between single fibers.

[0023] Although not intended to be limited by theory, the blended yarn according to the present disclosure uses recycled carbon fiber with a low content of residual carbon component as a raw material, so entanglement between single fibers is likely to be obtained.

[0024] For the above reasons, the blended yarn according to the present disclosure is likely to obtain the frictional force due to entanglement between single fibers, so it is considered that the tensile strength for stable production can be easily obtained without causing yarn breakage against the spinning process tension.

[0025] In one embodiment according to the present disclosure, the carbon fiber reinforced thermoplastic resin strand has a core-sheath structure, the blended yarn is the core component, and the thermoplastic resin is the sheath component, is characterized by.

[0026] The carbon fiber reinforced thermoplastic resin strand with a core-sheath structure according to one embodiment of the present disclosure can be manufactured by coating the blended yarn with a thermoplastic resin in the same manner as the manufacturing method of a general long fiber reinforced strand, except that the blended yarn according to the present disclosure is used as a substitute for continuous carbon fiber. Therefore, it can contain recycled carbon fiber with a relatively long fiber length compared to a short fiber reinforced thermoplastic resin strand in which discontinuous carbon fiber is kneaded and dispersed in a thermoplastic resin. That is, the carbon fiber reinforced thermoplastic resin strand according to the present disclosure can be supplied to an injection molding machine or the like, or a three-dimensional shaping device or the like to manufacture a carbon fiber-containing product having excellent mechanical properties and the like.

[0027] Hereinafter, the invention according to the present disclosure will be described in more detail.

[0028] <Recycled carbon fiber> Recycled carbon fiber (recycled carbon fiber) contains a carbon fiber component and a carbon component other than the carbon fiber component (particularly a residual carbon component). Usually, in recycled carbon fiber, the carbon component other than the carbon fiber component adheres to the surface of the carbon fiber component.

[0029] The recycled carbon fiber according to the present disclosure has a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, and contains a residual carbon component, and the content of the residual carbon component is more than 0% by weight and 5.0% by weight or less with respect to the recycled carbon fiber.

[0030] For the recycled carbon fiber having such characteristics, the recycling method is not particularly limited. For example, it may be recycled carbon fiber obtained by heat-treating a carbon fiber-containing plastic product such as carbon fiber-reinforced plastic (CFRP).

[0031] Particularly preferably, the recycled carbon fiber is recycled carbon fiber obtained by the semiconductor thermal activation method. That is, a particularly preferred embodiment of the present disclosure includes recycled carbon fiber produced by decomposing the plastic component contained in a carbon fiber-containing plastic product by the semiconductor thermal activation method.

[0032] Note that the "semiconductor thermal activation method" (TASC method) is a method of decomposing a compound to be decomposed such as a polymer by utilizing the thermal activation of a semiconductor (Thermal Activation of Semi-conductors, TASC).

[0033] A method for obtaining recycled carbon fiber having the characteristics according to the present disclosure using the semiconductor thermal activation method will be described later.

[0034] <Single fiber tensile strength> The single fiber tensile strength is preferably 3.1 GPa or more, 3.2 GPa or more, 3.3 GPa or more, or 3.4 GPa or more. The upper limit of the single fiber tensile strength is not particularly limited, but may be 6.0 GPa or less.

[0035] The single-fiber tensile strength can be measured in accordance with JIS R7606 as follows: Collect at least 30 single fibers from the fiber bundle, Measure the diameter of the single fiber in the side image of the single fiber taken by a digital microscope, calculate the cross-sectional area, Fix the sampled single fibers to a perforated mount using an adhesive, Attach the mount with the single fibers fixed to a tensile testing machine, conduct a tensile test at a gauge length of 10 mm and a strain rate of 1 mm / min to measure the tensile breaking stress, Calculate the tensile strength from the cross-sectional area and the tensile breaking stress of the single fiber, Take the average of the tensile strengths of at least 30 single fibers as the single-fiber tensile strength.

[0036] <Weibull shape factor> The Weibull shape factor is preferably 6.5 or more, 7.0 or more, 7.5 or more, 8.0 or more, or 8.5 or more. The upper limit of the Weibull shape factor is not particularly limited and may be 15.0 or less. Note that a high Weibull shape factor of the single-fiber tensile strength means a small variation in the single-fiber tensile strength.

[0037] The Weibull shape factor can be calculated according to the following formula: lnln{1 / (1 - F)} = m×lnσ + C In the formula, F is the fracture probability obtained by the symmetric sample cumulative distribution method, σ is the single-fiber tensile strength (MPa), m is the Weibull shape factor, and C is a constant.

[0038] Perform a Weibull plot with lnln{1 / (1 - F)} and lnσ, and obtain the Weibull shape factor m from the slope of the first-order approximation.

[0039] <Carbon fiber component> The carbon fiber component in recycled carbon fiber usually originates from the carbon fiber contained in carbon fiber-containing products or the like that served as the raw material for the recycled carbon fiber. The carbon fiber component in recycled carbon fiber may be modified by undergoing heat treatment or the like during the manufacturing process of the recycled carbon fiber.

[0040] The carbon fiber component in recycled carbon fiber may be, for example, PAN-based carbon fiber or pitch-based carbon fiber.

[0041] The form of the carbon fiber component in recycled carbon fiber is not particularly limited, but it may be in the form of a carbon fiber bundle composed of a plurality of single filaments (monofilaments, filaments). The number of filaments constituting the carbon fiber bundle may be in the range of 1,000 to 80,000, or 3,000 to 50,000. Also, the diameter of the filaments constituting the carbon fiber component in recycled carbon fiber may be 0.1 μm to 30 μm, 1 μm to 10 μm, or 3 μm to 8 μm.

[0042] <Residual carbon component> The residual carbon component contained in recycled carbon fiber is, in particular, residual carbon derived from the resin contained in the carbon fiber-containing plastic product used as the raw material when manufacturing the recycled carbon fiber.

[0043] In the present disclosure, the residual carbon component is more than 0% by weight and 5.0% by weight or less with respect to the recycled carbon fiber. In this case, it is possible to obtain a blended yarn with improved resistance to yarn breakage against the spinning process tension.

[0044] Also, when the residual carbon component is more than 0% by weight and 5.0% by weight or less, it is possible to avoid contamination due to a relatively large amount of carbon component (especially carbon), and it is possible to reduce the carbon component that can become a foreign substance when manufacturing carbon fiber-containing products or the like using the blended yarn as a material.

[0045] Preferably, the residual carbon component is 4.0 wt% or less, 3.0 wt% or less, or 2.0 wt% or less with respect to the recycled carbon fiber. Although it is preferable that the residual carbon component is reduced as much as possible, it may be 0.1 wt% or more, 0.2 wt% or more, 0.4 wt% or more, 0.6 wt% or more, 0.8 wt% or more, 1.0 wt% or more, or 1.2 wt% or more with respect to the carbon fiber.

[0046] The content of the residual carbon component in the recycled carbon fiber can be measured by thermogravimetric analysis (TGA method).

[0047] The residual carbon component by thermogravimetric analysis can be measured by the following procedure: (i) For a 1 - 4 mg sample piece obtained by pulverizing the recycled carbon fiber, in a thermogravimetric analyzer, at an air supply rate of 0.2 L / min, a heating rate of 5 °C / min, and a recording rate of 1 / 6 s, heating from room temperature to 100 °C, holding at 100 °C for 30 minutes, heating from 100 °C to 400 °C, and holding at 400 °C perform thermogravimetric analysis with a total of 300 minutes including these steps, (ii) In a graph plotting the weight loss rate against time, identify the inflection point of the slope, and calculate the residual carbon amount by subtracting the weight loss rate during the holding period at 100 °C from the value of the weight loss rate at the inflection point.

[0048] If the inflection point of the slope cannot be identified under the above conditions, instead of performing thermogravimetric analysis for a total of 300 minutes, thermogravimetric analysis for a total of about 600 minutes with a 480 - minute holding at 400 °C may be performed. Further, instead of holding at 400 °C for 480 minutes, it may be held at a specific temperature within the range exceeding 400 °C and not exceeding 500 °C for 480 minutes.

[0049] In addition, when the recycled carbon fiber has a resin derived from a sizing agent or the like, the above measurement can be performed after removing the resin.

[0050] <Thermoplastic resin fiber> Examples of the thermoplastic resin fiber contained in the blended yarn according to the present disclosure include polyolefin resin fibers (for example, polypropylene resin fibers and polyethylene resin fibers), polyester resin fibers (for example, polyethylene terephthalate resin fibers, polybutylene terephthalate resin fibers, and polylactic acid resin fibers), polyamide resin fibers, polyether ketone resin fibers, polycarbonate resin fibers, phenoxy resin fibers, and polyphenylene sulfide resin fibers. The thermoplastic resin fiber may be only one kind, or may be a mixture of two or more thermoplastic resin fibers.

[0051] <Blended yarn> The blended yarn is a spun yarn containing recycled carbon fiber and thermoplastic resin fiber. The blended yarn may also contain, for example, a binder or the like applied to the recycled carbon fiber. In particular, the blended yarn is a spun yarn substantially composed of recycled carbon fiber and thermoplastic resin fiber.

[0052] <Content of recycled carbon fiber> The content of the recycled carbon fiber is preferably more than 50% by weight and 98% by weight or less with respect to the blended yarn. Particularly preferably, it may be more than 55% by weight, more than 60% by weight, more than 65% by weight, or more than 70% by weight, and / or 97% by weight or less, 96% by weight or less, 95% by weight or less, 94% by weight or less, 93% by weight or less, 92% by weight or less, 91% by weight or less, or 90% by weight or less.

[0053] When the content of the recycled carbon fiber is more than 50% by weight, when manufacturing the carbon fiber reinforced thermoplastic resin strand according to the present disclosure using this recycled carbon fiber, it is not necessary to reduce the coating amount with the thermoplastic resin for the purpose of increasing the carbon fiber content, and the stability of the coating treatment is improved. When the content of the recycled carbon fiber is 98% by weight or less, the entanglement with the thermoplastic resin fiber to be blended becomes sufficient, and it is less likely to cause yarn breakage due to the spinning process tension.

[0054] The content of the thermoplastic resin fiber may be 50% by weight or less, 40% by weight or less, or 30% by weight or less with respect to the blended yarn, and / or may be more than 3% by weight, more than 4% by weight, more than 5% by weight, more than 6% by weight, more than 7% by weight, more than 8% by weight, more than 9% by weight, or more than 10% by weight.

[0055] <Average length of fiber> The recycled carbon fiber contained in the blended yarn according to the present disclosure can have an average length of 20 mm or more and 80 mm or less. Fibers having a length within this range can be obtained, for example, by cutting fibers having a relatively long dimension. The average length of the recycled carbon fiber may be 20 mm or more, 30 mm or more, or 40 mm or more, and / or may be 80 mm or less, 70 mm or less, or 60 mm or less.

[0056] The thermoplastic resin fiber contained in the blended yarn according to the present disclosure can have an average length of 20 mm or more and 80 mm or less. Fibers having a length within this range can be obtained, for example, by cutting fibers having a relatively long dimension. The average length of the thermoplastic resin fiber may be 20 mm or more, 30 mm or more, or 40 mm or more, and / or may be 80 mm or less, 70 mm or less, or 60 mm or less.

[0057] In the production of the blended yarn, when the average lengths of the recycled carbon fiber and the thermoplastic resin fiber are 20 mm or more, the resistance to yarn breakage against the spinning process tension of the sliver can be improved. When the average lengths of the recycled carbon fiber and the thermoplastic resin fiber are 80 mm or less, winding around the manufacturing equipment parts can be reduced.

[0058] The average lengths of the recycled carbon fiber and the thermoplastic resin fiber can be calculated by measuring the lengths of 50 fibers visually using a caliper or the like, or in an image obtained by a digital camera or an optical microscope, and averaging the measured values.

[0059] <Method for manufacturing blended yarn> As described above, the blended yarn of recycled carbon fiber and thermoplastic resin according to the present disclosure can be manufactured by a general spinning method. That is, the method for manufacturing the blended yarn according to the present disclosure includes a carding process of separating and loosening an aggregate of discontinuous fibers to open the fibers, mixing the single fibers, and aligning them in one direction to produce a thick sliver, a roving process of combining several slivers, stretching while further improving the fiber orientation degree, and a roving process of further stretching this sliver and applying twist to wind up the blended yarn.

[0060] When manufacturing the blended yarn, a binder can be applied. The binder particularly has a role of promoting the bonding of recycled carbon fiber to the thermoplastic resin fiber. The timing of applying the binder is not particularly limited, and it may be applied directly to the recycled carbon fiber, or may be applied to the blended yarn containing the recycled carbon fiber and the thermoplastic resin fiber. The binder may be, for example, an epoxy resin. The application method of the binder is not particularly limited and known methods can be used. For example, the recycled carbon fiber or the blended yarn can be immersed in a solution or dispersion of the binder and dried to apply the binder. Note that the amount of the binder may be 0.1% to 25% by weight, or 1% to 20% by weight based on the recycled carbon fiber.

[0061] <Carbon fiber reinforced thermoplastic resin strand with core-sheath structure> According to one embodiment of the present disclosure, by coating the above blended yarn according to the present disclosure with a thermoplastic resin, a carbon fiber reinforced thermoplastic resin strand with a core-sheath structure is provided, where the blended yarn is the core component and the thermoplastic resin is the sheath component. This strand contains recycled carbon fibers with a relatively long fiber length compared to a short fiber reinforced strand obtained by kneading and dispersing recycled carbon fibers in a thermoplastic resin. Therefore, by supplying it to a three-dimensional shaping device or the like, a carbon fiber-containing product with particularly excellent mechanical properties can be manufactured.

[0062] <Manufacturing method of carbon fiber reinforced thermoplastic resin strand with core-sheath structure> The carbon fiber reinforced thermoplastic resin strand with a core-sheath structure according to one embodiment of the present disclosure can be manufactured by coating a blended yarn with a thermoplastic resin. More specifically, as described above, it can be manufactured by coating the blended yarn with a thermoplastic resin in the same manner as the manufacturing method of a general long fiber reinforced strand, except that the blended yarn according to the present disclosure is used instead of continuous carbon fibers. That is, it can be manufactured by a method including a coating step in which the continuously conveyed blended yarn is passed through a die in which the molten thermoplastic resin is continuously supplied from a supply port different from the blended yarn, and a discharging step of discharging from the die.

[0063] <Thermoplastic resin> Examples of the thermoplastic resin used for the coating treatment in the manufacture of the above carbon fiber reinforced thermoplastic resin strand (i.e., the thermoplastic resin serving as the sheath component of the carbon fiber reinforced thermoplastic resin strand with a core-sheath structure) include polyolefin resins (e.g., polypropylene resin and polyethylene resin), polyester resins (e.g., polyethylene terephthalate resin, polybutylene terephthalate resin, and polylactic acid resin), polyamide resins, polyether ketone resins, polycarbonate resins, phenoxy resins, and polyphenylene sulfide resins. This thermoplastic resin may be only one type, or may be a mixture of two or more thermoplastic resins.

[0064] Also, the thermoplastic resin serving as the sheath component of the carbon fiber reinforced thermoplastic resin strand may be of the same type as or different from the above thermoplastic resin fibers contained in the blended yarn according to the present disclosure. In particular, when the melting point T0 (°C) of the thermoplastic resin serving as the sheath component of the carbon fiber reinforced thermoplastic resin strand is lower than the melting point of the thermoplastic resin fiber T1 (°C) contained in the blended yarn according to the present disclosure (especially when T1 - T0 > 10), when manufacturing the carbon fiber reinforced thermoplastic resin strand according to the present disclosure, the blended yarn can be coated with a thermoplastic resin melted at a temperature lower than the melting point of the thermoplastic resin fiber contained in the blended yarn, so that the blended yarn may be stably passed through the die.

[0065] In addition, for the above-mentioned thermoplastic resin used for the coating treatment, various polymers, fillers, stabilizers, pigments, etc. may be blended within a range that does not impair the mechanical strength for the purpose of improving fluidity, appearance gloss, flame retardant properties, thermal stability, weather resistance, impact resistance, etc.

[0066] <Core-sheath structure of the strand> Since the carbon fiber reinforced thermoplastic resin strand according to one embodiment of the present disclosure is manufactured by coating the above-mentioned blended spun yarn according to the present disclosure with a thermoplastic resin, the blended spun yarn becomes the core component and the thermoplastic resin becomes the sheath component.

[0067] The carbon fiber reinforced thermoplastic resin strand according to the present disclosure is particularly suitable for manufacturing three-dimensional shaped objects. Also, from the viewpoint of the stability of three-dimensional shaping, the average diameter of the strand is preferably used in the range of 0.7 mm or more and 2.2 mm or less, and more preferably used in the range of 1.0 mm or more and 2.0 mm or less.

[0068] FIG. 1 is a schematic general view of a carbon fiber reinforced thermoplastic resin strand 100 according to the present disclosure. The drawing is a schematic view for explanation and is not to scale. The strand 100 in FIG. 1 has a core-sheath structure and has a core component 110 made of blended spun yarn and a sheath component 120 made of a thermoplastic resin.

[0069] Regarding the ratio of the thermoplastic resin as the sheath component in the carbon fiber reinforced thermoplastic resin strand having a core-sheath structure, the thermoplastic resin as the sheath component is preferably 50 parts by weight to 1000 parts by weight, more preferably 100 parts by weight to 750 parts by weight, and most preferably 250 parts by weight to 500 parts by weight with respect to 100 parts by weight of the recycled carbon fiber contained in the blended spun yarn.

[0070] ≪Three-dimensional shaped object≫ The present disclosure includes a method for manufacturing a three-dimensional shaped object by a fused deposition method using the above-mentioned carbon fiber reinforced thermoplastic resin strand according to the present disclosure.

[0071] In three-dimensional modeling, solid modeling is performed by sequentially laminating resin for each cross-section obtained by cutting the object to be modeled with a plurality of parallel planes, and a modeled object that becomes a three-dimensional model of the object to be modeled is generated. Such a three-dimensional modeled object can be used, for example, in prototype parts and product manufacturing. As a method of three-dimensional modeling, in particular, a fused deposition method in which resin is melted and deposited can be used.

[0072] The method for manufacturing a three-dimensional modeled object according to the present disclosure can be carried out according to a known fused deposition method, except for using the above-described carbon fiber reinforced thermoplastic resin strand according to the present disclosure.

[0073] Specifically, for example, the above-described carbon fiber reinforced thermoplastic resin strand according to the present disclosure is supplied to a discharge head of a fused deposition three-dimensional modeling apparatus, the carbon fiber reinforced thermoplastic resin strand is melted in the discharge head, and the melted carbon fiber reinforced thermoplastic resin strand is discharged from the discharge head and repeatedly deposited in layers to manufacture a three-dimensional modeled object.

[0074] ≪Method for Manufacturing Recycled Carbon Fibers by Semiconductor Thermal Activation Method≫ A method for obtaining recycled carbon fibers having the characteristics according to the present disclosure using the semiconductor thermal activation method will be described below. In the following, first, a method for decomposing a plastic-containing material will be described, and then, using this decomposition method, a method for recovering an inorganic material (carbon fiber) from a plastic-containing material containing a plastic and an inorganic material (carbon fiber) will be described.

[0075] <Method for Decomposing Plastic-Containing Material> The method for decomposing a plastic-containing material according to the present disclosure is heating the plastic-containing material to a first surface temperature in the atmosphere in a heating furnace into which a low oxygen concentration gas having an oxygen concentration of less than 10% by volume is introduced, in the presence of a semiconductor material, to decompose the plastic in the plastic-containing material, including.

[0076] Figure 2 is a conceptual cross-sectional view for explaining the decomposition method according to the present invention. The decomposition mechanism of the plastic-containing material according to the present invention will be described below. It should be noted that the present invention is not intended to be limited by theory.

[0077] When the semiconductor material 11 is heated in an oxygen atmosphere, holes h + and electrons e - are generated in the semiconductor material 11, and this electron e - is considered to react with oxygen O2 in the atmosphere to generate O2 - radicals (active oxygen). Then, in the plastic-containing material 12 arranged adjacent to the semiconductor material 11, radical propagation occurs, and the plastic-containing material 12 is decomposed into low-molecular components, and further, oxidative decomposition occurs into decomposition gases such as CO2, H2O, and CH4. Radicals are considered to promote the oxidative decomposition of plastics by extracting hydrogen from plastics.

[0078] By using a semiconductor material, the heat introduced for the decomposition of plastics can be reduced as compared with the case where no semiconductor material is used, and as a result, the energy consumption can be reduced.

[0079] In the conventional plastic decomposition method based on the thermal activation of semiconductors, excessive exothermic oxidation may occur during the heat treatment process. In the conventional method, since the heat treatment was performed in the atmosphere where the oxygen concentration was not controlled, excessive radicals were generated, and as a result, excessive exothermic oxidation was considered to have occurred.

[0080] On the other hand, the inventors of the present case have found that even in the presence of a semiconductor material, by setting the oxygen concentration to a relatively low value, plastics can be efficiently heat-treated while suppressing excessive exothermic oxidation.

[0081] In particular, at the initial stage of the thermal decomposition of plastics, due to the relatively large amount of plastics, there is a high risk of excessive exothermic oxidation. On the other hand, according to the method according to the present disclosure, since the heat treatment is efficiently performed at a relatively low oxygen concentration, even at the initial stage of decomposition, the occurrence of excessive exothermic oxidation can be suppressed.

[0082] Therefore, according to the method according to the present disclosure, since the heat treatment is performed in the presence of a semiconductor material, good decomposition efficiency can be obtained even at a relatively low oxygen concentration, and by setting the oxygen concentration in the heating furnace to a relatively low value, excessive exothermic oxidation can be suppressed, and it is possible to achieve a decomposition treatment with improved stability.

[0083] The decomposition method according to the present invention will be described with reference to the drawings depicting exemplary embodiments.

[0084] FIG. 3 is a cross-sectional view schematically showing one embodiment of the decomposition method according to the present disclosure. The heating furnace 20 shown in FIG. 3 has a heat source (heater) 23, a gas supply unit 24, an exhaust port 25, and an internal space 26. A porous carrier 21 is disposed in the internal space 26 of the heating furnace 20, and a semiconductor material is supported on the surface of the carrier 21. In the embodiment of FIG. 3, a plastic-containing material 22 is disposed in contact with this carrier 21.

[0085] The temperature of the atmosphere in the internal space 26 of the heating furnace 20 can be controlled via the heat source (heater) 23 of the heating furnace 20, whereby the surface temperature of the plastic-containing material 22 can be made to reach a specific temperature. The surface temperature of the plastic-containing material 22 can be measured via a temperature sensor 27 disposed within 5 mm from the surface of the plastic-containing material 22.

[0086] A low-oxygen concentration gas with an oxygen concentration of less than 10% by volume is introduced into the internal space 26 of the heating furnace 20 through the gas supply unit 24. By setting the introduction rate of the low-oxygen concentration gas according to the furnace internal volume, the oxygen concentration of the atmosphere in the heating furnace 20 can be controlled. The low-oxygen concentration gas can be pushed into the heating furnace, for example, through a gas supply unit provided in the heating furnace, or can be sucked into the heating furnace by applying a suction pressure to the exhaust port 25.

[0087] The low-oxygen concentration gas is, for example, a mixed gas of air and nitrogen gas. By selecting the ratio of air and nitrogen gas, the oxygen concentration in the heating furnace can be controlled.

[0088] In an atmosphere where the oxygen concentration is controlled to less than 10% by volume by introducing the low-oxygen concentration gas, the plastic-containing material is heated to a first surface temperature, for example, a first surface temperature of 300°C to 600°C. As a result, the plastic contained in the plastic-containing material 22 is decomposed into decomposition gases such as water vapor, carbon dioxide, and methane, and the decomposition gases are discharged from the exhaust port 25 of the heating furnace 20.

[0089] After the heat treatment at the above oxygen concentration of less than 10% by volume, a heat treatment with the oxygen concentration increased to 10% by volume or more can be further performed.

[0090] Also, after the heat treatment, the inorganic material contained in the plastic-containing material can be recovered.

[0091] Hereinafter, the decomposition method according to the present disclosure will be described in more detail.

[0092] <Plastic-containing material> The plastic-containing material contains plastic. The plastic-containing material may be a plastic material or a plastic composite material.

[0093] Examples of the plastic contained in the plastic-containing material include thermoplastic resins and thermosetting resins.

[0094] Examples of the thermoplastic resin contained in the plastic-containing material include polycarbonate (PC) resin, polyethylene (PE) resin, polypropylene (PP) resin, polyvinyl chloride (PVC) resin, polystyrene (PS) resin, polyethylene terephthalate (PET) resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide (PA) resin, polylactic acid (PLA) resin, polyimide (PI) resin, polymethyl methacrylate (PMMA) resin, methacrylic resin, polyvinyl alcohol (PVA) resin, polyacetal resin, petroleum resin, AS resin, modified polyphenylene ether resin, polybutylene terephthalate (PBT) resin, polybutene (PB) resin, fluororesin, polyacrylate resin, polyether ether ketone (PEEK) resin, and polyphenylene sulfide (PPS) resin.

[0095] Examples of the thermosetting resin contained in the plastic-containing material include phenol resin, urethane foam resin, polyurethane resin, urea resin, epoxy resin, unsaturated polyester resin, melamine resin, alkyd resin, vinyl ester resin, and cyanate resin.

[0096] The plastic-containing material can contain at least one selected from the group consisting of the above thermoplastic resins and thermosetting resins.

[0097] (Plastic composite material) The plastic-containing material is particularly a plastic composite material. The plastic composite material is, for example, a fiber-reinforced plastic (FRP: Fiber Reinforced Platic). Examples of the reinforcing fiber contained in the fiber-reinforced plastic include carbon fiber.

[0098] (Carbon fiber reinforced plastic) The plastic composite material is, in particular, a carbon fiber-containing plastic product such as carbon fiber reinforced plastic (CFRP). The carbon fiber reinforced plastic contains a plastic and a carbon fiber material. The carbon fiber reinforced plastic may include other members and / or materials (for example, reinforcing fibers other than carbon fibers, resin molded products, metals, ceramics, etc.).

[0099] The carbon fibers contained in the carbon fiber reinforced plastic are not particularly limited, and examples thereof include PAN-based carbon fibers and pitch-based carbon fibers. The carbon fibers may be of one type or may be composed of two or more types.

[0100] The carbon fiber material contained in the carbon fiber reinforced plastic may be in any form, for example, a carbon fiber bundle, a fabric formed from carbon fiber bundles, or a non-woven fabric of carbon fibers.

[0101] <Introduction of low oxygen concentration gas> In the method according to the present disclosure, A low oxygen concentration gas having an oxygen concentration of less than 10% by volume is introduced into the atmosphere of the heating furnace.

[0102] Preferably, the oxygen concentration of the low oxygen concentration gas introduced into the atmosphere of the heating furnace is more than 0% by volume, 1% by volume or more, 2% by volume or more, 3% by volume or more, or 4% by volume or more, and / or 9% by volume or less, 8% by volume or less, or 7% by volume or less.

[0103] The timing of introducing the low oxygen concentration gas into the heating furnace can be determined according to the type of plastic contained in the plastic-containing material and the surface temperature at which the decomposition of the plastic starts. Also, the timing of introducing the low oxygen concentration gas into the heating furnace can be determined based on data obtained in advance regarding the self-heating of the plastic-containing material.

[0104] In one preferred embodiment according to the present disclosure, while the surface temperature of the plastic-containing material held in the heating furnace is less than 300 °C, a low-oxygen concentration gas is introduced into the atmosphere of the heating furnace.

[0105] More preferably, while the surface temperature of the plastic-containing material held in the heating furnace is 250 °C or lower, 200 °C or lower, or 150 °C or lower, a low-oxygen concentration gas having an oxygen concentration of less than 10% by volume is introduced into the atmosphere of the heating furnace.

[0106] More preferably, a low-oxygen concentration gas having an oxygen concentration of less than 10% by volume is introduced into the atmosphere of the heating furnace holding the plastic-containing material having a surface temperature of less than 300 °C, thereby making the oxygen concentration of the atmosphere in the heating furnace less than 10% by volume.

[0107] More preferably, a low-oxygen concentration gas having an oxygen concentration of less than 10% by volume is introduced into the atmosphere of the heating furnace holding the plastic-containing material having a surface temperature of less than 300 °C, thereby controlling the oxygen concentration in the atmosphere in the heating furnace to be more than 0% by volume, 1% by volume or more, 2% by volume or more, 3% by volume or more, or 4% by volume or more, and / or 9% by volume or less, 8% by volume or less, or 7% by volume or less.

[0108] The oxygen concentration in the heating furnace can be directly measured by an oxygen concentration meter (oxygen monitor), or can be determined based on the furnace volume and the amount of gas introduced into the furnace. The oxygen concentration in the heating furnace is preferably the average oxygen concentration during the heat treatment.

[0109] The introduction of the low-oxygen concentration gas into the furnace can be performed, for example, by pushing the low-oxygen concentration gas into the furnace through a gas supply unit provided in the heating furnace, or by performing suction from a suction port (or exhaust port) provided in the furnace, thereby allowing gas to flow into the furnace from a gas supply unit provided at a location different from the suction port. The gas supply unit of the heating furnace may have, for example, an opening and / or may have a gas-permeable material.

[0110] The amount of gas introduced into the furnace can be set according to the capacity of the heating furnace and the desired oxygen concentration, etc., based on the amount of resin per unit resin to be decomposed (for example, epoxy resin).

[0111] For example, the amount of gas introduced into the furnace per unit resin amount can be determined in the range of 1 to 1000 (L / min) / kg or less, preferably in the range of 2 to 700 (L / min) / kg or less. Also, based on the determined gas introduction amount and the volume of the heating furnace used, the time for the atmosphere in the furnace to be replaced by the introduced gas can be determined.

[0112] In particular, set the introduction amount of the low-oxygen concentration gas with respect to the furnace content volume, so that the atmosphere in the heating furnace can be replaced by the introduced low-oxygen concentration gas while the surface temperature of the plastic-containing material held in the heating furnace is less than 300°C.

[0113] The low-oxygen concentration gas introduced into the heating furnace can contain a dilution gas, and in particular, it is a mixed gas of air and a dilution gas. Examples of the dilution gas include nitrogen gas, carbon dioxide gas, water vapor, and superheated water vapor. Note that superheated water vapor is water vapor heated to a temperature above the boiling point. Superheated water vapor has the advantage of relatively high heat transfer performance to the object to be decomposed.

[0114] (Heating furnace) The heating furnace can be a combustion furnace or an electric furnace. The heating furnace has, for example, an internal space for accommodating a plastic-containing material and a semiconductor material, a heat source (heater) for heating the atmosphere in the heating furnace, a gas supply section for introducing a low-oxygen concentration gas into the heating furnace, an exhaust port for discharging the decomposition gas, and optionally, a suction port for applying a suction pressure inside the heating furnace. Note that one structure can also be used as both the exhaust port and the suction port. As the exhaust port and / or the suction port, for example, one or more openings provided in the heating furnace can be used.

[0115] (Surface temperature) The "surface temperature" of the plastic-containing material can be determined by measuring the temperature within 5 mm around the plastic-containing material during the heat treatment.

[0116] The surface temperature of the plastic-containing material can be controlled, for example, by controlling the temperature in the heating furnace via the heat source of the heating furnace, and / or by introducing a low-temperature gas into the heating furnace, and / or by reducing the oxygen concentration to suppress exothermic oxidation.

[0117] Also, the surface temperature of the plastic-containing material can be measured via a temperature sensor disposed within 5 mm from the surface of the plastic-containing material, and the surface temperature can be controlled with higher accuracy by feeding back this measured value to the heat source of the heating furnace.

[0118] Furthermore, for example, data regarding the correlation between the temperature in the heating furnace and / or the output of the heat source and the surface temperature measured by the sensor can be acquired in advance, and the heat treatment may be performed based on this data.

[0119] <Heat treatment> The method according to the present disclosure heating the plastic-containing material to a first surface temperature in the presence of a semiconductor material in an atmosphere in a heating furnace into which a low-oxygen-concentration gas having an oxygen concentration of less than 10% by volume is introduced to decompose the plastic in the plastic-containing material including.

[0120] Preferably, this heat treatment is performed in an atmosphere in which the oxygen concentration becomes less than 10% by volume due to the introduction of the low-oxygen-concentration gas, particularly at an oxygen concentration of more than 0% by volume, 1% by volume or more, 2% by volume or more, 3% by volume or more, or 4% by volume or more, and / or at an oxygen concentration of 9% by volume or less, 8% by volume or less, or 7% by volume or less.

[0121] (First surface temperature) "The first surface temperature" is the surface temperature of the plastic-containing material. "The first surface temperature" can be determined by measuring the temperature within 5 mm around the plastic-containing material during the heat treatment, similar to the above-mentioned "surface temperature".

[0122] The first surface temperature may be 300 °C or higher, 325 °C or higher, or 350 °C or higher, and / or may be 600 °C or lower, 550 °C or lower, 500 °C or lower, or 450 °C or lower. The first surface temperature is, for example, 300 °C to 600 °C, 300 °C to 550 °C, 300 °C to 500 °C, or 300 °C to 450 °C.

[0123] If the first surface temperature is less than the above range, plastic decomposition may not occur. Also, if the first surface temperature exceeds the above range, when the plastic-containing material contains valuable substances such as carbon fibers, deterioration and / or ablation of carbon fibers, etc. due to heating in the presence of oxygen may become significant. By setting the first surface temperature to a relatively low temperature, the effect of suppressing excessive oxidation heat generation is further enhanced.

[0124] In a preferred embodiment of the present disclosure, during the heat treatment at an oxygen concentration of less than 10% by volume, the first surface temperature is set to a temperature of 450 °C or higher. When the heating temperature is relatively low, further decomposition of the plastic may be suppressed by the carbide formed on the surface of the plastic-containing material, but by setting the surface temperature to a temperature of 450 °C or higher, the carbide can be removed even at a relatively low oxygen concentration. Therefore, it is possible to further improve the decomposition efficiency of the plastic.

[0125] Preferably, the heat treatment under the introduction of a low-oxygen concentration gas is performed over a predetermined time. This predetermined time may be 1 minute to 600 minutes, preferably 30 minutes to 300 minutes, and more preferably 60 minutes to 180 minutes. Note that the time when the temperature of the heating furnace reaches 300 °C or the time when the start of plastic decomposition is confirmed can be set as the starting point of the above-mentioned "predetermined time".

[0126] (Semiconductor material) The semiconductor material may be placed in a heating furnace together with the plastic-containing material, or the semiconductor material may be placed in the heating furnace in advance, and then the plastic-containing material may be placed adjacent to or in contact with the semiconductor material.

[0127] In one embodiment according to the present disclosure, the plastic-containing material and the semiconductor material to be heat-treated are arranged at a distance of 50 mm or less from each other. For this purpose, for example, a spacer arranged between the plastic-containing material and the semiconductor material can be used.

[0128] The distance between the plastic-containing material and the semiconductor material can be measured at the location where they are closest to each other.

[0129] Also, in another preferred embodiment according to the present disclosure, the plastic-containing material and the semiconductor material to be heat-treated are arranged in contact with each other.

[0130] The mode of contact between the plastic-containing material and the semiconductor material is not particularly limited. For example, the two can be brought into contact by placing the plastic-containing material on the semiconductor material. Also, the plastic-containing material may be placed on the semiconductor material supported on the surface of the carrier. Furthermore, the two can also be brought into contact by surrounding or covering at least a part or the whole of the plastic-containing material with the semiconductor material.

[0131] The semiconductor material is not particularly limited as long as it is stable at the temperature and oxygen concentration of the present invention. The semiconductor material contains, for example, at least one selected from the group consisting of the following substances: BeO, MgO, CaO, SrO, BaO, CeO2, ThO2, UO3, U3O8, TiO2, ZrO2, V2O5, Y2O3, Y2O2S, Nb2O5, Ta2O5, MoO3, WO3, MnO2, Fe2O3, MgFe2O4, NiFe2O4, ZnFe2O4, ZnCo2O4, ZnO, CdO, Al2O3, MgAl2O4, ZnAl2O4, Tl2O3, In2O3, SiO2, SnO2, PbO2, UO2, Cr2O3, MgCr2O4, FeCrO4, CoCrO4, ZnCr2O4, WO2, MnO, Mn3O4, Mn2O3, FeO, NiO, CoO, Co3O4, PdO, CuO, Cu2O, Ag2O, CoAl2O4, NiAl2O4, Tl2O, GeO, PbO, TiO, Ti2O3, VO, MoO2, IrO2, RuO2, CdS, CdSe, CdTe, Cu2O, Sb2O3, MnO3, and CoCrO4.

[0132] Preferably, the semiconductor material is an oxide semiconductor material. Preferred oxide semiconductor materials include chromium oxide, titanium oxide, zinc oxide, vanadium oxide, tungsten oxide, molybdenum oxide, cobalt oxide, iron oxide, and copper oxide.

[0133] The form of the semiconductor material is not particularly limited and may be, for example, plate-like, granular, or honeycomb-shaped. From the viewpoint of promoting the decomposition of plastics, it is preferable that the semiconductor material is supported on the surface of a carrier having air permeability. The carrier having air permeability may be a porous body made of ceramics or the like, a honeycomb-shaped support, or the like. The semiconductor material may be a sintered body of a semiconductor.

[0134] <Two-step heating> The heat treatment method according to one preferred embodiment of the present disclosure is heating the plastic-containing material subjected to the heat treatment at the first surface temperature in an atmosphere having an oxygen concentration of 10% by volume or more in the presence of a semiconductor material, including.

[0135] The heat treatment at an oxygen concentration of 10% by volume or more is preferably carried out at an oxygen concentration of more than 10% by volume, 12% by volume or more, 15% by volume or more, or 20% by volume or more, and / or at an oxygen concentration of 30% by volume or less, or 25% by volume or less.

[0136] In this mode, also referred to as two-stage heating, the plastic-containing material heat-treated at a relatively low oxygen concentration is further heat-treated at an increased oxygen concentration.

[0137] In the initial stage of the thermal decomposition of plastics, due to the relatively large amount of plastics, there is a high risk of excessive exothermic oxidation. In contrast, in the above-described embodiment involving two-stage heating, after the heat treatment is carried out at a relatively low oxygen concentration, the heat treatment is carried out with the oxygen concentration increased. That is, heating is carried out with the oxygen concentration increased at the stage where the decomposition of plastics has progressed and the amount of plastics has been reduced, so that the occurrence of excessive exothermic oxidation can be suppressed.

[0138] Also, in the heat treatment at a relatively low oxygen concentration, part of the plastics may not vaporize and may remain as carbides. In contrast, in the above-described embodiment involving two-stage heating, since the heat treatment is further carried out with the oxygen concentration increased, the remaining carbides can be efficiently decomposed and removed, and as a result, the decomposition efficiency can be further improved.

[0139] The heat treatment under the introduction of a low-oxygen-concentration gas and the heat treatment at an oxygen concentration of 10% by volume or more can be continuously carried out in the same heating furnace. That is, for example, after heating the plastic-containing material to the first surface temperature, in the same heating furnace, the oxygen concentration can be increased to 10% by volume or more and the heat treatment can be further carried out. In the conventional plastic decomposition method, it was necessary to carry out processing such as shredding of the object to be processed following the batch processing, but by continuously carrying out the heat treatment under the introduction of a low-oxygen-concentration gas and the heat treatment at an oxygen concentration of 10% by volume or more in the same heating furnace, it becomes possible to save the number of steps.

[0140] An atmosphere with an oxygen concentration of 10% by volume or more can be formed, for example, by introducing a high-oxygen-concentration gas with an oxygen concentration of 10% by volume or more into a heating furnace. In particular, it can be formed by introducing air and / or oxygen gas into the heating furnace. The oxygen concentration of the high-oxygen-concentration gas may be more than 10% by volume, 12% by volume or more, 15% by volume or more, or 20% by volume or more, and / or may be 30% by volume or less, or 25% by volume or less.

[0141] In the heat treatment at an oxygen concentration of 10% by volume or more, the semiconductor material used in the heat treatment at the first surface temperature can be used.

[0142] (Second surface temperature) In particular, the plastic-containing material subjected to the heat treatment at the first surface temperature is heated to the second surface temperature in an atmosphere with an oxygen concentration of 10% by volume or more in the presence of a semiconductor material.

[0143] The "second surface temperature" is the surface temperature of the plastic-containing material to be processed. The "second surface temperature" can be determined by measuring the temperature within 5 mm around the plastic-containing material during the heat treatment, similar to the above-mentioned "surface temperature" and "first surface temperature".

[0144] The second surface temperature may be in the range of 400°C to 600°C. More preferably, the second surface temperature is 425°C to 575°C, or 450°C to 550°C.

[0145] If the second surface temperature is less than the above range, the improvement of the decomposition efficiency may not be observed. Also, if the second surface temperature exceeds the above range, when the plastic-containing material contains valuable substances such as carbon fibers, the deterioration and / or ablation of carbon fibers and the like due to heating in the presence of oxygen may become significant.

[0146] The second surface temperature may be substantially the same as the first surface temperature.

[0147] Further, the second surface temperature may be equal to or higher than the first surface temperature, or may be at least 5°C, at least 10°C, at least 25°C, at least 50°C, or at least 75°C higher than the first surface temperature.

[0148] Heat treatment at an oxygen concentration of 10% by volume or more can be performed for a predetermined time. This predetermined time may be, for example, 1 minute to 600 minutes, 60 minutes to 360 minutes, or 90 minutes to 300 minutes.

[0149] <Use> According to the method for decomposing a plastic-containing material according to the present disclosure, a wide variety of plastics can be efficiently vaporized and decomposed. Further, the decomposition method according to the present disclosure is also applicable to volatile organic compounds (VOCs), flue gas, particulate matter (PM), etc., and can also be used for exhaust gas treatment.

[0150] ≪Method for recovering inorganic material≫ The method according to the present disclosure for recovering the inorganic material contained in the plastic composite material will be described below.

[0151] In one embodiment of the recovery method according to the present disclosure, the plastic-containing material, which is a plastic composite material, contains a plastic and an inorganic material, and this recovery method decomposes the plastic in the plastic-containing material by the above-described decomposition method to recover the inorganic material, and includes.

[0152] For the decomposition method according to the present disclosure that can be used in the recovery method according to the present disclosure and its details, reference can be made to the above description regarding the method for decomposing a plastic-containing material.

[0153] As described above, according to the decomposition method according to the present disclosure, plastics can be efficiently decomposed. Therefore, according to the recovery method according to the present disclosure, the plastic contained in the plastic composite material can be efficiently and selectively decomposed, so that the inorganic material having good physical properties can be efficiently recovered.

[0154] Further, in the recovery method according to the present disclosure, inorganic materials can be recovered without crushing the plastic composite material. Note that crushing the plastic composite material is not particularly excluded, and crushing can be performed optionally.

[0155] Furthermore, when recovering inorganic materials from the plastic composite material, it is necessary to suppress the influence of heat treatment on the inorganic materials as much as possible from the viewpoint of maintaining the quality of the recovered inorganic materials. In this regard, in the decomposition method according to the present disclosure, excessive exothermic oxidation is suppressed by a relatively low oxygen concentration. Therefore, according to the recovery method of the present disclosure, it is possible to recover inorganic materials having relatively good physical properties.

[0156] (Two-stage heating) In another embodiment of the recovery method according to the present disclosure, a plastic-containing material as a plastic composite material is subjected to two-stage heating. That is, the plastic composite material is subjected to heating under introduction of a low oxygen concentration gas and subsequent heat treatment at an oxygen concentration of 10% by volume or more, thereby decomposing the plastic and recovering the inorganic material.

[0157] When recovering inorganic materials, it is desirable to suppress deterioration of the physical properties of the inorganic materials due to excessive exothermic oxidation, and further, it is also preferable to suppress deterioration of the physical properties of the inorganic materials due to carbonization of the plastic and adhesion to and remaining on the inorganic materials. In this regard, in the mode of subjecting the plastic composite material to two-stage heating, the relatively low oxygen concentration in the initial stage where excessive exothermic oxidation is likely to occur suppresses deterioration of the physical properties of the inorganic materials caused by excessive exothermic oxidation. Furthermore, since subsequent heat treatment with an increased oxygen concentration is performed, the carbonized resin remaining on the inorganic materials can be efficiently removed. As a result, by the recovery method of the inorganic materials through two-stage heat treatment, it is possible to ensure better physical properties of the recovered inorganic materials.

[0158] (Inorganic material) Examples of plastic composite materials containing inorganic materials and plastics include carbon fiber reinforced plastics.

[0159] The inorganic material is, in particular, carbon fiber (carbon fiber material).

[0160] (Carbon fiber) The carbon fiber contained in the carbon fiber reinforced plastic is not particularly limited, and examples include PAN-based carbon fiber and pitch-based carbon fiber. The carbon fiber may be of one type or may be composed of two or more types.

[0161] The carbon fiber contained in the carbon fiber reinforced plastic may be in any form, for example, a carbon fiber bundle, a fabric formed from carbon fiber bundles, or a non-woven fabric of carbon fiber.

[0162] (Recycled material) According to one embodiment of the recovery method according to the present disclosure, the residual carbon derived from the plastic recovered together with the inorganic material is reduced, and in particular, the residual carbon is 5% by weight or less of the inorganic material to be recovered. Preferably, the residual carbon is 4% by weight or less, 3% by weight or less, 2% by weight or less, 1% by weight or less, 0.9% by weight or less, 0.5% by weight or less, or 0.1% by weight or less of the inorganic material to be recovered. Although it is preferable that the residual carbon is reduced as much as possible, the lower limit may be 0.001% by weight or more.

[0163] Furthermore, according to the recovery method according to the present disclosure, a carbon fiber material having physical properties superior to those of the carbon fiber material before manufacturing the carbon fiber reinforced plastic can be recovered.

[0164] In particular, according to the recovery method according to the present disclosure, a carbon fiber material having a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more can be obtained as an inorganic material from the carbon fiber reinforced plastic.

[0165] (Single fiber tensile strength) The single fiber tensile strength is preferably 3.1 GPa or more, 3.2 GPa or more, 3.3 GPa or more, or 3.4 GPa or more. The upper limit of the single fiber tensile strength is not particularly limited, but it may be 6.0 GPa or less.

[0166] The single fiber tensile strength can be measured according to JIS R7606 as follows: Collect at least 30 single fibers from the fiber bundle, Measure the diameter of the single fiber in the side image of the single fiber taken by a digital microscope, calculate the cross-sectional area, Fix the sampled single fibers to a perforated mounting board using an adhesive, Attach the mounting board with the single fibers fixed to a tensile testing machine, conduct a tensile test at a gauge length of 10 mm and a strain rate of 1 mm / min to measure the tensile fracture stress, Calculate the tensile strength from the cross-sectional area and tensile fracture stress of the single fiber, Take the average of the tensile strengths of at least 30 single fibers as the single fiber tensile strength.

[0167] (Weibull shape factor) The Weibull shape factor is preferably 6.5 or more, 7.0 or more, 7.5 or more, 8.0 or more, or 8.5 or more. The upper limit of the Weibull shape factor is not particularly limited, but it may be 15.0 or less.

[0168] The Weibull shape factor can be calculated according to the following formula: lnln{1 / (1 - F)} = m×lnσ + C In the formula, F is the fracture probability obtained by the symmetric sample cumulative distribution method, σ is the single fiber tensile strength (MPa), m is the Weibull shape factor, and C is a constant.

[0169] Perform a Weibull plot with lnln{1 / (1 - F)} and lnσ, and obtain the Weibull shape factor m from the slope of the first-order approximation.

[0170] <Use> According to the recovery method according to the present disclosure, for example, only the matrix resin such as fiber reinforced plastic (FRP), solar cell panel, electronic circuit, etc. can be efficiently decomposed, and valuable materials such as reinforcing fibers and rare metals can be efficiently recovered.

[0171] ≪Recycled Carbon Fiber Material≫ The recycled carbon fiber material (recycled carbon fiber) according to the present disclosure can be manufactured by recovering the carbon fiber material from carbon fiber reinforced plastic. In one embodiment of the present disclosure, this recycled carbon fiber material can have physical properties superior to those of carbon fibers before manufacturing carbon fiber reinforced plastic.

[0172] The method for manufacturing the recycled carbon fiber material is not particularly limited. For example, the recycled carbon fiber material can be manufactured by recovering the recycled carbon fiber material from carbon fiber reinforced plastic by the recovery method according to the present disclosure.

[0173] In one embodiment, the recycled carbon fiber material has a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more. The single fiber tensile strength and the Weibull shape factor can be measured and determined by the methods described above.

[0174] The single fiber tensile strength of the recycled carbon fiber material is preferably 3.1 GPa or more, 3.2 GPa or more, 3.3 GPa or more, or 3.4 GPa or more.

[0175] The Weibull shape factor of the recycled carbon fiber material is preferably 6.5 or more, 7.0 or more, 7.5 or more, 8.0 or more, or 8.5 or more.

[0176] (Method for Manufacturing Recycled Carbon Fiber) In particular, a method for manufacturing recycled carbon fiber having a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, and a content of the residual carbon component of more than 0 wt% and 5.0 wt% or less with respect to the recycled carbon fiber is In an atmosphere in a heating furnace into which a low-oxygen-concentration gas having an oxygen concentration of less than 10% by volume is introduced, in the presence of a semiconductor material, heat a plastic-containing material to a first surface temperature to decompose the plastic in the plastic-containing material. including wherein the plastic-containing material is a carbon fiber reinforced plastic containing a carbon fiber material.

[0177] Moreover, in particular, a method for producing a recycled carbon fiber material having a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, and having a content of a residual carbon component of more than 0% by weight and 5.0% by weight or less with respect to the recycled carbon fiber, In an atmosphere in a heating furnace into which a low-oxygen-concentration gas having an oxygen concentration of less than 10% by volume is introduced, in the presence of a semiconductor material, heat a plastic-containing material to a first surface temperature, and heat the plastic-containing material subjected to the heat treatment at the first surface temperature in an atmosphere having an oxygen concentration of 10% by volume or more in the presence of a semiconductor material, thereby decomposing the plastic in the plastic-containing material. including wherein the plastic-containing material is a carbon fiber reinforced plastic containing a carbon fiber material.

[0178] In a preferred embodiment of the method for producing a recycled carbon fiber material according to the present disclosure, the low-oxygen-concentration gas is introduced into the atmosphere of the heating furnace while the surface temperature of the plastic-containing material is less than 300°C.

[0179] (Residual carbon) Preferably, in the recycled carbon fiber material according to the present disclosure, the amount of residual carbon is reduced, and in particular, the residual carbon is 5% by weight or less with respect to the recycled carbon fiber material. More preferably, the residual carbon is 4% by weight or less, 3% by weight or less, 2% by weight or less, 1% by weight or less, 0.9% by weight or less, 0.5% by weight or less, or 0.1% by weight or less with respect to the recycled carbon fiber material.

[0180] The "residual carbon" is a carbonized component derived from the plastic contained in the carbon fiber reinforced plastic, which is the raw material when manufacturing the recycled carbon fiber material.

[0181] The amount of residual carbon in the recycled carbon fiber material can be determined by thermogravimetric analysis (TGA).

[0182] The determination of the amount of residual carbon by thermogravimetric analysis can be carried out according to the following procedure: (i) For a 1 - 4 mg sample piece obtained by pulverizing the recycled carbon fiber material, in a thermogravimetric analyzer, at an air supply rate of 0.2 L / min, a heating rate of 5 °C / min, and a recording rate of 1 / 6 s, heating from room temperature to 100 °C, holding at 100 °C for 30 minutes, heating from 100 °C to 400 °C, and holding at 400 °C perform thermogravimetric analysis with these steps over a total of 300 minutes, (ii) In a graph plotting the weight loss rate against time, identify the inflection point of the slope, and calculate the amount of residual carbon by subtracting the weight loss rate during the holding period at 100 °C from the value of the weight loss rate at the inflection point.

[0183] If the inflection point of the slope cannot be identified under the above conditions, instead of performing thermogravimetric analysis over a total of 300 minutes, thermogravimetric analysis over a total of about 600 minutes with a 480 - minute holding at 400 °C can be performed. Furthermore, instead of holding at 400 °C for 480 minutes, it may be held at a specific temperature within the range above 400 °C and below 500 °C for 480 minutes.

Example

[0184] The present disclosure will be further specifically described below using examples. Note that the examples are illustrative and the present application is not limited thereto.

[0185] ≪Example 1≫ <Preparation of Materials> (Recycled Carbon Fiber) As the recycled carbon fiber, the recycled carbon fiber with an average length of 50 mm, an average single fiber diameter of 6.7 μm, a single fiber tensile strength of 4.7 GPa, a Weibull shape factor of 7.0, and a residual carbon content of 0.6 wt%, which was recycled by the semiconductor thermal activation method using CFRP as a raw material by the method according to the present disclosure, was used.

[0186] (Single Fiber Tensile Strength) The single fiber tensile strength was measured as follows in accordance with JIS R7606: At least 30 single fibers were collected from the fiber bundle, The diameter of the single fiber was measured in the side image of the single fiber photographed by a digital microscope to calculate the cross-sectional area, The sampled single fibers were fixed to a perforated mount using an adhesive, The mount with the single fibers fixed was attached to a tensile testing machine, and a tensile test was performed at a gauge length of 10 mm and a strain rate of 1 mm / min to measure the tensile fracture stress, The tensile strength was calculated from the cross-sectional area and the tensile fracture stress of the single fiber, The average of the tensile strengths of at least 30 single fibers was defined as the single fiber tensile strength.

[0187] (Weibull Shape Factor) The Weibull shape factor was calculated according to the following formula: lnln{1 / (1 - F)} = m×lnσ + C (In the formula, F is the fracture probability obtained by the symmetric sample cumulative distribution method, σ is the single fiber tensile strength (MPa), m is the Weibull shape factor, and C is a constant.)

[0188] A Weibull plot was made with lnln{1 / (1 - F)} and lnσ, and the Weibull shape factor m was obtained from the slope of the first-order approximation.

[0189] (Residual Carbon Content) The amount of the residual carbon component in the recycled carbon fiber was determined by thermogravimetric analysis (TGA method) as follows: (i) A 4 mg sample piece obtained by pulverizing recycled carbon fiber was subjected to thermogravimetric analysis in a thermogravimetric analyzer at an air supply rate of 0.2 L / min, a heating rate of 5 °C / min, and a recording rate of 1 / 6 s. The thermogravimetric analysis consisted of a temperature increase from room temperature to 100 °C, a holding at 100 °C for 30 minutes, a temperature increase from 100 °C to 400 °C, and a holding at 400 °C for 480 minutes, and was carried out over a total of about 600 minutes. (ii) In a graph plotting the weight loss rate against time, the inflection point of the slope was identified, and the amount of residual carbon was calculated by subtracting the weight loss rate during the holding period at 100 °C from the value of the weight loss rate at the inflection point.

[0190] After immersing the above-mentioned recycled carbon fiber in an aqueous dispersion of an epoxy resin and pulling it out, it was dried in a dryer, and 2% by weight of the epoxy resin was applied to the recycled carbon fiber as a binder with a thermoplastic resin.

[0191] (Thermoplastic resin fiber) As the thermoplastic resin fiber, polyamide 66 resin fiber with an average length of 38 mm (PA66 resin fiber (manufactured by Toray Industries, Inc., 1401 - 1.3T - 38 E9), single fiber fineness of 1.3 dtex, number of crimps of 17 mountains / 25 mm, melting point of 265 °C) was used.

[0192] <Manufacture of blended yarn> 80% by weight of the recycled carbon fiber with a binder and 20% by weight of the PA66 resin fiber were mixed, and spun through carding, roving, and drawing processes to produce a continuous blended yarn at 0.86 g / m. In the drawing process, a twist of 200 turns / m was applied.

[0193] <Manufacture of carbon fiber reinforced thermoplastic resin strand> Next, the blended yarn obtained above was coated with polyamide 6 (manufactured by DSM: Akulon® F-X9182, melting point 220°C) using a crosshead die for wire coating with an outlet diameter of 2.3 mm, and this was wound up with a winder to obtain a strand-shaped fiber-reinforced plastic having a core-sheath structure with a carbon fiber content of 17% by mass (463 parts by mass of polyamide 6 per 100 parts by mass of carbon fiber) and an average diameter of 2.0 mm (carbon fiber-reinforced thermoplastic resin strand according to Example 1).

[0194] <Modeling by a three-dimensional modeling device> The above strand-shaped fiber-reinforced plastic with an average diameter of 2.0 mm was set in a fused deposition three-dimensional modeling device ("BS01" manufactured by Bonsai Lab Co., Ltd.), and a modeling test was conducted under the following conditions at a discharge head temperature of 280°C. Discharge head moving speed: 30 mm / min (during resin discharge), 130 mm / min (when discharge stops). Discharge amount (magnification): 100% Lamination pitch: 0.2 mm Lamination bed temperature: 25°C Atmospheric temperature: 25°C Atmospheric relative humidity: 40% During modeling, the molded object was not cooled by a fan or a blower.

[0195] (1) Sag evaluation: Two cubes with sides of 10 mm each were used as bridge girders, and they were arranged parallel to each other on a horizontal plane so that the center-to-center distance between the bridge girders was 50 mm. A bridge-shaped three-dimensional model with a plate having a length of 60 mm, a width of 10 mm, and a thickness of 0.2 mm placed on top was designed in 3D CAD, and this model was molded under the above conditions to manufacture a three-dimensional molded object. The distance Z between the part of the plate-shaped portion of the molded three-dimensional model closest to the lamination bed and the lamination bed was measured, and the sag amount was calculated from the following formula. Sag amount (mm) = 10 - Z The molding was repeated 3 times to calculate the average value of the sag amount. An average value of 0 mm or more and less than 2 mm was rated as excellent pass (◎), 2 mm or more and less than 4 mm was rated as pass (○), and 4 mm or more was rated as fail (×). When the sag evaluation of the obtained strand was carried out, the average value of the sag amount was 3.4 mm.

[0196] (2) Evaluation of ejection / stop responsiveness: A three-dimensional model was designed using 3D CAD, in which 25 prisms with a square cross-section of 2 mm per side and a height of 20 mm were each placed upright on a 5×5 square lattice point drawn on a horizontal plane at 10 mm intervals. This model was shaped under the above conditions to manufacture a three-dimensional shaped object. The dimensions of the shaped three-dimensional model were measured with a caliper, and the number of prisms with a portion of 3 mm or more on two sides of the cross-section of the prism was defined as the number of shaping failures. The shaping was repeated three times to calculate the average value of the number of shaping failures. If this average value was 0 or more and less than 2, it was rated as excellent pass (◎); if it was 2 or more and less than 5, it was rated as pass (○); if it was 5 or more, it was rated as fail (×). When the ejection / stop responsiveness evaluation of the obtained strand was carried out, the average value of the number of shaping failures was 3.7.

[0197] (3) Evaluation of shaping stability: A three-dimensional model was designed using 3D CAD, in which 25 prisms with a square cross-section of 10 mm and a height of 100 mm were each placed upright on a 5×5 square lattice point drawn on a horizontal plane at 20 mm intervals. This model was shaped under the above conditions to manufacture a three-dimensional shaped object. The strand used for shaping was one that sufficiently exceeded 300 g in weight (volume 250 cm 3 and a continuous length of about 104 m). If the shaping ended normally, it was rated as pass (○); if the ejection amount decreased during the process or the ejection stopped, it was rated as fail (×). When the shaping stability evaluation of the obtained strand was carried out, the shaping ended normally.

[0198] The results according to Example 1 are shown in Table 1 below.

[0199] ≪Comparative Example 1≫ Attempts were made to manufacture blended spun yarns in the same manner as in Example 1, except that recycled carbon fibers with a residual carbon content of 7.1% by weight were used. In the recycled carbon fibers, the single fiber tensile strength and Weibull shape coefficient were difficult to measure because the binding between single fibers due to residual carbon was strong.

[0200] In Comparative Example 1, in the carding process, it was observed that the binding between single fibers of the recycled carbon fiber was not sufficiently opened and the entanglement between single fibers was small, resulting in yarn breakage, so continuous blended yarn could not be produced. The results are shown in Table 1 below.

[0201]

Table 1

[0202] ≪Reference Examples 1 to 3 and Reference Comparative Example 1≫ In Reference Examples 1 to 3 and Reference Comparative Example 1, a carbon fiber reinforced plastic (CFRP) plate as a plastic-containing material was heat-treated to evaluate the plastic decomposition efficiency.

[0203] <Reference Example 1> Reference Example 1 was carried out as follows.

[0204] (Provision and Arrangement of Materials) As the semiconductor material, a material in which chromium oxide (Cr2O3, purity 99% or more, manufactured by Junsei Chemical Co., Ltd.) was applied to the surface of a carrier having a honeycomb structure was used. The carrier having a honeycomb structure had 13 cells / 25 mm.

[0205] As the plastic-containing material, a CFRP plate with an epoxy resin content ratio of 41% by weight was used.

[0206] The furnace volume of the heating furnace was 9 L. Inside the heating furnace, the CFRP plate was placed on the carrier carrying chromium oxide as the semiconductor material. The carrier and the CFRP plate were placed in contact with each other.

[0207] The surface temperature of the CFRP plate was measured by a sensor arranged within 5 mm from the surface of the CFRP plate.

[0208] (Heat Treatment) The internal temperature of the heating furnace was controlled via the heater output of the heating furnace to raise the internal temperature of the heating furnace.

[0209] Before the surface temperature of the CFRP plate reached 300°C, a mixed gas of air with an oxygen concentration of 6% by volume and nitrogen gas was introduced into the heating furnace. The introduction of the mixed gas into the heating furnace was carried out by sucking at a gas introduction rate of 70 L / min from a suction port provided in the upper part of the heating furnace and allowing the mixed gas to flow in from a gas supply port provided in the lower part of the heating furnace. The oxygen concentration in the heating furnace was measured by an oxygen monitor.

[0210] Under the atmosphere controlled to an oxygen concentration of 6% by volume by the introduction of the above mixed gas, heat treatment was carried out for 30 minutes. During the heat treatment, the heater output of the heating furnace was adjusted to raise the surface temperature of the CFRP plate to a first surface temperature of 376°C.

[0211] (Evaluation) The evaluation of the plastic decomposition efficiency in the method according to Reference Example 1 was carried out by calculating the weight reduction rate (wt%) from the difference between the weight of the CFRP plate before the heat treatment and the weight of the CFRP plate after the heat treatment. The results are shown in Table 2.

[0212] <Reference Example 2> In the heating furnace, except that the carrier and the CFRP plate were arranged 30 mm apart from each other and the surface temperature of the CFRP plate was raised to 377°C during the heat treatment, the heat treatment and evaluation of Reference Example 2 were carried out in the same manner as in Reference Example 1. The results are shown in Table 2.

[0213] <Reference Example 3> Except that the heat treatment time was 60 minutes and the surface temperature of the CFRP plate was raised to 371°C during the heat treatment, the heat treatment and evaluation of Reference Example 3 were carried out in the same manner as in Reference Example 1. The results are shown in Table 2.

[0214] <Reference Comparative Example 1> Except that no semiconductor material was used and the surface temperature of the CFRP plate was raised to 370°C during the heat treatment, the heat treatment and evaluation of Reference Comparative Example 1 were carried out in the same manner as in Reference Example 1. The results are shown in Table 2.

[0215]

Table 2

[0216] As shown in Table 2, in the presence of a semiconductor material, under the introduction of a low oxygen concentration gas with an oxygen concentration of 6% by volume, Reference Examples 1 to 3 heated to a surface temperature of 371°C to 377°C had a higher decomposition efficiency of the plastic-containing material compared to Reference Comparative Example 1 without using a semiconductor material.

[0217] In addition, in Reference Example 3, although the treatment time was extended to 60 minutes, the increase in the weight loss rate was limited compared to Reference Example 1 with a treatment time of 30 minutes. This is presumably because the sample surface was covered with carbide during the heat treatment, resulting in a decrease in the decomposition efficiency.

[0218] ≪Reference Example 4 and Reference Comparative Example 2≫ <Reference Example 4> The treatment and evaluation according to Reference Example 4 were carried out in the same manner as in Reference Example 1, except that heating was performed at a surface temperature of 500°C for 60 minutes. The results are shown in Table 3 below.

[0219] <Reference Comparative Example 2> The treatment and evaluation according to Reference Comparative Example 2 were carried out in the same manner as in Reference Example 4, except that no semiconductor material was used. The results are shown in Table 3 below.

[0220]

Table 3

[0221] Photographs of the samples after the treatments according to Reference Example 4 and Reference Comparative Example 2 are shown in FIGS. 5 and 6, respectively. Also, a photograph of the sample before the treatment is shown in FIG. 4.

[0222] As shown in Table 3, Reference Example 4 in which heat treatment was performed under a semiconductor material under the introduction of a low oxygen concentration gas with an oxygen concentration of 6% by volume showed higher plastic decomposition efficiency as compared with Reference Comparative Example 2 in which heat treatment was performed without a semiconductor material under the introduction of a low oxygen concentration gas with an oxygen concentration of 6% by volume.

[0223] Also, as shown in FIG. 6, residual carbon derived from plastic adhered in lumps on the surface of the sample after the treatment according to Reference Comparative Example 2. On the other hand, as shown in FIG. 5, in the sample after the treatment according to Reference Example 4, such adhesion of residual carbon was not confirmed, and it had a relatively smooth and highly uniform surface similar to the surface of the sample before the treatment shown in FIG. 4.

[0224] ≪Reference Examples 5 to 9≫ In Reference Examples 5 to 9, a two-stage heat treatment was performed on a CFRP plate or a pressure vessel as a plastic-containing material. Then, the decomposition efficiency was evaluated, and the physical properties of the carbon fiber material obtained by the heat treatment were evaluated.

[0225] <Reference Example 5> Reference Example 5 was carried out as follows.

[0226] (Provision and Arrangement of Materials) As the semiconductor material, a carrier having a honeycomb structure with chromium oxide (Cr2O3, purity 99% or more, manufactured by Junsei Chemical Co., Ltd.) applied to the surface thereof was used. The carrier having a honeycomb structure had 13 cells / 25 mm.

[0227] As the plastic-containing material, a CFRP plate having an epoxy resin content ratio of 41% by weight was used. The physical properties of the carbon fiber material contained in the CFRP plate before the treatment are shown in Table 4 as Reference Example 1.

[0228] The furnace volume of the heating furnace was 0.0525 m 3 Therein. Inside the heating furnace, the CFRP plate was placed on the carrier supporting chromium oxide as the semiconductor material. The carrier and the CFRP plate were placed in contact with each other.

[0229] The surface temperature of the CFRP plate was measured by a sensor placed within 5 mm from the surface of the CFRP plate.

[0230] (Heat treatment) The internal temperature of the heating furnace was controlled via the heater output of the heating furnace to raise the internal temperature of the heating furnace. And before the surface temperature of the CFRP plate reached 300 °C, a mixed gas of air with an oxygen concentration of 8% by volume and nitrogen gas was introduced into the heating furnace. The introduction of the mixed gas into the heating furnace was performed by suction at a gas introduction rate of 190 L / min and allowing the mixed gas to flow in from the gas supply section provided in the heating furnace.

[0231] In addition, in Reference Example 5, as well as the following Reference Example 6 and Reference Comparative Example 4, the oxygen concentration inside the heating furnace was measured by an oxygen monitor installed inside the heating furnace. Regarding Reference Examples 7 to 9, the oxygen concentration inside the furnace was determined based on the furnace volume and the gas introduction amount.

[0232] When the surface temperature of the CFRP plate reached 300 °C, the generation of decomposition gas was confirmed.

[0233] Heat treatment was performed for 120 minutes in an atmosphere controlled to an oxygen concentration of 8% by volume by the introduction of the above mixed gas. During the heat treatment, the heater output of the heating furnace was adjusted to raise the surface temperature of the CFRP plate to a first surface temperature of 450 °C.

[0234] (Secondary heat treatment) Then, while maintaining the gas suction pressure, the supply of nitrogen gas was stopped and only air was supplied. After confirming that the oxygen concentration inside the heating furnace became 10% by volume or more, further heat treatment was performed. During the heat treatment for 260 minutes, the surface temperature of the CFRP plate was raised to 500 °C. Incidentally, the average oxygen concentration over 260 minutes was 14% by volume and the maximum oxygen concentration was 18% by volume.

[0235] In Reference Example 5, 0.8 kg of CFRP plates were processed. The processing amount per furnace volume was 15.2 kg / m 3 It was.

[0236] (Residual carbon content) The residual carbon content derived from plastic in the carbon fiber material recovered after heat treatment was determined by thermogravimetric analysis.

[0237] Thermogravimetric analysis was performed as follows: (i) For a 1 - 4 mg sample piece obtained by pulverizing the recovered carbon fiber material, in a thermogravimetric analyzer, at an air supply rate of 0.2 L / min, a heating rate of 5 °C / min, and a recording rate of 1 / 6 s, a thermogravimetric analysis having a process consisting of heating from room temperature to 100 °C, holding at 100 °C for 30 minutes, heating from 100 °C to 400 °C, and holding at 400 °C was performed over a total of 300 minutes. (ii) In a graph plotting the weight loss rate against time, the inflection point of the slope was identified, and the residual carbon content was calculated by subtracting the weight loss rate during the holding period at 100 °C from the value of the weight loss rate at the inflection point.

[0238] Also, for the carbon fiber material recovered after heat treatment, the fiber single - filament diameter and the single - fiber tensile strength were measured, and the Weibull shape factor was calculated.

[0239] (Single - fiber tensile strength) The single - fiber tensile strength was measured in accordance with JIS R7606 as follows: At least 30 single fibers were sampled from the fiber bundle. The diameter of the single fiber was measured in a side - view image of the single fiber taken by a digital microscope to calculate the cross - sectional area. The sampled single fibers were fixed to a perforated mount using an adhesive. The mount with the fixed single fibers was attached to a tensile testing machine, and a tensile test was performed at a gauge length of 10 mm and a strain rate of 1 mm / min to measure the tensile fracture stress. The tensile strength was calculated from the cross - sectional area and the tensile fracture stress of the single fiber. The average of the tensile strengths of at least 30 single fibers was taken as the single - fiber tensile strength.

[0240] (Weibull shape factor) The Weibull shape factor was calculated according to the following formula: lnln{1 / (1 - F)} = m×lnσ + C (where F is the fracture probability determined by the symmetric sample cumulative distribution method, σ is the single fiber tensile strength (MPa), m is the Weibull shape factor, and C is a constant.)

[0241] The Weibull plot was made with lnln{1 / (1 - F)} and lnσ, and the Weibull shape factor m was obtained from the slope of the first-order approximation.

[0242] The evaluation results are shown in Table 4. The fiber fineness is the average of the diameters of at least 30 single fibers measured as described above.

[0243] <Reference Example 6>

[0244] The treatment was carried out in the same manner as in Reference Example 5, except that a pressure vessel was used as the plastic-containing material, the mixed gas was aspirated at a gas introduction rate of 127 L / min, and the oxygen concentration, surface temperature, and heat treatment time were as shown in Table 4 below.

[0245] The pressure vessel treated in Reference Example 6 had an aluminum liner and 44 wt% of FRP (fiber-reinforced plastic), and the FRP contained 31 wt% of reinforcing fibers and 13% of epoxy resin. The reinforcing fibers were mainly composed of carbon fibers and contained a small amount of glass fibers. The capacity of the pressure vessel was 2.0 L.

[0246] The amount of FRP treated in Reference Example 6 was 0.47 kg. The treatment amount per furnace volume was 9.0 kg / m 3 It was.

[0247] The evaluation results of the plastic decomposition efficiency and the evaluation results of the physical properties of the recovered carbon fiber material for Reference Example 6 are shown in Table 4. The average oxygen concentration over 180 minutes of secondary heat treatment was 18 vol%, and the maximum oxygen concentration was 20 vol%.

[0248] The physical properties of the carbon fiber material contained in the pressure vessel before treatment are shown in Table 4 as Reference Example 2.

[0249] <Reference Example 7> The furnace volume of the heating furnace was 0.1435 m 3 Heat treatment was performed in the same manner as in Reference Example 5, except that the mixed gas of superheated steam and air was introduced into the heating furnace at a gas introduction rate of 29 L / min, and the surface temperature and the heat treatment time were as shown in Table 4 below.

[0250] The internal temperature of the heating furnace and the surface temperature of the sample were controlled via the heater output of the heating furnace and the temperature of the superheated steam.

[0251] In Reference Example 7, 1.0 kg of CFRP plates were processed. The processing amount per furnace volume was 7.0 kg / m 3 It was.

[0252] The evaluation results of the plastic decomposition efficiency and the evaluation results of the physical properties of the recovered carbon fiber material for Reference Example 7 are shown in Table 4. In the secondary heat treatment, only air was pushed into the furnace at 29 L / min.

[0253] <Reference Example 8> Treatment was performed in the same manner as in Reference Example 7, except that a pressure vessel was used as the plastic-containing material and the surface temperature and the heat treatment time were as shown in Table 4 below.

[0254] The pressure vessel used in Reference Example 8 is the same as the pressure vessel used in Reference Example 6.

[0255] The amount of FRP processed in Reference Example 8 was 0.47 kg. The processing amount per furnace volume was 3.3 kg / m 3 It was.

[0256] The evaluation results of the plastic decomposition efficiency and the evaluation results of the physical properties of the recovered carbon fiber material for Reference Example 8 are shown in Table 4. In the secondary heat treatment, only air was pushed into the furnace at 29 L / min.

[0257] <Reference Example 9> The furnace volume of the heating furnace was 0.049 m 3 Except that it was so, the mixed gas of superheated steam and air was introduced into the heating furnace at a gas introduction rate of 25 L / min, and the surface temperature and the heat treatment time were as shown in Table 4 below, the treatment was carried out in the same manner as in Reference Example 7.

[0258] In Reference Example 9, a CFRP plate with an epoxy resin ratio of 38% was treated. The processing amount per furnace volume was 1.6 kg / m 3 It was.

[0259] The evaluation results of the plastic decomposition efficiency and the evaluation results of the physical properties of the recovered carbon fiber material for Reference Example 9 are shown in Table 4. In the secondary heat treatment, while continuing the supply of superheated steam, the amount of air was increased, and a gas with an oxygen concentration of 11% by volume was pushed into the furnace at 38 L / min.

[0260] The physical properties of the carbon fiber material contained in the above CFRP plate according to Reference Example 9 before treatment are shown in Table 4 as Reference Example 3.

[0261] ≪Reference Comparative Example 3≫ In Reference Comparative Example 3, the material was provided and arranged in the same manner as in Reference Example 5, and then, without adjusting the oxygen concentration in the atmosphere in the heating furnace, the internal temperature of the heating furnace was raised.

[0262] As a result, excessive self-heating occurred at the heater output when the surface temperature of the CFRP plate reached 300 °C, and the surface temperature of the CFRP plate rose to 485 °C. The results are described in Table 4.

[0263] In Reference Comparative Example 3, 0.8 kg of CFRP plates were treated. The processing amount per furnace volume was 15.2 kg / m 3It was.

[0264] <<Reference Comparative Example 4>>

[0265] The treatment was carried out in the same manner as in Reference Example 6, except that no semiconductor material was used.

[0266] The amount of FRP processed in Reference Comparative Example 4 was 0.47 kg. The processing amount with respect to the furnace internal volume was 9.0 kg / m 3 It was.

[0267] Regarding Reference Comparative Example 4, the evaluation results of the physical properties of the recovered carbon fiber material are shown in Table 4. The average oxygen concentration over 180 minutes of secondary heat treatment was 18% by volume, and the maximum oxygen concentration was 20% by volume.

[0268]

Table 4

[0269] As can be seen in Table 4, Reference Examples 5 to 9, in which a low-oxygen-concentration gas with an oxygen concentration of 6 to 8% by volume was introduced, primary heat treatment was carried out in the presence of a semiconductor material, and then secondary heat treatment was further carried out under the increased oxygen concentration, showed a low residual carbon amount and very excellent plastic decomposition efficiency.

[0270] Also, in Reference Comparative Example 3 where the oxygen concentration was not controlled, excessive self-heating occurred, whereas in Reference Examples 5 to 9 where a low-oxygen-concentration gas with an oxygen concentration of 6 to 8% by volume was introduced into the heating furnace, no excessive self-heating was observed. In Reference Comparative Example 3, since the decomposition treatment was started without previously lowering the oxygen concentration, the oxygen concentration became excessive, and as a result, it is considered that the control of the decomposition temperature in the presence of the semiconductor material could not be appropriately carried out.

[0271] Furthermore, the carbon fiber materials recovered in Reference Examples 5 to 9 had the fiber single filament diameter and the single fiber tensile strength maintained at approximately the same level as those of the carbon fiber materials before treatment (Reference Examples 1 to 3), and the Weibull shape factor of the single fiber tensile strength was high. That is, in Reference Examples 5 to 9, carbon fiber materials having physical properties superior to those of the carbon fiber materials before manufacturing the carbon fiber reinforced plastic were recovered.

[0272] Furthermore, the carbon fiber materials recovered in Reference Example 6 involving heat treatment under a semiconductor material had excellent quality, particularly in terms of the single fiber tensile strength and the Weibull shape factor, compared to the carbon fiber materials recovered in Comparative Reference Example 4 where heat treatment was performed without a semiconductor material.

Description of Signs

[0273] 100 Carbon fiber reinforced thermoplastic resin strands according to the present disclosure 110 Core component 120 Sheath component 11 Semiconductor material 12 Plastic-containing material 20 Heating furnace 21 Carrier having a semiconductor material 22 Plastic-containing material 23 Heat source (heater) 24 Gas supply unit 25 Exhaust port 26 Internal space of the heating furnace 27 Temperature sensor

Claims

1. A carbon fiber reinforced thermoplastic resin strand comprising a blended yarn containing recycled carbon fiber and thermoplastic resin fiber, wherein the recycled carbon fiber has a single fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, the recycled carbon fiber contains a residual carbon component, and the content of the residual carbon component is more than 0% by weight and 5.0% by weight or less based on the recycled carbon fiber, and the content of the recycled carbon fiber is more than 60% by weight and 98% by weight or less based on the blended yarn A carbon fiber reinforced thermoplastic resin strand characterized by the above.

2. The carbon fiber reinforced thermoplastic resin strand according to claim 1, wherein the content of the recycled carbon fiber is more than 70% by weight and 98% by weight or less based on the blended yarn.

3. The carbon fiber reinforced thermoplastic resin strand according to claim 1 or 2, wherein the average lengths of the recycled carbon fiber and the thermoplastic resin fiber are each 20 mm or more and 80 mm or less.

4. The carbon fiber reinforced thermoplastic resin strand according to any one of claims 1 to 3, wherein the thermoplastic resin fiber is selected from polyolefin resin fiber, polyester resin fiber, polyamide resin fiber, polyether ketone resin fiber, polycarbonate resin fiber, phenoxy resin fiber, polyphenylene sulfide resin fiber, and mixtures thereof.

5. Having a core-sheath structure, the blended yarn being the core component, and the thermoplastic resin being the sheath component, The carbon fiber reinforced thermoplastic resin strand according to any one of claims 1 to 4, characterized by the above.

6. The carbon fiber reinforced thermoplastic resin strand according to claim 5, wherein the melting point T0 (°C) of the thermoplastic resin as the sheath component is lower than the melting point T1 (°C) of the thermoplastic resin fiber contained in the blended yarn, and T1 - T0 > 10.

7. Manufacturing recycled carbon fiber by decomposing the plastic component contained in a carbon fiber-containing plastic product by a semiconductor thermal activation method, and Manufacturing a blended yarn by blending the recycled carbon fiber and the thermoplastic resin fiber A method for manufacturing a carbon fiber reinforced thermoplastic resin strand according to any one of claims 1 to 6, including the above.

8. A method for manufacturing a three-dimensional shaped object by a fused deposition method using the carbon fiber reinforced thermoplastic resin strand according to any one of claims 1 to 6.

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