Blended yarns of recycled carbon fibers and thermoplastic resin fibers, and carbon fiber-reinforced thermoplastic resin pellets

Abstract

To provide a blended yarn of recycled carbon fiber and thermoplastic resin fiber, which can be stably produced from a raw material recycled carbon fiber obtained through decomposition by heat treatment.SOLUTION: A blended yarn comprises a recycled carbon fiber and a thermoplastic resin fiber. The recycled carbon fiber has a single fiber tensile strength of 3.0 GPa or more, and a Weibull shape coefficient of 6.0 or more. The recycled carbon fiber contains a residual carbon component at a content of more than 0 wt.% and 5.0 wt.% or less relative to the recycled carbon fiber.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to blended yarns of recycled carbon fibers and thermoplastic resin fibers, and carbon fiber-reinforced thermoplastic resin pellets formed from these blended yarns. The present invention also relates to methods for producing these materials. [Background technology]

[0002] Carbon fiber is used as a reinforcing fiber for thermoplastic resins due to its excellent specific strength, specific modulus of elasticity, and lightweight properties. Carbon fiber reinforced polymer (CFRP) composite materials are used in a wide range of applications, including sports and general industrial use, as well as aerospace and automotive applications.

[0003] One form of carbon fiber reinforced resin composite material is carbon fiber reinforced thermoplastic resin pellets. There are two types of carbon fiber reinforced thermoplastic resin pellets: long fiber reinforced pellets, which are produced by cutting resin strands in which continuous carbon fibers are coated with thermoplastic resin, and short fiber reinforced pellets, which are produced by cutting resin strands in which discontinuous carbon fibers are kneaded and dispersed in thermoplastic resin. Compared to short fiber reinforced pellets, long fiber reinforced pellets contain carbon fibers with relatively long fibers, and when supplied to injection molding machines, etc., they can be used to produce carbon fiber-containing products with superior mechanical properties.

[0004] In recent years, there has been a growing demand for recycled carbon fibers recovered from used carbon fiber-containing products. Most recycled carbon fibers are discontinuously cut, and methods for producing spun yarn from recycled carbon fibers have been investigated so that they can be treated the same as unused continuous carbon fibers as raw materials for carbon fiber-containing products such as carbon fiber reinforced resin composites.

[0005] Patent Document 1 describes a method for producing spun yarn by blending a carbide containing recycled carbon fibers, obtained by heat-treating scrap of carbon fiber reinforced resin composite material at a temperature of 900°C or higher, with thermoplastic resin fibers.

[0006] Patent Document 2 describes a method for utilizing spun yarn made by blending cut, unused discontinuous carbon fibers with synthetic fibers, mimicking recycled carbon fibers that do not contain carbides, rather than recycled carbon fibers recovered through heat treatment of carbon fiber reinforced resin composite materials.

[0007] Patent Document 3 describes a method for producing spun yarn using only carbon fibers or recycled carbon fibers, without blending them with thermoplastic fibers. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2018-35492 [Patent Document 2] Japanese Patent Publication No. 2018-123438 [Patent Document 3] Japanese Patent Publication No. 2020-90738 [Overview of the project] [Problems that the invention aims to solve]

[0009] Methods for decomposing used carbon fiber reinforced resin composite materials to obtain recycled carbon fibers include decomposing the resin components by heat treatment, dissolving and removing them using solvents, and electrolysis. However, the method that has been widely used conventionally is decomposition by heat treatment.

[0010] However, there were cases where it was not possible to manufacture blended yarns with thermoplastic resin fibers using recycled carbon fibers obtained by heat treatment and decomposition as raw materials.

[0011] This disclosure aims to provide a blended yarn of thermoplastic resin fibers that can be stably manufactured using recycled carbon fibers obtained by a heat treatment and decomposition method as a raw material. Furthermore, this disclosure aims to provide carbon fiber-reinforced thermoplastic resin fiber pellets formed from this blended yarn. [Means for solving the problem]

[0012] According to the following aspects of the present invention, the above problems can be solved: <Aspect 1> A blended yarn containing recycled carbon fiber and thermoplastic resin fiber, 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 residual carbon components, and the content of the residual carbon components is greater than 0% by weight and 5.0% by weight or less relative to the recycled carbon fiber. A blended yarn characterized by the following features. <Aspect 2> The blended yarn according to embodiment 1, wherein the content of the recycled carbon fibers is more than 50% by weight and 98% by weight or less relative to the blended yarn. <Aspect 3> The blended yarn according to embodiment 1 or 2, wherein the average length of the recycled carbon fiber and the thermoplastic resin fiber is 20 mm or more and 80 mm or less, respectively. <Aspect 4> The blended yarn according to any one of embodiments 1 to 3, wherein the thermoplastic resin fiber contained in the blended yarn is selected from polyolefin resin fiber, polyester resin fiber, polyamide resin fiber, polyetherketone resin fiber, polycarbonate resin fiber, phenoxy resin fiber, and polyphenylene sulfide resin fiber, and mixtures thereof. <Aspect 5> It has a core-sheath structure, The blended yarn described in any one of the embodiments 1 to 4 is a core component, and The thermoplastic resin is the sheath component. Carbon fiber reinforced thermoplastic resin pellets characterized by the following features. <Aspect 6> The carbon fiber reinforced thermoplastic resin pellet according to embodiment 5, wherein the thermoplastic resin as the sheath component is selected from polyolefin resin, polyester resin, polyamide resin, polyetherketone resin, polycarbonate resin, phenoxy resin, and polyphenylene sulfide resin, and mixtures thereof. <Aspect 7> 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 fiber, and satisfies T1 - T0 > 10. The carbon fiber reinforced thermoplastic resin pellet according to Aspect 5 or 6. <Aspect 8> The carbon fiber reinforced thermoplastic resin pellet according to any one of Aspects 5 to 7, having a cut length of 3 mm or more and 10 mm or less. <Aspect 9> Decomposing the plastic component contained in the carbon fiber-containing plastic product by the semiconductor thermal activation method to produce recycled carbon fiber, and Blending the recycled carbon fiber and the thermoplastic resin fiber. A method for producing a blended fiber, comprising: <Aspect 10> A method for producing a core-sheath structured carbon fiber reinforced thermoplastic resin pellet, comprising coating the blended fiber obtained by the method according to Aspect 9 with a thermoplastic resin.

Advantages of the Invention

[0013] According to the present invention, it is possible to provide a blended fiber with a thermoplastic resin fiber, which is stably produced using recycled carbon fiber obtained by a method of heat treatment and decomposition as a raw material. Further, according to the present invention, it is possible to provide a carbon fiber reinforced thermoplastic resin pellet formed from the blended fiber.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 is a schematic general view of a carbon fiber reinforced thermoplastic resin pellet according to the present disclosure, and a carbon fiber reinforced thermoplastic resin strand used in the process of manufacturing the pellet according to the present disclosure. [Figure 2] FIG. 2 is a conceptual cross-sectional view for explaining a decomposition method according to the present invention. [Figure 3] FIG. 3 is a schematic cross-sectional view schematically showing one embodiment of the decomposition method according to the present disclosure. [Figure 4] FIG. 4 is a photograph of a CFRP plate before heat treatment. [Figure 5] Figure 5 is a photograph of the CFRP board after undergoing the processing according to Reference Example 4. [Figure 6] Figure 6 is a photograph of the CFRP board after undergoing the treatment according to Reference Comparative Example 2. [Modes for carrying out the invention]

[0015] The blended yarn of recycled carbon fiber and thermoplastic resin fiber relating to this disclosure is The recycled carbon fiber has a single-fiber tensile strength of 3.0 GPa or higher and a Weibull shape factor of 6.0 or higher, and The recycled carbon fiber contains residual carbon components, and the content of the residual carbon components is greater than 0% by weight and 5.0% by weight or less relative to the recycled carbon fiber. It is characterized by the following.

[0016] The blended yarn according to this disclosure can be manufactured by a general spinning method. This spinning method may include combing, drawing, and roving steps. Here, the combing step may be a step of separating and unraveling the discontinuous aggregates of individual fibers to open them and orienting the mixed single fibers in one direction to produce a thick sliver; the drawing step may be a step of joining several slivers together and stretching them to further improve the degree of fiber orientation; and the roving step may be a step of further stretching the sliver and twisting it to wind up the blended yarn.

[0017] The tensile strength of sliver is given by the frictional force due to contact or entanglement between individual fibers. Therefore, if each fiber opens well and the contact area or entanglement between individual fibers increases, the tensile strength improves. Furthermore, suppressing the breakage of individual fibers and avoiding an increase in the number of joints between individual fibers can suppress the decrease in tensile strength. Increasing the twist also increases the contact area between individual fibers, thus improving the tensile strength. To compensate for the frictional force, an oil may be applied to each fiber or to the sliver as needed.

[0018] Generally, carbon fibers have poor crimpability and high surface smoothness, resulting in weak entanglement between individual fibers. Furthermore, their high modulus of elasticity, low elongation, and hardness make them relatively easy to break. Thermoplastic resin fibers blended with recycled carbon fibers enhance the entanglement between individual fibers, and even a small amount of thermoplastic resin fibers can significantly improve the tensile strength of the sliver.

[0019] Although there is no intention to limit the scope to theory, the blended yarn relating to this disclosure has a high Weibull shape factor in the tensile strength of the single fibers of recycled carbon fiber. As a result, the variation in tensile strength is small, and compared to general unused carbon fiber with equivalent tensile strength, there are relatively few single fibers with low tensile strength. Therefore, it is thought that the breakage of single fibers of recycled carbon fiber is relatively suppressed.

[0020] Furthermore, a general characteristic of recycled carbon fibers obtained by heat treatment and decomposition is that oxidation defects tend to form in the recycled carbon fibers, which reduces their tensile strength, and that carbides from the resin components may be present in the recycled carbon fibers as residual carbon components. These residual carbon components can strongly bind the individual fibers of the recycled carbon fiber together. In the manufacture of spun yarn, these residual carbon components are thought to hinder fiber opening and entanglement during the combing process.

[0021] Although there is no intention to limit the scope by theory, the blended yarn relating to this disclosure uses recycled carbon fibers with a relatively low residual carbon content as raw material, making it easier to achieve entanglement between individual fibers.

[0022] For the reasons stated above, the blended yarn according to this disclosure is likely to easily obtain sufficient tensile strength for stable production without yarn slippage under spinning tension, due to the frictional force generated by the entanglement of the single fibers.

[0023] This disclosure also includes carbon fiber reinforced thermoplastic resin pellets having the blended yarns described above. These carbon fiber reinforced thermoplastic resin pellets are Having a core-sheath structure, The blended yarn is the core component, and The thermoplastic resin is the sheath component. It is characterized by the following.

[0024] The carbon fiber reinforced thermoplastic resin pellets according to this disclosure can be manufactured in the same manner as general long fiber reinforced pellet manufacturing methods, except that the blended yarn according to this disclosure is used as a substitute for continuous carbon fibers. This is achieved by cutting resin strands obtained by coating blended yarn with thermoplastic resin. Therefore, compared to short fiber reinforced pellets manufactured by cutting resin strands in which discontinuous carbon fibers are kneaded and dispersed in thermoplastic resin, the pellets can contain recycled carbon fibers with relatively long fiber lengths. In other words, the carbon fiber reinforced thermoplastic resin pellets according to this disclosure can be supplied to injection molding machines and the like to manufacture carbon fiber-containing products with superior mechanical properties.

[0025] The invention related to this disclosure will be described in more detail below.

[0026] <Recycled carbon fiber> Recycled carbon fiber contains carbon fiber components and carbon components other than carbon fiber components (particularly residual carbon components). Typically, in recycled carbon fiber, carbon components other than carbon fiber components are attached to the surface of the carbon fiber components.

[0027] The recycled carbon fiber relating to this disclosure is characterized by having a single-fiber tensile strength of 3.0 GPa or more and a Weibull shape factor of 6.0 or more, and containing residual carbon components, the content of which is greater than 0% by weight and 5.0% by weight or less relative to the recycled carbon fiber.

[0028] The recycling method is not particularly limited as long as the recycled carbon fiber has the aforementioned characteristics, but for example, it may be recycled carbon fiber obtained by heat-treating carbon fiber-containing plastic products such as carbon fiber reinforced plastic (CFRP).

[0029] Particularly preferred is the recycled carbon fiber obtained by a semiconductor thermal activation method. That is, a particularly preferred embodiment of the present disclosure includes recycled carbon fiber produced by decomposing plastic components contained in a carbon fiber-containing plastic product by a semiconductor thermal activation method.

[0030] The "thermal activation of semiconductors" (TASC method) is a method that utilizes the thermal activation of semiconductors (TASC) to decompose compounds such as polymers.

[0031] A method for obtaining recycled carbon fibers having the properties described herein using a semiconductor thermal activation method will be described later.

[0032] <Tensile strength of a single fiber> The tensile strength of the single fiber is preferably 3.1 GPa or higher, 3.2 GPa or higher, 3.3 GPa or higher, or 3.4 GPa or higher. There is no particular upper limit to the tensile strength of the single fiber, but it may be 6.0 GPa or lower.

[0033] The tensile strength of a single fiber can be measured in accordance with JIS R7606 as follows: At least 30 single fibers are taken from the fiber bundle, By measuring the diameter of a single fiber in a lateral image of a single fiber taken with a digital microscope, the cross-sectional area is calculated. The sampled single fibers are fixed to a perforated cardboard base using adhesive. A base with a single fiber fixed to it is attached to a tensile testing machine, and a tensile test is performed with a test length of 10 mm and a strain rate of 1 mm / min to measure the tensile breaking stress. The tensile strength is calculated from the cross-sectional area and tensile fracture stress of a single fiber. The average tensile strength of at least 30 individual fibers is defined as the single-fiber tensile strength.

[0034] <Weibull shape factor> The Weibull shape factor is preferably 6.5 or higher, 7.0 or higher, 7.5 or higher, 8.0 or higher, or 8.5 or higher. The upper limit of the Weibull shape factor is not particularly limited, but may be 15.0 or lower. A high Weibull shape factor for single-fiber tensile strength indicates small variation in single-fiber tensile strength.

[0035] 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 probability of failure 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.

[0036] By plotting lnln{1 / (1-F)} and lnσ using a Weibull plot, the Weibull shape coefficient m can be determined from the linearly approximated slope.

[0037] <Carbon fiber components> The carbon fiber components in recycled carbon fibers typically originate from carbon fibers contained in carbon fiber-containing products that served as raw materials for the recycled carbon fibers. The carbon fiber components in recycled carbon fibers may be modified during the manufacturing process of the recycled carbon fibers by heat treatment or other methods.

[0038] The carbon fiber component in recycled carbon fiber may be, for example, PAN-based carbon fiber or pitch-based carbon fiber.

[0039] 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 multiple single threads (single fibers, 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. Furthermore, 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.

[0040] <Residual carbon content> The residual carbon components contained in recycled carbon fibers are, in particular, residual carbon derived from the resin contained in the carbon fiber-containing plastic products used as raw materials in the production of recycled carbon fibers.

[0041] In this disclosure, the residual carbon component is greater than 0% by weight and 5.0% by weight or less relative to the recycled carbon fiber. In this case, a blended yarn with improved resistance to yarn shedding under spinning process tension can be obtained.

[0042] Furthermore, if the residual carbon content is greater than 0% by weight and 5.0% by weight or less, contamination due to a relatively high amount of carbon (especially charcoal) can be avoided, and carbon components that could become foreign matter when manufacturing carbon fiber-containing products etc. using blended yarn as a material can be reduced.

[0043] Preferably, the residual carbon content is 4.0% by weight or less, 3.0% by weight or less, or 2.0% by weight or less relative to the recycled carbon fibers. It is preferable that the residual carbon content be reduced as much as possible, but it may be 0.1% by weight or more, 0.2% by weight or more, 0.4% by weight or more, 0.6% by weight or more, 0.8% by weight or more, 1.0% by weight or more, or 1.2% by weight or more relative to the carbon fibers.

[0044] The residual carbon content in recycled carbon fibers can be measured by thermogravimetric analysis (TGA).

[0045] The residual carbon content can be measured by thermogravimetric analysis using the following procedure: (i) For a sample piece of 1-4 mg obtained by crushing recycled carbon fiber, a thermogravimetric analyzer was used with an air supply rate of 0.2 L / min, a heating rate of 5°C / min, and a recording rate of 1 / 6 s. Temperature increase from room temperature to 100°C, Holding at 100°C for 30 minutes, Temperature increase from 100°C to 400°C, and, Holding at 400°C The process involves thermogravimetric analysis lasting 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 residual carbon amount by subtracting the weight loss rate during the holding period at 100°C from the weight loss rate value at that inflection point.

[0046] Furthermore, if the inflection point of the slope cannot be identified under the above conditions, instead of thermogravimetric analysis over a total of 300 minutes, thermogravimetric analysis over a total of approximately 600 minutes, including holding at 400°C for 480 minutes, may be performed. Moreover, instead of holding at 400°C for 480 minutes, holding at a specific temperature in the range of over 400°C and up to 500°C may be performed for 480 minutes.

[0047] Furthermore, if the recycled carbon fibers contain resin derived from sizing agents or the like, the above measurements can be performed after removing the resin.

[0048] <Thermoplastic resin fiber> Examples of thermoplastic resin fibers contained in the blended yarn according to this disclosure include polyolefin resin fibers (e.g., polypropylene resin fibers and polyethylene resin fibers), polyester resin fibers (e.g., polyethylene terephthalate resin fibers, polybutylene terephthalate resin fibers, and polylactic acid resin fibers), polyamide resin fibers, polyetherketone resin fibers, polycarbonate resin fibers, phenoxy resin fibers, and polyphenylene sulfide resin fibers. The thermoplastic resin fiber may be just one type, or a mixture of two or more types of thermoplastic resin fibers.

[0049] Blended yarn Blended yarn is a spun yarn containing recycled carbon fibers and thermoplastic resin fibers. Blended yarn may also include, for example, a binder applied to the recycled carbon fibers. Alternatively, blended yarn may be a spun yarn consisting substantially of recycled carbon fibers and thermoplastic resin fibers.

[0050] <Content of recycled carbon fiber> The recycled carbon fiber content is preferably more than 50% by weight and 98% by weight or less relative to the blended yarn. Particularly preferably it is 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.

[0051] If the recycled carbon fiber content exceeds 50% by weight, when manufacturing carbon fiber-reinforced thermoplastic resin pellets according to this disclosure using these recycled carbon fibers, it is not necessary to reduce the amount of thermoplastic resin coating in order to increase the carbon fiber content, and the stability of the coating process is improved. If the recycled carbon fiber content is 98% by weight or less, sufficient entanglement with the blended thermoplastic resin fibers is achieved, making it less likely for yarn to slip out due to the tension of the spinning process.

[0052] The content of thermoplastic resin fibers may be 50% by weight or less, 40% by weight or less, or 30% by weight or less relative 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.

[0053] <Average fiber length> The recycled carbon fibers contained in the blended yarn may have an average length of 20 mm to 80 mm. Fibers having this length range can be obtained, for example, by cutting relatively long fibers. The average length of the recycled carbon fibers may be 20 mm or more, 30 mm or more, or 40 mm or more, and / or 80 mm or less, 70 mm or less, or 60 mm or less.

[0054] The thermoplastic resin fibers contained in the blended yarn may have an average length of 20 mm to 80 mm. Fibers having this length range can be obtained, for example, by cutting relatively long fibers. The average length of the thermoplastic resin fibers may be 20 mm or more, 30 mm or more, or 40 mm or more, and / or 80 mm or less, 70 mm or less, or 60 mm or less.

[0055] In the production of blended yarns, if the average length of the recycled carbon fiber and thermoplastic resin fiber is 20 mm or more, the resistance of the sliver to yarn shedding under spinning tension can be improved. When the average length of recycled carbon fibers and thermoplastic resin fibers is 80 mm or less, entanglement with manufacturing equipment parts can be reduced.

[0056] The average length of recycled carbon fibers and thermoplastic resin fibers can be calculated by measuring the length of 50 fibers visually using calipers or similar tools, or by using images acquired with a digital camera or optical microscope, and then averaging the measured values.

[0057] <Method for manufacturing blended yarn> As described above, the blended yarn of recycled carbon fiber and thermoplastic resin fiber according to this disclosure can be manufactured by a general spinning method. That is, the method for manufacturing the blended yarn according to this disclosure may include a combing step of separating and unraveling the discontinuous aggregates of each fiber to open them and orienting the mixed single fibers in one direction to produce a thick sliver, a drawing step of combining several slivers and stretching them to further improve the degree of fiber orientation, and a roving step of further stretching and twisting the sliver to wind up the blended yarn.

[0058] A binder can be applied when manufacturing blended yarn. The binder, in particular, plays a role in promoting the bonding of recycled carbon fibers to thermoplastic resin fibers. The timing of binder application is not particularly limited, but it may be applied directly to the recycled carbon fibers or to the blended yarn containing recycled carbon fibers and thermoplastic resin fibers. The binder may be, for example, an epoxy resin. The method of binder application is not particularly limited and known methods can be used. For example, the binder can be applied by immersing the recycled carbon fibers or blended yarn in a binder solution or dispersion and then drying it. The amount of binder may be 0.1% to 25% by weight, or 1% to 20% by weight, relative to the recycled carbon fibers.

[0059] Carbon fiber reinforced thermoplastic resin pellets According to the present invention, a carbon fiber-reinforced thermoplastic resin pellet having a core-sheath structure is provided, wherein the blended yarn according to the present disclosure is the core component and the thermoplastic resin is the sheath component. Compared to short-fiber-reinforced pellets obtained by kneading and dispersing recycled carbon fibers in a thermoplastic resin, the pellet according to the present disclosure contains recycled carbon fibers with relatively long fiber lengths, and when supplied to an injection molding machine or the like, it is possible to manufacture carbon fiber-containing products with superior mechanical properties.

[0060] <Method for manufacturing carbon fiber reinforced thermoplastic resin pellets> The carbon fiber reinforced thermoplastic resin pellets with a core-sheath structure according to this disclosure can be manufactured by a method that includes manufacturing carbon fiber reinforced thermoplastic resin strands by coating blended yarn with thermoplastic resin, and cutting the strands. More specifically, as described above, they can be manufactured by cutting resin strands coated with thermoplastic resin, similar to the general method for manufacturing long fiber reinforced pellets, except that the blended yarn according to this disclosure is used instead of continuous carbon fibers. That is, they can be manufactured by a method that includes a coating step in which a blended yarn, which is continuously conveyed while being wound, is passed through a die into which molten thermoplastic resin is continuously supplied from a separate supply port from the blended yarn, and a cutting step in which the carbon fiber reinforced thermoplastic resin strands discharged from the die are cut after they have cooled.

[0061] <Thermoplastic resin> Examples of thermoplastic resins used for coating in the production of the above-mentioned pellets (i.e., thermoplastic resins constituting the sheath component of the pellets) 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 a single type or a mixture of two or more thermoplastic resins.

[0062] Furthermore, the thermoplastic resin constituting the sheath component of the pellet may be of the same type as the thermoplastic resin fibers contained in the blended yarn according to this disclosure, or it may be of a different type. In particular, it is preferable that the melting point (T0 (°C)) of the thermoplastic resin constituting the sheath component of the pellet is more than 10 lower than the melting point (T1 (°C)) of the thermoplastic resin fibers contained in the blended yarn according to this disclosure. In this case, when manufacturing the carbon fiber reinforced thermoplastic resin pellets according to this disclosure, it becomes easier to set manufacturing conditions in which the thermoplastic resin fibers contained in the blended yarn do not melt, and only the thermoplastic resin coating the blended yarn melts, which can allow the blended yarn to be stably passed through the die.

[0063] Furthermore, the thermoplastic resin used for the coating treatment may be blended with various polymers, fillers, stabilizers, pigments, etc., to the extent that it does not impair mechanical strength, in order to improve fluidity, gloss, flame retardancy, thermal stability, weather resistance, impact resistance, etc.

[0064] <Pellet core sheath structure> The carbon fiber reinforced thermoplastic resin pellets relating to this disclosure are manufactured by cutting (slicing) carbon fiber reinforced thermoplastic resin strands obtained by coating the blended yarn relating to this disclosure with a thermoplastic resin. Therefore, the blended yarn becomes the core component and the thermoplastic resin becomes the sheath component.

[0065] Regarding the proportion of thermoplastic resin as the sheath component in carbon fiber reinforced thermoplastic resin pellets with a core-sheath structure, it is preferable that the amount of thermoplastic resin as the sheath component be 50 to 1000 parts by weight, more preferably 100 to 750 parts by weight, and most preferably 250 to 500 parts by weight, per 100 parts by weight of recycled carbon fiber contained in the blended yarn.

[0066] <Pellet cutting length> The cut length of the pellet is preferably 3 mm to 10 mm. Particularly preferably it may be 5 mm or less. The cut length of the pellet corresponds in particular to the length in the axial direction of the core structure of the pellet.

[0067] If the pellet cutting length is 3 mm or more, the average length of the recycled carbon fibers will be relatively long, which may further improve the mechanical properties of carbon fiber-containing products made from pellets as a molding material. If the pellet cutting length is 10 mm or less, the recycled carbon fibers will disperse more easily during molding, which may further improve the mechanical properties of carbon fiber-containing products.

[0068] There are no particular restrictions on the diameter of the core-sheath type pellet, but it may be between 1 / 10 and 2 times the pellet's cut length, and preferably between 1 / 4 and 1 time the pellet's cut length. If the pellet's diameter is too small, there may be areas that cannot be covered. Conversely, if the pellet's diameter is too large, it may not feed properly into the molding machine, making molding difficult.

[0069] The cut length and diameter of the pellets can be calculated by visually measuring the cut length or diameter of 30 or more pellets using calipers or similar tools, or by measuring images acquired with a digital camera or optical microscope, and then averaging the measured values.

[0070] Figure 1 is a schematic diagram illustrating a core-sheath structure carbon fiber reinforced thermoplastic resin pellet 200 according to this disclosure. The figure is a schematic diagram for illustrative purposes and is not to scale. The core-sheath structure pellet 200 has a core component 210 and a sheath component 220. The pellet 200 also has a cut length L and a diameter R. The core-sheath structure pellet 200 can be manufactured by cutting (cutting process, "C" in Figure 1) a core-sheath structure carbon fiber reinforced thermoplastic resin strand 100 having a core component 110 made of blended yarn and a sheath component 120 made of thermoplastic resin.

[0071] ≪Method for producing recycled carbon fiber using the semiconductor thermal activation method≫ A method for obtaining recycled carbon fibers having the properties described herein using a semiconductor thermal activation method is described below. First, a method for decomposing a plastic-containing material is described, and then a method for recovering inorganic materials (carbon fibers) from a plastic-containing material containing plastic and inorganic materials (carbon fibers) using this decomposition method is described.

[0072] <Method for decomposing plastic-containing materials> The method for decomposing plastic-containing materials related to this disclosure is: A plastic-containing material is heated to a first surface temperature in a heating furnace atmosphere where a low-oxygen gas with an oxygen concentration of less than 10% by volume is introduced, in the presence of a semiconductor material, thereby decomposing the plastic in the plastic-containing material. Includes.

[0073] Figure 2 is a conceptual cross-sectional view illustrating 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. Note that there is no intention to limit the present invention by theory.

[0074] When the semiconductor material 11 is heated in an oxygen atmosphere, holes h are released into the semiconductor material 11. + and electronic e - This electron e is generated, - It reacts with oxygen (O2) in the atmosphere to form O2 - It is thought that radicals (reactive oxygen species) are generated. Then, radical propagation occurs in the plastic-containing material 12, which is located adjacent to the semiconductor material 11, causing the plastic-containing material 12 to decompose into low-molecular-weight components, and further to be oxidatively decomposed into decomposition gases such as CO2, H2O, and CH4. It is thought that the radicals promote the oxidative decomposition of the plastic by extracting hydrogen from the plastic.

[0075] By using semiconductor materials, the heat required to decompose plastics can be reduced compared to cases where semiconductor materials are not used, and as a result, energy consumption can be reduced.

[0076] Conventional plastic decomposition methods based on the thermal activity of semiconductors sometimes resulted in excessive oxidative heat generation during the heating process. It is believed that this was because conventional methods involved heating in an atmosphere with uncontrolled oxygen concentration, leading to the generation of excessive radicals and, consequently, excessive oxidative heat generation.

[0077] In response to this, the inventors of this case have found that even in the presence of semiconductor materials, by keeping the oxygen concentration at a relatively low level, it is possible to efficiently heat-treat plastics while suppressing excessive oxidation and heat generation.

[0078] In particular, in the initial stages of thermal decomposition of plastics, there is a high risk of excessive oxidative heat generation due to the relatively large amount of plastic present. In contrast, the method according to this disclosure efficiently performs heat treatment at a relatively low oxygen concentration, so it is possible to suppress the generation of excessive oxidative heat even in the initial stages of decomposition.

[0079] Therefore, according to the method of this 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, it is possible to suppress excessive oxidation heat generation and achieve a decomposition treatment with improved stability.

[0080] The disassembly method according to the present invention will be described with reference to drawings illustrating exemplary embodiments.

[0081] Figure 3 is a schematic cross-sectional view showing one embodiment of the disassembly method according to the present disclosure. The heating furnace 20 shown in Figure 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 placed 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 Figure 3, a plastic-containing material 22 is placed in contact with the carrier 21.

[0082] The temperature of the atmosphere in the internal space 26 of the heating furnace 20 is controlled via the heat source (heater) 23 of the heating furnace 20, thereby allowing the surface temperature of the plastic-containing material 22 to reach a specific temperature. The surface temperature of the plastic-containing material 22 can be measured via a temperature sensor 27 placed within 5 mm of the surface of the plastic-containing material 22.

[0083] A low-oxygen 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. The oxygen concentration of the atmosphere inside the heating furnace 20 can be controlled by setting the introduction rate of the low-oxygen gas according to the furnace volume. The low-oxygen gas can be forced into the heating furnace, for example, through a gas supply unit provided in the heating furnace, or it can be drawn into the heating furnace by applying suction pressure to the exhaust port 25.

[0084] Low-oxygen gases are, for example, mixtures of air and nitrogen gas. By selecting the ratio of air to nitrogen gas, the oxygen concentration inside the heating furnace can be controlled.

[0085] In an atmosphere where the oxygen concentration is controlled to less than 10% by volume by introducing a low-oxygen gas, the plastic-containing material is heated to a first surface temperature, for example, 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 these decomposition gases are discharged from the exhaust port 25 of the heating furnace 20.

[0086] After the heat treatment at an oxygen concentration of less than 10% by volume as described above, a further heat treatment can be performed with an oxygen concentration of 10% by volume or more.

[0087] Furthermore, inorganic materials contained in the plastic-containing material can be recovered after heat treatment.

[0088] The disassembly method related to this disclosure will be explained in more detail below.

[0089] <Plastic-containing materials> Plastic-containing materials contain plastic. Plastic-containing materials may be plastic materials or plastic composite materials.

[0090] Examples of plastics contained in plastic-containing materials include thermoplastic resins and thermosetting resins.

[0091] Examples of thermoplastic resins contained in plastic-containing materials 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.

[0092] Examples of thermosetting resins contained in plastic-containing materials include phenolic resins, urethane foam resins, polyurethane resins, urea resins, epoxy resins, unsaturated polyester resins, melamine resins, alkyd resins, vinyl ester resins, and cyanate resins.

[0093] The plastic-containing material may contain at least one selected from the group consisting of thermoplastic resins and thermosetting resins.

[0094] (Plastic composite materials) Plastic-containing materials are, in particular, plastic composite materials. Examples of plastic composite materials include fiber-reinforced plastics (FRP). Carbon fiber is an example of a reinforcing fiber contained in fiber-reinforced plastics.

[0095] (Carbon fiber reinforced plastic) Plastic composite materials are, in particular, carbon fiber-containing plastic products such as carbon fiber reinforced plastics (CFRP). Carbon fiber reinforced plastics contain plastic and carbon fiber material. Carbon fiber reinforced plastics may also contain other components and / or materials (e.g., reinforcing fibers other than carbon fiber, resin molded products, metals, ceramics, etc.).

[0096] The carbon fibers contained in carbon fiber reinforced plastics are not particularly limited, but examples include PAN-based carbon fibers and pitch-based carbon fibers. The carbon fibers may be of one type or composed of two or more types.

[0097] The carbon fiber material contained in the carbon fiber reinforced plastic may be in any form, for example, a bundle of carbon fibers, a fabric formed from a bundle of carbon fibers, or a nonwoven fabric of carbon fibers.

[0098] <Introduction of low-oxygen gas> The method relating to this disclosure, A low-oxygen gas with an oxygen concentration of less than 10% by volume is introduced into the atmosphere of the heating furnace.

[0099] Preferably, the oxygen concentration of the low-oxygen gas introduced into the atmosphere of the heating furnace is greater than 0 volume%, 1 volume% or more, 2 volume% or more, 3 volume% or more, or 4 volume% or more, and / or 9 volume% or less, 8 volume% or less, or 7 volume% or less.

[0100] The timing for introducing a low-oxygen 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 begins. Alternatively, the timing for introducing the low-oxygen gas into the heating furnace can be determined based on data obtained in advance regarding the self-heating of the plastic-containing material.

[0101] In one preferred embodiment of the present disclosure, a low-oxygen gas is introduced into the atmosphere of the heating furnace while the surface temperature of the plastic-containing material held in the heating furnace is below 300°C.

[0102] 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 gas with an oxygen concentration of less than 10 volume percent is introduced into the atmosphere of the heating furnace.

[0103] More preferably, a low-oxygen-concentration gas with an oxygen concentration of less than 10% by volume is introduced into the atmosphere of the heating furnace holding the plastic-containing material with a surface temperature of less than 300°C, thereby reducing the oxygen concentration of the atmosphere inside the heating furnace to less than 10% by volume.

[0104] More preferably, a low-oxygen gas with an oxygen concentration of less than 10 volume% is introduced into the atmosphere of a heating furnace holding a plastic-containing material with a surface temperature of less than 300°C, thereby controlling the oxygen concentration in the atmosphere inside the heating furnace to greater than 0 volume%, 1 volume% or more, 2 volume% or more, 3 volume% or more, or 4 volume% or more, and / or 9 volume% or less, 8 volume% or less, or 7 volume% or less.

[0105] The oxygen concentration inside the heating furnace can be measured directly using an oxygen concentration meter (oxygen monitor), or it can be determined based on the furnace volume and the amount of gas introduced into the furnace. Preferably, the oxygen concentration inside the heating furnace is the average oxygen concentration throughout the heating process.

[0106] The introduction of a low-oxygen gas into the furnace can be done, for example, by forcing the low-oxygen gas into the furnace through a gas supply unit provided in the heating furnace, or by drawing gas in through a suction port (or exhaust port) provided in the furnace, thereby causing the gas to flow into the furnace from a gas supply unit located at a different location from the suction port. The gas supply unit of the heating furnace may, for example, have an opening and / or be made of a gas-permeable material.

[0107] The amount of gas introduced into the furnace can be set according to the capacity of the heating furnace and the desired oxygen concentration, based on the amount of resin to be decomposed (e.g., epoxy resin) per unit area.

[0108] For example, the amount of gas introduced into the furnace per unit amount of resin 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. Furthermore, based on the determined amount of gas introduced and the volume of the heating furnace used, the time required for the atmosphere inside the furnace to be replaced by the introduced gas can be determined.

[0109] In particular, the amount of low-oxygen gas introduced relative to the furnace volume can be set so that the atmosphere inside the heating furnace is replaced by the introduced low-oxygen gas while the surface temperature of the plastic-containing material held inside the heating furnace is below 300°C.

[0110] The low-oxygen gas introduced into the heating furnace may include a diluent gas, and in particular, a mixture of air and a diluent gas. Examples of diluent gases include nitrogen gas, carbon dioxide gas, water vapor, and superheated steam. Superheated steam is water vapor heated to a temperature above its boiling point. Superheated steam has the advantage of relatively high heat transfer to the material to be decomposed.

[0111] (heating furnace) The heating furnace may be a combustion furnace or an electric furnace. The heating furnace may have, for example, an internal space for containing plastic-containing materials and semiconductor materials, a heat source (heater) for heating the atmosphere inside the heating furnace, a gas supply unit for introducing low-oxygen concentration gas into the heating furnace, an exhaust port for discharging decomposition gases, and optionally, a suction port for applying suction pressure inside the heating furnace. One structure may also be used as both the exhaust port and the suction port. For example, one or more openings provided in the heating furnace can be used as the exhaust port and / or suction port.

[0112] (Surface temperature) The "surface temperature" of a plastic-containing material can be determined by measuring the temperature within 5 mm of the plastic-containing material during the heat treatment process.

[0113] The surface temperature of plastic-containing materials can be controlled, for example, by controlling the temperature inside a heating furnace via a heat source in the furnace, and / or by introducing a low-temperature gas into the heating furnace, and / or by reducing the oxygen concentration to suppress oxidative heat generation.

[0114] Furthermore, by measuring the surface temperature of the plastic-containing material via a temperature sensor placed within 5 mm of its surface and feeding this measurement back to the heat source of the heating furnace, the surface temperature can be controlled with even greater precision.

[0115] Furthermore, for example, data on the correlation between the temperature inside the heating furnace and / or the output of the heat source and the surface temperature measured by a sensor may be acquired in advance, and the heating process may be performed based on this data.

[0116] <Heat treatment> The method relating to this disclosure is: A plastic-containing material is heated to a first surface temperature in a heating furnace atmosphere where a low-oxygen gas with an oxygen concentration of less than 10% by volume is introduced, in the presence of a semiconductor material, thereby decomposing the plastic in the plastic-containing material. Includes.

[0117] Preferably, this heat treatment is carried out in an atmosphere in which the oxygen concentration is reduced to less than 10 volume percent by introducing a low-oxygen gas, and more particularly, under an oxygen concentration of greater than 0 volume percent, 1 volume percent or more, 2 volume percent or more, 3 volume percent or more, or 4 volume percent or more, and / or under an oxygen concentration of 9 volume percent or less, 8 volume percent or less, or 7 volume percent or less.

[0118] (1st 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 of the plastic-containing material during the heat treatment, similar to the "surface temperature" described above.

[0119] The first surface temperature may be 300°C or higher, 325°C or higher, or 350°C or higher, and / or 600°C or lower, 550°C or lower, 500°C or lower, or 450°C or lower. For example, the first surface temperature may be 300°C to 600°C, 300°C to 550°C, 300°C to 500°C, or 300°C to 450°C.

[0120] If the first surface temperature is below the above range, decomposition of the plastic may not occur. Furthermore, if the first surface temperature exceeds the above range, and the plastic-containing material contains valuable materials such as carbon fibers, the deterioration and / or burning of these materials due to heating in the presence of oxygen may become significant. By keeping the first surface temperature relatively low, the effect of suppressing excessive oxidative heat generation is further enhanced.

[0121] In preferred embodiments of this disclosure, the first surface temperature is raised to 450°C or higher during the heat treatment at an oxygen concentration of less than 10% by volume. When the heating temperature is relatively low, the carbides formed on the surface of the plastic-containing material may suppress further decomposition of the plastic. However, by raising the surface temperature to 450°C or higher, the carbides can be removed even at relatively low oxygen concentrations. Therefore, it is possible to further improve the efficiency of plastic decomposition.

[0122] Preferably, the heat treatment is carried out under the introduction of a low-oxygen gas for a predetermined period of time. This predetermined period may be 1 minute to 600 minutes, preferably 30 minutes to 300 minutes, and more preferably 60 minutes to 180 minutes. The starting point of the "predetermined period" can be the time when the temperature of the heating furnace reaches 300°C, or when the start of plastic decomposition is confirmed.

[0123] (Semiconductor materials) The semiconductor material may be placed in the heating furnace together with the plastic-containing material, or the semiconductor material may be placed in the heating furnace beforehand, and then the plastic-containing material may be placed adjacent to or in contact with the semiconductor material.

[0124] In one embodiment of the present disclosure, the plastic-containing material to be heat-treated and the semiconductor material are placed at a distance of 50 mm or less from each other. For this purpose, for example, a spacer can be placed between the plastic-containing material and the semiconductor material.

[0125] The distance between the plastic-containing material and the semiconductor material can be measured at the point where they are closest to each other.

[0126] In another preferred embodiment of the present disclosure, the plastic-containing material to be heat-treated and the semiconductor material are placed in contact with each other.

[0127] 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 top of the semiconductor material. Alternatively, the plastic-containing material may be placed on top of a semiconductor material supported on the surface of a carrier. Furthermore, the two can be brought into contact by surrounding or covering at least part or all of the plastic-containing material with the semiconductor material.

[0128] 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 includes, 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,Fe2 O3,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,C oAl2O4, NiAl2O4, Tl2O, GeO, PbO, TiO, Ti2O3, VO, MoO2, IrO2, RuO2, CdS, CdSe, CdTe, Cu2O, Sb2O3, MnO3, and CoCrO4.

[0129] 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.

[0130] The form of the semiconductor material is not particularly limited and may be, for example, plate-shaped, granular, or honeycomb-shaped. From the viewpoint of promoting the decomposition of the plastic, it is preferable that the semiconductor material is supported on the surface of a breathable carrier. The breathable carrier may be a porous body made of ceramics or the like, a honeycomb-shaped support, etc. The semiconductor material may be a sintered semiconductor body.

[0131] <Two-stage heating> A heat treatment method according to one preferred embodiment of the present disclosure is: A plastic-containing material subjected to heat treatment at a first surface temperature is heated in the presence of a semiconductor material in an atmosphere with an oxygen concentration of 10% by volume or more. Includes.

[0132] Heat treatment at an oxygen concentration of 10% by volume or higher is preferably carried out at an oxygen concentration of more than 10% by volume, 12% or higher, 15% or higher, or 20% or higher, and / or at an oxygen concentration of 30% or lower, or 25% or lower.

[0133] In this embodiment, also referred to as two-stage heating, a plastic-containing material that has been heat-treated at a relatively low oxygen concentration is further heat-treated at an increased oxygen concentration.

[0134] In the initial stages of thermal decomposition of plastics, there is a high risk of excessive oxidative heat generation due to the relatively large amount of plastic present. In contrast, the above embodiment involving two-stage heating involves a heat treatment performed at a relatively low oxygen concentration followed by a heat treatment with an increased oxygen concentration. That is, by performing heating with an increased oxygen concentration at a stage when the decomposition of the plastic has progressed and the amount of plastic has decreased, the generation of excessive oxidative heat can be suppressed.

[0135] Furthermore, in heat treatment at relatively low oxygen concentrations, some of the plastic may not vaporize and may remain as char. In contrast, in the above embodiment involving two-stage heating, the oxygen concentration is increased and further heat treatment is performed, so the remaining char can be efficiently decomposed and removed, and as a result, the decomposition efficiency can be further improved.

[0136] Heat treatment under low oxygen concentration gas introduction and heat treatment at an oxygen concentration of 10% by volume or higher can be performed continuously in the same heating furnace. That is, for example, after heating a plastic-containing material to a first surface temperature, the oxygen concentration can be increased to 10% by volume or higher in the same heating furnace, and further heat treatment can be performed. Conventional plastic decomposition methods required processing such as shredding of the material to be processed after batch processing, but by performing heat treatment under low oxygen concentration gas introduction and heat treatment at an oxygen concentration of 10% by volume or higher continuously in the same heating furnace, the number of steps can be reduced.

[0137] An atmosphere with an oxygen concentration of 10% by volume or higher can be created, for example, by introducing a high-oxygen-concentration gas with an oxygen concentration of 10% by volume or higher into a heating furnace, and more particularly by introducing air and / or oxygen gas into the heating furnace. The oxygen concentration of the high-oxygen-concentration gas may be greater than 10% by volume, 12% or more by volume, 15% or more by volume, or 20% or more by volume, and / or 30% or less by volume, or 25% or less by volume.

[0138] In heat treatment at an oxygen concentration of 10 volume% or higher, the semiconductor material used in the heat treatment at the first surface temperature can be used.

[0139] (2nd surface temperature) In particular, a plastic-containing material subjected to heat treatment at a first surface temperature is heated to a second surface temperature in an atmosphere with an oxygen concentration of 10% by volume or more, in the presence of a semiconductor material.

[0140] The "second surface temperature" is the surface temperature of the plastic-containing material being treated. The "second surface temperature" can be determined by measuring the temperature within 5 mm of the plastic-containing material during the heat treatment, similar to the "surface temperature" and "first surface temperature" described above.

[0141] 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.

[0142] If the second surface temperature is below the above range, no improvement in decomposition efficiency may be observed. Furthermore, if the second surface temperature exceeds the above range, and the plastic-containing material contains valuable materials such as carbon fibers, the deterioration and / or burning of carbon fibers due to heating in the presence of oxygen may become significant.

[0143] The second surface temperature may be substantially the same as the first surface temperature.

[0144] Furthermore, the second surface temperature may be equal to or higher than the first surface temperature, or it 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.

[0145] A heat treatment at an oxygen concentration of 10% by volume or higher can be carried out for a predetermined period of time. This predetermined period may be, for example, 1 minute to 600 minutes, 60 minutes to 360 minutes, or 90 minutes to 300 minutes.

[0146] <Application> The decomposition method for plastic-containing materials described herein can efficiently vaporize and decompose a wide range of plastics. Furthermore, the decomposition method described herein is applicable to volatile organic compounds (VOCs), flue gas, particulate matter (PM), etc., and can be used for exhaust gas treatment.

[0147] ≪Methods for recovering inorganic materials≫ The method for recovering inorganic materials contained in plastic composite materials, as described in this disclosure, is explained below.

[0148] In one embodiment of the recovery method relating to this disclosure, the plastic-containing material, which is a plastic composite material, contains plastic and inorganic materials, and this recovery method The above decomposition method involves decomposing the plastic in the plastic-containing material and recovering the inorganic material. Includes.

[0149] For details of the decomposition method and its use in the recovery method relating to this disclosure, please refer to the above description regarding the decomposition method of plastic-containing materials.

[0150] As previously stated, the decomposition method described herein allows for the efficient decomposition of plastics. Therefore, the recovery method described herein allows for the efficient and selective decomposition of plastics contained in plastic composite materials, thereby enabling the efficient recovery of inorganic materials with good physical properties.

[0151] Furthermore, the recovery method described herein allows for the recovery of inorganic materials without crushing the plastic composite material. However, crushing the plastic composite material is not particularly excluded and can be done as desired.

[0152] Furthermore, when recovering inorganic materials from plastic composite materials, it is necessary to minimize the effects of heat treatment on the inorganic materials from the viewpoint of maintaining the quality of the recovered inorganic materials. In this regard, the decomposition method according to this disclosure suppresses excessive oxidative heat generation by using a relatively low oxygen concentration. Therefore, according to the recovery method according to this disclosure, it is possible to recover inorganic materials with relatively good physical properties.

[0153] (Two-stage heating) In another embodiment of the recovery method described herein, the plastic-containing material, as a plastic composite material, is subjected to two-stage heating. Specifically, the plastic composite material is subjected to heating under the introduction of a low-oxygen concentration gas, followed by a heat treatment at an oxygen concentration of 10% by volume or more, thereby decomposing the plastic and recovering the inorganic material.

[0154] When recovering inorganic materials, it is desirable to suppress the deterioration of the inorganic materials' properties due to excessive oxidative heat generation, and furthermore, to suppress the deterioration of the inorganic materials' properties caused by the carbonization of plastics that adhere to and remain on the inorganic materials. In this regard, in the method of subjecting plastic composite materials to two-stage heating, the oxygen concentration is kept relatively low in the initial stage, where excessive oxidative heat generation is likely to occur, thereby suppressing the deterioration of the inorganic materials' properties caused by excessive oxidative heat generation. Furthermore, since the subsequent heat treatment involves increasing the oxygen concentration, the carbonized resin remaining on the inorganic materials can be efficiently removed. As a result, the two-stage heat treatment method for recovering inorganic materials ensures even better physical properties of the recovered inorganic materials.

[0155] (Inorganic materials) Examples of plastic composite materials containing inorganic materials and plastics include carbon fiber reinforced plastics.

[0156] Inorganic materials, in particular, include carbon fibers (carbon fiber materials).

[0157] (Carbon fiber) The carbon fibers contained in the carbon fiber reinforced plastic are not particularly limited, but examples include PAN-based carbon fibers and pitch-based carbon fibers. The carbon fibers may be of one type or composed of two or more types.

[0158] The carbon fibers contained in the carbon fiber reinforced plastic may be in any form, for example, carbon fiber bundles, fabrics formed from carbon fiber bundles, or carbon fiber nonwovens.

[0159] (Collected items) According to one embodiment of the recovery method described herein, residual carbon derived from plastics recovered together with the inorganic material is reduced, and in particular, the residual carbon is 5% by weight or less of the recovered inorganic material. 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 recovered inorganic material. It is preferable that the residual carbon is reduced as much as possible, but the lower limit may be 0.001% by weight or more.

[0160] Furthermore, according to the recovery method described herein, it is possible to recover carbon fiber material that has superior physical properties to the carbon fiber material used before manufacturing carbon fiber reinforced plastic.

[0161] In particular, according to the recovery method described herein, carbon fibers having a single-fiber tensile strength of 3.0 GPa or higher and a Weibull shape modulus of 6.0 or higher can be obtained from carbon fiber reinforced plastic as an inorganic material.

[0162] (Single fiber tensile strength) The tensile strength of the single fiber is preferably 3.1 GPa or higher, 3.2 GPa or higher, 3.3 GPa or higher, or 3.4 GPa or higher. There is no particular upper limit to the tensile strength of the single fiber, but it may be 6.0 GPa or lower.

[0163] The tensile strength of a single fiber can be measured in accordance with JIS R7606 as follows: At least 30 single fibers are taken from the fiber bundle, By measuring the diameter of a single fiber in a lateral image of a single fiber taken with a digital microscope, the cross-sectional area is calculated. The sampled single fibers are fixed to a perforated cardboard base using adhesive. A base with a single fiber fixed to it is attached to a tensile testing machine, and a tensile test is performed with a test length of 10 mm and a strain rate of 1 mm / min to measure the tensile breaking stress. The tensile strength is calculated from the cross-sectional area and tensile fracture stress of a single fiber. The average tensile strength of at least 30 individual fibers is defined as the single-fiber tensile strength.

[0164] (Weibull shape factor) The Weibull shape factor is preferably 6.5 or higher, 7.0 or higher, 7.5 or higher, 8.0 or higher, or 8.5 or higher. The upper limit of the Weibull shape factor is not particularly limited, but it may be 15.0 or lower.

[0165] 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 probability of failure 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.

[0166] By plotting lnln{1 / (1-F)} and lnσ using a Weibull plot, the Weibull shape coefficient m can be determined from the linearly approximated slope.

[0167] <Application> According to the recovery method described herein, for example, only the matrix resin of fiber-reinforced plastics (FRP), solar panels, electronic circuits, etc., can be efficiently decomposed, and valuable materials such as reinforcing fibers and rare metals can be efficiently recovered.

[0168] Recycled carbon fiber materials The recycled carbon fiber material (recycled carbon fiber) according to this disclosure can be manufactured by recovering carbon fiber material from carbon fiber reinforced plastics. In one embodiment of this disclosure, this recycled carbon fiber material may have superior physical properties to the carbon fiber used before manufacturing the carbon fiber reinforced plastic.

[0169] The method for producing recycled carbon fiber material is not particularly limited. For example, recycled carbon fiber material can be produced by recovering recycled carbon fiber material from carbon fiber reinforced plastic using the recovery method described herein.

[0170] In one embodiment, the recycled carbon fiber material has a single-fiber tensile strength of 3.0 GPa or higher and a Weibull shape factor of 6.0 or higher. The single-fiber tensile strength and the Weibull shape factor can be measured and determined by the methods described above.

[0171] The single-fiber tensile strength of the recycled carbon fiber material is preferably 3.1 GPa or higher, 3.2 GPa or higher, 3.3 GPa or higher, or 3.4 GPa or higher.

[0172] The Weibull shape factor of the recycled carbon fiber material is preferably 6.5 or higher, 7.0 or higher, 7.5 or higher, 8.0 or higher, or 8.5 or higher.

[0173] (Method for manufacturing recycled carbon fiber materials) 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 residual carbon component content of more than 0% by weight and 5.0% by weight or less relative to recycled carbon fiber, A plastic-containing material is heated to a first surface temperature in a heating furnace atmosphere where a low-oxygen gas with an oxygen concentration of less than 10% by volume is introduced, in the presence of a semiconductor material, thereby decomposing the plastic in the plastic-containing material. Includes, Here, the plastic-containing material is a carbon fiber-reinforced plastic containing carbon fiber material.

[0174] Furthermore, a method for producing recycled carbon fiber having a single-fiber tensile strength of 3.0 GPa or higher and a Weibull shape factor of 6.0 or higher, and a residual carbon component content of more than 0% by weight and 5.0% by weight or less relative to the recycled carbon fiber, The plastic in the plastic-containing material is decomposed by heating the plastic-containing material to a first surface temperature in an atmosphere within a heating furnace where a low-oxygen gas with an oxygen concentration of less than 10 volume percent is introduced, in the presence of a semiconductor material, and then heating the plastic-containing material subjected to the heat treatment at the first surface temperature in an atmosphere with an oxygen concentration of 10 volume percent or more, in the presence of a semiconductor material. Includes, Here, the plastic-containing material is a carbon fiber-reinforced plastic containing carbon fibers.

[0175] In one preferred embodiment of the method for producing recycled carbon fiber material according to this disclosure, a low-oxygen gas is introduced into the atmosphere of a heating furnace while the surface temperature of the plastic-containing material is below 300°C.

[0176] (Residual carbon) Preferably, the recycled carbon fiber material according to this disclosure has a reduced amount of residual carbon, and in particular, the residual carbon is 5% by weight or less relative 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 relative to the recycled carbon fiber material.

[0177] Furthermore, "residual carbon" refers to carbonized components derived from the plastic contained in the carbon fiber reinforced plastic, which is a raw material used in the production of recycled carbon fiber materials.

[0178] The amount of residual carbon in recycled carbon fiber materials can be determined by thermogravimetric analysis (TGA).

[0179] The amount of residual carbon can be determined by thermogravimetric analysis using the following procedure: (i) For a sample piece of 1-4 mg obtained by crushing recycled carbon fiber material, a thermogravimetric analyzer was used with an air supply rate of 0.2 L / min, a heating rate of 5°C / min, and a recording rate of 1 / 6 s. Temperature increase from room temperature to 100°C, Holding at 100°C for 30 minutes, Temperature increase from 100°C to 400°C, and, Holding at 400°C The process involves thermogravimetric analysis lasting 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 residual carbon amount by subtracting the weight loss rate during the holding period at 100°C from the weight loss rate value at that inflection point.

[0180] If the inflection point of the slope cannot be identified under the above conditions, instead of thermogravimetric analysis for a total of 300 minutes, thermogravimetric analysis for a total of approximately 600 minutes, including holding at 400°C for 480 minutes, may be performed. Furthermore, instead of holding at 400°C for 480 minutes, holding at a specific temperature in the range of over 400°C and not exceeding 500°C may be performed for 480 minutes. [Examples]

[0181] The present invention will be described in more detail below using examples. Note that these examples are illustrative and the present application is not limited thereto.

[0182] Example 1 <Preparation of materials> (Recycled carbon fiber) In Example 1, recycled carbon fibers were used, which were recycled using CFRP as a raw material by the semiconductor thermal activation method according to the method of this disclosure. The recycled carbon fibers had 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%.

[0183] (Single fiber tensile strength) The tensile strength of the single fiber was measured in accordance with JIS R7606 as follows: At least 30 single fibers are taken from the fiber bundle, By measuring the diameter of a single fiber in a lateral image of a single fiber taken with a digital microscope, the cross-sectional area is calculated. The sampled single fibers are fixed to a perforated cardboard base using adhesive. A base with a single fiber fixed to it is attached to a tensile testing machine, and a tensile test is performed with a test length of 10 mm and a strain rate of 1 mm / min to measure the tensile breaking stress. The tensile strength is calculated from the cross-sectional area and tensile fracture stress of a single fiber. The average tensile strength of at least 30 individual fibers was defined as the single-fiber tensile strength.

[0184] (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 probability of failure 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.) Weibull plots were created using lnln{1 / (1-F)} and lnσ, and the Weibull shape coefficient m was determined from the linearly approximated slope.

[0185] (Residual carbon content) The amount of residual carbon in recycled carbon fibers was determined by thermogravimetric analysis (TGA method) as follows: (i) A 4 mg sample piece obtained by crushing recycled carbon fiber is subjected to thermogravimetric analysis using a thermogravimetric analyzer for a total of approximately 600 minutes, with an air supply rate of 0.2 L / min, a heating rate of 5 °C / min, and a recording rate of 1 / 6 s, 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 for 480 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 weight loss rate value at that inflection point.

[0186] The recycled carbon fibers described above were immersed in an aqueous dispersion of epoxy resin and then removed. After drying in a dryer, 2% by weight of epoxy resin was applied to the recycled carbon fibers as a binder with the thermoplastic resin.

[0187] (Thermoplastic resin fiber) In Example 1, polyamide 66 resin fibers with an average length of 38 mm (PA66 resin fibers (Toray Industries, Inc., 1401-1.3T-38 E9), single filament fineness of 1.3 dtex, crimp count of 17 crimps / 25 mm, melting point of 265°C) were used as thermoplastic resin fibers.

[0188] <Manufacturing of blended yarns> By mixing the above-mentioned recycled carbon fibers with a binder at a ratio of 80% by weight and the above-mentioned PA66 resin fibers at a ratio of 20% by weight, and spinning the mixture through the processes of combing, drawing, and roving, a continuous blended yarn (blended yarn according to Example 1) with a weight of 0.86 g / m was produced. In the roving process, a twist of 200 turns / m was applied.

[0189] <Manufacturing of carbon fiber reinforced thermoplastic resin pellets> Next, the blended yarn obtained above was coated with polyamide 6 (DSM: Akulon® F-X9182, melting point 220°C) using a crosshead die for wire coating with an outlet diameter of 3 mm. This was then cut to a length of 3 mm to obtain core-sheath type pellets suitable for injection molding (carbon fiber reinforced thermoplastic resin pellets according to Example 1) with a carbon fiber content of 17% by mass (463 parts by mass of polyamide 6 per 100 parts by mass of carbon fiber), a diameter of 2.6 mm, and a cut length of 3 mm.

[0190] <Injection Molding Evaluation> Using the obtained carbon fiber reinforced thermoplastic resin pellets as raw material, injection molding was performed using a 110-ton electric injection molding machine (manufactured by Japan Steel Works, J110AD) with cylinder temperatures C1 / C2 / C3 / C4 / N = 265℃ / 270℃ / 280℃ / 280℃ / 280℃ (C1~C4 are cavity temperatures, N is nozzle temperature) for a molding cycle of 40 seconds to obtain a tensile test dumbbell with a wall thickness of 4 mm (molded body according to Example 1). The obtained molded body showed no clumps of fibrous material or air bubbles due to poor dispersion, and had a good appearance.

[0191] The resulting dumbbells were used as test specimens, and their tensile strength was measured in accordance with ISO 527 (JIS K7161). The tensile strength was 200 MPa, demonstrating excellent mechanical properties.

[0192] Furthermore, the average fiber length of the recycled carbon fibers contained in the molded product was 0.33 mm.

[0193] The average fiber length of recycled carbon fibers in the molded product was evaluated as follows: A 20mm x 10mm test piece was cut from the obtained molded body and heated at 550°C for 1.5 hours in an aerobic atmosphere to burn off the resin components. The remaining carbon fibers were placed in water and thoroughly stirred using ultrasonic vibration. The stirred dispersion was randomly sampled using a measuring spoon to obtain evaluation samples. The length of 3000 fibers was measured using a Nireco Luzex AP image analysis system, and the average length was calculated to determine the average fiber length of the carbon fibers in the molded body.

[0194] The results for Example 1 are shown in Table 1 below.

[0195] ≪Comparative Example 1≫ A blended yarn was attempted 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. However, the tensile strength of the single fibers and the Weibull shape factor of the recycled carbon fibers could not be evaluated because the bonding between the single fibers due to residual carbon was so strong that it was not possible to separate and collect the single fibers.

[0196] In Comparative Example 1, it was observed that the bonding between individual recycled carbon fibers was not sufficiently opened during the combing process, and that there was little entanglement between the individual fibers, resulting in yarn shedding. Therefore, it was not possible to produce a continuous blended yarn. The results are shown in Table 1 below.

[0197] [Table 1]

[0198] <Reference Examples 1-3 and Reference Comparative Example 1> In Reference Examples 1-3 and Reference Comparative Example 1, carbon fiber reinforced plastic (CFRP) sheets were heat-treated as plastic-containing materials, and the plastic decomposition efficiency was evaluated.

[0199] <Reference Example 1> Reference Example 1 was carried out as follows.

[0200] (Provision and arrangement of materials) As the semiconductor material, a support having a honeycomb structure was used, with chromium oxide (Cr2O3, purity 99% or higher, manufactured by Junsei Chemical Co., Ltd.) applied to its surface. The honeycomb support had 13 cells / 25 mm.

[0201] As the plastic-containing material, a CFRP board with an epoxy resin content of 41% by weight was used.

[0202] The internal volume of the heating furnace was 9 L. Inside the heating furnace, a CFRP plate was placed on a carrier supporting chromium oxide as a semiconductor material. The carrier and the CFRP plate were placed in contact with each other.

[0203] The surface temperature of the CFRP board was measured using a sensor placed within 5 mm of the surface of the CFRP board.

[0204] (Heat treatment) The internal temperature of the heating furnace was increased by controlling it via the heater output of the heating furnace.

[0205] Before the surface temperature of the CFRP plate reached 300°C, a mixture of air with an oxygen concentration of 6 vol% and nitrogen gas was introduced into the heating furnace. The mixed gas was introduced into the heating furnace by drawing in gas at a rate of 70 L / min from a suction port located at the top of the heating furnace and letting the mixed gas flow in from a gas supply port located at the bottom of the heating furnace. The oxygen concentration inside the heating furnace was measured using an oxygen monitor.

[0206] The above mixed gas was introduced to create an atmosphere with an oxygen concentration controlled to 6% by volume, and the 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.

[0207] (evaluation) The plastic decomposition efficiency in the method according to Reference Example 1 was evaluated by calculating the weight loss rate (wt%) from the difference between the weight of the CFRP plate before heat treatment and the weight of the CFRP plate after heat treatment. The results are shown in Table 2.

[0208] <Reference Example 2> The heat treatment and evaluation of Reference Example 2 were carried out in the same manner as in Reference Example 1, except that the carrier and the CFRP plate were placed 30 mm apart in the heating furnace, and the surface temperature of the CFRP plate was raised to 377°C during the heat treatment. The results are shown in Table 2.

[0209] <Reference Example 3> Except for the fact that the heat treatment time was set to 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.

[0210] <Reference Example 1> Except for not using semiconductor materials and raising the surface temperature of the CFRP plate 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.

[0211] [Table 2]

[0212] As can be seen in Table 2, Reference Examples 1 to 3, which were heated to a surface temperature of 371°C to 377°C in the presence of a semiconductor material and under the introduction of a low oxygen concentration gas with an oxygen concentration of 6 volume%, showed higher decomposition efficiency of the plastic-containing material compared to Reference Comparative Example 1, which did not use a semiconductor material.

[0213] In Reference Example 3, the processing time was extended to 60 minutes, but the increase in weight loss was limited compared to Reference Example 1, where the processing time was 30 minutes. This is thought to be because the sample surface was covered with carbides during the heat treatment, resulting in a decrease in decomposition efficiency.

[0214] <Reference Example 4 and Reference Comparative Example 2> <Reference Example 4> The processing and evaluation according to Reference Example 4 were carried out in the same manner as in Reference Example 1, except that the surface temperature was heated at 500°C for 60 minutes. The results are shown in Table 3 below.

[0215] <Reference Comparison Example 2> Except for not using semiconductor materials, the processing and evaluation for Reference Comparative Example 2 were carried out in the same manner as in Reference Example 4. The results are shown in Table 3 below.

[0216] [Table 3]

[0217] Photographs of the samples after undergoing the processing described in Reference Example 4 and Reference Comparative Example 2 are shown in Figures 5 and 6, respectively. A photograph of the sample before processing is shown in Figure 4.

[0218] As can be seen in Table 3, Reference Example 4, in which heat treatment was performed under a semiconductor material with the introduction of a low oxygen concentration gas of 6 volume%, showed higher plastic decomposition efficiency compared to Reference Comparative Example 2, in which heat treatment was performed without a semiconductor material under the introduction of a low oxygen concentration gas of 6 volume%,.

[0219] Furthermore, as can be seen in Figure 6, the surface of the treated sample according to Reference Comparative Example 2 had clumps of residual carbon derived from the plastic attached to it. On the other hand, as can be seen in Figure 5, no such attachment of residual carbon was observed in the treated sample according to Reference Example 4, and it had a relatively smooth and highly uniform surface, similar to the surface of the untreated sample shown in Figure 4.

[0220] ≪Reference Examples 5-9≫ In Reference Examples 5-9, a two-stage heat treatment was performed on CFRP plates or pressure vessels as plastic-containing materials. The decomposition efficiency was evaluated, and the physical properties of the carbon fiber material obtained by the heat treatment were also evaluated.

[0221] <Reference Example 5> Reference Example 5 was carried out as follows.

[0222] (Provision and arrangement of materials) As the semiconductor material, a support having a honeycomb structure was used, with chromium oxide (Cr2O3, purity 99% or higher, manufactured by Junsei Chemical Co., Ltd.) applied to its surface. The honeycomb support had 13 cells / 25 mm.

[0223] As the plastic-containing material, a CFRP plate with 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 treatment are shown in Table 4 as Reference Example 1.

[0224] The furnace volume of the heating furnace was 0.0525 m 3 It was. Inside the heating furnace, the CFRP plate was placed on a carrier supporting chromium oxide as a semiconductor material. The carrier and the CFRP plate were arranged in contact with each other.

[0225] The surface temperature of the CFRP plate was measured by a sensor arranged within 5 mm from the surface of the CFRP plate.

[0226] (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 sucking 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.

[0227] In addition, in Reference Example 5, as well as the following Reference Example 6 and Reference Comparative Example 4, the oxygen concentration in the heating furnace was measured by an oxygen monitor installed in the heating furnace. Regarding Reference Examples 7 to 9, the oxygen concentration in the furnace was determined based on the furnace volume and the gas introduction amount.

[0228] When the surface temperature of the CFRP plate reached 300 °C, the generation of decomposition gas was confirmed.

[0229] 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 the first surface temperature of 450 °C.

[0230] (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 in the heating furnace reached 10% by volume or higher, further heat treatment was performed. During the 260-minute heat treatment, the surface temperature of the CFRP plate was raised to 500°C. The average oxygen concentration over the 260 minutes was 14% by volume, and the maximum oxygen concentration was 18% by volume.

[0231] In Reference Example 5, a 0.8 kg CFRP plate was processed. The processing rate relative to the furnace volume was 15.2 kg / m³. 3 That was the case.

[0232] (Residual carbon content) The amount of residual carbon derived from plastic in the carbon fiber material recovered after heat treatment was determined by thermogravimetric analysis.

[0233] Thermogravimetric analysis was performed as follows: (i) A sample piece of 1-4 mg obtained by crushing the recovered carbon fiber material is subjected to thermogravimetric analysis for a total of 300 minutes, with an air supply rate of 0.2 L / min, a heating rate of 5°C / min, and a recording rate of 1 / 6 s, 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. (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 weight loss rate value at that inflection point.

[0234] Furthermore, the fiber diameter and tensile strength of the single fiber were measured for the carbon fiber material recovered after heat treatment, and the Weibull shape factor was calculated.

[0235] (Single fiber tensile strength) The tensile strength of the single fiber was measured in accordance with JIS R7606 as follows: At least 30 single fibers are taken from the fiber bundle, By measuring the diameter of a single fiber in a lateral image of a single fiber taken with a digital microscope, the cross-sectional area is calculated. The sampled single fibers are fixed to a perforated cardboard base using adhesive. A base with a single fiber fixed to it is attached to a tensile testing machine, and a tensile test is performed with a test length of 10 mm and a strain rate of 1 mm / min to measure the tensile breaking stress. The tensile strength is calculated from the cross-sectional area and tensile fracture stress of a single fiber. The average tensile strength of at least 30 individual fibers was defined as the single-fiber tensile strength.

[0236] (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 probability of failure 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.)

[0237] Weibull plots were created using lnln{1 / (1-F)} and lnσ, and the Weibull shape coefficient m was determined from the linearly approximated slope.

[0238] The evaluation results are shown in Table 4. The fiber single-fiber diameter is the average of the diameters of at least 30 single fibers measured as described above.

[0239] <Reference Example 6>

[0240] 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.

[0241] The pressure vessel processed 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.

[0242] The amount of FRP processed in Reference Example 6 was 0.47 kg. The processing amount per furnace volume was 9.0 kg / m 3 It was.

[0243] The evaluation results of the plastic decomposition efficiency and the physical properties of the recovered carbon fiber material for Reference Example 6 are shown in Table 4. Incidentally, the average oxygen concentration over 180 minutes of the secondary heat treatment was 18 vol%, and the maximum oxygen concentration was 20 vol%.

[0244] Incidentally, the physical properties of the carbon fiber material contained in the above pressure vessel before processing are shown in Table 4 as Reference Example 2.

[0245] <Reference Example 7> The furnace volume of the heating furnace was 0.1435 m 3 It was, 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 heat treatment was carried out in the same manner as in Reference Example 5 except that the surface temperature and the heat treatment time were as shown in Table 4 below.

[0246] Incidentally, the internal temperature of the heating furnace and the surface temperature of the sample were controlled through the heater output of the heating furnace and the temperature of the superheated steam.

[0247] In Reference Example 7, 1.0 kg of CFRP plate was processed. The processing amount per furnace volume was 7.0 kg / m 3 It was.

[0248] The evaluation results of the plastic decomposition efficiency and the physical properties of the recovered carbon fiber material for Reference Example 7 are shown in Table 4. Incidentally, in the secondary heat treatment, only air was pushed into the furnace at 29 L / min.

[0249] <Reference Example 8> The treatment was carried out 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 heat treatment time were as shown in Table 4 below.

[0250] The pressure vessel used in Reference Example 8 is the same as the pressure vessel used in Reference Example 6.

[0251] The amount of FRP processed in Reference Example 8 was 0.47 kg. The processing rate relative to the furnace volume was 3.3 kg / m³. 3 That was the case.

[0252] Table 4 shows 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. In the secondary heat treatment, only air was forced into the furnace at a rate of 29 L / min.

[0253] <Reference Example 9> The internal volume of the heating furnace is 0.049 m³. 3 The treatment was carried out in the same manner as in Reference Example 7, except that the following conditions were met: a 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 heating treatment time were as shown in Table 4 below.

[0254] In Reference Example 9, a CFRP board with an epoxy resin ratio of 38% was processed. The processing rate relative to the furnace volume was 1.6 kg / m³. 3 That was the case.

[0255] Table 4 shows the evaluation results of the plastic decomposition efficiency and the physical properties of the recovered carbon fiber material for Reference Example 9. In the secondary heat treatment, the supply of superheated steam was continued while increasing the amount of air, and gas with an oxygen concentration of 11 volume% was forced into the furnace at 38 L / min.

[0256] The physical properties of the carbon fiber material contained in the CFRP plate described above in Reference Example 9 before processing are shown in Table 4 as Reference Example 3.

[0257] ≪Reference Comparison Example 3≫ In Reference Comparative Example 3, the provision and arrangement of materials were carried out in the same manner as in Reference Example 5, but after that, the internal temperature of the heating furnace was increased without adjusting the oxygen concentration of the atmosphere inside the heating furnace.

[0258] As a result, excessive self-heating occurred while maintaining the heater output at the same level as when the CFRP board surface temperature reached 300°C, causing the CFRP board surface temperature to rise to 485°C. The results are shown in Table 4.

[0259] In Reference Example 3, a 0.8 kg CFRP plate was processed. The processing rate relative to the furnace volume was 15.2 kg / m³. 3 That was the case.

[0260] ≪Reference Comparison Example 4≫

[0261] The process was carried out in the same manner as in Reference Example 6, except that semiconductor materials were not used.

[0262] In Reference Comparison 4, the amount of FRP processed was 0.47 kg. The processing rate relative to the furnace volume was 9.0 kg / m³. 3 That was the case.

[0263] Table 4 shows the results of the evaluation of the physical properties of the recovered carbon fiber material for Reference Comparative Example 4. The average oxygen concentration over the 180-minute secondary heat treatment was 18% by volume, and the maximum oxygen concentration was 20% by volume.

[0264] [Table 4]

[0265] As can be seen in Table 4, Reference Examples 5-9, in which a low oxygen concentration gas with an oxygen concentration of 6-8 volume% was introduced, a primary heat treatment was performed in the presence of a semiconductor material, and then a secondary heat treatment was performed under the increased oxygen concentration, showed low residual carbon content and excellent plastic decomposition efficiency.

[0266] Furthermore, in Comparative Example 3, where oxygen concentration was not controlled, excessive self-heating occurred, whereas in Comparative Examples 5-9, where a low-oxygen gas with an oxygen concentration of 6-8 volume% was introduced into the heating furnace, excessive self-heating was not observed. In Comparative Example 3, the decomposition process was started without lowering the oxygen concentration beforehand, resulting in an excessive oxygen concentration, and consequently, it is thought that the decomposition temperature in the presence of the semiconductor material could not be properly controlled.

[0267] Furthermore, the carbon fiber materials recovered in Reference Examples 5-9 maintained similar fiber diameter and tensile strength compared to the carbon fiber materials before processing (Reference Examples 1-3), and also showed a higher Weibull shape factor for tensile strength. In other words, Reference Examples 5-9 recovered carbon fiber materials with superior physical properties compared to the carbon fiber materials used before manufacturing carbon fiber reinforced plastics.

[0268] Furthermore, the carbon fiber material recovered in Reference Example 6, which involved heat treatment under a semiconductor material, exhibited superior quality, particularly in terms of single-fiber tensile strength and Weibull shape factor, compared to the carbon fiber material recovered in Reference Comparative Example 4, which was heat-treated without a semiconductor material. [Explanation of Symbols]

[0269] 100 Carbon Fiber Reinforced Thermoplastic Strands 110 strand core components 120 strands of sheath components 200 Carbon Fiber Reinforced Thermoplastic Pellets 210 pellet core components 220 pellets of sheath components L Pellet Cut Length R Pellet Diameter C Cutting process 11 Semiconductor Materials 12 Plastic-containing materials 20 Furnace 21 Semiconductor material carrier 22 Plastic-containing materials 23 Heat source (heater) 24 Gas Supply Department 25 Exhaust vents 26 Internal space of the heating furnace 27 Temperature sensor

Claims

1. A blended yarn containing recycled carbon fiber and thermoplastic resin fiber, 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 residual carbon components, and the content of the residual carbon components is greater than 0% by weight and 2.0% by weight or less relative to the recycled carbon fiber, and The content of the recycled carbon fibers is greater than 60% by weight and less than or equal to 98% by weight relative to the blended yarn. A blended yarn characterized by the following features.

2. The blended yarn according to claim 1, wherein the content of the recycled carbon fibers is more than 70% by weight and 98% by weight or less relative to the blended yarn.

3. The blended yarn according to claim 1 or 2, wherein the average length of the recycled carbon fiber and the thermoplastic resin fiber is 20 mm or more and 80 mm or less, respectively.

4. The blended yarn according to any one of claims 1 to 3, wherein the thermoplastic resin fiber contained in the blended yarn is selected from polyolefin resin fiber, polyester resin fiber, polyamide resin fiber, polyetherketone resin fiber, polycarbonate resin fiber, phenoxy resin fiber, and polyphenylene sulfide resin fiber, and mixtures thereof.

5. It has a core-sheath structure, The blended yarn described in any one of claims 1 to 4 is a core component, and The thermoplastic resin is the sheath component. Carbon fiber reinforced thermoplastic resin pellets characterized by the following features.

6. The carbon fiber reinforced thermoplastic resin pellet according to claim 5, wherein the thermoplastic resin as the sheath component is selected from polyolefin resin, polyester resin, polyamide resin, polyetherketone resin, polycarbonate resin, phenoxy resin, and polyphenylene sulfide resin, and mixtures thereof.

7. The carbon fiber reinforced thermoplastic resin pellet according to claim 5 or 6, characterized in that 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 fibers contained in the blended yarn, and T1 - T0 > 10.

8. A carbon fiber reinforced thermoplastic resin pellet according to any one of claims 5 to 7, wherein the cut length is 3 mm or more and 10 mm or less.

9. The process involves decomposing the plastic components contained in carbon fiber-containing plastic products using a semiconductor thermal activation method to produce recycled carbon fiber, and Blending the recycled carbon fibers with thermoplastic resin fibers, A method for producing blended yarn, including, The content of the recycled carbon fibers is greater than 60% by weight and 98% by weight or less relative to the blended yarn, and The recycled carbon fiber contains residual carbon components, and the content of the residual carbon components is greater than 0% by weight and 2.0% by weight or less relative to the recycled carbon fiber. method.

10. The manufacturing method according to claim 9, wherein the content of the recycled carbon fibers is more than 70% by weight and 98% by weight or less relative to the blended yarn.

11. A method for producing carbon fiber reinforced thermoplastic resin pellets with a core-sheath structure, comprising coating a blended yarn obtained by the method described in claim 9 or 10 with a thermoplastic resin.

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