Method for manufacturing carbon fiber-containing resin molded products

Abstract

To provide a method for manufacturing a resin molded product containing a carbon fiber with excellent mechanical property by eliminating a process of mixing the carbon fiber and a thermoplastic resin for manufacturing a secondary intermediate material by adding a thermoplastic resin fiber to a carbon fiber assembly in advance when making a primary intermediate material.SOLUTION: In a method for manufacturing a resin molded product containing a carbon fiber, a spindle-shaped assembly containing the carbon fiber, a thermoplastic resin fiber, and a binder is fed into a molding machine and heated for molding.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a carbon fiber-containing resin molded article. [Background technology]

[0002] Carbon fiber has excellent specific strength and specific modulus, and is lightweight, so it is used as a reinforcing fiber for thermoplastic resins. Carbon fiber reinforced plastic composite materials (also known as carbon fiber reinforced plastics, CFRP) are used in a wide range of applications, including sports and general industrial applications, as well as aerospace and automotive applications.

[0003] One molding method for carbon fiber reinforced resin composite materials is injection molding using carbon fiber reinforced thermoplastic resin pellets. There are two types of carbon fiber reinforced thermoplastic resin pellets: long fiber reinforced pellets, which are manufactured by cutting resin strands in which continuous carbon fibers are coated with thermoplastic resin, and short fiber reinforced pellets, which are manufactured by cutting resin strands in which discontinuous carbon fibers are kneaded and dispersed in thermoplastic resin. Short fiber reinforced thermoplastic resin pellets are widely used as a method of manufacturing them inexpensively, although their mechanical properties are inferior to long fiber reinforced thermoplastic resin pellets.

[0004] Furthermore, with regard to carbon fibers that are used as raw materials for carbon fiber-containing products such as carbon fiber reinforced resin composite materials, methods have been studied for granulating particulate carbon fiber aggregates from carbon fibers and sizing agents, etc. Methods for granulating carbon fiber aggregates have also been studied for recycled carbon fibers (recycled carbon fibers) recovered from used carbon fiber-containing products, etc.

[0005] Patent Documents 1 and 2 describe methods for producing recycled carbon fiber-containing composites by melt kneading carbon fibers. The carbon fibers used in these methods are recovered from waste carbon fiber-reinforced resin composite materials by pyrolysis, and have residual carbon attached to them, which is the carbonized matrix component.

[0006] Patent Document 3 describes a carbon fiber aggregate in which a fiber processing agent is added to recycled carbon fibers recovered from carbon fiber reinforced composite materials, and the fibers are formed into a cylindrical shape using an extrusion granulator, thereby improving the feedability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2020-49820 [Patent Document 2] Japanese Patent Application Publication No. 2019-155634 [Patent Document 3] Patent Publication No. 2021-55198 Summary of the Invention [Problem to be solved by the invention]

[0008] Generally, when producing a carbon fiber-containing resin molded product using the above-mentioned carbon fiber aggregate, a thermoplastic resin is added to the carbon fiber aggregate (primary intermediate material), and the mixture is fed into a kneader or the like to be kneaded to produce pellets (secondary intermediate material) containing carbon fiber and thermoplastic resin. These pellets are then fed into an injection molding machine or the like to produce a carbon fiber-containing resin molded product. When using recycled carbon fiber (recycled carbon fiber), the sizing agent is lost, making it difficult to handle, so it is essential to produce a primary intermediate material that is easy to handle.

[0009] Furthermore, when producing the secondary intermediate materials, the carbon fibers often break, resulting in a deterioration in their physical properties. When using recycled carbon fibers, the physical properties are doubly reduced due to damage to the carbon fibers during production and the breakage of the carbon fibers during kneading.

[0010] The present disclosure aims to provide a method for producing a carbon fiber-containing resin molded product with excellent mechanical properties, by adding thermoplastic resin fibers to a carbon fiber aggregate in advance when producing a primary intermediate material, thereby eliminating the process of kneading carbon fiber and thermoplastic resin to produce a secondary intermediate material. [Means for solving the problem]

[0011] The above-mentioned problems can be solved by the following aspects of the present invention: <Aspect 1> A method for producing a carbon fiber-containing resin molded product, comprising: feeding a spindle-shaped aggregate containing carbon fiber, thermoplastic resin fiber, and a binder into a molding machine and heat-molding the aggregate. <Aspect 2> The method according to aspect 1, wherein the aggregates have an average length of 1.5 mm to 60 mm. <Aspect 3> 3. The method according to claim 1, wherein the carbon fibers and the thermoplastic resin fibers each have an average length of 1 mm or more and less than 30 mm. <Aspect 4> The method according to any one of Aspects 1 to 3, wherein the average length of the aggregates is 1.2 to 5.0 times the average length of the carbon fibers and the average length of the thermoplastic resin fibers contained in the aggregates. <Aspect 5> A manufacturing method according to any one of aspects 1 to 4, wherein the content of the binder is 0.1% by weight to 10% by weight with respect to the aggregate. <Aspect 6> Aspects 6. The method according to any one of Aspects 1 to 5, wherein the thermoplastic resin fibers are selected from polyolefin resin fibers, polyester resin fibers, polyamide resin fibers, polyether ketone resin fibers, polycarbonate resin fibers, phenoxy resin fibers, and polyphenylene sulfide resin fibers, and mixtures thereof. <Aspect 7> Aspect 7. The method according to any one of aspects 1 to 6, wherein the carbon fibers comprise recycled carbon fibers. <Aspect 8> A method according to any one of aspects 1 to 7, wherein the carbon fibers are recycled carbon fibers. <Aspect 9> A method according to any one of aspects 1 to 8, wherein the recycled carbon fibers contain residual carbon components, and the amount of the residual carbon components is more than 0% by weight and 5.0% by weight or less, based on the weight of the recycled carbon fibers. <Aspect 10> providing a mixture comprising at least carbon fibers, thermoplastic resin fibers, and a binder-containing liquid; tumbling the mixture in a container to produce a spindle-shaped precursor; and drying the precursor; Including, A method for producing the spindle-shaped aggregate according to any one of aspects 1 to 9. <Aspect 11> 11. The method of embodiment 10, wherein the mixture is tumbled in a vessel with a clearance between an inner wall of the vessel and a rotating body within the vessel to produce a spindle-shaped precursor. <Aspect 12> 12. The method of claim 10 or 11, wherein the carbon fibers comprise recycled carbon fibers. <Aspect 13> Aspect 13. The method of any one of aspects 10 to 12, wherein the carbon fibers are recycled carbon fibers. <Aspect 14> A method according to any one of aspects 12 to 13, comprising decomposing a plastic component contained in a carbon fiber-containing plastic product by a semiconductor thermal activation method to produce the recycled carbon fiber. [Effects of the Invention]

[0012] According to the present invention, a molded article can be produced directly using an aggregate of carbon fibers and a thermoplastic resin without pre-mixing the carbon fibers and the thermoplastic resin, thereby providing a carbon fiber-containing resin molded article that maintains high mechanical properties with almost no breakage of the carbon fibers. [Brief explanation of the drawings]

[0013] [Figure 1]FIG. 1 is a schematic diagram of one embodiment of an agitator granulator that can be used in the present disclosure. [Figure 2] FIG. 2 is a photograph of a plurality of assemblies according to Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] The spindle-shaped aggregate of thermoplastic resin fibers and carbon fibers according to the present disclosure is carbon fibers, thermoplastic resin fibers, and a binder; The carbon fibers and thermoplastic resin fibers contained in the aggregate are oriented along the longitudinal axis of the aggregate.

[0015] The aggregate according to the present disclosure contains thermoplastic resin fibers, i.e., a fibrous thermoplastic resin. While not intending to be limited by theory, it is believed that the fibrous nature of the thermoplastic resin makes it easier for the carbon fibers and thermoplastic fibers to align in a certain direction, which in turn makes them more likely to aggregate into granular aggregates and furthermore causes them to assume a spindle shape. When the aggregate is granular, the handleability is improved when using the aggregate to manufacture a carbon fiber-containing molded product. Furthermore, it is believed that an aggregate having a spindle shape has particularly good feedability (supplyability) when using the aggregate to manufacture a carbon fiber-containing resin molded product. While not intending to be limited by theory, it is believed that an aggregate having a spindle shape has a relatively low contact resistance and can therefore flow relatively smoothly through the supply port of an extruder or the like without clogging the supply port.

[0016] Furthermore, since the aggregate according to the present disclosure contains thermoplastic resin fibers in addition to carbon fibers, unlike conventional carbon fiber aggregates that contain only carbon fibers, it is possible to omit the step of kneading the carbon fiber aggregate with a thermoplastic resin to produce pellets, and to directly produce carbon fiber-containing resin molded products.

[0017] Furthermore, the aggregate according to the present disclosure can omit the step of producing pellets, which is necessary for conventional carbon fiber aggregates, and therefore, breakage of the carbon fibers during pellet production can be reduced or avoided. Therefore, it is believed that by producing a carbon fiber-containing resin molded article using the aggregate according to the present disclosure, a molded article with improved physical properties can be obtained.

[0018] The invention according to the present disclosure will be described in further detail below.

[0019] <Assembly of thermoplastic resin fiber and carbon fiber> The aggregate of thermoplastic resin fibers and carbon fibers according to the present disclosure is spindle-shaped, carbon fibers, thermoplastic resin fibers, and a binder; The carbon fibers and thermoplastic resin fibers contained in the aggregate are oriented along the longitudinal axis of the aggregate.

[0020] The aggregate according to the present disclosure includes carbon fibers, thermoplastic resin fibers, and a binder. In the aggregate, fiber components composed of carbon fibers and a thermoplastic resin are bound to each other by the binder. The aggregate is preferably substantially composed of carbon fibers, thermoplastic resin fibers, and a binder, and particularly preferably consists of these components.

[0021] The amount of binder in the aggregate may preferably be 0.1% to 10% by weight, in particular 0.5% to 9% by weight, or 1% to 8% by weight, relative to the aggregate.

[0022] The aggregate can contain 1 to 1000 parts by weight, 5 to 900 parts by weight, 10 to 750 parts by weight, 20 to 500 parts by weight, or 50 to 250 parts by weight of thermoplastic resin fibers per 100 parts by weight of recycled carbon fibers.

[0023] The aggregate according to the present disclosure has a spindle-like shape, which means that the center is thick and gradually tapers toward both ends.

[0024] The average extension direction of the fibers relative to the longitudinal axis of the aggregate can be determined by calculating the average value based on measurements of N=30 randomly selected fibers in a cross section parallel to the longitudinal axis of the aggregate using a digital camera or optical microscope, etc. Note that this calculation excludes fluffy fibers (fibers that are partially detached from the aggregate).

[0025] The average extension direction of the fibers relative to the longitudinal axis of the aggregate can also be determined simply by calculating the average value based on the measurements of N=30 randomly selected fibers on the surface of the aggregate using a digital camera or optical microscope, etc. In this case, too, fluffy fibers (fibers that are partially detached from the aggregate) are excluded.

[0026] In addition, when the aggregate has a deformed spindle shape (e.g., a curved spindle shape), the fiber orientation and extension direction can be determined relative to the axis of the aggregate. The length and aspect ratio of the aggregate can also be determined in a similar manner.

[0027] (average length of aggregates) The average length of the aggregates according to the present disclosure may be 1.5 mm to 60 mm. Preferably, the average length of the aggregates is 1.8 mm or more, 2.0 mm or more, 3.0 mm or more, 4.0 mm or more, 5.0 mm or more, 6.0 mm or more, 7.0 mm or more, 8.0 mm or more, 9.0 mm or more, 10 mm or more, 11 mm or more, 12 mm or more, or 15 mm or more, and / or 50 mm or less, 40 mm or less, 30 mm or less, or 25 mm or less. When the average length of the aggregates is within the above range, it is believed that particularly good feedability can be obtained.

[0028] The average length of the aggregates can be calculated by measuring the longitudinal length of 50 aggregates visually using a caliper or the like, or by measuring the length of the aggregates in the longitudinal direction using an image obtained using a digital camera or optical microscope, and averaging the measured values.

[0029] Preferably, the average length of the aggregates is 1.2 to 5.0 times the average length of the carbon fibers and the average length of the thermoplastic resin fibers contained in the aggregates. When the average length of the aggregates is within the above range, particularly good feedability may be obtained.

[0030] Particularly preferably, the average length of the aggregates is 1.4 times or more, 1.5 times or more, or 1.6 times or more, and / or 4.5 times or less, 4.0 times or less, 3.5 times or less, 3.0 times or less, or 2.5 times or less, the average length of the carbon fibers and the average length of the thermoplastic resin fibers. When the average length of the aggregates is within the above ranges, particularly good feedability may be obtained.

[0031] The average length of the carbon fibers and the average length of the thermoplastic resin fibers can be calculated by measuring the lengths of 50 fibers visually using a vernier caliper or the like, or by measuring the lengths of images obtained with a digital camera or an optical microscope, and averaging the measured values.

[0032] (aspect ratio) The aspect ratio of the aggregate is preferably 2 to 20, 3 to 15, or 3 to 10. When the aspect ratio is within this range, an aggregate that is particularly excellent in shape stability and feedability may be obtained.

[0033] The aspect ratio is the longest diameter of a spindle-shaped aggregate divided by its shortest diameter, i.e., longest diameter / shortest diameter. The more elongated the aggregate, the higher the aspect ratio.

[0034] The aspect ratio can be obtained by measuring the major and minor axes of the aggregate visually using a vernier caliper or by using a digital camera or an optical microscope, and then calculating the ratio of major axis to minor axis. The largest length (width) in the direction perpendicular to the major axis can be taken as the "minor axis."

[0035] The method for producing the assembly according to the present disclosure is not particularly limited. The assembly according to the present disclosure can be produced, for example, by the method according to the present disclosure described below.

[0036] (carbon fiber) Carbon fibers are raw materials for aggregates, and examples thereof include ordinary carbon fibers (carbon fibers that are not recycled, so-called virgin carbon fibers), recycled carbon fibers, and mixtures thereof. The carbon fibers may be, for example, PAN-based carbon fibers or pitch-based carbon fibers.

[0037] The form of the carbon fiber is not particularly limited, but may be a carbon fiber bundle composed of a plurality of single threads (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. The diameter of the filaments constituting the carbon fiber may be 0.1 μm to 30 μm, 1 μm to 10 μm, or 3 μm to 8 μm.

[0038] (recycled carbon fiber) Recycled carbon fibers (recycled carbon fibers) contain carbon fiber components and carbon components other than the carbon fiber components (particularly residual carbon components). In recycled carbon fibers, the carbon components other than the carbon fiber components are usually attached to the surface of the carbon fiber components.

[0039] The recycled carbon fiber is not particularly limited, but may be, for example, recycled carbon fiber obtained by heat treating a carbon fiber-containing plastic product such as carbon fiber reinforced plastic (CFRP).

[0040] Particularly preferably, the recycled carbon fibers are recycled carbon fibers obtained by a semiconductor thermal activation method. A particularly preferred embodiment of the following method according to the present disclosure includes decomposing a plastic component contained in a carbon fiber-containing plastic product by a semiconductor thermal activation method to produce recycled carbon fibers.

[0041] The "thermal activation of semiconductors" (TASC method) is a method for decomposing compounds such as polymers using the thermal activation of semiconductors (TASC). For information on methods for producing recycled carbon fiber by decomposing plastic components contained in carbon fiber-containing plastic products using the thermal activation of semiconductors, see, for example, Japanese Patent No. 4517146 and Japanese Patent Laid-Open No. 2019-189674.

[0042] The carbon fiber component in the recycled carbon fiber may be modified by heat treatment or the like during the manufacturing process of the recycled carbon fiber. For details of the carbon fiber component in the recycled carbon fiber, please refer to the above description of the carbon fiber.

[0043] The residual carbon component in recycled carbon fiber is usually derived from the resin contained in the carbon fiber-containing plastic product used as a raw material in producing the recycled carbon fiber. Generally, during the heat treatment process of the carbon fiber-containing plastic product, the plastic component is thermally decomposed, leaving residual carbon on the surface of the carbon fiber component.

[0044] In the present disclosure, the residual carbon component is preferably more than 0% by weight and not more than 5.0% by weight based on the recycled carbon fiber, which may result in an aggregate with improved feedability.

[0045] Furthermore, when the residual carbon component is more than 0 wt % and 5.0 wt % or less, contamination due to a relatively large amount of carbon components (particularly charcoal) can be avoided, the carbon components that can become foreign matter when manufacturing carbon fiber-containing products, etc. using the aggregate as a material can be reduced, and the uniform distribution of fibers in carbon fiber-containing products can be improved.

[0046] Preferably, the residual carbon component 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 fiber. It is preferable that the residual carbon component is as low 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 fiber.

[0047] The content of residual carbon components in recycled carbon fibers can be measured by thermogravimetric analysis (TGA).

[0048] The residual carbon content by thermogravimetry can be measured by the following procedure: (i) A sample piece of 1 to 4 mg obtained by pulverizing the recycled carbon fiber was subjected to a thermogravimetric analysis at an air supply rate of 0.2 L / min, a heating rate of 5 °C / min, and a recording speed of 1 / 6 s. Temperature rise from room temperature to 100°C, Hold at 100°C for 30 minutes, Temperature increase from 100°C to 400°C, and 480 minutes at 400°C The thermogravimetric analysis was carried out over a total of approximately 600 minutes. (ii) In a graph plotting the weight loss rate against time, the inflection point of the slope is identified, and the amount of residual carbon is calculated by subtracting the weight loss rate during the holding period at 100°C from the weight loss rate value at that inflection point.

[0049] If the inflection point of the slope cannot be identified under the above conditions, instead of holding at 400°C for 480 minutes, the sample may be held at a specific temperature in the range of more than 400°C and not more than 500°C for 480 minutes.

[0050] Furthermore, if the recycled carbon fiber contains a resin derived from a sizing agent or the like, the above measurement can be carried out after removing the resin.

[0051] (thermoplastic resin fiber) Examples of thermoplastic resin fibers include polyolefin resin fibers (e.g., polypropylene resin fibers and polyethylene), polyester resin fibers (e.g., polyethylene terephthalate resin fibers, polybutylene terephthalate resin fibers, and polylactic acid), polyamide resin fibers, polyether ketone resin fibers, polycarbonate resin fibers, phenoxy resin fibers, and polyphenylene sulfide resin fibers. The thermoplastic resin fibers may be of one type only, or may be a mixture of two or more types of thermoplastic resin fibers.

[0052] (average fiber length) The carbon fibers can have an average length of 1 mm or more and less than 30 mm. Fibers having lengths in this range can be obtained, for example, by cutting fibers having a relatively long dimension. The average length of the carbon fibers can be 2 mm or more, 3 mm or more, or 4 mm or more, and / or 29 mm or less, 28 mm or less, 27 mm or less, 26 mm or less, 25 mm or less, 24 mm or less, 23 mm or less, 22 mm or less, 21 mm or less, or 20 mm or less. In particular, the average length of the carbon fibers can be 8 mm to 25 mm, or 9 mm to 20 mm.

[0053] In one embodiment of the present disclosure, the average length of the recycled carbon fibers is more than 1 mm and less than 10 mm, particularly 2 mm or more and 5 mm or less. In this case, when a carbon fiber-containing product is produced using the aggregate according to the present disclosure, the fiber aggregate can be supplied in a fixed amount to an injection molding machine, and a recycled carbon fiber-containing product having particularly excellent physical properties such as strength can be obtained.

[0054] The thermoplastic resin fibers can have an average length of 1 mm or more and less than 30 mm. Fibers having lengths in this range can be obtained, for example, by cutting fibers having a relatively long dimension. The average length of the thermoplastic resin fibers can be 1.5 mm or more, 2 mm or more, or 3 mm or more, and / or 28 mm or less, 26 mm or less, 24 mm or less, 22 mm or less, 20 mm or less, 18 mm or less, 16 mm or less, 14 mm or less, 12 mm or less, 10 mm or less, or 8 mm or less.

[0055] When the average length of the recycled carbon fiber and thermoplastic resin fiber is 1 mm or more and less than 30 mm, it is believed that uniform fiber orientation is promoted, resulting in a spindle-shaped aggregate with particularly good feedability. While not intending to be limited by theory, it is believed that a sufficiently long average length of the raw material fibers makes it easier for the fibers to be oriented in one direction, resulting in a spindle-shaped aggregate. Furthermore, it is believed that a sufficiently short average fiber length prevents the fibers from becoming entangled with each other, thereby promoting uniform fiber orientation.

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

[0057] <Assembly manufacturing method> The present disclosure includes a method for producing an assembly according to the present disclosure, comprising: Providing a mixture at least comprising recycled carbon fibers, thermoplastic resin fibers, and a binder-containing liquid (providing step); The mixture is rolled in a container to produce a spindle-shaped precursor (granulation step); Drying the precursor (drying step).

[0058] For each component involved in the above manufacturing method, reference can be made to the above description of the assembly according to the present disclosure.

[0059] <Providing process> The method according to the present disclosure provides a mixture comprising at least recycled carbon fibers, thermoplastic resin fibers, and a binder-containing liquid. The mixture particularly comprises recycled carbon fibers, thermoplastic resin fibers, and a binder-containing liquid.

[0060] The amount of binder-containing liquid in the mixture is preferably 20% by weight to 70% by weight, and particularly preferably 25% by weight to 60% by weight, or 30% by weight to 50% by weight. In this case, the liquid contained in the binder allows the fibers to be bundled particularly well. Also, in this case, the load of the drying process can be reduced because the amount of liquid contained in the binder is not excessive.

[0061] The amounts of recycled carbon fibers and thermoplastic resin fibers in the mixture can be appropriately set so that the weight ratio of these fibers in the resulting aggregate is a desired value. In particular, the contents of recycled carbon fibers and thermoplastic resin fibers in the mixture may be 2.5% by weight to 80% by weight, 5% by weight to 70% by weight, or 10% by weight to 60% by weight, respectively.

[0062] (binder-containing liquid) The binder-containing liquid is a binder dispersion or binder solution, and contains a binder and a solvent or dispersion medium.

[0063] (binder) The binder serves to bundle the fibers (carbon fibers and thermoplastic resin fibers) in the aggregate and maintain the shape of the aggregate. The binder is not particularly limited, but is preferably a thermoplastic resin or a thermosetting resin. More specifically, examples of binders include epoxy resins, urethane-modified epoxy resins, polyester resins, phenolic resins, polyamide resins, polyurethane resins, polycarbonate resins, polyetherimide resins, polyamideimide resins, polyimide resins, bismaleimide resins, polysulfone resins, polyethersulfone resins, epoxy-modified urethane resins, polyvinyl alcohol resins, and polyvinylpyrrolidone resins. These resins may be used alone or in combination of two or more.

[0064] Examples of binders include bentonite, lignin sulfonate, molasses, carboxymethyl cellulose, konjac flour, sodium alginate, polyacrylamide, polyvinyl acetate, polyvinyl alcohol, and starch. These can be used alone or in combination of two or more, and can also be used in combination with the above-mentioned resins.

[0065] (solvent, dispersion medium) The solvent or dispersion medium is not particularly limited as long as it is a liquid that can dissolve or disperse the binder. Examples of the solvent or dispersion medium include water, alcohol (e.g., methanol or ethanol), ketone (e.g., methyl ethyl ketone or acetone), hydrocarbon (e.g., cyclohexane, toluene, or xylene), halogenated hydrocarbon (e.g., dichloromethane), amide (e.g., N-methylpyrrolidone or dimethylformamide), and ether (e.g., tetrahydrofuran). The solvent or dispersion medium is particularly preferably water.

[0066] The binder-containing liquid used in the present disclosure can be prepared, for example, by further adding a solvent or dispersion medium to a commercially available sizing agent having a relatively high concentration, which is composed of a binder and a solvent or dispersion medium. In particular, the binder-containing liquid can be prepared by adding a dispersion medium (particularly water) to a sizing agent having a binder and a dispersion medium (particularly water).

[0067] The sizing agent (and the binder-containing liquid obtained by adding a solvent or dispersion medium to the sizing agent) may be, for example, in the form of a water emulsion in which the binder is dispersed in water, and may in particular be a water-based polyurethane.

[0068] The concentration of the binder in the sizing agent is not particularly limited, but may be, for example, 10 to 80% by weight, 20 to 60% by weight, or 30 to 50% by weight.

[0069] The amount of the binder may be 0.5% by weight or more, 1% by weight or more, 1.5% by weight or more, 2.0% by weight or more, or 3.0% by weight or more, and / or 20% by weight or less, 15% by weight or less, 10% by weight or less, 9% by weight or less, or 8% by weight or less, based on the binder-containing liquid. The amount of the binder is particularly preferably 1% by weight to 10% by weight, or 2% by weight to 8% by weight, based on the binder-containing liquid.

[0070] The amount of binder is preferably 0.1 to 10% by weight, particularly preferably 0.5 to 9.0% by weight, 1.0 to 8.0% by weight, or 2.0 to 7.0% by weight, based on the total weight of the carbon fibers and the thermoplastic resin fibers.

[0071] (Open fiber) The fiber components, particularly recycled carbon fibers, can be subjected to a fiber-opening treatment in advance. This may eliminate entanglement between the fibers and promote the orientation of the fibers in one direction during the granulation process.

[0072] The method of opening the fibers is not particularly limited, but can be performed by using, for example, a rotary blade. The rotary blade for opening the fibers may be an auxiliary blade provided in the granulator.

[0073] The opening process can also be carried out by high speed stirring.

[0074] (mixture) The method for obtaining a mixture from recycled carbon fibers, thermoplastic resin fibers, and a binder-containing liquid is not particularly limited. The recycled carbon fibers, thermoplastic resin fibers, and binder-containing liquid can be placed in the form of a mixture in a container used in the granulation process. For example, a mixture can be obtained by pouring the binder-containing liquid into a mass of recycled carbon fibers and thermoplastic resin fibers and optionally stirring, and then placing this mixture in a container. Alternatively, the recycled carbon fibers, thermoplastic resin fibers, and binder-containing liquid can be placed separately in a container and mixed in the container to form a mixture. Mixing and granulation can also be performed simultaneously.

[0075] The carbon fibers, thermoplastic resin fibers, and binder-containing liquid in the mixture do not necessarily need to be uniformly distributed within the mixture. The mixture can be stirred during the granulation process to improve uniformity.

[0076] <Granulation process> In the method according to the present disclosure, a spindle-shaped precursor is produced by rolling the mixture in a container (hereinafter, this process may be referred to as a "granulation process").

[0077] The method for rolling the mixture in the container is not particularly limited, and any known method (particularly a known granulation method) can be used.

[0078] In particular, a spindle-shaped precursor is produced by rolling the mixture in a container in the clearance between the inner wall of the container and a rotating body inside the container. Without intending to be limited by theory, it is believed that by rolling the mixture containing carbon fibers, thermoplastic resin fibers, and a binder-containing liquid in the clearance between the inner wall of the container and a rotating body inside the container, the fibers are bonded to each other via the binder while being oriented in a specific direction, and as a result, a precursor having a spindle shape can be particularly efficiently obtained.

[0079] The method for rolling the mixture in the clearance between the inner wall of the container and the rotating body inside the container is not particularly limited, and an exemplary method for doing so will be described below with reference to FIG.

[0080] FIG. 1 is a schematic diagram of one embodiment of an agitation granulator that can be used in the present disclosure. The agitation granulator 10 in FIG. 1 has a cylindrical container portion 12 as a container and an agitation blade 14 as a rotating body. The agitation granulator 10 in FIG. 1 is horizontal, and in normal use, the opening of the container portion 12 opens to the side. FIG. 1 is a view seen from a perspective looking into the inside of the container portion. A shaft portion 16 is attached to the inner wall of the container portion 12 facing the opening (the wall on the far side from the above perspective). The shaft portion 16 extends horizontally. The agitation blade 14 can rotate around this shaft portion 16 (counterclockwise (“A”) in the example in FIG. 1, but clockwise rotation is also possible). In other words, the agitation blade 14 in FIG. 1 is configured to rotate in a plane parallel to the direction of gravity. Although not shown in FIG. 1, an auxiliary blade for opening fibers can also be installed in the container portion 12.

[0081] In the granulation process, the mixture containing the carbon fibers, thermoplastic resin fibers, and binder-containing liquid is mixed and stirred as desired by the stirring blade 14 rotating in the container portion 12, and is rolled in the clearance (indicated by the symbol "C" in Figure 1) between the inner wall of the container portion 12 and the stirring blade 14 inside the container portion 12.

[0082] The granulation process can be carried out at ambient temperature or with heating, for example, for 1 minute to 1 hour, 5 minutes to 20 minutes, or 8 minutes to 15 minutes.

[0083] (container) The container of the present disclosure is not particularly limited as long as it is suitable for holding the mixture therein and for subjecting the mixture to the above-described granulation treatment. The container is preferably made of a material that is excellent in rigidity and durability. In particular, it is preferable that the inner wall of the container be made of a material that does not undergo wear during the rolling of the mixture, or that the surface of the material be treated to prevent wear.

[0084] In one embodiment according to the present disclosure, the container is not inclined and is substantially parallel to the horizontal direction. For example, a portion of the inner wall of the container that is located lower in the direction of gravity may be not inclined and is substantially parallel to the horizontal direction.

[0085] (rotating body) The rotating body is configured to rotate within the container, thereby causing the mixture containing the carbon fibers, the thermoplastic resin fibers, and the binder-containing liquid to roll between the rotating body itself and the inner wall of the container. The rotating body is attached to a shaft portion installed within the container, for example, and is configured to rotate around the shaft portion.

[0086] The rotating body preferably has the form of a blade (impeller). The rotating body is particularly preferably an agitating blade (agitating impeller). The agitating blade is preferably made of a material having excellent rigidity and durability, and in particular, is preferably made of a material that does not wear out while the mixture is rolling, or is preferably surface-treated for this purpose.

[0087] (clearance) The size of the clearance between the inner wall of the container and the rotating body, i.e., the distance between the inner wall of the container and the rotating body, may be constant or may vary continuously or discontinuously.

[0088] The size of the clearance between the inner wall of the container and the rotating body inside the container, i.e., the distance between the inner wall of the container and the rotating body, can be set appropriately depending on the desired size of the assembly, and may be, for example, 1 to 10 mm.

[0089] (Agitating granulator) As the device having the above-mentioned container and rotor, a known agitation granulator can be used. The agitation granulator is not particularly limited, but for example, a Henschel-type granulator (Henschel mixer), a bag mill-type granulator, or an Eirich-type agitation granulator can be used. The agitation granulator can be either a vertical or horizontal type.

[0090] (fusiform precursor) The spindle-shaped precursor contains carbon fibers, thermoplastic resin fibers, and a binder, and also contains a liquid (particularly water) derived from the binder-containing liquid. The liquid (particularly water) in the precursor can be removed by the drying step described below.

[0091] <Drying process> In the method according to the present disclosure, the resulting spindle-shaped precursor is dried.

[0092] The method for drying the precursor is not particularly limited, and the temperature conditions, time conditions, etc. can be determined appropriately depending on the moisture content of the obtained precursor, etc.

[0093] ≪Resin molded products≫ A resin molded product can be produced by molding the spindle-shaped aggregate of thermoplastic resin fibers and carbon fibers according to the present disclosure using an extrusion molding machine or the like.

[0094] Examples of production methods for obtaining a resin molded product using the spindle-shaped aggregates obtained by the above method include hot molding methods such as injection molding, injection press molding, extrusion molding, and extrusion press molding. The temperature during molding (e.g., cylinder temperature) varies depending on the melt viscosity and melting point of the thermoplastic resin fiber used, but is preferably in the range of 150 to 350°C, or 250 to 300°C when polyamide 6 is used. Furthermore, during molding, stabilizers, various fillers, etc. may be added as needed. [Example]

[0095] The present invention will be described in more detail below using examples. Note that the examples are merely illustrative and the present application is not limited thereto.

[0096] Example 1 <Material Preparation> (carbon fiber) The carbon fibers used were recycled carbon fibers with a residual carbon content of 1.4% by weight obtained by semiconductor thermal activation.

[0097] The amount of residual carbon in the recycled carbon fiber was determined by thermogravimetric analysis (TGA method) as follows: (i) A 4 mg sample piece obtained by pulverizing the recycled carbon fiber was subjected to a thermogravimetric analysis for a total of approximately 600 minutes, the analysis comprising steps 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, with an air supply rate of 0.2 L / min, a heating rate of 5°C / min, and a recording speed of 1 / 6 s, in a thermogravimetric analyzer; (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.

[0098] The recycled carbon fibers had an average length of 3 mm.

[0099] (thermoplastic resin fiber) As the thermoplastic resin fiber, polyamide 6 resin fiber (PA6 resin fiber, single fiber fineness 9.8 decitex) with an average length of 3 mm was used.

[0100] (fiber component) The amount of PA6 resin fiber used as the thermoplastic resin fiber in Example 1 was 450 g, and the amount of recycled carbon fiber used as the carbon fiber was 50 g.

[0101] (binder-containing liquid) A binder-containing liquid (water emulsion sizing agent) containing 10 g of urethane resin as a binder and 204 g of water as a dispersion medium was prepared.

[0102] <Granulation process> A vertical agitator granulator (30 L MTI mixer, manufactured by Tsukishima Kikai Co., Ltd.) was used for the granulation process. This agitator granulator had an agitator blade. This agitator blade was connected to a shaft attached vertically to the lower inner wall of the vessel of the agitator granulator and was configured to rotate around this shaft. The agitator blade was also configured to have a clearance of approximately 5 mm between it and the inner wall of the vessel.

[0103] The agitator granulator also had auxiliary blades to facilitate opening of the fibers.

[0104] At the same time as the stirring blade started to rotate, 50 g of the recycled carbon fiber, 450 g of the PA6 resin fiber, and 95 g of the binder-containing liquid were added to the container of the stirring granulator, and mixing and granulation treatment was carried out at ambient temperature for 15 minutes to obtain a spindle-shaped precursor.

[0105] The water content in the mixture was 30.0% by weight. The rotation speed of the stirring blade was 235 rpm, and the rotation speed of the auxiliary blade was 3000 rpm.

[0106] <Drying process> The obtained precursor was dried in a dryer to obtain the assembly according to Example 1.

[0107] <Aggregation> The aggregate of thermoplastic resin fibers and carbon fibers according to Example 1 had a spindle shape (see FIG. 2). The thermoplastic resin fibers and carbon fibers contained in the aggregate were oriented along the longitudinal axis of the aggregate.

[0108] (binder content) The binder content in the assembly of Example 1 was 2.0 wt %.

[0109] (aspect ratio) The aspect ratio (major axis / minor axis) of the aggregates of Example 1 was calculated using a vernier caliper. The major axis is the length of the aggregate. The minor axis was measured at the point where the width of the aggregate was greatest. The average value was measured for 50 specimens (N=50), and the aspect ratio was found to be 3.2 (average value: major axis=9.7 mm, see below; minor axis=3.0 mm).

[0110] (average length) Measurements were performed using a vernier caliper on 50 samples (N=50), and the average length of the aggregates according to Example 1 was 9.7 mm. Since the average length of the recycled carbon fibers was 3 mm, the average length of the aggregates was 3.2 times the average length of the recycled carbon fibers. Furthermore, since the average length of the PA6 resin fibers was 3 mm, the average length of the aggregates was 3.2 times the average length of the PA6 resin fibers.

[0111] (Molding evaluation) Dumbbell test pieces were prepared using an injection molding machine, and the tensile strength and bending strength were measured. The injection molding machine used was a 130t injection molding machine manufactured by Toshiba Machine, and the molding was carried out at a cylinder temperature of 280°C, a mold temperature of 100°C, and a molding cycle of 200 seconds.

[0112] The results of manufacturing and evaluating the assembly according to Example 1 are shown in Table 1 below. The length of the remaining fibers in the obtained molded body was measured and found to be 317 μm (N=300). Example 2 The assembly according to Example 2 was prepared as follows.

[0113] <Material Preparation> (carbon fiber) Virgin carbon fibers were used, and the carbon fibers had an average length of 3 mm.

[0114] (thermoplastic resin fiber) As the thermoplastic resin fiber, polyamide 6 resin fiber (PA6 resin fiber, single fiber fineness 9.8 decitex) with an average length of 3 mm was used.

[0115] (fiber component) The amount of PA6 resin fiber used as the thermoplastic resin fiber in Example 2 was 450 g, and the amount of carbon fiber used as the carbon fiber was 50 g.

[0116] (binder-containing liquid) A binder-containing liquid (water emulsion sizing agent) containing 10.0 g of urethane resin as a binder and 209 g of water as a dispersion medium was prepared.

[0117] <Granulation process> For the granulation process, a vertical stirring granulator (30 L MTI mixer, manufactured by Tsukishima Kikai Co., Ltd.) was used.

[0118] The agitator granulator had an agitator blade and also had an auxiliary blade to promote opening of the fibers.

[0119] At the same time as the stirring blade started to rotate, 50 g of the carbon fiber, 450 g of the PA6 resin fiber, and 219 g of the binder-containing liquid were added to the container of the stirring granulator, and mixing and granulation treatment were carried out at ambient temperature for 15 minutes to obtain a spindle-shaped precursor.

[0120] The water content in the mixture was 30.0% by weight. The rotation speed of the stirring blade was 235 rpm, and the rotation speed of the auxiliary blade was 3,000 rpm.

[0121] <Drying process> The obtained precursor was dried in a dryer to obtain an assembly according to Example 2.

[0122] (binder content) The binder content in the assembly of Example 2 was 2.0 wt %.

[0123] (aspect ratio) The aspect ratio (major axis / minor axis) of the aggregates of Example 2 was calculated using a vernier caliper. The major axis is the length of the aggregate. The minor axis was measured at the point where the width of the aggregate was greatest. The average value was measured for 50 specimens (N=50), and the aspect ratio was found to be 4.5 (average value: major axis=10.2 mm, see below; minor axis=2.3 mm).

[0124] (average length) Measurements were performed using a vernier caliper on 50 samples (N=50), and the average length of the aggregates according to Example 2 was 10.2 mm. Since the average length of the carbon fibers was 3 mm, the average length of the aggregates was 3.4 times the average length of the carbon fibers. Furthermore, since the average length of the PA6 resin fibers was 3 mm, the average length of the aggregates was 3.4 times the average length of the PA6 resin fibers.

[0125] The results of manufacturing and evaluating the assembly according to Example 2 are shown in Table 1 below. The remaining fiber length in the obtained molded body was measured and found to be 271 μm (N=300).

[0126] Comparative Example 1 Instead of creating an aggregate of recycled carbon fiber and thermoplastic fiber, an aggregate was created using only recycled carbon fiber (fiber length = 5 mm), and this aggregate was mixed with PA6 resin to obtain pellets, which were then evaluated for injection molding. The PA6 resin used was 1013B manufactured by Ube Industries. The carbon fiber content in the pellets was adjusted to 10 wt%.

[0127] The results of the injection molding evaluation of the above pellets are shown in Table 1 below. The remaining fiber length in the obtained molded body was measured and found to be 231 μm (N=300).

[0128] Comparative Example 2 An aggregate was created using only virgin carbon fiber (fiber length = 5 mm), and the aggregate was mixed with PA6 resin to obtain pellets, which were then evaluated for injection molding. The PA6 resin used was 1013B manufactured by Ube Industries. The carbon fiber content in the pellets was adjusted to 10 wt%.

[0129] The results of the injection molding evaluation of the above pellets are shown in Table 1 below. The length of the remaining fibers in the obtained molded body was measured and found to be 210 μm (N=300). [Table 1] [Explanation of symbols]

[0130] 10 Stirring granulator 12 Container section 14 stirring blades 16 Shaft A Rotation direction C Clearance

Claims

1. A method for producing a carbon fiber-containing resin molded product, comprising supplying a spindle-shaped aggregate containing carbon fiber, thermoplastic resin fiber, and a binder to a molding machine and heat-molding the aggregate, wherein the carbon fiber contains recycled carbon fiber, and the recycled carbon fiber contains a residual carbon component, and the residual carbon component is more than 0% by weight and not more than 5.0% by weight relative to the recycled carbon fiber.

2. The method according to claim 1, wherein the average length of the aggregate is 1.5 mm to 60 mm.

3. The method according to claim 1 or 2, wherein the carbon fibers and the thermoplastic resin fibers each have an average length of 1 mm or more and less than 30 mm.

4. The manufacturing method according to claim 1 or 2, wherein the average length of the aggregate is 1.2 to 5.0 times the average length of the carbon fibers and the average length of the thermoplastic resin fibers contained in the aggregate.

5. 3. The manufacturing method according to claim 1, wherein the content of the binder is 0.1% by weight to 10% by weight with respect to the aggregate.

6. 3. The manufacturing method according to claim 1 or 2, wherein the thermoplastic resin fiber is selected from polyolefin resin fiber, polyester resin fiber, polyamide resin fiber, polyether ketone resin fiber, polycarbonate resin fiber, phenoxy resin fiber, polyphenylene sulfide resin fiber, and mixtures thereof.

7. The manufacturing method described in claim 1, wherein the carbon fiber is recycled carbon fiber.

8. Providing a mixture at least consisting of carbon fibers, thermoplastic resin fibers, and a binder-containing liquid; producing a spindle-shaped precursor by tumbling the mixture in a container; and drying the precursor; Including, A method for producing the spindle-shaped aggregate according to claim 1.

9. The method described in claim 8, wherein the mixture is rolled in a container with a clearance between the inner wall of the container and a rotating body within the container to produce a spindle-shaped precursor.

10. The method of claim 8 or 9, wherein the carbon fiber comprises recycled carbon fiber.

11. The method described in claim 10, wherein the carbon fiber is recycled carbon fiber.

12. A manufacturing method as described in claim 10, which includes decomposing plastic components contained in a carbon fiber-containing plastic product using a semiconductor thermal activation method to produce the recycled carbon fiber.

13. A manufacturing method as described in claim 11, which includes decomposing plastic components contained in a carbon fiber-containing plastic product using a semiconductor thermal activation method to produce the recycled carbon fiber.

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