Polyamide resin composition containing polyamide resin, carbon fibers, and resin carbide, and molded body using same

Abstract

Provided is a polyamide resin composition that contains a polyamide resin, carbon fibers, and a resin carbide. The amount of the polyamide resin is 60 to 90 mass%, and the total of the carbon fiber content and the resin carbide content is 10 to 40 mass%, relative to 100 mass% of the entire composition. The resin carbide is observed as non-fibrous materials which have a long diameter L of 50 μm or less and for which the aspect ratio L / D of the long diameter L to the short diameter D is 5 or less. The average area per non-fibrous material is 5 μm2 to 15 μm2. The polyamide resin composition exhibits fluidity and an elastic modulus equivalent or superior to those in a case in which virgin carbon fibers are added.

Description

Polyamide resin composition containing polyamide resin, carbon fiber and resin carbide, and molded articles using the same.

[0001] The present invention relates to a resin composition comprising a polyamide resin, carbon fibers, and resin carbides, and to a molded article using the same.

[0002] In recent years, efforts to reduce carbon dioxide emissions have been made globally, and technological development is being carried out in various fields. As part of this effort, there is a trend to replace metal components with plastics in order to improve fuel efficiency through weight reduction. In particular, crystalline thermoplastic resins are widely used in various equipment parts, but while resins alone are lighter than metal components, their strength is insufficient. Therefore, it is common practice to use reinforcing fibers to increase the mechanical strength of molded products formed from crystalline thermoplastic resins. One of the representative examples of such reinforcing fibers is carbon fiber. Because carbon fiber is lighter and harder than metal, carbon fiber reinforced plastic (CFRP) is increasingly being used in parts where weight reduction is required, such as aircraft fuselages.

[0003] On the other hand, carbon fiber requires a very large amount of heat during manufacturing, and its carbon dioxide emissions per unit mass are more than twice as high as those of aluminum and steel, which also enhance the mechanical strength of materials. Furthermore, most carbon fiber is disposed of in landfills, and currently, materials using carbon fiber reinforced plastics present several challenges from an environmental perspective.

[0004] From the perspective of effectively utilizing limited resources, the reuse of carbon fiber is being considered. Since the carbon dioxide emissions during the production of recycled carbon fiber are said to be less than half that of virgin carbon fiber, recycled carbon fiber is expected to be an environmentally friendly material. With these challenges in mind, there is a growing need for technologies that recycle carbon fiber and upcycle it to a commercially usable state. Examples of recycled carbon fiber that reuses carbon fiber are those described in Patent Documents 1 to 4.

[0005] Japanese Patent Publication No. 2023-81805, Japanese Patent Publication No. 2023-81807, Japanese Patent Publication No. 2020-189916, International Publication No. 2023 / 090374

[0006] However, conventional resin compositions blended with recycled carbon fibers tended to have inferior fluidity and elastic modulus compared to those blended with newly manufactured carbon fibers, i.e., virgin carbon fibers. In CFRP, carbon fibers are blended to enhance the mechanical strength of the plastic, so there is a demand for maintaining strength. Furthermore, since fluidity affects handling and moldability, there is always a demand for manufacturing molded products with high efficiency. Therefore, the present invention aims to provide a resin composition blended with carbon fibers in a thermoplastic resin that has fluidity and elastic modulus comparable to or improved compared to those blended with virgin carbon fibers.

[0007] The specific means for solving the above-mentioned problems are as follows: [1] A polyamide resin composition comprising a polyamide resin, carbon fibers, and resin carbides, wherein the amount of polyamide resin is 60 to 90% by mass of the total composition, and the total content of carbon fibers and resin carbides is 10 to 40% by mass, and the resin carbides are observed as non-fibrous material with a major axis L of 50 μm or less and an aspect ratio L / D of the major axis L to the minor axis D of 5 or less when the insoluble material obtained by adding the polyamide resin composition to 24% by mass hydrochloric acid and standing at 150°C for 16 hours is observed using image analysis software, and the average area per non-fibrous material measured as the average of 50 areas on the image analysis software is 5 μm ２ 15 μm or more ２The following are polyamide resin compositions: [2] The polyamide resin composition of [1] that satisfies the following relationship when hydrochloric acid treatment and heat treatment are performed independently on the same mass of the polyamide resin composition: {(mass of insoluble matter after 24% by mass hydrochloric acid treatment) / (total mass before hydrochloric acid treatment)-(mass of residue after heat treatment at 500°C for 0.5 hours) / (total mass before heat treatment)} × 100 is 0.5 to 12 (%) [3] The polyamide resin composition of [1] or [2], wherein the carbon fiber content is 7 to 38% by mass relative to 100% by mass of the polyamide resin composition. [4] The polyamide resin composition of any of [1] to [3], wherein the carbon fibers include carbon fibers to which resin carbides are attached. [5] The polyamide resin composition of [4], wherein the carbon fibers to which resin carbides are attached contain resin carbides at a concentration of 5% by mass or more and 28% by mass or less relative to the total amount of carbon fibers and resin carbides. [6] The bulk density of the carbon fiber with resin carbide attached is 0.05 g / cm³. ３ 0.32g / cm or more ３The polyamide resin composition of [4] is as follows: [7] A polyamide resin composition of any of [1] to [6] in which the carbon fibers include carbon fiber bundles and the average value of the carbon fiber bundle thickness is 0.01 to 1 mm. [8] A polyamide resin composition of any of [1] to [7] in which the carbon fibers include carbon fiber bundles and the standard deviation of the carbon fiber bundle thickness is 0.01 to 0.5 mm. [9] A polyamide resin composition of any of [1] to [8] in which the carbon fibers include recycled carbon fibers.

[10] A polyamide resin composition of any of [1] to [9] in which the polyamide resin includes a copolymer containing polyamide 5, polyamide 6, polyamide 12, polyamide 46, polyamide 56, polyamide 6 / 66, polyamide 510, or polyamide 66.

[11] A polyamide resin composition according to any of [1] to

[10] , wherein the polyamide resin is dissolved in 100 ml of 96% concentrated sulfuric acid in accordance with JIS K 6920, and the relative viscosity measured at 25°C is 1.5 to 4.2.

[12] A molded article made from any of the polyamide resin compositions according to [1] to

[11] .

[13] A molded article according to

[12] , which is at least one part selected from the group consisting of automobile parts, railway parts, machine parts, industrial materials, industrial supplies, electrical parts, electronic parts, medical parts, food packaging parts, household parts, office parts, building material-related parts, furniture parts, bicycle parts and fishing tackle parts.

[14] A method for producing any of the polyamide resin compositions according to [1] to

[11] , comprising the step of kneading each component contained in the polyamide resin composition using a twin-screw extruder, a single-screw extruder or a multi-screw extruder.

[0008] The present invention provides a resin composition in which carbon fibers are blended into a thermoplastic resin, exhibiting comparable or improved fluidity and elastic modulus compared to a resin blended with virgin carbon fibers. Furthermore, this makes it possible to reduce the manufacturing cost of carbon fiber reinforced plastics in an environmentally friendly manner.

[0009] This image shows a scan electron microscope (SEM) image obtained by observing a filtered sample of a hydrochloric acid-treated polyamide resin composition for size measurement of resin carbides.

[0010] The embodiments for carrying out the present invention will be described in detail below. The following descriptions are illustrative for explaining the present invention, and the present invention is not limited to the embodiments embodied in the following descriptions. In this specification, "~" is used to mean that the numerical values ​​described before and after it are included as the lower limit and upper limit. In this specification, all physical properties and characteristic values ​​are given at 23°C unless otherwise specified, and if the measurement methods etc. of the standards shown in this specification differ from year to year, unless otherwise specified, the latest standards as of January 1, 2024 shall be used.

[0011] The resin composition of the present invention is a polyamide resin composition comprising a polyamide resin, carbon fibers, and resin carbides, characterized in that the amount of polyamide resin is 60 to 90% by mass, and the total amount of carbon fibers and resin carbides is 10 to 40% by mass, based on 100% by mass of the entire composition. Here, the resin carbides are observed as non-fibrous material with a major axis L of 50 μm or less and an aspect ratio L / D of the major axis L to the minor axis D of 5 or less when the insoluble matter is observed with image analysis software after adding the polyamide resin composition to 24% by mass hydrochloric acid, and the average area per non-fibrous material measured as the average of 50 areas on the image analysis software is 5 μm. ２ 15 μm or more ２ The following applies. By adopting this configuration, a resin composition can be obtained that has high fluidity, excellent handling and moldability, and also excellent physical properties related to strength, such as tensile strength. The insoluble matter when added to 24% by mass hydrochloric acid is the insoluble matter obtained when added to 24% by mass hydrochloric acid and left to stand at 150°C for 16 hours. For example, it is the insoluble matter (carbon fibers and resin carbides) obtained by separating the suspension obtained by filtration or other commonly known methods from a suspension obtained by mixing 1 g of polyamide resin composition with 50 ml of 24% by mass hydrochloric acid and leaving it to stand at 150°C for 16 hours.

[0012] [Polyamide Resins] Examples of polyamide resins include aliphatic polyamide resins (A) that do not have aromatic rings, and aromatic polyamide resins (B) that contain aromatic rings. Examples of aliphatic polyamide resins (A) include aliphatic homopolyamide resins (A-1) and aliphatic copolymer polyamide resins (A-2). Examples of aromatic polyamide resins (B) include aromatic homopolyamide resins (B-1) and aromatic copolymer polyamide resins (B-2).

[0013] <Aliphatic Homopolyamide Resin (A-1)> Aliphatic homopolyamide resin (A-1) refers to a polyamide resin in which the monomer component constituting the aliphatic polyamide resin is of one type. Here, examples of monomer components constituting the aliphatic polyamide resin include a combination of aliphatic diamine and aliphatic dicarboxylic acid, lactam, or aminocarboxylic acid. Furthermore, if the monomer component constituting the aliphatic polyamide resin is a combination of aliphatic diamine and aliphatic dicarboxylic acid, then the combination of one type of aliphatic diamine and one type of aliphatic dicarboxylic acid shall be considered as one type of monomer component.

[0014] The number of carbon atoms in aliphatic diamines is preferably 2 to 20, and particularly preferably 4 to 12. The number of carbon atoms in aliphatic dicarboxylic acids is preferably 2 to 20, and particularly preferably 6 to 12. The number of carbon atoms in lactams is preferably 5 to 12. The number of carbon atoms in aminocarboxylic acids is preferably 5 to 12.

[0015] Examples of aliphatic diamines include ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, tridecanediamine, tetradecanediamine, pentadecanediamine, hexadecanediamine, heptadecanediamine, octadecanediamine, nonadecanediamine, and eicosanediamine. Examples of aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedionic acid, dodecanedionic acid, tridecanedionic acid, tetradecanedionic acid, pentadecanedionic acid, hexadecanedionic acid, octadecanedionic acid, and eicosanedionic acid.

[0016] Examples of aliphatic diamine and aliphatic dicarboxylic acid combinations include hexamethylenediamine and adipic acid, pentamethylenediamine and sebacic acid, hexamethylenediamine and sebacic acid, and hexamethylenediamine and dodecanedionic acid. Preferably, the combination of aliphatic diamine and aliphatic dicarboxylic acid is an equimolar salt of the said combination.

[0017] Examples of lactams include γ-butyrolactam, δ-valerolactam, ε-caprolactam, enantractam, undecanelactam, and dodecanelactam. Examples of aminocarboxylic acids include 5-aminopentanoic acid, 6-aminohexanoic acid, 7-aminoheptanoic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid. From the viewpoint of productivity, the lactam is preferably ε-caprolactam, undecanelactam, or dodecanelactam.

[0018] Specific examples of aliphatic homopolyamide resins (A-1) include polyvalerolactam (polyamide 5), polycaprolactam (polyamide 6), polyenanthractam (polyamide 7), polyundecanelactam (polyamide 11), polylauryllactam (polyamide 12), polytetramethyleneadipamide (polyamide 46), polytetramethylenedodecamid (polyamide 412), polypentamethyleneadipamide (polyamide 56), polypentamethyleneazeramid (polyamide 59), polypentamethylenesebacamide (polyamide 510), polypentamethylenedodecamid (polyamide 512), polyhexamethyleneadipamide (polyamide 66), polyhexamethyleneazeramid (polyamide 69), polyhexamethylenesebacamide (polyamide 610), and polyhex Examples include samethylene dodecamide (polyamide 612), polynonameethylene adipamide (polyamide 96), polynonameethylene azeramide (polyamide 99), polynonameethylene sebaamide (polyamide 910), polynonameethylene dodecamide (polyamide 912), polydecamethylene adipamide (polyamide 106), polydecamethylene azeramide (polyamide 109), polydecamethylene sebaamide (polyamide 1010), polydecamethylene dodecamide (polyamide 1012), polydodecamethylene adipamide (polyamide 126), polydodecamethylene azeramide (polyamide 129), polydodecamethylene sebaamide (polyamide 1210), polydodecamethylene dodecamide (polyamide 1212), and polydodecamethylene oxamide (polyamide 122).

[0019] <Aliphatic Copolymer Polyamide Resin (A-2)> Aliphatic copolymer polyamide resin (A-2) is an aliphatic polyamide resin in which the monomer components constituting the aliphatic polyamide resin are two or more types and which do not have aromatic rings. Therefore, an example of aliphatic copolymer polyamide resin (A-2) is an aliphatic copolymer polyamide resin which is a copolymer of two or more monomers selected from the group consisting of a combination of aliphatic diamine and aliphatic dicarboxylic acid, lactam and aminocarboxylic acid.

[0020] Specific examples of aliphatic copolymer polyamide resins (A-2) include caprolactam / hexamethylenediaminoadipic acid copolymer (polyamide 6 / 66), caprolactam / hexamethylenediaminoazelaic acid copolymer (polyamide 6 / 69), caprolactam / hexamethylenediaminosebacic acid copolymer (polyamide 6 / 610), caprolactam / hexamethylenediaminoundecanoic acid copolymer (polyamide 6 / 611), caprolactam / hexamethylenediaminododecanoic acid copolymer (polyamide 6 / 612), and caprolactam / aminoundecanoic acid copolymer (polyamide 6 / 11) Examples include caprolactam / lauryl lactam copolymer (polyamide 6 / 12), caprolactam / hexamethylenediaminoadipic acid / lauryl lactam copolymer (polyamide 6 / 66 / 12), caprolactam / hexamethylenediaminoadipic acid / hexamethylenediaminosebacic acid copolymer (polyamide 6 / 66 / 610), caprolactam / hexamethylenediaminoadipic acid / hexamethylenediaminododecanedicarboxylic acid copolymer (polyamide 6 / 66 / 612), hexamethylenediaminoadipic acid / caprolactam copolymer (polyamide 66 / 6), etc.

[0021] <Aromatic Homopolyamide Resin (B-1)> Aromatic homopolyamide resin (B-1) refers to a polyamide resin in which one monomer component constitutes the aromatic polyamide resin and which contains an aromatic compound. Therefore, examples of monomer components constituting aromatic homopolyamide resin (B-1) include combinations of aliphatic and alicyclic diamines and aromatic dicarboxylic acids, combinations of aromatic diamines and aliphatic and alicyclic dicarboxylic acids, and combinations of aromatic diamines and aromatic dicarboxylic acids. Here, aliphatic diamines and aliphatic dicarboxylic acids are those mentioned above.

[0022] <Aromatic Copolyamide Resin (B-2)> The aromatic copolyamide resin (B-2) is an aromatic polyamide resin in which the monomer components constituting the aromatic polyamide resin are two or more kinds. Here, examples of the aromatic copolyamide resin (B-2) include aromatic polyamide resins that are copolymers of monomers selected from combinations of aliphatic and / or alicyclic diamines and aromatic dicarboxylic acids, combinations of aromatic diamines and aliphatic and / or alicyclic dicarboxylic acids, and combinations of aromatic diamines and aromatic dicarboxylic acids. Here, when the monomer components constituting the aromatic polyamide resin are a combination of diamine and dicarboxylic acid, a combination of one kind of diamine and one kind of dicarboxylic acid shall be regarded as one kind of monomer component. Here, examples of the aliphatic diamine, alicyclic diamine, aromatic diamine, aliphatic dicarboxylic acid, alicyclic dicarboxylic acid, and aromatic dicarboxylic acid are those described above.

[0023] From the viewpoint of molding processability, the polyamide resin is preferably an aliphatic polyamide resin (A). When the polyamide resin is an aliphatic polyamide resin (A), the ratio of the number of methylene groups to the number of amide groups in the polyamide resin is preferably less than 12.0, more preferably less than 7.0, and even more preferably 6.0 or less. Also, the ratio of the number of methylene groups to the number of amide groups in the polyamide resin is preferably 3.0 or more, more preferably 4.0 or more, and even more preferably 5.0 or more. Also, the ratio of the number of methylene groups to the number of amide groups in the polyamide resin is preferably 3.0 or more and less than 12.0, more preferably 4.0 or more and less than 7.0, and even more preferably 5.0 or more and 6.0 or less. The ratio [CH ２ of the number of methylene groups to the number of amide groups ([NHCO]) [CH ２ / [NHCO] (hereinafter, the ratio of the number of methylene groups to the number of amide groups may be referred to as [CH ２ / [NHCO]) of less than 7.0 for polyamide resins include polyvalerolactam (polyamide 5): [CH ２ / [NHCO] = 4.0, polycaprolactam (polyamide 6): [CH ２] / [NHCO] = 5.0, polyenanthractam (polyamide 7): [CH ２ ] / [NHCO] = 6.0, polytetramethylene adipamide (polyamide 46): [CH ２ ] / [NHCO] = 4.0, polypentamethylene adipamide (polyamide 56): [CH ２ ] / [NHCO] = 4.5, polypentamethyleneazeramide (polyamide 59): [CH ２ ] / [NHCO] = 6.0, polypentamethylene sevacamide (polyamide 510): [CH ２ ] / [NHCO] = 6.5, polyhexamethylene adipamide (polyamide 66): [CH ２ ] / [NHCO] = 5.0, polyhexamethyleneazeramide (polyamide 69): [CH ２ ] / [NHCO] = 6.5, polynonameethyleneadipamide (polyamide 96): [CH ２ Examples include ] / [NHCO] = 6.5.

[0024] If the polyamide resin is a copolymer, the ratio of the number of methylene groups to the number of amide groups is [CH ２ [CH] / [NHCO] is the ratio of the number of methylene groups to the number of amide groups in the homopolymer of monomers that constitute the constituent repeating units of the copolymer [CH ２ The value obtained by multiplying ] / [NHCO] by the molar ratio of its constituent repeating units and adding this value up for all constituent repeating units. In addition, if the polyamide resin is a mixture of two or more polyamide resins, the ratio of the number of methylene groups to the number of amide groups [CH ２ [CH] / [NHCO] is the ratio of the number of methylene groups to the number of amide groups in each polyamide resin [CH ２ The value obtained by multiplying ] / [NHCO] by the mixing ratio expressed as a molar ratio and adding it up for all polyamide resins can be determined.

[0025] Examples of polyamide resins that can be preferably used include one or more selected from the group consisting of polyamide 5, polyamide 6, polyamide 46, polyamide 56, polyamide 510, polyamide 66, polyamide 610, polyamide 612, polyamide 11, and polyamide 12. Further, the polyamide resin preferably contains a copolymer containing polyamide 5, polyamide 6, polyamide 12, polyamide 46, polyamide 56, polyamide 6 / 66, polyamide 510, or polyamide 66. Further, it is also preferable that the polyamide resin is one or more selected from the group consisting of polyamide 6, polyamide 66, and polyamide 12.

[0026] Examples of the production apparatus for polyamide resins include known polyamide production apparatuses such as batch reactors, single-tank to multi-tank continuous reaction apparatuses, tubular continuous reaction apparatuses, kneading reaction extruders such as single-screw kneading extruders and twin-screw kneading extruders. As the polymerization method, known methods such as melt polymerization, solution polymerization, and solid-phase polymerization can be used, and polymerization can be carried out by repeating normal pressure, reduced pressure, and pressurization operations. These polymerization methods can be used alone or in combination as appropriate.

[0027] The polyamide resin is produced by a polymerization reaction using the above raw materials. For example, it is produced by polymerizing or copolymerizing polyamide raw materials by known methods such as melt polymerization, solution polymerization, or solid-phase polymerization. Compounds obtained by modifying plant-derived components can also be used as raw materials for the production of polyamide resins. Here, in the production of polyamide resins, additional amines may be added for polymerization or copolymerization in addition to the polyamide raw materials. When adding additional amines, after polymerization, the amines may be added and melt-kneaded to produce a polyamide resin. Thus, amines can be added at any stage during polymerization or, after polymerization, at any stage during melt-kneading. Examples of the above amines include monoamines, diamines, triamines, and polyamines. In addition to amines, carboxylic acids such as monocarboxylic acids, dicarboxylic acids, and tricarboxylic acids may be added as necessary. These amines and carboxylic acids may be added simultaneously or separately. Also, one or more of the amines and carboxylic acids exemplified below can be used. By adjusting the amounts of amines and carboxylic acids, the molecular weight, the amount of terminal amino groups, and the amount of terminal carboxy groups of the produced aliphatic polyamide can also be adjusted.

[0028] The amount of amines to be added can be appropriately determined by known methods. Usually, based on 1 mol of polyamide raw material (1 mol of monomer or monomer unit constituting the repeating unit), the addition amount of amines is preferably 0.5 meq / mol or more and 20 meq / mol or less, and more preferably 1.0 meq / mol or more and 10 meq / mol or less, from the viewpoints of obtaining sufficient reactivity and facilitating the production of a polyamide having a desired viscosity (the equivalent (eq) of an amino group is defined as the amount of an amino group that reacts with a carboxy group in a 1:1 ratio to form an amide group). The amount of carboxylic acids to be used can also be appropriately determined.

[0029] In polyamide resins, it is preferable to add diamines and / or polyamines from the above-mentioned amine examples during polymerization. From the viewpoint of suppressing gel formation, it is more preferable to add at least one selected from the group consisting of aliphatic diamines, alicyclic diamines, and polyamines during polymerization. It is even more preferable to add polyamines during polymerization to satisfy the desired relative viscosity for extrusion applications and to set the terminal amino group concentration within a suitable range.

[0030] From the viewpoint of moldability, the relative viscosity of the polyamide resin is preferably 1.5 or higher, and more preferably 1.9 or higher, measured at 25°C by dissolving 1 g of the polyamide resin in 100 ml of 96% concentrated sulfuric acid, in accordance with JIS K 6920. Furthermore, the relative viscosity is preferably 4.2 or lower, more preferably 3.2 or lower, and even more preferably 2.7 or lower. Specifically, it is preferably 1.5 to 4.2, more preferably 1.9 to 4.2, even more preferably 1.9 to 3.2, even more preferably 2.3 to 3.2, and even more preferably 2.3 to 2.7. When the polyamide resin contains two or more polyamide resins with different relative viscosities, the relative viscosity of the polyamide resin is preferably measured as described above. However, if the relative viscosity of each polyamide resin and its mixing ratio are known, the average value calculated by summing the values ​​obtained by multiplying each relative viscosity by its mixing ratio may be used as the relative viscosity of the polyamide resin.

[0031] [Carbon Fiber] Carbon fiber is a fiber in which carbon atoms have crystallized, obtained by heating and carbonizing acrylic fibers, pitch, etc., at high temperatures. It is used as a material for carbon fiber reinforced plastic (CFRP) in combination with resins such as polyamide. Carbon fiber is broadly classified into PAN-based carbon fiber, which is produced from acrylic fibers, and pitch-based carbon fiber, which is produced from pitch, a by-product of coal, petroleum, coal tar, etc. Carbon fiber derived from either of these can be used, but PAN-based carbon fiber is preferred.

[0032] In this invention, carbon fibers are defined as fibrous materials with an aspect ratio (aspect ratio L / D of the major axis L to the minor axis D) greater than 5 when observed with an instrument such as an optical microscope, and with a fiber length greater than 50 μm. The length of the carbon fibers is not particularly limited, but as described later, recycled carbon fibers are preferred, so it is preferable to include fibers whose length has been shortened to a range greater than 50 μm as a result of the fibers being cut during the recycling process. The fiber diameter of the carbon fibers is not particularly limited. In addition, the individual strands of carbon fibers may be bonded together. Such a bundle of carbon fibers is called a carbon fiber bundle. The average value and standard deviation of the carbon fiber bundle thickness are preferably the same as the average value and standard deviation of the recycled carbon fiber bundle thickness described later.

[0033] The carbon fibers preferably include carbon fibers to which resin carbides, as described later, are attached. Carbon fibers to which resin carbides are attached can be obtained by recycling carbon fibers. When composites of resin-impregnated carbon fibers, such as CFRP and prepregs, are recycled, resin carbides derived from the impregnating resin are attached. Hereinafter, in this specification, carbon fibers to which resin carbides have been attached through the recycling process will be specifically referred to as "recycled carbon fibers." Therefore, in the polyamide resin composition of the present invention, it is preferable that the carbon fibers include recycled carbon fibers. However, carbon fibers without resin carbides attached may also be mixed and used. As such carbon fibers, carbon fibers that have not undergone the recycling process (virgin fibers) can be used.

[0034] [Resin Carbides] Resin carbides are obtained by heating and carbonizing thermosetting resins or thermoplastic resins. They can be mainly obtained by firing resins such as epoxy resins and phenolic resins at 1000°C or lower, preferably 300 to 700°C, more preferably 400 to 700°C, and even more preferably 500 to 700°C. By including resin carbides in a polyamide resin composition, the melt flow rate (MFR) can be increased in particular. Therefore, the handling properties of the polyamide resin composition are improved by the resin carbides. Furthermore, by including carbon fibers and resin carbides, it is possible to obtain a resin composition with improved productivity while maintaining various properties such as mechanical strength compared to CFRP using virgin fibers.

[0035] In this specification, "resin carbide" is defined as a non-fibrous material observed with image analysis software, having a major axis L of 50 μm or less and an aspect ratio L / D of the major axis L to the minor axis D of 5 or less, with an average area of ​​5 μm per non-fibrous material. ２ 15 μm or more ２ The following characteristics apply. Here, the average area per non-fibrous material is measured as the average of the areas of 50 non-fibrous materials observed on the image analysis software. The shape of the non-fibrous material can be any shape that is observed within the above-mentioned aspect ratio and area range, such as granular. Furthermore, the method described in the examples below can be used for processing the sample for observation of the resin carbide.

[0036] The equipment used for observing resin carbides can be any commercially available device that has a camera for microscopic photography with magnification and resolution capable of photographing non-fibrous materials of about 1 μm, and image analysis software capable of measuring the size of a specified area in the captured image. The equipment used to explain specific embodiments of the present invention will be described in detail in the Examples section.

[0037] It is preferable that the resin carbides are partially present, attached to the carbon fibers. As mentioned above, when a composite of resin-impregnated carbon fibers is recycled, resin carbides derived from the impregnating resin are attached to it. Therefore, it is preferable that the carbon fibers and resin carbides in the polyamide resin composition be supplied as recycled carbon fibers. The following describes "recycled carbon fibers" in detail. The mixture of carbon fibers and resin carbides may include fibers with a major axis greater than 50 μm and an aspect ratio of 5 or less, or fibers with a major axis less than 50 μm and an aspect ratio greater than 5. However, recycled carbon fibers usually do not contain these in significant amounts. Furthermore, the following preferred ranges for the physical properties and quantity of recycled carbon fibers can also be applied to carbon fibers to which resin carbides are attached, regardless of the recycling process.

[0038] [Recycled Carbon Fiber] Recycled carbon fiber is carbon fiber that has been recycled. For example, it is carbon fiber recovered from scraps of carbon fiber reinforced polymer (CFRP) used in applications such as aircraft, vehicles, and electrical and electronic equipment, as well as from intermediate products (prepregs) of carbon fiber reinforced resin generated during the CFRP manufacturing process. Recycled carbon fiber is a material that has high suitability from the standpoint of reducing carbon dioxide emissions and protecting the environment, and it is possible to obtain resin compositions with high environmental suitability using recycled carbon fiber. Furthermore, by using recycled carbon fiber, it is possible to obtain resin compositions that have improved handling and productivity while maintaining various properties such as mechanical strength compared to CFRP using virgin fibers.

[0039] Recycled carbon fibers typically have the resin that was mixed in with CFRP (carbon fiber reinforced polymer) attached as char, resulting in a composite of carbon fibers and resin char. Examples of resins used as the matrix for CFRP from which recycled carbon fibers are derived include thermosetting resins and thermoplastic resins. Specifically, epoxy resins, aromatic polyester resins, aromatic polycarbonate resins, fully aromatic polyesters, aromatic polyamides, aromatic polyethers, and polyphenylenes are examples. There are no particular restrictions on the type of resin used in the composite of recycled carbon fibers, and it is not a matter of whether or not additives other than resin, such as curing agents or flame retardants, were included. However, if the resin contains a benzene ring, the char in the recycled carbon fibers tends to form char, which makes it easier to block oxygen, thus improving the flame retardancy of the resin composition.

[0040] In recycled carbon fibers, the individual carbon fiber strands may be bonded together by the resin or thermal decomposition products of the resin used in the product before recycling, forming carbon fiber bundles. These carbon fiber bundles encompass the fabric. The carbon fiber bundles are formed before the components of the polyamide resin composition (i.e., polyamide resin, recycled carbon fibers, and optionally other components) are kneaded together. Depending on the manufacturing method, the carbon fibers may also contain these carbon fiber bundles. When carbon fibers contain carbon fiber bundles, as in recycled carbon fibers, the average thickness of the carbon fiber bundles is preferably 0.01 mm or more, more preferably 0.1 mm or more. It is also preferably 1 mm or less, more preferably 0.8 mm or less, and even more preferably 0.7 mm or less. Furthermore, the average thickness of the carbon fiber bundles is preferably 0.01 mm or more and 1 mm or less, and more preferably 0.1 mm or more and 0.8 mm or less. Having the carbon fiber bundle thickness within this range makes it easier to obtain resin compositions with improved mechanical properties. Here, the average carbon fiber bundle thickness is calculated by measuring the bundle thickness at 30 arbitrary points on an unspecified carbon fiber bundle and averaging those values.

[0041] When carbon fibers contain carbon fiber bundles, such as recycled carbon fibers, the standard deviation of the carbon fiber bundle thickness is preferably 0.01 to 0.5 mm, more preferably 0.03 to 0.3 mm, and even more preferably 0.05 to 0.2 mm. If the standard deviation of the carbon fiber bundle thickness is above the lower limit of the above range, productivity is good. If the standard deviation of the carbon fiber bundle thickness is below the upper limit of the above range, secondary processing such as cutting, crushing, and pulverizing is easy, and wear on cutting tools can be reduced. Furthermore, compared to recycled carbon fibers that have not undergone layer separation treatment such as crushing and are subjected to secondary heat treatment in an oxidizing atmosphere, recycled carbon fibers that have undergone layer separation treatment such as crushing can have their surface area of ​​the carbon fiber bundles greatly increased, allowing for uniform heat treatment. In addition, quantitative feedability is improved. Here, the standard deviation of the carbon fiber bundle thickness is a value calculated from the following formula (1) by measuring the bundle thickness x at any 30 points of an unspecified carbon fiber bundle.

[0042] The average fiber length (D50) of recycled carbon fibers in the resin composition is not particularly limited as long as it is longer than 50 μm and the aspect ratio is greater than 5, but it is preferably 80 to 500 μm, and more preferably 100 to 400 μm. The average fiber length and fiber diameter of the recycled carbon fibers can be measured with an optical microscope, and the aspect ratio can be calculated from these measurement results.

[0043] Recycled carbon fibers are mainly produced by heating CFRP, but depending on the manufacturing method, the surface may deteriorate due to oxygen. Therefore, it is preferable for recycled carbon fibers to have a low oxygen content. Recycled carbon fibers with a low oxygen content can be obtained by methods such as carrying out the heating process in a non-oxidizing atmosphere in the manufacturing method described later. The oxygen content when the total amount of carbon fibers and resin carbides, or the amount of recycled carbon fibers, is taken as 100% by mass, is preferably less than 5.0% by mass, more preferably less than 4.5% by mass, even more preferably less than 4.0% by mass, and particularly preferably less than 3.0% by mass. The mass used as the basis for the oxygen content can be the mass of insoluble matter when a polyamide resin composition is added to 24% by mass hydrochloric acid, which can be taken as 100% by mass of the total amount of carbon fibers and resin carbides, or the amount of recycled carbon fibers. The oxygen content can be measured using instruments such as energy-dispersive X-ray analysis (EDS) and X-ray photoelectron spectroscopy (XPS).

[0044] Recycled carbon fiber preferably contains 3% by mass or more of resin carbide relative to the total amount of carbon fiber and resin carbide, more preferably 5% by mass or more, even more preferably 10% by mass or more, even more preferably 11% by mass or more, even more preferably 12% by mass or more, and even more preferably 13% by mass or more. It is presumed that by setting the amount above the lower limit, the effect of the carbon fiber as a bonding agent will be effectively exhibited. Furthermore, recycled carbon fiber preferably contains 28% by mass or less of resin carbide, more preferably 25% by mass or less, even more preferably 20% by mass or less, even more preferably 18% by mass or less, and even more preferably 16% by mass or less. By setting the amount below the upper limit, it is easier to obtain the effect of improving productivity while minimizing the reduction in mechanical strength due to resin residue. Furthermore, the recycled carbon fiber preferably contains 3% to 28% by mass of resin carbides, more preferably 5% to 28% by mass of resin carbides, even more preferably 10% to 25% by mass, even more preferably 11% to 20% by mass, and even more preferably 12% to 18% by mass.

[0045] The bulk density of recycled carbon fiber is 0.05 g / cm³. ３ 0.32g / cm or more ３ The following is preferable: When the bulk density of the recycled carbon fibers is within this range, the recycled carbon fibers are more easily dispersed uniformly in the polyamide resin composition, and the recycled carbon fibers are less likely to break or shatter. From the viewpoint of improving the mechanical properties (especially the tensile modulus and / or bending strength) of the molded article formed from the polyamide resin composition, the bulk density of the recycled carbon fibers is 0.10 g / cm³. ３ Super 0.32g / cm ３ Preferably, it is 0.11 g / cm³. ３ Super 0.32g / cm ３ It is more preferable that the following is the case: 0.11 g / cm³ ３ Super 0.31g / cm ３ It is more preferable that the following is the case: 0.11 g / cm³３ 0.30g / cm or more ３ The following is particularly preferable. The bulk density of the recycled carbon fiber can be measured by the method described in the examples.

[0046] The method for recovering carbon fibers through recycling, that is, the method for separating resin from carbon fibers contained in carbon fiber reinforced materials, is not limited. Applicable methods include pyrolysis and chemical dissolution. Pyrolysis by burning the resin-carbon fiber composite is a preferred method for reliably obtaining resin char. The amount of resin-derived residue is achieved by firing in a continuous incinerator, firing under a nitrogen atmosphere, firing at a predetermined temperature, etc. Specifically, the process includes the following steps (a) to (g).

[0047] Step (a): Step of cutting the CFRP as needed. The CFRP is cut to an appropriate size using a cutting machine as needed so that it can be applied to a heat treatment device and a crushing machine. In this case, it is preferable to cut along the longitudinal direction of the long fiber bundles contained in the CFRP, as this allows for the recovery of long fiber bundles in long lengths.

[0048] Step (b): Step to obtain a heat-treated product by thermally decomposing the matrix resin by heating the CFRP. The matrix resin is thermally decomposed (gasified, carbonized, etc.) by heating the CFRP to obtain a heat-treated product. The heat-treated product is one in which multiple carbon fiber substrates are fixed together by resin residue such as thermal decomposition products (carbides, etc.) of the matrix resin. Heating of the CFRP is carried out using a heat treatment apparatus equipped with an input chamber and a slow-cooling chamber purged with nitrogen gas, and a heating furnace adjusted to a non-oxidizing atmosphere. Examples of heating furnaces include batch-type heating furnaces such as electric furnaces; and continuous-type heating furnaces with pusher conveying or belt conveying. It is preferable that the heating furnace has a non-oxidizing atmosphere with an inert gas such as nitrogen gas or superheated steam introduced. The heating temperature is preferably 300 to 700°C, more preferably 400 to 700°C, and even more preferably 500 to 700°C. The pressure during heating is usually slightly pressurized or slightly negative (reduced pressure), and the heating time can be appropriately set within the range of 10 to 180 minutes depending on the heating temperature.

[0049] Step (c): A step in which multiple carbon fiber substrates are separated into individual recycled carbon fiber bundles by layer separation treatment such as crushing of the heat-treated material. Layer separation treatment such as crushing of the heat-treated material can be performed by applying pressure, compression, tension, shear stress, or impact to the heat-treated material while suppressing the breakage of the carbon fiber substrates. Examples of crushers used for layer separation treatment such as crushing of the heat-treated material include twin-screw roller crushers, multi-screw roller crushers with three or more axes, and hammer crushers. Multiple crushers may be used in combination. By performing layer separation treatment such as crushing of the heat-treated material, excess resin residue is removed, and the variation in the resin residue content in the recovered recycled carbon fiber bundles is reduced.

[0050] Step (d): A step to separate the recycled carbon fiber bundles separated by layer separation treatment such as crushing, as needed, according to the form of the recycled carbon fiber bundles. If there are two or more forms of carbon fiber substrates contained in the CFRP, it is preferable to separate the recycled carbon fiber bundles separated by layer separation treatment such as crushing of the heat-treated material according to the form of the recycled carbon fiber bundles, as this increases their value as recycled carbon fibers.

[0051] Step (e): A step to process the recycled carbon fiber bundles separated by layer separation treatment such as crushing into another form, if necessary. For example, the separated recycled carbon fiber bundles may be cut with a cutting machine such as a slitter, guillotine, or rotary cutter to obtain chip-shaped recycled carbon fiber bundles.

[0052] Step (f): If necessary, the recycled carbon fiber bundles separated by layer separation treatment such as crushing are further heated in an oxidizing atmosphere to reduce the amount of resin residue. Any atmosphere containing oxygen gas can be used as the oxidizing atmosphere. The oxygen gas concentration is preferably 0.1 to 25 volume percent. The temperature when heating the recycled carbon fiber bundles is preferably 300 to 700°C, more preferably 400 to 600°C, and even more preferably 450 to 550°C.

[0053] Step (g): A step of processing recycled carbon fiber bundles separated by layer separation treatment such as crushing, or recycled carbon fibers obtained by further heating in an oxidizing atmosphere, into recycled carbon fiber milled, as necessary. For more specific methods of each step, refer to the description in International Publication No. 2018 / 212016, which is incorporated herein by reference.

[0054] Examples of commercially available recycled carbon fibers include those manufactured by ELG Carbon Fiber (CARBISO® series), Carbon Fiber Recycle Industry Co., Ltd. (T8S103, 106 series), Procotex (CF.OS.A), and Carbon Conversions (re-Evo® series). In addition, recycled carbon fibers described in Japanese Patent Publication No. 2019-136932, Japanese Patent Publication No. 2013-87269, Japanese Patent Publication No. 2021-138077, and Japanese Patent Publication No. 2020-75493 can be used.

[0055] Recycled carbon fiber may consist of one component or a combination of two or more components. If two or more types of recycled carbon fiber are present, the bulk density, aspect ratio, and average fiber length shall be the average values ​​of the existing recycled carbon fiber.

[0056] [Other Components] The polyamide resin composition may contain other components besides polyamide resin, carbon fiber, and resin carbides (recycled carbon fiber), to the extent that it does not impair the effects of the present invention. Examples of such other components include other resins, inorganic compounds, nitrogen-containing compounds, plasticizers, heat-resistant agents, foaming agents, weather-resistant agents, crystal nucleating agents, antioxidants, crystallization accelerators, mold release agents, lubricants, antistatic agents, flame retardants, flame retardant aids, pigments, dyes, functional additives such as glass fibers, cellulose fibers, and aramid fibers, and other functional additives.

[0057] Other resins include polyolefin resins such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, and polybutene; modified polyolefins obtained by modifying polyolefins with organic acids such as maleic acid; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyester elastomers; vinyl aromatic resins such as polystyrene, ABS resin, and AS resin; polyurethane resins; acrylic resins; polycarbonate; polyacetal; polyvinyl alcohol; and rosin-based resins.

[0058] It is preferable that the polyamide resin composition does not contain fluororesins. Fluorine resins are resins containing fluorine atoms. Examples of fluororesins include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), and polychlorotrifluoroethylene (PCTFE). By not containing chemically stable and decomposable fluororesins, the costs associated with recycling or disposal can be reduced.

[0059] Examples of inorganic compounds include metal halides and inorganic compounds other than metal halides.

[0060] Metal halides are compounds of halogens and metals. Examples of halogens include fluorine, chlorine, bromine, and iodine. Examples of metals include Group 1 elements (alkali metals), Group 2 elements (alkaline earth metals), and Group 3 to Group 12 elements (e.g., transition metals). Preferably, the metal halide is one or more selected from the group consisting of alkali metal halides and copper halides. Examples of alkali metal halides when the metal is a Group 1 element include potassium iodide, potassium bromide, potassium chloride, sodium iodide, or sodium chloride. Examples of copper halides include cuprous chloride, cupric chloride, cuprous bromide, cupric bromide, cuprous iodide, and cupric iodide. It is particularly preferable that the metal halide is potassium iodide and / or cuprous iodide.

[0061] Inorganic compounds other than metal halides include metals, metal oxides, metal hydroxides, metal nitrides, metal phosphates, metal phosphites, metal carbonates, metal silicates, metal titanates, metal borates, metal sulfates, and metal nitrates. Specific examples of inorganic compounds other than metal halides include talc, mica, synthetic mica, glass flakes, non-swelling mica, fullerenes, carbon nanotubes, carbon black, graphite, metal foil, ceramic beads, clay, sericite, zeolite, bentonite, aluminum hydroxide, dolomite, kaolin, silica, fine silica powder, feldspar powder, potassium titanate, shirasu balloons, calcium carbonate, magnesium carbonate, barium sulfate, calcium oxide, aluminum oxide, titanium oxide, and acids. Examples include magnesium oxide, aluminum silicate, silicon dioxide, magnesium hydroxide, gypsum, novaculite, dawsonite, white clay, glass fiber, carbon fiber, graphite fiber, metal fiber, potassium titanate whisker, aluminum borate whisker, magnesium-based whisker, silicon-based whisker, warlastenite, sepiolite, slag fiber, zonolite, elestadite, gypsum fiber, silica fiber, silica-alumina fiber, zirconia fiber, boron nitride fiber, silicon nitride fiber, and boron fiber.

[0062] Examples of nitrogen-containing compounds include melamine, benguanamine, dimethylolurea, and cyanuric acid.

[0063] Other functional additives not mentioned above include, for example, the components described in Japanese Patent Publication No. 2002-370551.

[0064] The other components may each consist of one component or a combination of two or more components.

[0065] [Content] The content of each component relative to 100% by mass of the polyamide resin composition is as follows. Note that in the polyamide resin composition, the total of the polyamide resin, carbon fiber and resin carbide, and other components is 100% by mass.

[0066] The polyamide resin content is 60 to 90% by mass per 100% by mass of the polyamide resin composition. From the viewpoint of mechanical properties (particularly tensile modulus and / or flexural strength being better) and moldability, the polyamide resin content per 100% by mass of the polyamide resin composition is preferably 62 to 88% by mass, more preferably 63 to 86% by mass, and particularly preferably 64 to 85% by mass.

[0067] The carbon fiber content can be 7 to 38% by mass per 100% by mass of the polyamide resin composition. From the viewpoint of mechanical properties (particularly in terms of better tensile modulus and / or bending strength) and moldability, the lower limit of the carbon fiber content per 100% by mass of the polyamide resin composition is preferably 8% by mass, more preferably 11% by mass, and even more preferably 12% by mass. The upper limit of the carbon fiber content is preferably 36% by mass, more preferably 32% by mass, and even more preferably 31% by mass. Furthermore, from the viewpoint of mechanical properties and moldability, the carbon fiber content per 100% by mass of the polyamide resin composition is more preferably 8 to 36% by mass, even more preferably 11 to 32% by mass, and particularly preferably 12 to 31% by mass.

[0068] The resin carbide content can be 0.5 to 12% by mass per 100% by mass of the polyamide resin composition. The lower limit of the resin carbide content per 100% by mass of the polyamide resin composition is preferably 0.5% by mass, more preferably 0.6% by mass, even more preferably 0.7% by mass, even more preferably 0.8% by mass, even more preferably 1% by mass, particularly preferably 2% by mass, and most preferably 3% by mass. Furthermore, the upper limit of the resin carbide content per 100% by mass of the polyamide resin composition is preferably 12% by mass, more preferably 11% by mass, even more preferably 9% by mass, even more preferably 8% by mass, even more preferably 7% by mass, particularly preferably 6% by mass, and most preferably 5% by mass, from the viewpoint of improving handling. Furthermore, the content of resin carbides relative to 100% by mass of the polyamide resin composition is preferably 0.6 to 11% by mass, more preferably 0.8 to 9% by mass, even more preferably 1 to 7% by mass, even more preferably 2 to 6% by mass, and even more preferably 3 to 6% by mass, from the viewpoint of improving handling properties.

[0069] The amount of carbon fibers or resin carbides can also be measured as the total content of carbon fibers and resin carbides, or as the amount of recycled carbon fibers. In this case, the total content of carbon fibers and resin carbides is 10 to 40% by mass per 100% by mass of the polyamide resin composition. The lower limit of the total content of carbon fibers and resin carbides per 100% by mass of the polyamide resin composition is preferably 12% by mass, more preferably 14% by mass, even more preferably 15% by mass, and even more preferably 20% by mass, from the viewpoint of mechanical properties (particularly from the viewpoint of better tensile modulus and / or bending strength) and moldability. The upper limit of the total content of carbon fibers and resin carbides per 100% by mass of the polyamide resin composition is preferably 38% by mass, more preferably 36% by mass, even more preferably 35% by mass, and even more preferably 30% by mass. The total content of carbon fibers and resin carbides per 100% by mass of the polyamide resin composition is preferably 12 to 38% by mass, more preferably 14 to 36% by mass, and particularly preferably 15 to 35% by mass, from the viewpoint of mechanical properties (especially in terms of better tensile modulus and / or flexural strength) and moldability. When recycled carbon fibers are used, the amount of carbon fibers or resin carbides per 100% by mass of the polyamide resin composition should satisfy the range indicated above for the amount of resin carbides contained in the recycled carbon fibers. For example, if 30% by mass of recycled carbon fibers is included per 100% by mass of the polyamide resin composition, the amount of carbon fibers can be in the range of 21 to 28.5% by mass per 100% by mass of the polyamide resin composition, and the amount of resin carbides can be 1.5 to 9% by mass per 100% by mass of the polyamide resin composition.

[0070] Furthermore, the amounts of carbon fibers and resin carbides in recycled carbon fibers can also be verified based on the amount of residue obtained after independently treating the polyamide resin composition with acid or heat. Of the polyamide resin, carbon fibers, and resin carbides, the polyamide resin decomposes and dissolves with acid (e.g., hydrochloric acid or sulfuric acid, especially 24% by mass hydrochloric acid), so the carbon fibers and resin carbides can be separated by treating the polyamide resin composition with acid. For example, in the 24% by mass hydrochloric acid treatment, 1 g of polyamide resin composition is mixed with 50 ml of 24% by mass hydrochloric acid, and the suspension is left to stand at 150°C for 16 hours. Insoluble materials (carbon fibers and resin carbides) can then be separated from the suspension by filtration or other commonly known methods. Also, since carbon fibers have the highest heat resistance among the three materials (polyamide resin, carbon fibers, and resin carbides), the carbon fibers can be separated by treating the polyamide resin composition at a certain high temperature. For example, carbon fibers can be separated by heat-treating 1 g of polyamide resin composition at 500°C for 0.5 hours. Heat treatment can be carried out using an electric furnace, muffle furnace, etc. Therefore, the proportion (mass%) of resin carbides contained in the polyamide resin composition can be estimated using the following relational formula. Here, "independently treating the polyamide resin composition with acid or heat" means treating the polyamide resin composition with acid, and separately treating the polyamide resin composition that has not been treated with acid with heat. {(mass of insoluble matter after 24 mass% hydrochloric acid treatment) / (total mass before hydrochloric acid treatment) - (mass of residue after 0.5 hr heat treatment at 500°C) / (total mass before heat treatment)} × 100 When the same mass of polyamide resin composition is independently treated with 24 mass% hydrochloric acid and heat treatment at 500°C, the lower limit of the amount of resin carbides estimated by the above relational formula is preferably 0.5 mass%, preferably 0.6 mass%, preferably 0.7 mass%, preferably 0.8 mass%, preferably 1 mass%, preferably 2 mass%, and preferably 3 mass%.The upper limit of the amount of resin carbide estimated by the above formula is preferably 12% by mass, preferably 11% by mass, preferably 9% by mass, preferably 8% by mass, preferably 7% by mass, preferably 6% by mass, and preferably 5% by mass. Furthermore, the amount of resin carbide estimated by the above formula is preferably 0.5 to 12% by mass, more preferably 0.6 to 11% by mass, even more preferably 0.8 to 9% by mass, even more preferably 1 to 7% by mass, even more preferably 2 to 6% by mass, and particularly preferably 3 to 6% by mass.

[0071] The total content of polyamide resin, carbon fibers, and resin carbides is preferably 70 to 100% by mass per 100% by mass of the polyamide resin composition. Therefore, the content of other components is preferably 0 to 30% by mass per 100% by mass of the polyamide resin composition. From the viewpoint of not impairing the functions and properties of the polyamide resin, carbon fibers, and resin carbides, the content of other components per 100% by mass of the polyamide resin composition is more preferably 0% to 25% by mass, even more preferably greater than 0% to 20% by mass, and particularly preferably greater than 0% to 15% by mass.

[0072] [Further Properties of Polyamide Resin Composition] The density of the polyamide resin composition is not particularly limited, but from the viewpoint of the mechanical strength of the molded article, it is 1.10 to 1.35 g / cm³. ３ Preferably, it is 1.15 to 1.30 g / cm³. ３ It is particularly preferable that this be the case.

[0073] The polyamide resin composition preferably has a ratio of the physical properties of the polyamide resin composition to the physical properties of the composition containing virgin carbon fibers (hereinafter also referred to as "retention rate") of 90% or more, more preferably 95% or more, even more preferably 100% or more, and particularly preferably 110% or more, with respect to physical properties measured using test pieces molded from the polyamide resin composition and physical properties measured using test pieces molded from a composition containing virgin carbon fibers. Here, "composition containing virgin carbon fibers" is a composition in which the recycled carbon fibers contained in the polyamide resin composition are replaced with an equal amount of virgin carbon fibers.

[0074] In terms of specific physical properties, it is preferable that the polyamide resin composition has a tensile strength of 90% or more when measured using an ISO multipurpose test piece molded from the polyamide resin composition according to ISO 527-1,2, and when measured using an ISO multipurpose test piece molded from a composition containing virgin carbon fibers according to the same standard, with respect to the tensile strength of the polyamide resin composition relative to the tensile strength of the composition containing virgin carbon fibers (hereinafter also simply referred to as "tensile strength retention rate").

[0075] The polyamide resin composition preferably has a tensile modulus of 90% or more, as measured using an ISO multipurpose test piece molded from the polyamide resin composition according to ISO 527-1,2, and a tensile modulus of 90% or more, as measured using an ISO multipurpose test piece molded from a composition containing virgin carbon fibers according to the same standard.

[0076] Preferably, the polyamide resin composition has a tensile fracture strain of 90% or more (hereinafter also simply referred to as "tensile fracture strain retention rate") when measured using an ISO multipurpose test piece molded from a polyamide resin composition in accordance with ISO 527-1,2, and when measured using an ISO multipurpose test piece molded from a composition containing virgin carbon fibers in accordance with the same standard.

[0077] The polyamide resin composition preferably has a ratio of 90% or more of the bending strength of the polyamide resin composition to the bending strength of the virgin carbon fiber composition (hereinafter also simply referred to as "bending strength retention rate") when measured using a test piece molded from the polyamide resin composition according to ISO 178, and when measured using a test piece molded from a composition containing virgin carbon fiber according to the same standard. Furthermore, the polyamide resin composition preferably has a high maximum bending strength when molded into a 4 mm thick ISO multipurpose test piece. Specifically, the maximum bending strength is preferably 170 MPa or more, more preferably 176 MPa or more, and even more preferably 180 MPa or more. There is no particular upper limit for the maximum bending strength, but for example, 400 MPa or less is practical.

[0078] The polyamide resin composition preferably has a flexural modulus of 90.0% or higher when measured according to ISO 178 using an ISO multipurpose test piece molded from the polyamide resin composition according to ISO 178, and when measured according to ISO 178 using an ISO multipurpose test piece molded from a composition containing virgin carbon fibers according to ISO 178. Furthermore, it is preferable that the polyamide resin composition has a high flexural modulus when molded into a 4 mm thick ISO multipurpose test piece. Specifically, the flexural modulus is preferably 7.5 GPa or higher, more preferably 8.0 GPa or higher, even more preferably 9.0 GPa or higher, and most preferably 10.0 GPa or higher. There is no upper limit to the flexural modulus, but for example, 30.0 GPa or less is practical.

[0079] It is preferable that the polyamide resin composition has a ratio of 90% or more of the numerical value

[0080] The polyamide resin composition preferably has a melt flow rate (MFR) of 90% or more, as measured according to ISO 1113 (JIS K 7210), and the MFR of the composition containing virgin carbon fibers, as measured according to the same standard. This ratio of the MFR of the polyamide resin composition to the MFR of the composition containing virgin carbon fibers (hereinafter also simply referred to as "MFR retention rate") is 90% or more. Here, the MFR is measured under a 2.16 kg load at the temperature at which the resin composition was melted. The specific measurement conditions for the polyamide resin composition will be described in detail in the Examples section.

[0081] [Method for Manufacturing Polyamide Resin Composition] There are no particular restrictions on the method for manufacturing the polyamide resin composition, as long as it is a method that can knead each component. For example, a method using a twin-screw extruder, a single-screw extruder, a multi-screw extruder, etc. is possible. Therefore, the method for manufacturing the polyamide resin composition is preferably a manufacturing method that includes a step of kneading the components contained in the polyamide resin composition (i.e., polyamide resin, recycled carbon fiber, and optionally other components) using a twin-screw extruder, a single-screw extruder, or a multi-screw extruder. The polyamide resin, recycled carbon fiber, and optionally other components can each be selected and used independently.

[0082] The polyamide resin composition of the present invention exhibits various physical properties such as tensile strength and flexural strength that are equivalent to or better than those of compositions using virgin fibers. Furthermore, the polyamide resin composition of the present invention contributes significantly to reducing the amount of various CFRP waste generated through carbon fiber recycling, and from the viewpoint of reducing the energy required for the production of virgin carbon fibers and the energy required for combustion during disposal, it can contribute to achieving SDGs (Sustainable Development Goals) Goal 7, etc.

[0083] [Molded articles of polyamide resin compositions] Polyamide resin compositions can be used in the manufacture of molded articles. Molded articles containing polyamide resin compositions can be obtained as molded articles having a desired shape by molding the polyamide resin composition. The molding method is not particularly limited and includes extrusion molding, injection molding, blow molding, etc. Molded articles containing polyamide resin compositions can be used as the molded article itself or as a part containing the molded article for various applications such as automobile parts, railway parts, machine parts, industrial materials, industrial supplies, electrical parts, electronic parts, medical parts, food packaging parts, household parts, office parts, building material parts, furniture parts, bicycle parts, fishing tackle parts, etc. In parts used for various applications, the part containing the molded article can be used in combination with known components as appropriate.

[0084] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples.

[0085] [Ingredients Used] 1. Polyamide Resin Polyamide 6: Manufactured by UBE, relative viscosity 2.47 Polyamide 66: Manufactured by UBE, relative viscosity 2.45 Polyamide 12: Manufactured by UBE, relative viscosity 1.60 The relative viscosity was measured in accordance with JIS K 6920, by dissolving 1 g of the polyamide resin in 100 ml of 96% concentrated sulfuric acid and measuring it at 25°C. 2. Recycled Carbon Fiber Recycled carbon fiber: Manufactured by Shinryo Co., Ltd., product name reCina (registered trademark), bulk density 0.12 g / cm³ ３ , Average thickness of carbon fiber bundles: 0.3 mm, Standard deviation of carbon fiber bundle thickness: 0.08 mm, Oxygen content: 3-4% 3. Virgin carbon fiber: Manufactured by Teijin Corporation, Product name: HT C415, Bulk density: 0.551 g / cm³ ３

[0086] [Examples 1-5, Comparative Examples 1-5] Each component listed in Table 1 was melt-kneaded in a TEM-48BS manufactured by Toshiba Machine Co., Ltd. to produce the target polyamide resin composition pellets. Here, the amount of resin carbide listed in Table 1 is the percentage when the total polyamide resin composition is considered to be 100% by mass. Next, the obtained pellets were injection-molded at a cylinder temperature of 290°C and a mold temperature of 80°C to produce various test pieces, and their various physical properties were evaluated. In Table 1, ms% means mass%.

[0087] The values ​​shown in the table were measured using the following methods: (1) Tensile strength and tensile modulus of elasticity An ISO multipurpose test specimen was prepared using the pellets in accordance with ISO 527-1,2. A tensile test was performed using this specimen in a 23°C atmosphere in accordance with ISO 527-1,2. (2) Flexural modulus of elasticity An ISO multipurpose test specimen was prepared using the pellets in accordance with ISO 178. A flexural test was performed using this specimen in a 23°C atmosphere in accordance with ISO 178. (3) Temperature deflection under load An ISO multipurpose test specimen was prepared using the pellets in accordance with ISO 178. The temperature deflection under load was measured using this specimen at loads of 1.8 MPa and 0.45 MPa in accordance with ISO 75. (4) Melt Flow Rate (MFR) Using the pellets, the MFR was measured in accordance with ISO 1133-2 under the following conditions: when the base resin was PA6 (Examples 1, 2, Comparative Example 1, Comparative Example 2), the MFR was measured at 250°C and 2160g load; when the base resin was PA66 (Example 3, Comparative Example 3), the MFR was measured at 275°C and 2160g load; and when the base resin was PA12 (Examples 4, 5, Comparative Example 4, Comparative Example 5), the MFR was measured at 235°C and 2160g load. (5) Size of Resin Carbide 1 g of the pellets was added to 50 mL of 24% by mass hydrochloric acid and allowed to stand at 150°C for 16 hours. The suspension obtained was filtered by suction filtration, and the filtered material was observed under a scanning electron microscope (SEM) (JEOL JSM-IT200) to obtain an image. Fifty non-fibrous materials with a major axis L of 50 μm or less and an aspect ratio L / D of 5 or less to the minor axis D were measured in area using image analysis software, and the average value was measured. (6) Bulk density After filling a 200 mL measuring container with carbon fibers until it overflowed, a square was slid along the edge of the top surface of the measuring container to remove the carbon fibers that protruded from the container. The weight of these carbon fibers was measured, and the value obtained by dividing it by the volume of the measuring container was taken as the bulk density. (7) Oxygen content 1 g of the pellet was added to 50 mL of 24 mass% hydrochloric acid, and the suspension obtained by standing at 150°C for 16 hours was filtered by suction filtration, and the insoluble material (carbon fibers and resin carbides) was observed using an energy-dispersive X-ray spectrometer attached to a scanning electron microscope (SEM) (JEOL JSM-IT200) at an acceleration voltage of 15 kV and a field magnification of 3000x. The mass ratio of oxygen atoms to the total elemental mass within the field of view was determined, and this ratio was defined as the oxygen content in the recycled carbon fiber.(8) Separation of carbon fibers and resin carbides In the 24% by mass hydrochloric acid treatment, 1 g of polyamide resin composition was mixed with 150 ml of 24% by mass hydrochloric acid and allowed to stand at 150°C for 16 hours. The insoluble matter (carbon fibers and resin carbides) was separated from the suspension obtained by filtration. Furthermore, carbon fibers were separated by heat treatment of 1 g of polyamide resin composition in an electric furnace at 500°C for 0.5 hours. After drying the insoluble matter and carbon fibers, their masses were measured and the proportion (by mass) of resin carbides was determined.

[0088]

[0089]

[0090] The results shown in Table 2 indicate the following: When comparing polyamide resin compositions having equivalent composition except for the type of carbon fiber, the polyamide resin compositions of the examples showed tensile modulus and flexural modulus that were 90% or higher than those of polyamide resin compositions containing virgin carbon fibers. In particular, the tensile modulus of the polyamide resin compositions of the examples were 100% or higher than that of compositions containing virgin carbon fibers. Furthermore, the flexural modulus of the polyamide resin compositions of the examples were 95% or higher than that of compositions containing virgin carbon fibers. These tests demonstrate that the polyamide resin compositions of the examples have mechanical strength equivalent to or greater than that of polyamide resin compositions containing virgin carbon fibers. The polyamide resin compositions of the examples showed a load deflection temperature that was almost the same as that of polyamide resin compositions containing virgin carbon fibers. Even when the load deflection temperature was lower compared to polyamide resin compositions containing virgin carbon fibers, the decrease was within 0.5% when the polyamide resin composition using virgin carbon fibers was set to 100, demonstrating that heat resistance was maintained. The polyamide resin composition of the example exhibits a higher MFR (Metal Flow Rate) compared to the polyamide resin composition containing virgin carbon fibers. This indicates that the polyamide resin composition of the example has high fluidity and excellent moldability.

Claims

1. A polyamide resin composition comprising a polyamide resin, carbon fibers, and resin carbides, wherein the amount of polyamide resin is 60 to 90% by mass of the total composition, and the total content of carbon fibers and resin carbides is 10 to 40% by mass, and the resin carbides are observed as non-fibrous material with a major axis L of 50 μm or less and an aspect ratio L / D of the major axis L to the minor axis D of 5 or less when the insoluble material obtained by adding the polyamide resin composition to 24% by mass hydrochloric acid and standing at 150°C for 16 hours is observed using image analysis software, and the average area per non-fibrous material measured as the average of 50 areas on the image analysis software is 5 μm. ２ 15 μm or more ２ The following is a polyamide resin composition.

2. The polyamide resin composition according to claim 1, which satisfies the following relationship when hydrochloric acid treatment and heat treatment are performed independently on the same mass of polyamide resin composition: {(mass of insoluble matter after 24% hydrochloric acid treatment) / (total mass before hydrochloric acid treatment) - (mass of residue after heat treatment at 500°C for 0.5 hours) / (total mass before heat treatment)} × 100 is 0.5 to 12 (%).

3. The polyamide resin composition according to claim 1, wherein the carbon fiber content is 7 to 38% by mass based on 100% by mass of the polyamide resin composition.

4. The polyamide resin composition according to claim 1, wherein the carbon fibers include carbon fibers to which resin carbides are attached.

5. The polyamide resin composition according to claim 4, wherein the carbon fibers to which resin carbides are attached contain resin carbides in an amount of 5% by mass or more and 28% by mass or less, relative to the total amount of carbon fibers and resin carbides.

6. The bulk density of the carbon fiber with resin carbide attached is 0.05 g / cm³. ３ 0.32g / cm or more ３ The polyamide resin composition according to claim 4, which is as follows:

7. The polyamide resin composition according to claim 1, wherein the carbon fibers include carbon fiber bundles, and the average thickness of the carbon fiber bundles is 0.01 to 1 mm.

8. The polyamide resin composition according to claim 1, wherein the carbon fibers include carbon fiber bundles, and the standard deviation of the carbon fiber bundle thickness is 0.01 to 0.5 mm.

9. The polyamide resin composition according to claim 1, wherein the carbon fibers include recycled carbon fibers.

10. The polyamide resin composition according to claim 1, wherein the polyamide resin comprises a copolymer containing polyamide 5, polyamide 6, polyamide 12, polyamide 46, polyamide 56, polyamide 6 / 66, polyamide 510, or polyamide 66.

11. The polyamide resin composition according to claim 1, wherein the polyamide resin conforms to JIS K 6920, and the relative viscosity measured at 25°C when 1 g of the polyamide resin is dissolved in 100 ml of 96% concentrated sulfuric acid is 1.5 to 4.

2.

12. A molded article comprising the polyamide resin composition according to any one of claims 1 to 11.

13. The molded body according to claim 12, which is at least one part selected from the group consisting of automobile parts, railway parts, machine parts, industrial materials, industrial supplies, electrical parts, electronic parts, medical parts, food packaging parts, household parts, office parts, building materials related parts, furniture parts, bicycle parts and fishing tackle parts.

14. A method for producing a polyamide resin composition according to any one of claims 1 to 11, comprising the step of kneading each component contained in the polyamide resin composition using a twin-screw extruder, a single-screw extruder, or a multi-screw extruder.

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