Composite material and molded article

Abstract

To provide a composite material that uses reinforcing fibers having a resin present on the surface, that has high interfacial shear strength between the thermoplastic resin and the reinforcing fibers, and that yields a high-strength molded article, and to provide a molded article molded from the composite material. The composite material contains: a xylylenediamine-based polyamide resin which contains a diamine constituent unit and a dicarboxylic acid constituent unit and in which 70 mol% or more of the diamine constituent unit is derived from xylylenediamine; and reinforcing fibers which have a thermosetting resin on the surface thereof. The reinforcing fibers contain the thermosetting resin in a proportion of from more than 1.5 mass% to 30 mass%.

Description

Composites and Molded Products

[0001] The present invention relates to composite materials and molded articles.

[0002] Various reinforced fiber resin composite materials have been proposed as lightweight, high-strength structural members for automobiles and electrical equipment. Generally, structural members used in industrial applications are required to be lightweight and have high mechanical properties. While metal materials have traditionally been used for such structural members, the use of reinforced fiber resin composite materials, which are lighter and stronger than metal materials, has been studied in recent years. Various materials can be used as the matrix resin for reinforced fiber resin composite materials, but CFRP (CFRTP) made from thermoplastic resins, which have a shorter molding cycle than thermosetting resins, is industrially useful. Examples of such fiber reinforced resin composite materials include those described in Patent Document 1.

[0003] Japanese Patent Application Laid-Open No. 2021-020331

[0004] On the other hand, in recent years, the use of recycled reinforcing fibers has been considered from the perspective of environmental impact. However, molded articles formed from composite materials using thermoplastic resins and recycled reinforcing fibers tend to have low interfacial shear strength between the thermoplastic resin and the reinforcing fibers. Furthermore, the mechanical strength of the resulting molded articles also tends to be weak. The reason for this is that the surface of recycled reinforcing fibers does not contain the surface treatment agents that are usually applied to the surface of reinforcing fibers, and instead, resin derived from the recycled product remains. The present invention aims to solve this problem and to provide a composite material using reinforcing fibers with resin present on the surface, such as recycled reinforcing fibers, which has high interfacial shear strength between the thermoplastic resin and the reinforcing fibers and results in high strength molded articles, as well as molded articles formed from the composite material.

[0005] In light of the above-mentioned problems, the present inventors conducted research and found that the above-mentioned problems can be solved by using a xylylenediamine-based polyamide resin as a thermoplastic resin and further using reinforcing fibers having a predetermined amount of thermosetting resin on their surfaces. Specifically, the above-mentioned problems were solved by the following means. <1> A composite material comprising a xylylenediamine-based polyamide resin containing diamine structural units and dicarboxylic acid structural units, wherein 70 mol % or more of the diamine structural units are derived from xylylenediamine, and reinforcing fibers having a thermosetting resin on their surfaces, wherein the reinforcing fibers contain the thermosetting resin in an amount of more than 1.5 mass % and not more than 30 mass %. <2> The composite material according to <1>, wherein the reinforcing fibers are recycled reinforcing fibers. <3> The composite material according to <1>, wherein the reinforcing fibers are recycled carbon fibers. <4> The composite material according to any one of <1> to <3>, wherein 50 mol % or more of the dicarboxylic acid structural units in the xylylenediamine-based polyamide resin are structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms. <5> The composite material according to any one of <1> to <4>, wherein the reinforcing fiber is contained in an amount of 100 to 250 parts by mass per 100 parts by mass of the xylylenediamine-based polyamide resin. <6> The composite material according to any one of <1> to <5>, wherein the reinforcing fiber is a continuous reinforcing fiber. <7> The composite material according to any one of <1> to <6>, wherein the xylylenediamine-based polyamide resin and the thermosetting resin contained in the reinforcing fiber account for 90 mass % or more of the resin components contained in the composite material. <8> The composite material according to any one of <1> to <7>, wherein the reinforcing fibers are recycled carbon fibers, 50 mol % or more of the dicarboxylic acid structural units in the xylylenediamine-based polyamide resin are structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms, the composite material contains 100 to 250 parts by mass of the reinforcing fibers per 100 parts by mass of the xylylenediamine-based polyamide resin, the reinforcing fibers are continuous reinforcing fibers, and the xylylenediamine-based polyamide resin and the thermosetting resin contained in the reinforcing fibers account for 90 mass % or more of the resin components contained in the composite material. <9> The composite material according to any one of <1> to <8>, wherein the reinforcing fibers are woven.<10> The composite material according to any one of <1> to <8>, which is in the form of pellets. <11> A molded article formed from the composite material according to any one of <1> to <10>.

[0006] The present invention provides a composite material using reinforcing fibers with resin present on the surface, which has high interfacial shear strength between the thermoplastic resin and the reinforcing fibers and results in a molded article with high strength, as well as a molded article molded from the composite material.

[0007] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. Note that the following present embodiment is an example for explaining the present invention, and the present invention is not limited to this embodiment. Note that in this specification, the expression "to" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit. In this specification, various physical property values ​​and characteristic values ​​are those at 23°C unless otherwise specified.

[0008] In this specification, unless otherwise specified, the weight average molecular weight and number average molecular weight are polystyrene-equivalent values ​​measured by GPC (gel permeation chromatography). In this specification, unless otherwise specified, the weight average molecular weight and number average molecular weight can be measured according to the description in paragraph 0047 of JP 2018-165298 A, the contents of which are incorporated herein. If the measurement method etc. described in the specifications shown in this specification differs depending on the fiscal year, it is based on the specifications as of January 1, 2023, unless otherwise specified.

[0009] The composite material of this embodiment includes a xylylenediamine-based polyamide resin containing diamine structural units and dicarboxylic acid structural units, with at least 70 mol% of the diamine structural units derived from xylylenediamine, and reinforcing fibers having a thermosetting resin on their surfaces, the reinforcing fibers containing more than 1.5% by mass and not more than 30% by mass of the thermosetting resin. This configuration results in a composite material with high interfacial shear strength between the thermoplastic resin and the reinforcing fibers, resulting in molded articles with high strength. In particular, even when recycled textiles are used as reinforcing fibers, the reinforcing fibers are protected by the thermosetting resin, resulting in molded articles with high interfacial shear strength between the thermoplastic resin and the reinforcing fibers and excellent mechanical strength. Furthermore, even when no surface treatment agent (including binders, sizing agents, bundling agents, etc.) is present between the xylylenediamine-based polyamide resin and the reinforcing fibers, the interfacial shear strength between the thermoplastic resin and the reinforcing fibers is high, resulting in molded articles with excellent mechanical strength.

[0010] <Xylylenediamine-Based Polyamide Resin> The composite material of this embodiment contains a xylylenediamine-based polyamide resin. The xylylenediamine-based polyamide resin of this embodiment is a polyamide resin containing diamine structural units and dicarboxylic acid structural units, with 70 mol % or more of the diamine structural units being derived from xylylenediamine. Preferably, the xylylenediamine-based polyamide resin contains 50 mol % or more of the dicarboxylic acid structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms. The composite material of this embodiment can exhibit the strength and chemical resistance inherent to the xylylenediamine-based polyamide resin.

[0011] The diamine constituent units of the xylylenediamine-based polyamide resin are preferably derived from xylylenediamine (preferably paraxylylenediamine and / or metaxylylenediamine, more preferably metaxylylenediamine) for 75 mol% or more, more preferably 80 mol% or more, even more preferably 85 mol% or more, still more preferably 90 mol% or more, even more preferably 95 mol% or more, and particularly preferably 99 mol% or more. The dicarboxylic acid constituent units of the xylylenediamine-based polyamide resin are preferably derived from α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms for 60 mol% or more, even more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, still more preferably 95 mol% or more, and particularly preferably 99 mol% or more.

[0012] In this embodiment, the molar ratio of metaxylylenediamine to paraxylylenediamine in the xylylenediamine, when the total of metaxylylenediamine and paraxylylenediamine is 100 moles, is preferably metaxylylenediamine / paraxylylenediamine is 00 to 100 / 100 to 0, preferably 10 to 100 / 90 to 0, more preferably 20 to 100 / 80 to 0, even more preferably 50 to 90 / 50 to 10, and still more preferably 60 to 80 / 40 to 20. By including paraxylylenediamine, the melting point of the polyamide resin can be increased.

[0013] Diamines other than metaxylylenediamine and paraxylylenediamine that can be used as raw diamine components for xylylenediamine-based polyamide resins include aliphatic diamines such as tetramethylenediamine, pentamethylenediamine, 2-methylpentanediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 2,2,4-trimethyl-hexamethylenediamine, and 2,4,4-trimethylhexamethylenediamine; 1,3-bis( Examples of the diamine include alicyclic diamines such as bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminomethyl)decalin, and bis(aminomethyl)tricyclodecane; and diamines having an aromatic ring such as bis(4-aminophenyl)ether, paraphenylenediamine, and bis(aminomethyl)naphthalene, and these can be used alone or in combination of two or more.

[0014] As described above, the xylylenediamine-based polyamide resin preferably has 50 mol % or more of the dicarboxylic acid constituent units derived from an α,ω-straight-chain aliphatic dicarboxylic acid having 4 to 20 carbon atoms. The number of carbon atoms in the α,ω-straight-chain aliphatic dicarboxylic acid having 4 to 20 carbon atoms is preferably 6 or more, and is preferably 18 or less, more preferably 16 or less, even more preferably 14 or less, even more preferably 13 or less, and even more preferably 12 or less. Examples of α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms suitable for use as the raw dicarboxylic acid component of xylylenediamine-based polyamide resins include succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, adipic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid. These can be used alone or in combination of two or more. Among these, one or more of adipic acid, sebacic acid, and dodecanedioic acid are more preferred, with sebacic acid being even more preferred. A preferred embodiment of the xylylenediamine-based polyamide resin in this embodiment is one in which 50 mol % or more (preferably 70 mol % or more, more preferably 90 mol % or more) of the dicarboxylic acid constituent units are derived from one or more of adipic acid, sebacic acid, and dodecanedioic acid (preferably sebacic acid).

[0015] Examples of dicarboxylic acid components other than the above-mentioned α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms include phthalic acid compounds such as isophthalic acid, terephthalic acid, and orthophthalic acid, and isomers of naphthalenedicarboxylic acid such as 1,2-naphthalenedicarboxylic acid, 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,6-naphthalenedicarboxylic acid, 1,7-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid, and these can be used alone or in combination of two or more.

[0016] Although the xylylenediamine-based polyamide resin contains diamine structural units and dicarboxylic acid structural units as its main components, it does not completely exclude other structural units, and may, of course, contain structural units derived from lactams such as ε-caprolactam and laurolactam, and aliphatic aminocarboxylic acids such as aminocaproic acid and aminoundecanoic acid. Here, "main component" refers to the structural units constituting the xylylenediamine-based polyamide resin in which the total number of diamine structural units and dicarboxylic acid structural units is the largest among all structural units. In this embodiment, the total of the diamine structural units and dicarboxylic acid structural units in the xylylenediamine-based polyamide resin preferably accounts for 90% by mass or more of all structural units, more preferably 95% by mass or more, even more preferably 97% by mass or more, and even more preferably 99% by mass or more.

[0017] It is also preferable to use the above-mentioned thermoplastic resins (particularly polyamide resins, and furthermore xylylenediamine-based polyamide resins), recycled resins, and thermoplastic resins produced using biomass raw materials (biomass thermoplastic resins). The use of biomass thermoplastic resins can reduce the environmental impact. For example, bioadipic acid can be used as the biomass raw material for xylylenediamine-based polyamide resins. Mass balance certified (ISCC PLUS) adipic acid can also be used. Mass balance certification means that the amount of renewable raw materials or biomaterials used at each factory or production facility and the amount of products produced or shipped are quantified and guaranteed together with the quality.

[0018] The melting point of the xylylenediamine-based polyamide resin is preferably 150°C or higher, more preferably 180°C or higher, even more preferably 200°C or higher, and even more preferably 205°C or higher. The melting point of the xylylenediamine-based polyamide resin is preferably 350°C or lower, more preferably 330°C or lower, even more preferably 300°C or lower, even more preferably 280°C or lower, even more preferably 260°C or lower, and even more preferably 250°C or lower. When the composite material of this embodiment contains two or more xylylenediamine-based polyamide resins, the melting point of the xylylenediamine-based polyamide resin with the highest melting point is taken as the melting point. The melting point is measured by differential scanning calorimetry (DSC) in accordance with ISO 11357. Specifically, it can be measured according to the description in paragraph 0036 of WO 2016 / 084475, the contents of which are incorporated herein by reference.

[0019] The lower limit of the number average molecular weight (Mn) of the xylylenediamine-based polyamide resin is preferably 6,000 or more, more preferably 8,000 or more, and even more preferably 10,000 or more, and is preferably 10,000 or less, more preferably 50,000 or less. When two or more types of xylylenediamine-based polyamide resins are used in the present embodiment, the number average molecular weight is the number average molecular weight of the mixture.

[0020] The number average molecular weight (Mn) of the xylylenediamine-based polyamide resin is measured by gel permeation chromatography (GPC) using a standard polymethyl methacrylate (PMMA) equivalent value. Two columns packed with a styrene polymer are used as the packing material, and hexafluoroisopropanol (HFIP) with a sodium trifluoroacetate concentration of 2 mmol / L is used as the solvent. The resin concentration is 0.02% by mass, the column temperature is 40 ° C, the flow rate is 0.3 mL / min, and the measurement is performed using a refractive index detector (RI). The calibration curve is measured by dissolving six levels of PMMA in HFIP.

[0021] The content of the xylylenediamine-based polyamide resin in the composite material of this embodiment is preferably 25% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, and even more preferably 38% by mass or more, based on 100% by mass of the composite material. By adjusting the content to above the lower limit, the xylylenediamine-based polyamide resin content increases, the unimpregnated regions in the composite material become smaller, and the mechanical strength of the resulting molded article tends to be improved. Furthermore, the content of the xylylenediamine-based polyamide resin in the composite material of this embodiment is preferably 70% by mass or less, more preferably 65% ​​by mass or less, even more preferably 60% by mass or less, even more preferably 55% by mass or less, even more preferably 50% by mass or less, and even more preferably 45% by mass or less, based on 100% by mass of the composite material. Adjusting the content to below the upper limit can increase the proportion of reinforcing fibers in the composite material, thereby further improving the mechanical properties of the resulting molded article. The composite material of this embodiment may contain only one type of xylylenediamine-based polyamide resin, or two or more types of xylylenediamine-based polyamide resin. When two or more types are contained, the total amount is preferably within the above range.

[0022] The xylylenediamine-based polyamide resin used in this embodiment may contain resin additives such as antioxidants, stabilizers such as heat stabilizers, hydrolysis resistance improvers, weathering stabilizers, matting agents, UV absorbers, nucleating agents, plasticizers, dispersants, flame retardants, antistatic agents, coloring inhibitors, antigelling agents, colorants, and mold release agents, as long as the purpose and effects of the present invention are not impaired. For details, see paragraphs 0130 to 0155 of Japanese Patent No. 4,894,982 and paragraphs 0047 to 0103 of International Publication No. 2021 / 241471, the contents of which are incorporated herein by reference. Typically, the content of the resin additive in the xylylenediamine-based polyamide resin is 0 to 5% by mass, preferably 0 to 3% by mass, and may be 0 to 1% by mass.

[0023] The composite material of the present embodiment may or may not contain, in addition to the xylylenediamine-based polyamide resin, a polyamide resin other than the xylylenediamine-based polyamide resin, and a thermoplastic resin other than a polyamide resin.

[0024] The other polyamide resins may be aliphatic polyamide resins or aromatic polyamide resins. Aliphatic polyamide resins refer to polyamide resins in which aromatic monomer-derived structural units account for less than 20 mol% of the total structural units constituting the polyamide resin. Examples of aliphatic polyamide resins include polyamide 4, polyamide 46, polyamide 6, polyamide 66, polyamide 666, polyamide 610, polyamide 11, polyamide 116, polyamide 12, and polyamide 612. Aromatic polyamide resins contain diamine structural units and dicarboxylic acid structural units, and 20 to 80 mol% (preferably 30 to 80 mol%, more preferably 40 to 70 mol%) of the total structural units of the diamine structural units and dicarboxylic acid structural units contain aromatic rings. The use of such semi-aromatic polyamide resins can enhance the mechanical strength of the resulting molded products. Examples of semi-aromatic polyamide resins include polyhexamethylene terephthalamide (polyamide 6T), polyhexamethylene isophthalamide (polyamide 6I), polyamide 66 / 6T, polyamide 9T, polyamide 9MT, polyamide 10T, and polyamide 6I / 6T.

[0025] When the composite material of the present embodiment contains another polyamide resin, the content thereof is preferably 1 part by mass or more, and more preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the xylylenediamine-based polyamide resin contained in the composite material.

[0026] When the composite material of this embodiment contains a thermoplastic resin other than a polyamide resin, examples of the thermoplastic resin include polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyether ketone resins such as polyoxymethylene resin, polyether ketone, polyether ether ketone, polyether ketone ketone, and polyether ether ketone ketone, and thermoplastic polyimide resins such as polyether sulfone resin, polyether sulfide resin, thermoplastic polyether imide, thermoplastic polyamide imide, wholly aromatic polyimide, and semi-aromatic polyimide. When the composite material of this embodiment contains a thermoplastic resin other than a polyamide resin, the content thereof is preferably 1 part by mass or more, and preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and may be 5 parts by mass or less, per 100 parts by mass of the xylylenediamine-based polyamide resin contained in the composite material.

[0027] <Reinforcing Fibers Having Thermosetting Resin on Their Surfaces> The composite material of this embodiment includes reinforcing fibers having a thermosetting resin on their surfaces. By including the reinforcing fibers, the mechanical strength of the resulting molded article can be increased. In the composite material of this embodiment, the reinforcing fibers having a thermosetting resin on their surfaces include the reinforcing fibers themselves and the thermosetting resin on their surfaces. Typically, the total of the reinforcing fibers themselves and the thermosetting resin accounts for 95% by mass (preferably 99% by mass or more and 100% by mass or less) of the total reinforcing fibers.

[0028] The reinforcing fibers themselves in this embodiment may be long fibers (continuous reinforcing fibers) or short fibers. Long fibers refer to those having a number average fiber length of 6 mm or more, preferably reinforcing fibers exceeding 12 mm, more preferably reinforcing fibers exceeding 30 mm, and even more preferably reinforcing fibers exceeding 10 cm. They may be 1 m or more, and the upper limit may be 10,000 m or less. Short fibers refer to those having a number average fiber length of less than 6 mm.

[0029] Examples of materials for the reinforcing fibers themselves include inorganic fibers such as glass fibers, carbon fibers, metal fibers, boron fibers, basalt fibers, and ceramic fibers; and organic fibers such as aramid fibers, polyoxymethylene fibers, aromatic polyamide fibers, polyparaphenylene benzobisoxazole fibers, and ultra-high molecular weight polyethylene fibers. Among these, inorganic fibers are preferred from the viewpoint of achieving high strength. Because of their light weight, high strength, and high elastic modulus, at least one fiber selected from the group consisting of glass fibers, carbon fibers, and basalt fibers is more preferred, with carbon fibers being even more preferred. Examples of carbon fibers include polyacrylonitrile-based carbon fibers and pitch-based carbon fibers. Carbon fibers derived from plant-derived materials such as lignin and cellulose can also be used.

[0030] In a first embodiment of the reinforcing fibers in this embodiment, the reinforcing fibers (preferably continuous reinforcing fibers) are arranged with regularity. Arrangement with regularity includes continuous reinforcing fibers arranged in one direction, woven fibers, knitted fibers, and the like. It goes without saying that regularity in the present invention includes not only regularity in the geometric sense but also ordinary errors in the technical field of the present invention. Examples of non-regular arrangement include nonwoven fabrics. In the first embodiment of the reinforcing fibers, woven fabrics are preferred. Known woven fabrics such as twill, plain weave, and satin weave can be widely used as the woven fabric, with plain weave fabrics being preferred. In a second embodiment of the reinforcing fibers in this embodiment, staple fibers are used.

[0031] The reinforcing fiber used in this embodiment has a thermosetting resin on its surface. Examples of the thermosetting resin include epoxy resin, oxetane resin, phenol resin, polyurethane resin, melamine resin, maleimide resin, and cyanate resin, with epoxy resin being preferred. In this embodiment, the reinforcing fiber having a thermosetting resin on its surface is preferably a recycled reinforcing fiber, and more preferably a recycled carbon fiber. In particular, it is preferably a recycled reinforcing fiber derived from a fiber-reinforced epoxy resin.

[0032] In particular, the proportion of the thermosetting resin in the reinforcing fibers is greater than 1.5% by mass, preferably 2% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, even more preferably 5% by mass or more, and even more preferably 7% by mass or more, based on 100% by mass of the reinforcing fibers. Furthermore, the proportion of the thermosetting resin in the reinforcing fibers is 30% by mass or less, more preferably 25% by mass or less, even more preferably 18% by mass or less, even more preferably 15% by mass or less, even more preferably 14% by mass or less, even more preferably 13% by mass or less, and may even be 10% by mass or less, based on 100% by mass of the reinforcing fibers. By setting the proportion at or above the lower limit, damage to the reinforcing fibers in the resulting molded article can be reduced, and the mechanical strength of the resulting molded article can be further improved. By setting the proportion at or below the upper limit, the interfacial shear strength between the xylylenediamine-based polyamide resin and the reinforcing fibers can be increased in the resulting composite material. The reinforcing fibers may contain only one type of thermosetting resin, or two or more types. When two or more types are used, the total amount is preferably within the above range.

[0033] The thermosetting resin contained in the reinforcing fiber may be partially carbonized. In particular, when the reinforcing fiber is a recycled product, the proportion of carbonized resin tends to be high. The content of thermosetting resin in the reinforcing fiber used in this embodiment means the amount of thermosetting resin that remains after carbonization and has not been carbonized.

[0034] The content of the reinforcing fibers in the composite material of this embodiment is preferably 100 parts by mass or more, more preferably 120 parts by mass or more, even more preferably 130 parts by mass or more, even more preferably 140 parts by mass or more, and may even be 145 parts by mass or more, per 100 parts by mass of the xylylenediamine-based polyamide resin. By setting the content at or above the lower limit, the proportion of reinforcing fibers in the composite material can be increased, and the mechanical properties of the resulting molded article can be further improved. Furthermore, the content of the reinforcing fibers in the composite material of this embodiment is preferably 250 parts by mass or less, more preferably 200 parts by mass or less, and even more preferably 180 parts by mass or less, per 100 parts by mass of the xylylenediamine-based polyamide resin. By setting the content at or below the upper limit, the xylylenediamine-based polyamide resin can be increased, the unimpregnated regions in the composite material can be reduced, and the mechanical strength of the resulting molded article tends to be further improved. The composite material of this embodiment may contain only one type of reinforcing fiber, or two or more types. When two or more types are included, the total amount is preferably within the above range.

[0035] In the composite material of this embodiment, the xylylenediamine-based polyamide resin and the thermosetting resin contained in the reinforcing fibers preferably account for 90% by mass or more of the resin components contained in the composite material, more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more. The upper limit is 100% by mass. Here, the resin components contained in the composite material refer to components other than the reinforcing fibers (excluding the thermosetting resin portion) and other reinforcing fillers, including thermoplastic resins and resin additives.

[0036] In the composite material of this embodiment, the total amount of the xylylenediamine-based polyamide resin and the reinforcing fibers (including the thermosetting resin portion) preferably accounts for 90% by mass or more, more preferably 93% by mass or more, even more preferably 95% by mass or more, and even more preferably 97% by mass or more, of 100% by mass of the composite material. The upper limit may be 100% by mass.

[0037] <Configuration and Manufacturing Method of Composite Material> In the composite material of this embodiment, the xylylenediamine-based polyamide resin and the reinforcing fibers having a thermosetting resin on their surfaces are preferably integrated by heating. By heating, the interfacial shear strength between the xylylenediamine-based polyamide resin and the reinforcing fibers can be increased without the need for a surface treatment agent, binder, or the like.

[0038] A first embodiment of the composite material of this embodiment is exemplified by a material produced by hot pressing a xylylenediamine-based polyamide resin film and a woven fabric of reinforcing fibers having a thermosetting resin on the surface. In this case, the xylylenediamine-based polyamide resin and the reinforcing fibers themselves are bonded via the thermosetting resin or directly. An example of the composite material of the first embodiment is a prepreg. The composite material of the first embodiment is preferably in a film form. Here, the term "film form" broadly encompasses flat-plate-shaped molded products such as sheets and tapes. When the composite material of this embodiment is in a film form, its thickness is preferably 50 μm or more, more preferably 100 μm or more. By setting the thickness at or above the lower limit, wrinkles can be prevented when laminating multiple xylylenediamine-based polyamide resin films and woven fabric of reinforcing fibers having a thermosetting resin on the surface, which tends to effectively suppress resin unevenness in the resulting composite material. Furthermore, the thickness of the film-shaped composite material is preferably 300 μm or less, more preferably 200 μm or less. By setting the temperature to the upper limit or less, the impregnation time of the xylylenediamine-based polyamide resin tends to be shortened and resin deterioration due to heating can be effectively suppressed. In addition, the reinforcing fiber woven fabric having a thermosetting resin on its surface is preferably a recycled product of a prepreg containing a thermosetting resin.

[0039] A second embodiment of the composite material of this embodiment is exemplified by a material produced by melt-kneading a xylylenediamine-based polyamide resin film and reinforcing fibers having a thermosetting resin on the surface. In this case, melt-kneading can increase the interfacial shear strength between the xylylenediamine-based polyamide resin and the reinforcing fibers. An example of the composite material of the second embodiment is pellets. Furthermore, the reinforcing fibers having a thermosetting resin on the surface used in the second embodiment can be a molded product of a fiber-reinforced thermosetting resin.

[0040] The molded article of this embodiment is formed from the composite material of this embodiment. The manufacturing method of the molded article of this embodiment is not particularly limited. For example, molding can be performed by hot pressing, pultrusion molding, ultrasonic molding, laser molding, mold molding, internal pressure molding, or the like. As another example, a molded article may be obtained by various molding methods using pellets. The method for molding a molded article from a resin composition or pellets is not particularly limited, and any conventionally known molding method can be used, such as injection molding, injection compression molding, extrusion molding, profile extrusion, transfer molding, blow molding, gas-assisted blow molding, blow molding, extrusion blow molding, IMC (in-mold coating molding), rotational molding, multilayer molding, two-color molding, insert molding, sandwich molding, foam molding, and pressure molding.

[0041] The shape of the molded article of the present embodiment is not particularly limited and can be appropriately selected depending on the use and purpose of the molded article. Examples include plate-like, plate-like, rod-like, sheet-like, film-like, cylindrical, ring-like, circular, elliptical, gear-like, polygonal, irregular-shaped, hollow, frame-like, box-like, and panel-like shapes.

[0042] The application field of the molded product of this embodiment is not particularly limited, and it can be widely used in transportation equipment parts such as automobiles, general machine parts, precision machine parts, electronic and electrical equipment parts, office automation equipment parts, building materials and housing-related parts, medical devices, leisure and sporting goods, play equipment, medical supplies, daily necessities such as food packaging films, defense and aerospace products, etc.

[0043] The present invention will be explained in more detail below with reference to examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. If the measuring instruments used in the examples are difficult to obtain due to discontinuation or the like, measurements can be made using other instruments with equivalent performance.

[0044] 1. Raw materials CF: recycled carbon fiber plain weave, type of curable resin: epoxy resin, proportion of thermosetting resin remaining after carbonization that was not carbonized: 10 mass%. All recycled carbon fibers used were carbonized at 500°C for 1 hour. MPXD10: polyamide resin synthesized in Synthesis Example 1.

[0045] Synthesis Example 1 Synthesis of MPXD10 Sebacic acid (manufactured by CASDA) was placed in a jacketed reactor equipped with a stirrer, a partial condenser, a thermometer, a dropping tank, and a nitrogen gas inlet tube, and the inside was thoroughly purged with nitrogen. After heating and melting at 170°C, a mixed amine (70:30) of metaxylylenediamine and paraxylylenediamine (manufactured by Mitsubishi Gas Chemical Company, Inc., MPXDA) was gradually added dropwise to a molar ratio of 1:1 to sebacic acid while stirring the contents, and the temperature was raised to 240°C. After completion of the dropwise addition, the temperature was raised to 260°C and continued for 20 minutes. Thereafter, the pressure inside the reaction system was continuously reduced to 0.08 MPa, and the reaction was continued. After completion of the reaction, a pressure of 0.2 MPa was applied to the reactor with nitrogen gas, and the polymer was taken out as a strand from a nozzle at the bottom of the polymerization vessel. After water cooling, the polymer was pelletized using a pelletizer.

[0046] 2. Examples 1 and 2, Comparative Examples 1 and 2 <Production of Resin Film> A polyamide resin dried in a vacuum dryer was melt-extruded using a single-screw extruder having a screw with a diameter of 30 mm, extrusion-molded through a 500 mm wide T-die, and pressed using a stainless steel pair of rolls at a roll temperature of 70°C and a roll pressure of 0.4 MPa to form a 100 μm film.

[0047] <Production of Molded Article> The 100 μm film obtained above and a plain weave fabric of recycled carbon fiber were alternately laminated in the order of film, fabric, and film using a heat press machine (manufactured by Kodaira Manufacturing Co., Ltd.). Thereafter, the laminate was press-molded at a press temperature of 250° C., a press pressure of 3 MPa, and a press time of 15 minutes to obtain a molded article.

[0048] <Measurement of bending strength> The molded product obtained above was cut to a size conforming to the standard using a Makita sliding circular saw, and three-point bending was performed in accordance with ASTM D7264 using an Autograph testing machine (AG-Xplus 100 kN, manufactured by Shimadzu Corporation).

[0049] <Measurement of interlaminar shear strength> The molded product obtained above was cut to a size conforming to the standard using a Makita sliding circular saw, and the test was carried out using an autograph (AG-Xplus 100 kN, manufactured by Shimadzu Corporation) in accordance with ASTM D2344.

[0050]

[0051] As is clear from the above results, the composite materials of the present invention had high interlaminar shear strength (interfacial shear strength) between the reinforcing fibers and the xylylenediamine-based polyamide resin, and the resulting molded articles had excellent bending strength (mechanical strength) (Examples 1 and 2). In contrast, when the proportion of thermosetting resin in the reinforcing fibers was low (Comparative Example 1), the reinforcing fibers were damaged, and the resulting molded articles had low bending strength (mechanical strength). On the other hand, when the proportion of thermoplastic resin in the reinforcing fibers was high (Comparative Example 2), the reinforcing fibers were not sufficiently impregnated with the xylylenediamine-based polyamide resin, resulting in low interlaminar shear strength (interfacial shear strength) between the reinforcing fibers and the xylylenediamine-based polyamide resin, and the resulting molded articles had low bending strength (mechanical strength).

Claims

1. A composite material comprising: a xylylenediamine-based polyamide resin containing diamine structural units and dicarboxylic acid structural units, with 70 mol% or more of the diamine structural units being derived from xylylenediamine; and reinforcing fibers having a thermosetting resin on their surfaces, the reinforcing fibers containing the thermosetting resin in an amount of more than 1.5 mass% and not more than 30 mass%.

2. The composite material of claim 1, wherein the reinforcing fibers are recycled reinforcing fibers.

3. The composite material of claim 1, wherein the reinforcing fibers are recycled carbon fibers.

4. A composite material according to any one of claims 1 to 3, wherein 50 mol % or more of the dicarboxylic acid constituent units in the xylylenediamine-based polyamide resin are constituent units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms.

5. A composite material according to any one of claims 1 to 4, comprising 100 to 250 parts by mass of the reinforcing fiber per 100 parts by mass of the xylylenediamine-based polyamide resin.

6. The composite material according to any one of claims 1 to 5, wherein the reinforcing fibers are continuous reinforcing fibers.

7. A composite material according to any one of claims 1 to 6, wherein the xylylenediamine-based polyamide resin and the thermosetting resin contained in the reinforcing fibers account for 90 mass% or more of the resin components contained in the composite material.

8. The composite material according to any one of claims 1 to 7, wherein the reinforcing fibers are recycled carbon fibers, 50 mol % or more of the dicarboxylic acid constituent units in the xylylenediamine-based polyamide resin are constituent units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms, the composite material contains 100 to 250 parts by mass of the reinforcing fibers per 100 parts by mass of the xylylenediamine-based polyamide resin, the reinforcing fibers are continuous reinforcing fibers, and the xylylenediamine-based polyamide resin and the thermosetting resin contained in the reinforcing fibers account for 90 mass % or more of the resin components contained in the composite material.

9. The composite material according to any one of claims 1 to 8, wherein the reinforcing fibers are woven.

10. The composite material according to any one of claims 1 to 8, which is in the form of a pellet.

11. A molded article formed from the composite material according to any one of claims 1 to 10.

Images