Fiber-reinforced composite material and molded article

Abstract

The present invention provides a fiber-reinforced composite material and a molded article. Provided is a fiber-reinforced composite material containing 100-200 parts by mass of continuous reinforcing fibers per 100 parts by mass of a polyamide resin, wherein the polyamide resin contains a diamine unit and a dicarboxylic acid unit, 70 mol% or more of the diamine unit is derived from a xylylenediamine, and 70 mol% or more of the dicarboxylic acid unit is derived from a C11-20 α,ω-linear aliphatic dicarboxylic acid.

Description

Fiber-reinforced composite materials and moldings

[0001] The present invention relates to a fiber-reinforced composite material and a molded article, and more particularly to a fiber-reinforced composite material using a specific polyamide resin.

[0002] In recent years, there has been an increasing demand for fiber-reinforced composite materials, such as carbon fiber-reinforced thermoplastic resins (CFRTPs), which use thermoplastic resins and reinforcing fibers. Among thermoplastic resins, polyamide 6, polyamide 66, and polyamide 12 are often used as matrix resins for CFRTPs (see, for example, Patent Document 1). Fiber-reinforced composite materials using polyamide resins composed of adipic acid or sebacic acid and xylylenediamine have also been studied (see, for example, Patent Document 2).

[0003] JP 2023-147962 A International Publication No. 2020 / 174871

[0004] Here, the present inventors have investigated Patent Document 1 and found that fiber-reinforced composite materials obtained using polyamide 6 or polyamide 66 exhibit a significant decrease in interlaminar shear strength after water absorption. On the other hand, when polyamide 12 is used, the interlaminar shear strength after water absorption can be suppressed, but the interlaminar shear strength itself (initial interlaminar shear strength) is low. Meanwhile, when Patent Document 2 was also investigated, it was found that a polyamide resin composed of sebacic acid and xylylenediamine was able to maintain a significantly higher interlaminar shear strength after water absorption than polyamide 6 or polyamide 66. Furthermore, it was able to achieve a significantly higher initial interlaminar shear strength than when polyamide 12 was used. However, with recent technological advances, there is a demand for fiber-reinforced composite materials that have high initial interlaminar shear strength and an improved retention rate of interlaminar shear strength after water absorption. The present invention aims to solve this problem by providing a fiber-reinforced composite material and a molded article that have high initial interlaminar shear strength and an improved retention rate of interlaminar shear strength after water absorption.

[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 specific polyamide resin. Specifically, the above-mentioned problems were solved by the following means. <1> A fiber-reinforced composite material comprising 100 to 200 parts by mass of continuous reinforcing fibers per 100 parts by mass of polyamide resin, the polyamide resin containing diamine units and dicarboxylic acid units, 70 mol % or more of the diamine units being derived from xylylenediamine, and 70 mol % or more of the dicarboxylic acid units being derived from an α,ω-linear aliphatic dicarboxylic acid having 11 to 20 carbon atoms. <2> The fiber-reinforced composite material according to <1>, wherein 70 mol % or more of the dicarboxylic acid units are derived from dodecanedioic acid and / or tetradecanedioic acid. <3> The fiber-reinforced composite material according to <1>, wherein 70 mol % or more of the dicarboxylic acid units are derived from dodecanedioic acid. <4> The fiber-reinforced composite material according to any one of <1> to <3>, wherein 20 to 100 mol % of the diamine units are derived from meta-xylylenediamine and 80 to 0 mol % are derived from para-xylylenediamine (provided that the total does not exceed 100 mol %). <5> The fiber-reinforced composite material according to <1>, wherein 70 mol % or more of the dicarboxylic acid units are derived from dodecanedioic acid and / or tetradecanedioic acid, and wherein 20 to 100 mol % of the diamine units are derived from meta-xylylenediamine and 80 to 0 mol % are derived from para-xylylenediamine. <6> The fiber-reinforced composite material according to any one of <1> to <5>, wherein the continuous reinforcing fibers comprise at least one fiber selected from the group consisting of carbon fiber, glass fiber, and aramid fiber. <7> The fiber-reinforced composite material according to any one of <1> to <6>, wherein the number-average fiber length of the continuous reinforcing fibers is greater than 10 mm. <8> The fiber-reinforced composite material according to any one of <1> to <7>, which is a prepreg. <9> The fiber-reinforced composite material according to <8>, which is a prepreg in which the continuous reinforcing fibers are oriented in one direction and are impregnated with the polyamide resin. <10> The fiber-reinforced composite material according to <8>, which is a prepreg in which the continuous reinforcing fibers are a woven fabric and are impregnated with the polyamide resin. <11> A molded article formed from the fiber-reinforced composite material according to any one of <1> to <10>.

[0006] The present invention makes it possible to provide a fiber-reinforced composite material and a molded article that have high initial interlaminar shear strength and further improved retention of interlaminar shear strength after water absorption.

[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 word "to" is used to mean that the numerical values ​​before and after it are included as the upper and lower limits. Furthermore, any combination of the upper and lower limit values ​​of numerical values ​​in this specification is cited as an example of the present embodiment. In this specification, various physical property values ​​and characteristic values ​​are those at 23°C unless otherwise specified.

[0008] If the measurement methods, etc. described in the standards shown in this specification vary from year to year, they will be based on the standards in effect as of January 1, 2024, unless otherwise specified. If the measurement methods, etc. described in the standards shown in this specification are abolished as of January 1, 2024, they will be based on the standards in effect at the time of abolition.

[0009] The fiber-reinforced composite material of this embodiment is characterized in that it contains 100 to 200 parts by mass of continuous reinforcing fibers per 100 parts by mass of polyamide resin, and the polyamide resin contains diamine units and dicarboxylic acid units, with 70 mol % or more of the diamine units being derived from xylylenediamine and 70 mol % or more of the dicarboxylic acid units being derived from an α,ω-linear aliphatic dicarboxylic acid having 11 to 20 carbon atoms. This configuration makes it possible to provide a fiber-reinforced composite material and a molded article that have high initial interlaminar shear strength and an even improved retention rate of interlaminar shear strength after water absorption.

[0010] As described above, fiber-reinforced composite materials using polyamide resins composed of sebacic acid and xylylenediamine have high initial and post-water absorption interlaminar shear strength. However, recent technological innovations have led to a demand for fiber-reinforced composite materials with even higher post-water absorption interlaminar shear strength. Based on this situation, the inventors conducted research and found that by using a polyamide resin containing an α,ω-linear aliphatic dicarboxylic acid having 11 to 20 carbon atoms instead of sebacic acid, the decrease in post-water absorption interlaminar shear strength can be effectively suppressed. As shown in the examples below, when using the polyamide resin defined in this embodiment, the decrease in post-water absorption interlaminar shear strength was approximately 3%, whereas when using a polyamide resin composed of sebacic acid and xylylenediamine, the decrease in post-water absorption interlaminar shear strength was approximately 7%. Interlaminar shear strength varies depending on the interface between the polyamide resin and the reinforcing fibers, and it was estimated that this effect is greater for polyamide resins using sebacic acid and less for polyamide resins using dicarboxylic acids with a larger carbon number. In particular, it was estimated that when continuous reinforcing fibers are used as reinforcing fibers, the tendency for changes in physical properties changes significantly compared to when short fibers are used. As a result, it was estimated that a fiber-reinforced composite material was obtained that had high initial interlaminar shear strength and further improved retention of interlaminar shear strength after water absorption. Furthermore, it was found that the use of the polyamide resin used in this embodiment can effectively suppress the decrease in flexural strength after water absorption. The details of this embodiment are described below.

[0011] <Polyamide Resin> The fiber-reinforced composite material of the present embodiment contains a polyamide resin (hereinafter sometimes referred to as a "xylylenediamine-based polyamide resin") that contains diamine units and dicarboxylic acid units, in which 70 mol % or more of the diamine units are derived from xylylenediamine and 70 mol % or more of the dicarboxylic acid units are derived from a linear α,ω-aliphatic dicarboxylic acid having 11 to 20 carbon atoms.

[0012] The diamine units of the xylylenediamine-based polyamide resin are preferably derived from xylylenediamine (preferably paraxylylenediamine and / or metaxylylenediamine) at 75 mol% or more, 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.

[0013] The xylylenediamine is preferably paraxylylenediamine and / or metaxylylenediamine. The xylylenediamine preferably contains 0 to 100 mol% metaxylylenediamine and 100 to 0 mol% paraxylylenediamine (provided that the total of metaxylylenediamine and paraxylylenediamine does not exceed 100 mol%), more preferably 20 to 100 mol% metaxylylenediamine and 80 to 0 mol% paraxylylenediamine, and even more preferably 35 to 100 mol% metaxylylenediamine and 65 to 0 mol% paraxylylenediamine. By making the proportion of metaxylylenediamine 20 mol% or more, the melting point tends to be suppressed and the balance between processability and physical properties tends to be improved. In the xylylenediamine-based polyamide resin, the total of the paraxylylenediamine units and metaxylylenediamine units preferably accounts for 80 mol % or more, more preferably 85 mol % or more, even more preferably 90 mol % or more, still more preferably 95 mol % or more, still more preferably 98 mol % or more, and still more preferably 99 mol % or more of the diamine units. The upper limit of the total of the paraxylylenediamine units and metaxylylenediamine units is 100 mol %.

[0014] 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.

[0015] On the other hand, the dicarboxylic acid units of the xylylenediamine-based polyamide resin are preferably derived from 75 mol% or more, more preferably 80 mol% or more, even more preferably 85 mol% or more, still more preferably 90 mol% or more, still more preferably 95 mol% or more, and particularly preferably 99 mol% or more of straight-chain aliphatic α,ω-dicarboxylic acids preferably having 11 to 20 carbon atoms.

[0016] The α,ω-linear aliphatic dicarboxylic acid having 11 to 20 carbon atoms that is preferably used as the raw dicarboxylic acid component of the xylylenediamine-based polyamide resin is preferably an α,ω-linear aliphatic dicarboxylic acid having 11 to 16 carbon atoms, and more preferably an α,ω-linear aliphatic dicarboxylic acid having 12 to 14 carbon atoms. Specific examples of the α,ω-linear aliphatic dicarboxylic acid having 11 to 20 carbon atoms include dodecanedioic acid, tridecanedioic acid, and tetradecanedioic acid. Among these, at least one of dodecanedioic acid and / or tetradecanedioic acid is preferred, with dodecanedioic acid being more preferred, since the melting point of the polyamide resin falls within a range suitable for molding.

[0017] Examples of dicarboxylic acid components other than those mentioned above include α,ω-linear aliphatic dicarboxylic acids having 10 or less carbon atoms, such as adipic acid and sebacic acid; 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. These can be used alone or in combination of two or more.

[0018] Although the xylylenediamine-based polyamide resin is primarily composed of diamine units and dicarboxylic acid units, other structural units are not completely excluded. It goes without saying that the resin may contain lactams such as ε-caprolactam and laurolactam, and aliphatic aminocarboxylic acid units such as aminocaproic acid and aminoundecanoic acid. Here, "primary component" refers to the structural units constituting the xylylenediamine-based polyamide resin in which the total number of diamine units and dicarboxylic acid units is the largest among all structural units. In this embodiment, the total of the diamine units and dicarboxylic acid 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.

[0019] It is also preferable to use a polyamide resin produced using biomass raw materials (biomass polyamide resin) as the xylylenediamine-based polyamide resin. The use of biomass polyamide resin can reduce the environmental impact. Furthermore, raw material monomers that are mass balance certified (ISCC PLUS) can also be used for the xylylenediamine-based polyamide resin. Mass balance certification means that the amount of renewable raw materials or bio-based raw materials used in each factory or production facility and the amount of products produced or shipped are quantified, and the quality is guaranteed.

[0020] The melting point of the xylylenediamine-based polyamide resin is preferably 150°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, and even more preferably 180°C or higher, and is preferably 300°C or lower, more preferably 280°C or lower, even more preferably 260°C or lower, and even more preferably 205°C or lower. The melting point is measured according to the description in the Examples below. When the mixed yarn of this embodiment contains two or more types of xylylenediamine-based polyamide resins, the melting point is the weighted average of the respective polyamide resins.

[0021] 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, even more preferably 10,000 or more, and preferably 100,000 or less, more preferably 50,000 or less. Within this range, the heat resistance, elastic modulus, dimensional stability, and moldability of the resulting molded article are improved. The number average molecular weight is a polystyrene-equivalent value measured by GPC (gel permeation chromatography). More specifically, the 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 by reference.

[0022] The fiber-reinforced composite material of this embodiment may contain a polyamide resin other than a xylylenediamine-based polyamide resin. Examples of polyamide resins other than a xylylenediamine-based polyamide resin include aliphatic polyamide resins and semi-aromatic polyamide resins other than a xylylenediamine-based polyamide resin. Examples of aliphatic polyamide resins include polyamide 4, polyamide 46, polyamide 6, polyamide 66, polyamide 666, polyamide 610, polyamide 11, and polyamide 12. Examples of semi-aromatic polyamide resins include terephthalic acid-based polyamide resins (polyamide 6T, polyamide 9T, and polyamide 10T) and the xylylenediamine-based polyamide resins described below.

[0023] The content of polyamide resin (the total of xylylenediamine-based polyamide resin and other polyamide resins other than xylylenediamine-based polyamide resin) in the fiber-reinforced composite material of this embodiment is preferably 25% by mass or more, more preferably 30% by mass or more, and even more preferably 32% by mass or more, based on 100% by mass of the fiber-reinforced composite material. It is also preferably 50% by mass or less, more preferably 48% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. The fiber-reinforced composite material of this embodiment may contain only one type of polyamide resin, or may contain two or more types. When two or more types are contained, the total amount preferably falls within the above range. The fiber-reinforced composite material of this embodiment may also be configured to be substantially free of polyamide resins other than xylylenediamine-based polyamide resin. By "substantially free," it is meant that the content of other polyamide resins in the fiber-reinforced composite material is preferably less than 10% by mass of the content of continuous reinforcing fibers, more preferably less than 5% by mass, even more preferably less than 3% by mass, and even more preferably less than 1% by mass.

[0024] <Continuous Reinforcing Fiber> The fiber-reinforced composite material of this embodiment contains continuous reinforcing fiber. Continuous reinforcing fiber refers to a reinforcing fiber having an average fiber length of more than 6 mm, preferably more than 10 mm, more preferably more than 12 mm, even more preferably 30 mm or more, and even more preferably 10 cm or more. There are no particular restrictions on the average fiber length of the continuous reinforcing fiber used in this embodiment, but from the viewpoint of improving molding processability, it is preferably 1 m or more, more preferably 100 m or more, even more preferably 1,000 m or more, and preferably 20,000 m or less, more preferably 1,0000 m or less, and even more preferably 7,000 m or less.

[0025] Examples of continuous reinforcing fibers 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, it is preferable to include at least one fiber selected from the group consisting of carbon fibers, glass fibers, and aramid fibers, and carbon fibers are more preferable. Examples of carbon fibers include polyacrylonitrile-based carbon fibers and pitch-based carbon fibers. Examples of glass fibers include fibers obtained by melt spinning commonly supplied glasses such as E-glass, C-glass, A-glass, S-glass, and alkali-resistant glass.

[0026] The continuous reinforcing fibers may be surface-treated with a surface treatment agent. The cross section of the continuous reinforcing fibers may be either circular or non-circular. In addition to the above, the description of paragraph 0074 of Japanese Patent No. 7398028 can be referred to for continuous carbon fibers, the contents of which are incorporated herein by reference.

[0027] The form of the continuous reinforcing fibers is not particularly limited, but it is preferable that they are oriented in at least one direction. An example of the continuous reinforcing fibers in this embodiment is that the continuous reinforcing fibers are oriented in one direction. An example of the continuous reinforcing fibers oriented in one direction is an opened continuous reinforcing fiber roving. Another example of the continuous reinforcing fibers in this embodiment is that the continuous reinforcing fibers are a woven fabric. Examples of the woven fabric include plain weave, twill weave, and satin weave.

[0028] In the case of carbon fibers, the continuous reinforcing fibers preferably have a tensile strength of 1500 MPa or more, more preferably 2500 MPa or more, and even more preferably 3500 MPa or more. There is no particular upper limit, but it is practical to have a tensile strength of 8000 MPa or less. In the case of glass fibers, the tensile strength is preferably 800 MPa or more, more preferably 1800 MPa or more, and even more preferably 2800 MPa or more. There is no particular upper limit, but it is practical to have a tensile strength of 5000 MPa or less.

[0029] The content of continuous reinforcing fibers in the fiber-reinforced composite material of this embodiment is 100 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 120 parts by mass or more, and even more preferably 130 parts by mass or more, relative to 100 parts by mass of polyamide resin. It is also 200 parts by mass or less, preferably 190 parts by mass or less, more preferably 180 parts by mass or less, even more preferably 170 parts by mass or less, and even more preferably 160 parts by mass or less. By setting the content at or above the lower limit, molding time tends to be further shortened. Furthermore, by setting the content at or below the upper limit, the carbon fiber content in the composite material can be increased, and the mechanical properties of the molded product tend to be improved. The fiber-reinforced composite material of this embodiment may contain only one type of continuous reinforcing fiber, or may contain two or more types. When two or more types are contained, the total amount is preferably within the above range.

[0030] The fiber-reinforced composite material of this embodiment may or may not contain fillers other than the continuous reinforcing fibers. An example of the fiber-reinforced composite material of this embodiment is one that is substantially free of fillers other than the continuous reinforcing fibers. "Substantially free" means that the content of other fillers in the fiber-reinforced composite material is preferably less than 10% by mass of the content of the continuous reinforcing fibers, more preferably less than 5% by mass, even more preferably less than 3% by mass, and even more preferably less than 1% by mass.

[0031] <Other Components> The fiber-reinforced composite material of this embodiment may or may not contain other components besides the polyamide resin and continuous reinforcing fibers. Examples of the other components include thermoplastic resins other than polyamide resins, fillers other than continuous reinforcing fibers, nucleating agents, antioxidants, stabilizers such as heat stabilizers, hydrolysis resistance improvers, weathering stabilizers, delustering agents, UV absorbers, nucleating agents, plasticizers, dispersants, flame retardants, antistatic agents, coloring inhibitors, antigelling agents, colorants, and additives such as mold release agents. For details, see paragraphs

[0130] to

[0155] of Japanese Patent No. 4,894,982 and paragraphs

[0047] to

[0103] of International Publication No. 2021 / 241,471, the contents of which are incorporated herein by reference. When the fiber-reinforced composite material of this embodiment contains the other components, it is preferable to melt-knead them with the polyamide resin to form a polyamide resin composition, which is then combined with the continuous reinforcing fibers to form a composite material. For the polyamide resin composition, please refer to paragraph 0044 of WO 2023 / 188549, the contents of which are incorporated herein by reference. The content of these other components is preferably less than 10 mass% of the fiber-reinforced composite material, more preferably less than 5 mass%, even more preferably less than 3 mass%, and even more preferably less than 1 mass%. The fiber-reinforced composite material of this embodiment may also be configured to be substantially free of a colorant. "Substantially free" means that the content of the colorant is less than 0.01 parts by mass, preferably less than 0.005 parts by mass, and more preferably less than 0.001 parts by mass, per 100 parts by mass of the polyamide resin contained in the fiber-reinforced composite material. The fiber-reinforced composite material of this embodiment may also be configured to be substantially free of a phenylene benzimidazoperylene compound. "Substantially free" means that the content of the phenylene benzimidazoperylene compound is less than 0.01 part by mass, preferably less than 0.005 part by mass, and more preferably less than 0.001 part by mass, per 100 parts by mass of the polyamide resin contained in the fiber-reinforced composite material.Furthermore, in the fiber-reinforced composite material of the present embodiment, the total of the polyamide resin and the continuous reinforcing fibers preferably accounts for 90% by mass or more of the fiber-reinforced composite material, more preferably 95% by mass or more, and may even account for 99% by mass or more, or is 100% by mass or less.

[0032] <Fiber-reinforced composite material> In the fiber-reinforced composite material of this embodiment, it is preferable that the continuous reinforcing fibers are impregnated with a polyamide resin. That is, an example of the fiber-reinforced composite material of this embodiment is a prepreg. In the prepreg, the continuous reinforcing fibers may be oriented in one direction and the polyamide resin may be impregnated into the continuous reinforcing fibers, or the continuous reinforcing fibers may be a woven fabric and the polyamide resin may be impregnated into the continuous reinforcing fibers. In the continuously reinforced composite material, the impregnation rate of the polyamide resin into the continuous reinforcing fibers is preferably 90% or more, more preferably 95% or more. The upper limit is preferably 100%.

[0033] <<Method for Measuring Impregnation Rate>> For a mixed yarn, cross sections perpendicular to the longitudinal direction of the continuous reinforcing fibers are cut out together, embedded in epoxy resin, and the surfaces corresponding to the cross sections of the mixed yarn are polished. The cross sections are then photographed using an ultra-deep color 3D shape measuring microscope. The cross sections of the mixed yarn embedded in epoxy resin are observed using a digital microscope. From the obtained cross-sectional photograph, areas where the thermoplastic resin fibers have impregnated the continuous reinforcing fibers (areas where the thermoplastic resin fibers have melted and impregnated between the continuous reinforcing fibers) are selected using image analysis software ImageJ, and their areas are measured. The impregnation rate is expressed as the area where the thermoplastic resin fibers have impregnated the continuous reinforcing fibers / cross-sectional area (unit: %). The ultra-deep color 3D shape measuring microscope used was a VK-9500 (controller unit) / VK-9510 (measurement unit) (manufactured by Keyence Corporation).

[0034] <Applications of Fiber-Reinforced Composite Material> As described above, the fiber-reinforced composite material of this embodiment can be preferably used as a prepreg. The fiber-reinforced composite material of this embodiment can also be preferably used as a UD (Uni-Directional) tape. The fiber-reinforced composite material of this embodiment can be wound around a core material during storage, shipping, etc. That is, it can be a wound body having a core material and the fiber-reinforced composite material wound around the core material. The fiber-reinforced composite material of this embodiment can be processed and molded as is, or several layers can be laminated and processed and molded. That is, the form of a molded product formed from the fiber-reinforced composite material is not particularly limited. Examples include a method for manufacturing a molded product, which includes manufacturing a fiber-reinforced composite material, laminating multiple sheets of the fiber-reinforced composite material, and heat-processing the laminate, as well as a molded product obtained by the method. The thickness of the thinnest part of such a molded product can be determined appropriately depending on the application, etc., but can be, for example, 1 mm to 10 mm.

[0035] The fiber reinforced composite material of the present embodiment also includes, for example, a molded product obtained by alternately laminating polyamide resin films and woven fabrics of continuous reinforcing fibers and applying heat and pressure to the laminate.

[0036] The application field of the fiber reinforced composite material of this embodiment is not particularly limited, and it is 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.

[0037] The present invention will be explained in more detail below with reference to examples. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present embodiment. Therefore, the scope of the present embodiment is not limited to the specific examples shown below. If the measuring instruments used in the examples are difficult to obtain due to discontinuation, etc., measurements can be made using other instruments with equivalent performance.

[0038] <Raw Materials> Continuous carbon fiber: TR3523, PYROFIL (registered trademark) manufactured by Mitsubishi Chemical Corporation Short fiber (carbon fiber): TR50S, manufactured by Mitsubishi Chemical Corporation, cut length (number average fiber length) 12 mm MP12 (30): polyamide resin synthesized according to Synthesis Example 1 below MP12 (40): polyamide resin synthesized according to Synthesis Example 2 below MP14 (30): polyamide resin synthesized according to Synthesis Example 3 below MXD12: polyamide resin synthesized according to Synthesis Example 4 below PXD12: polyamide resin synthesized according to Synthesis Example 5 below PA6: polyamide 6, CM1017, manufactured by Toray Industries, Inc. PA66: polyamide 66, CM3001, manufactured by Toray Industries, Inc. PA12: polyamide 12, UBESTA, manufactured by UBE MP10 (30): polyamide resin synthesized according to Synthesis Example 6 below

[0039] Synthesis Example 1: Synthesis of MP12 (30) Dodecanedioic acid was placed in a jacketed reactor equipped with a stirrer, partial condenser, condenser, thermometer, dropping tank, and nitrogen gas inlet tube. The contents were thoroughly purged with nitrogen and heated to 180°C to melt. While stirring the contents, a mixed amine (70:30) of metaxylylenediamine and paraxylylenediamine (MPXDA, manufactured by Mitsubishi Gas Chemical Company, Inc.) was gradually added dropwise to a molar ratio of 1:1 to dodecanedioic acid, while the temperature was raised to 290°C. After the addition was completed, the liquid temperature was maintained at 290°C and the reaction was continued for 10 minutes. The internal pressure of the reaction system was then continuously reduced to 600 Torr over 10 minutes, and the reaction was continued for 20 minutes. During this time, the reaction temperature was continuously raised to 300°C. After the reaction was completed, the inside of the reactor was pressurized with nitrogen gas to 0.3 MPa, and the polymer was taken out as a strand from a nozzle at the bottom of the polymerization vessel, cooled with water, and then pelletized with a pelletizer.

[0040] Synthesis Example 2: Synthesis of MP12 (40) Dodecanedioic acid was placed in a jacketed reactor equipped with a stirrer, partial condenser, condenser, thermometer, dropping tank, and nitrogen gas inlet tube. The contents were thoroughly purged with nitrogen and heated to 180°C to melt. While stirring the contents, a mixed amine (60:40) of metaxylylenediamine and paraxylylenediamine (MXDA, manufactured by Mitsubishi Gas Chemical Company, Inc.; PXDA, manufactured by Showa Denko K.K.) was gradually added dropwise to a molar ratio of 1:1 to dodecanedioic acid, while the temperature was raised to 290°C. After the addition was completed, the liquid temperature was maintained at 290°C and the reaction was continued for 10 minutes. Thereafter, the internal pressure of the reaction system was continuously reduced to 600 Torr over 10 minutes, and the reaction was continued for 20 minutes. During this time, the reaction temperature was continuously raised to 300°C. After the reaction was completed, the reactor was pressurized with nitrogen gas at 0.3 MPa, and the polymer was taken out as strands from a nozzle at the bottom of the polymerization vessel, cooled with water, and then pelletized with a pelletizer.

[0041] Synthesis Example 3: Synthesis of MP14 (30) A precisely weighed amount of 60 mol of tetradecanedioic acid was placed in a jacketed reactor equipped with a stirrer, a partial condenser, a thermometer, a dropping tank, and a nitrogen gas inlet tube. The atmosphere was thoroughly purged with nitrogen and the temperature was raised to 180°C under a small amount of nitrogen gas flow to dissolve the tetradecanedioic acid and create a uniform fluid state. A mixed amine (70:30) of meta-xylylenediamine and para-xylylenediamine (MXDA, manufactured by Mitsubishi Gas Chemical Company, Inc.; PXDA, manufactured by Showa Denko KK) was gradually added dropwise to the reactor over a period of 160 minutes so that the molar ratio to tetradodecanedioic acid became 1:1. During this time, the internal pressure of the reaction system was maintained at atmospheric pressure, and the internal temperature was continuously raised to 240°C. Water distilled during the dropwise addition of para- / meta-xylylenediamine was removed from the system via the partial condenser and the condenser. After the dropwise addition of para / meta-xylylenediamine was completed, the liquid temperature was maintained at 240°C and the reaction was continued for 10 minutes. Thereafter, the pressure inside the reaction system was continuously reduced to 600 Torr over 10 minutes, and the reaction was continued for 20 minutes. During this time, the reaction temperature was continuously raised to 250°C. After the reaction was completed, the inside of the reactor was pressurized with nitrogen gas to 0.3 MPa, 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 cut into pellets to obtain pellets of a melt polymer product.

[0042] Synthesis Example 4: Synthesis of MXD12 Dodecanedioic acid was placed in a jacketed reactor equipped with a stirrer, partial condenser, cooler, thermometer, dropping tank, and nitrogen gas inlet tube, and the inside of the reactor was thoroughly purged with nitrogen. After heating and melting at 180°C, metaxylylenediamine (MXDA, manufactured by Mitsubishi Gas Chemical Company, Inc.) was gradually added dropwise while stirring the contents so that the molar ratio to dodecanedioic acid was 1:1, and the temperature was raised to 290°C. The reaction was continued for 10 minutes while maintaining the liquid temperature at 290°C. Thereafter, the internal pressure of the reaction system was continuously reduced to 600 Torr over 10 minutes, and the reaction was continued for 20 minutes. During this time, the reaction temperature was continuously raised to 300°C. After completion of the reaction, a pressure of 0.3 MPa was applied to the reactor with nitrogen gas, and the polymer was removed as a strand from a nozzle at the bottom of the polymerization vessel. After water cooling, the polymer was pelletized using a pelletizer.

[0043] Synthesis Example 5: Synthesis of PXD12 Dodecanedioic acid was placed in a jacketed reactor equipped with a stirrer, partial condenser, condenser, thermometer, dropping tank, and nitrogen gas inlet tube, and the inside was thoroughly purged with nitrogen. After heating to 180°C and melting, paraxylylenediamine (PXDA, manufactured by Showa Denko) was gradually added dropwise while stirring the contents so that the molar ratio to dodecanedioic acid was 1:1, and the temperature was raised to 290°C. The temperature was raised to 290°C. The reaction was continued for 10 minutes while maintaining the liquid temperature at 290°C. Thereafter, the internal pressure of the reaction system was continuously reduced to 600 Torr over 10 minutes, and the reaction was continued for 20 minutes. During this time, the reaction temperature was continuously raised to 300°C. After completion of the reaction, a pressure of 0.2 MPa was applied to the reactor with nitrogen gas, and the polymer was removed as a strand from a nozzle at the bottom of the polymerization vessel. After water cooling, the polymer was pelletized using a pelletizer.

[0044] Synthesis Example 6: Synthesis of MP10 (30) Sebacic acid 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 reactor was thoroughly purged with nitrogen. After heating and melting at 170°C, a mixed amine (70:30) of metaxylylenediamine and paraxylylenediamine (MPXDA, manufactured by Mitsubishi Gas Chemical Company, Inc.) was gradually added dropwise while stirring the contents so that the molar ratio to sebacic acid was 1:1, 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.

[0045] <Melting Point of Polyamide Resin> Unless otherwise specified, the melting point (Tm) of the polyamide resin was measured by differential scanning calorimetry (DSC) in accordance with ISO 11357. Specifically, a differential scanning calorimeter was used. The resin was placed in the measurement pan of the differential scanning calorimeter, heated to a temperature above the melting point at a heating rate of 10°C / min under a nitrogen atmosphere, and then rapidly cooled before measurement. The measurement conditions were a heating rate of 10°C / min, held at 280°C for 5 minutes, and then cooled to 100°C at a cooling rate of -5°C / min to determine the melting point (Tm). A "DSC-60" manufactured by Shimadzu Corporation was used as the differential scanning calorimeter. Tables 1 and 2 show the melting points of the polyamide resins used in each example and comparative example.

[0046] Example 1 <Production of Fiber-Reinforced Composite Material> A fiber-reinforced composite material was produced using continuous carbon fiber and the types of thermoplastic resins shown in Table 1. Specifically, the thermoplastic resin was processed into a 100 μm thermoplastic resin film, and carbon fiber fabric and thermoplastic resin films were alternately sandwiched thereon (the top layer was the thermoplastic resin film). A pressure of 3 MPa was applied at a temperature 20°C above the melting point of the thermoplastic resin to produce a molded product having a thickness specified in various standards described below. The thickness was determined by adjusting the number of layers of carbon fiber fabric and thermoplastic resin film. The proportion of carbon fiber in 100% by mass of the obtained fiber-reinforced composite material was 60% by mass. The obtained molded product was cut using an electric saw to sizes (length and width) conforming to the various standards described below.

[0047] <Flexural Properties> The molded article (3.9 mm thick) obtained above was cut out according to the size (length and width) specified in the ASTM D790 standard, and the flexural strength (unit: MPa) and flexural modulus (unit: GPa) were measured (initial) in accordance with ASTM D790 at a temperature of 23°C and a humidity of 50%. Furthermore, the test piece was immersed in water at 23°C for 120 days, after which the water on the surface was wiped off and the flexural strength was measured in the same manner as above. The rate of decrease in flexural strength after water absorption relative to the initial flexural strength was measured according to the following formula: [(initial flexural strength - flexural strength after water absorption) / initial flexural strength] x 100 (%)

[0048] <Interlaminar Shear Strength> The molded article (2 mm thick) obtained above was cut into the size (length and width) specified in JIS K7078 (1991), and the interlaminar shear strength was measured in accordance with JIS K7078 (1991). After immersing the test piece in water at 23°C for 120 days, the water on the surface was wiped off, and the interlaminar shear strength was measured in the same manner as above. The decrease rate of the interlaminar shear strength after water absorption relative to the initial interlaminar shear strength was measured according to the following formula: [(initial interlaminar shear strength - interlaminar shear strength after water absorption) / initial interlaminar shear strength] x 100 (%). The interlaminar shear strength was measured using an "Autograph" AG100kNX (Class 1, 1 / 1000 guaranteed type) manufactured by Shimadzu Corporation.

[0049] <Water absorption rate (after 120 days of immersion in water at 23°C)> The molded product (2 mm thick) obtained above was cut into a size of 50 mm length and 20 mm width, and after immersion in water at 23°C for 120 days, the water on the surface was wiped off and the mass was measured. The water absorption rate was measured using the following formula: [(mass of test piece after water absorption - initial mass of test piece) / initial mass of test piece] x 100 (%)

[0050] Examples 2 to 5 and Comparative Examples 1 to 4 In Example 1, the type of resin fiber was changed as shown in Table 1 or Table 2, but the other procedures were the same.

[0051] Comparative Example 5 <Production of Nonwoven Fabric> Carbon fibers and resin fibers were each cut to a fiber length of 12 mm. The cut fibers were dispersed in water, thoroughly mixed, and then scooped up with a wire mesh to form a sheet. The resulting sheet was dried with hot air at 80°C to obtain a nonwoven fabric with a basis weight of 80 gsm.

[0052] <Molding of Nonwoven Fabric> A plurality of sheets of the nonwoven fabric obtained above were stacked and press-molded at a temperature of 20°C above the melting point of the thermoplastic resin under a pressure of 3 MPa to obtain a molded product having a thickness of 3 mm. The obtained molded product was cut into test pieces of the same size as those used to measure the bending properties, interlaminar shear strength, and water absorption described in Example 1, and evaluated in the same manner as in Example 1. The proportion of carbon fiber in 100% by mass of the obtained fiber-reinforced composite material was 62% by mass.

[0053]

[0054]

[0055] As is clear from the above results, molded articles formed from the fiber-reinforced composite materials of the present invention had high initial interlaminar shear strength and were able to effectively suppress a decrease in interlaminar shear strength after water absorption (Examples 1 to 5). Furthermore, their initial and post-water absorption flexural strengths were also high. In contrast, molded articles formed from fiber-reinforced composite materials obtained using polyamide 6 or polyamide 66 exhibited a significant decrease in interlaminar shear strength after water absorption (Comparative Examples 1 and 2). Furthermore, molded articles formed from fiber-reinforced composite materials obtained using polyamide 12 exhibited low initial shear strength (Comparative Example 3). Furthermore, molded articles formed from fiber-reinforced composite materials obtained using a polyamide formed from sebacic acid and xylylenediamine exhibited well-balanced and excellent physical properties both initially and after water absorption compared to Comparative Examples 1 to 3, but were significantly inferior in these performances to the present invention (Comparative Example 4). On the other hand, even in the case of a fiber-reinforced composite material obtained using the polyamide resin specified in the present invention, when short fibers were used (Comparative Example 5), the flexural strength after water absorption was maintained at a high level, but the shear strength after water absorption was significantly inferior to that of the present invention, which used continuous fibers. In particular, it was found that there was a large difference in the rate of decrease in interlaminar shear strength after water absorption between Example 1 and Comparative Example 4, which are identical except for whether the dicarboxylic acid in the polyamide resin was dodecanedioic acid or sebacic acid.

Claims

1. A fiber-reinforced composite material comprising 100 to 200 parts by mass of continuous reinforcing fibers with respect to 100 parts by mass of a polyamide resin, wherein the polyamide resin contains diamine units and dicarboxylic acid units, at least 70 mol% of the diamine units are derived from xylylenediamine, and at least 70 mol% of the dicarboxylic acid units are derived from α,ω-linear aliphatic dicarboxylic acids having 11 to 20 carbon atoms.

2. The fiber-reinforced composite material according to claim 1, wherein at least 70 mol% of the dicarboxylic acid units are derived from dodecanedioic acid and / or tetradecanedioic acid.

3. The fiber-reinforced composite material according to claim 1, wherein at least 70 mol% of the dicarboxylic acid units are derived from dodecanedioic acid.

4. The fiber-reinforced composite material according to any one of claims 1 to 3, wherein 20 to 100 mol% of the diamine units are derived from metaxylylenediamine and 80 to 0 mol% are derived from p-xylylenediamine (however, the total does not exceed 100 mol%).

5. The fiber-reinforced composite material according to claim 1, wherein at least 70 mol% of the dicarboxylic acid units are derived from dodecanedioic acid and / or tetradecanedioic acid, 20 to 100 mol% of the diamine units are derived from metaxylylenediamine, and 80 to 0 mol% are derived from p-xylylenediamine.

6. The fiber-reinforced composite material according to any one of claims 1 to 5, wherein the continuous reinforcing fibers include at least one selected from the group consisting of carbon fibers, glass fibers, and aramid fibers.

7. The fiber-reinforced composite material according to any one of claims 1 to 6, wherein the number average fiber length of the continuous reinforcing fibers is more than 10 mm.

8. The fiber-reinforced composite material according to any one of claims 1 to 7, which is a prepreg.

9. The fiber-reinforced composite material according to claim 8, which is a prepreg in which the continuous reinforcing fibers are oriented in one direction and the continuous reinforcing fibers are impregnated with the polyamide resin.

10. The fiber-reinforced composite material according to claim 8, which is a prepreg in which the continuous reinforcing fibers are a fabric and the continuous reinforcing fibers are impregnated with the polyamide resin.

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

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