WO2025158763A1 - Fiber-reinforced composite material and molded article - Google Patents

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

The present invention relates to fiber-reinforced composite materials and molded articles. In particular, it relates to fiber-reinforced composite materials using a specific polyamide resin.

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

Japanese Patent Application Laid-Open No. 2023-147962 International Publication No. 2020/174871

Here, the present inventors have investigated Patent Document 1 and found that the interlaminar shear strength after water absorption is significantly reduced in fiber-reinforced composite materials obtained using polyamide 6 or polyamide 66. On the other hand, when polyamide 12 is used, the interlaminar shear strength after water absorption can be suppressed, but the value of the interlaminar shear strength itself (initial interlaminar shear strength) is low.
On the other hand, when the study of Patent Document 2 was also carried out, it was found that a polyamide resin composed of sebacic acid and xylylenediamine was able to maintain a significantly higher interlaminar shear strength after absorbing water than polyamide 6 or polyamide 66. Furthermore, it was possible 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 further improved retention of interlaminar shear strength after water absorption.
The present invention aims to solve these problems and to provide a fiber-reinforced composite material and a molded article thereof that have high initial interlaminar shear strength and an improved retention rate of interlaminar shear strength after water absorption.

In view of the above problems, the present inventors have conducted research and found that the above problems can be solved by using a specific polyamide resin.
Specifically, the above problems were solved by the following means.
<1> Contains 100 to 200 parts by mass of continuous reinforcing fibers relative to 100 parts by mass of polyamide resin,
The polyamide resin contains a diamine unit and a dicarboxylic acid unit,
70 mol % or more of the diamine units are derived from xylylenediamine,
A fiber-reinforced composite material in which 70 mol % or more of the dicarboxylic acid units are 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 (however, the total does not exceed 100 mol%).
<5> 70 mol% or more of the dicarboxylic acid units are derived from dodecanedioic acid and/or tetradecanedioic acid,
<1> The fiber-reinforced composite material according to <1>, wherein 20 to 100 mol % of the diamine units are derived from metaxylylenediamine, and 80 to 0 mol % are derived from paraxylylenediamine.
<6> The fiber-reinforced composite material according to any one of <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 <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 <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 the continuous reinforcing fibers are impregnated with the polyamide resin.
<10> The fiber-reinforced composite material according to <8>, wherein the continuous reinforcing fibers are woven and the continuous reinforcing fibers are impregnated with the polyamide resin to form a prepreg.
<11> A molded article formed from the fiber-reinforced composite material according to any one of <1> to <10>.

The present invention makes it possible to provide fiber-reinforced composite materials and molded articles that have high initial interlaminar shear strength and further improved retention of interlaminar shear strength after water absorption.

Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. Note that the present embodiment is an example for explaining the present invention, and the present invention is not limited to only this embodiment.
In this specification, the term "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 the numerical values in this specification is an example of this embodiment.
In this specification, various physical properties and characteristic values are those at 23° C. unless otherwise specified.

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 stated. 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.

The fiber-reinforced composite material of the present embodiment comprises 100 to 200 parts by mass of continuous reinforcing fibers relative to 100 parts by mass of polyamide resin, and the polyamide resin comprises 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.
By adopting such a configuration, it is possible to provide a fiber-reinforced composite material and a molded article that have a high initial interlaminar shear strength and an improved retention rate of the interlaminar shear strength after water absorption.

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 were used as reinforcing fibers, the tendency for changes in physical properties would be significantly different compared to when short fibers were used.
As a result, it is presumed 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 will be described below.

<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.

The diamine units of the xylylenediamine-based polyamide resin are preferably derived from xylylenediamine (preferably paraxylylenediamine and/or metaxylylenediamine) for 75 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, even more preferably 95 mol% or more, and particularly preferably 99 mol% or more.

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 %.

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-trimethylhexamethylenediamine, and 2,4,4-trimethylhexamethylenediamine; 1,3-bis( Examples of diamines 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. These can be used alone or in combination of two or more.

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

As the α,ω-linear aliphatic dicarboxylic acid having 11 to 20 carbon atoms that can be used as the raw material dicarboxylic acid component of the xylylenediamine-based polyamide resin, an α,ω-linear aliphatic dicarboxylic acid having 11 to 16 carbon atoms is preferred, and an α,ω-linear aliphatic dicarboxylic acid having 12 to 14 carbon atoms is more preferred.
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, and dodecanedioic acid is more preferred, since the melting point of the polyamide resin is in a range suitable for molding.

Other dicarboxylic acid components include α,ω-linear aliphatic dicarboxylic acids having 10 or fewer 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.

Note that while xylylenediamine-based polyamide resins are primarily composed of diamine units and dicarboxylic acid units, this does not mean that other structural units are completely excluded, and they may, of course, 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 that make up 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 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.

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

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 as described in the Examples below.
When the mixed yarn of this embodiment contains two or more types of xylylenediamine-based polyamide resins, the weighted average value of each polyamide resin is used.

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 100,000 or less, more preferably 50,000 or less. When the Mn is within such a 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.

The fiber-reinforced composite material of the present embodiment may contain a polyamide resin other than a xylylenediamine-based polyamide resin. Examples of the polyamide resin 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, polyamide 12, and the like.
Examples of semi-aromatic polyamide resins include terephthalic acid-based polyamide resins (polyamide 6T, polyamide 9T, polyamide 10T) and xylylenediamine-based polyamide resins, which will be described later.

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, and is 50% by mass or less, 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 the present 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 is preferably in the above range.
The fiber-reinforced composite material of the present embodiment may be configured to be substantially free of polyamide resins other than the 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, more preferably less than 5% by mass, even more preferably less than 3% by mass, and even more preferably less than 1% by mass of the content of the continuous reinforcing fibers.

<Continuous reinforcing fiber>
The fiber-reinforced composite material of this embodiment contains continuous reinforcing fibers. Continuous reinforcing fibers refer to reinforcing fibers 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 fibers 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.

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.
As the glass fiber, fibers obtained by melt spinning commonly supplied glass such as E-glass, C-glass, A-glass, S-glass, and alkali-resistant glass are used.

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 continuous carbon fibers in paragraph 0074 of Japanese Patent No. 7398028 can be referred to, the contents of which are incorporated herein by reference.

The shape of the continuous reinforcing fibers is not particularly limited, but it is preferable that the fibers 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 woven. Examples of the woven fabric include plain weave, twill weave, and satin weave.

When the continuous reinforcing fiber is carbon fiber, the tensile strength is preferably 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 keep it 8000 MPa or less. When the continuous reinforcing fiber is glass fiber, 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 keep it 5000 MPa or less.

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 it to the lower limit or more, molding time tends to be further shortened. On the other hand, by setting it to the upper limit or less, 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 the present embodiment may contain only one type of continuous reinforcing fiber, or may contain two or more types. When two or more types are contained, it is preferable that the total amount is in the above range.

The fiber-reinforced composite material of the present embodiment may or may not contain a filler 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 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.

<Other ingredients>
The fiber-reinforced composite material of the present embodiment may or may not contain components other than the polyamide resin and the continuous reinforcing fibers.
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, matting agents, UV absorbers, nucleating agents, plasticizers, dispersants, flame retardants, antistatic agents, coloring inhibitors, antigelling agents, colorants, and additives such as release agents can be added. For details of these, please refer to the descriptions in paragraphs 0130 to 0155 of Japanese Patent No. 4894982 and the descriptions in paragraphs 0047 to 0103 of WO 2021/241471, the contents of which are incorporated herein by reference.
When the fiber-reinforced composite material of the present embodiment contains the above-mentioned other components, it is preferable to melt-knead the other components into a polyamide resin to form a polyamide resin composition, and then form a composite material with continuous reinforcing fibers. For the polyamide resin composition, the description in paragraph 0044 of WO 2023/188549 can be referred to, and the content of this document can be incorporated herein.
The content of these other components is preferably less than 10% by mass of the fiber-reinforced composite material, more preferably less than 5% by mass, even more preferably less than 3% by mass, and even more preferably less than 1% by mass.
The fiber-reinforced composite material of the present embodiment may be configured to be substantially free of a colorant. "Substantially free" means that the content of the colorant 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.
The fiber-reinforced composite material of the present embodiment may 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.

<Fiber reinforced composite materials>
In the fiber-reinforced composite material of this embodiment, the continuous reinforcing fibers are preferably impregnated with the polyamide resin.
That is, an example of the fiber-reinforced composite material of this embodiment is a prepreg. In the prepreg, continuous reinforcing fibers may be oriented in one direction and impregnated with the polyamide resin, or the continuous reinforcing fibers may be a woven fabric and impregnated with the polyamide resin.
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, with the upper limit being preferably 100%.

<<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, the surface corresponding to the cross section of the mixed yarn is polished, and the cross section is photographed using an ultra-deep color 3D shape measuring microscope. The cross section of the mixed yarn embedded in the epoxy resin is observed using a digital microscope. For the obtained cross section photograph, the area where the thermoplastic resin fiber is impregnated into the continuous reinforcing fibers (the area where the thermoplastic resin fiber is melted and impregnated between the continuous reinforcing fibers) is selected using image analysis software ImageJ, and its area is measured. The impregnation rate is expressed as the area where the thermoplastic resin fiber is impregnated into the continuous reinforcing fibers / cross-sectional area (unit: %).
The ultra-deep color 3D shape measuring microscope used was VK-9500 (controller unit)/VK-9510 (measurement unit) (manufactured by Keyence Corporation).

<Applications of fiber reinforced composite materials>
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 may be wound around a core material during storage, shipping, etc. That is, it may be in the form of a wound body having a core material and the fiber-reinforced composite material wound around the core material.
The fiber-reinforced composite material of the present embodiment may be processed and molded as it is, or may be processed and molded after laminating several layers. In other words, the shape of a molded product formed from the fiber-reinforced composite material is not particularly limited.
Examples include a method for producing a molded article, which includes producing a fiber-reinforced composite material, laminating multiple sheets of the fiber-reinforced composite material, and heat-processing the laminated sheets. The thickness of the thinnest part of such a molded article can be determined appropriately depending on the application, and can be, for example, 1 mm to 10 mm.

Furthermore, the fiber-reinforced composite material of this embodiment is intended to include, for example, a molded product obtained by alternately laminating polyamide resin films and woven fabrics of continuous reinforcing fibers and then applying heat and pressure.

The field of use of the fiber-reinforced composite material of this embodiment is not particularly limited, and it can be widely used in automobile and other transportation vehicle parts, general machinery parts, precision machinery parts, electronic and electrical equipment parts, office equipment parts, building materials and housing-related parts, medical devices, leisure and sporting goods, play equipment, medical supplies, everyday items such as food packaging films, defense and aerospace products, etc.

The present invention will be described 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 appropriately changed 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 or the like, measurements can be made using other instruments with equivalent performance.

<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.

<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, and the contents were thoroughly purged with nitrogen. After heating and melting at 180°C, 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 stirring the contents, and the temperature was raised to 290°C. After completion of the dropwise addition, the reaction was continued for 10 minutes while maintaining the liquid temperature at 290°C. The internal pressure of the reaction system was then continuously reduced to 600 Torr over 10 minutes, and the reaction was then 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. The polymer was then cooled with water and pelletized using a pelletizer.

<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, and the contents were thoroughly purged with nitrogen. After heating and melting at 180°C, a mixed amine (60:40) of metaxylylenediamine and paraxylylenediamine (MXDA, manufactured by Mitsubishi Gas Chemical Company, Inc., PXDA, manufactured by Showa Denko) was gradually added dropwise to a molar ratio of 1:1 to dodecanedioic acid while stirring the contents, and the temperature was raised to 290°C. After completion of the dropwise addition, the reaction was continued for 10 minutes while maintaining a liquid temperature of 290°C. Thereafter, the internal pressure of the reaction system was continuously reduced to 600 Torr over 10 minutes, and then the reaction was continued for 20 minutes. During this time, the reaction temperature was continuously raised to 300°C. After completion of the reaction, the reactor was pressurized with 0.3 MPa of nitrogen gas, and the polymer was removed as a strand from a nozzle at the bottom of the polymerization vessel. After water cooling, it was pelletized using a pelletizer.

<Synthesis Example 3: Synthesis of MP14 (30)>
A precisely weighed 60 mol of tetradecanedioic acid was placed in a jacketed reactor equipped with a stirrer, partial condenser, condenser, thermometer, dropping tank, and nitrogen gas inlet tube. The atmosphere was thoroughly purged with nitrogen and the temperature was raised to 180°C under a small nitrogen stream 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 K.K.) was gradually added dropwise to the reactor over 160 minutes so that the molar ratio to tetradodecanedioic acid was 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 with the addition of para-/meta-xylylenediamine was removed from the system via the partial condenser and 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. The pressure inside 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 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 cooling with water, the strand was cut into pellets to obtain pellets of a melt polymer.

<Synthesis Example 4: Synthesis of MXD12>
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 contents were thoroughly purged with nitrogen. After heating and melting at 180°C, metaxylylenediamine (MXDA, manufactured by Mitsubishi Gas Chemical Company, Inc.) was gradually added dropwise to a molar ratio of 1:1 to dodecanedioic acid while stirring the contents, and the temperature was raised to 290°C. The reaction was continued for 10 minutes while maintaining a liquid temperature of 290°C. The internal pressure of the reaction system was then continuously reduced to 600 Torr over 10 minutes, and the reaction was then 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.

<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 contents were thoroughly purged with nitrogen. After heating and melting at 180°C, 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 pressure inside the reaction system was continuously reduced to 600 Torr over 10 minutes, and the reaction was then 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, it was pelletized using a pelletizer.

<Synthesis Example 6: Synthesis of MP10(30)>
Sebacic acid was placed in a jacketed reactor equipped with a stirrer, partial condenser, cooler, thermometer, dropping tank, and nitrogen gas inlet tube, and the contents were 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, it was pelletized using a pelletizer.

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

Example 1
<Production of fiber-reinforced composite materials>
Fiber-reinforced composite materials were 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 between the thermoplastic resin and the film (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 molded articles with thicknesses specified by various standards described below. The thickness was determined by adjusting the number of layers of carbon fiber fabric and thermoplastic resin films. The carbon fiber content was 60% by mass of the resulting fiber-reinforced composite material (100% by mass). The resulting molded articles were cut using an electric saw to sizes (length and width) conforming to the respective standards described below.

<Bending properties>
The molded article (thickness: 3.9 mm) 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%.
After the test piece was immersed in water at 23° C. for 120 days, the water on the surface was wiped off, and the bending strength was measured in the same manner as above.
The rate of decrease in bending strength after water absorption relative to the initial bending strength was measured according to the following formula.
[(initial flexural strength - flexural strength after water absorption) / initial flexural strength] x 100 (%)

<Interlaminar shear strength>
The molded article (thickness: 2 mm) obtained above was cut into a size (length and width) specified by JIS K7078 (1991), and the interlaminar shear strength was measured in accordance with JIS K7078 (1991).
After the test piece was immersed 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 rate of decrease in 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 Shimadzu Corporation's "Autograph" AG100kNX (class 1, 1/1000 guaranteed type).

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

Examples 2 to 5, 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.

Comparative Example 5
<Production of nonwoven fabric>
The 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.

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

As is clear from the above results, the 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 the decrease in interlaminar shear strength after water absorption (Examples 1 to 5).Furthermore, the molded articles also had high initial and post-water absorption flexural strength.
In contrast, molded articles formed from fiber-reinforced composite materials obtained using polyamide 6 or polyamide 66 showed a marked decrease in interlaminar shear strength after water absorption (Comparative Examples 1 and 2).
Furthermore, a molded article formed from a fiber-reinforced composite material obtained using polyamide 12 had low initial shear strength (Comparative Example 3).
Furthermore, molded articles formed from fiber-reinforced composite materials obtained using polyamides formed from sebacic acid and xylylenediamine had well-balanced and excellent physical properties both at the initial stage and after water absorption compared with Comparative Examples 1 to 3, but were significantly inferior in these performances to those of 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 bending 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 uses continuous fibers.
In particular, Example 1 and Comparative Example 4 were identical except for the fact that the dicarboxylic acid in the polyamide resin was dodecanedioic acid or sebacic acid, but it was found that there was a large difference in the rate of decrease in interlaminar shear strength after water absorption.

Claims (11)

Contains 100 to 200 parts by mass of continuous reinforcing fibers relative to 100 parts by mass of polyamide resin,
The polyamide resin contains a diamine unit and a dicarboxylic acid unit,
70 mol % or more of the diamine units are derived from xylylenediamine,
A fiber-reinforced composite material in which 70 mol % or more of the dicarboxylic acid units are derived from an α,ω-linear aliphatic dicarboxylic acid having 11 to 20 carbon atoms. The fiber-reinforced composite material according to claim 1, wherein 70 mol% or more of the dicarboxylic acid units are derived from dodecanedioic acid and/or tetradecanedioic acid. The fiber-reinforced composite material according to claim 1, wherein 70 mol% or more of the dicarboxylic acid units are derived from dodecanedioic acid. A 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 paraxylylenediamine (however, the total does not exceed 100 mol%). 70 mol % or more of the dicarboxylic acid units are derived from dodecanedioic acid and/or tetradecanedioic acid,
2. The fiber-reinforced composite material according to claim 1, wherein 20 to 100 mol % of the diamine units are derived from metaxylylenediamine, and 80 to 0 mol % are derived from paraxylylenediamine. A fiber-reinforced composite material according to any one of claims 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. A 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 greater than 10 mm. The fiber-reinforced composite material according to any one of claims 1 to 7, which is a prepreg. 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 are impregnated with the polyamide resin. The fiber-reinforced composite material according to claim 8, wherein the continuous reinforcing fibers are woven and the prepreg is formed by impregnating the continuous reinforcing fibers with the polyamide resin. A molded article formed from the fiber-reinforced composite material according to any one of claims 1 to 10.