Composite member and method for manufacturing the same

Abstract

To provide a composite member that breaks in a ductile manner, and a method for producing the same.SOLUTION: A composite member includes matrix material, and flake-shaped particles dispersed within the matrix material. The composite member has a bending strength in the range of 100-250 MPa, a flexural modulus in the range of 10-40 GPa, and a maximum bending strain in the range of 1-2%.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a composite member and a method for manufacturing a composite member. [Background technology]

[0002] Composite materials, which are made by adding fillers such as flake particles to resins to improve their strength, are widely used as materials for various structures.

[0003] For example, Patent Document 1 describes that uncalcined mica is crushed to obtain mica flakes, a slurry containing the mica flakes is paper-formed to obtain a laminated mica material, and the laminated mica material is impregnated with or coated with a thermosetting resin composition, and then molded under heat and pressure, thereby producing an laminated mica product with improved flexural modulus and flexural strength.

[0004] Patent Document 2 describes that a composite resin part is produced by orienting a mixture of a resin having a viscosity within a predetermined range at room temperature and flaky inorganic particles, and that the part produced in this manner has a high flexural modulus and flexural strength. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 57-82598 [Patent Document 2] Patent Publication No. 2021-88149 Summary of the Invention [Problem to be solved by the invention]

[0006] It is desirable that components used in applications such as vehicle exterior panels and fuel cell cases do not lose any part of their structure when broken. However, according to extensive research by the present inventors, conventional composite components in which a filler is added to a matrix material such as a resin undergo brittle fracture, which tends to cause fragments to break off. A composite component that undergoes ductile fracture can prevent fragments from falling off.

[0007] Therefore, a composite member that undergoes ductile fracture and a method for manufacturing the same are provided. [Means for solving the problem]

[0008] Aspects of the present disclosure include the following. [1] A composite member comprising a matrix material and flake particles dispersed in the matrix material, A composite member having a flexural strength in the range of 100 to 250 MPa, a flexural modulus in the range of 10 to 40 GPa, and a maximum flexural strain in the range of 1 to 2%. [2] 2. The composite material according to aspect 1, wherein the flaky particles are contained in an amount of 5 to 99% by volume based on the total volume of the composite material. [3] 2. The composite material according to embodiment 1, wherein the flaky particles are contained in an amount of 50 to 99% by volume based on the total volume of the composite material. [4] 300~500J / m 3 4. The composite member according to any one of aspects 1 to 3, having a fracture toughness value within the range of: [5] A composite member according to any one of aspects 1 to 4, wherein the flaky particles are mica particles. [6] A composite material according to any one of Aspects 1 to 5, wherein the matrix material is a cured product of an epoxy resin composition. [7] 7. The composite member of claim 6, wherein the epoxy resin composition comprises a bisphenol A type epoxy resin and poly(propylene glycol) diglycidyl ether. [8] Producing a paper product containing flake particles; impregnating the paper product with a curable resin composition; curing the curable resin composition under predetermined conditions; A method for manufacturing a composite member, comprising: The method, wherein the curable resin composition is a composition that forms a cured product having a tensile strength in the range of 1 to 30 MPa when cured under the predetermined conditions. [9] 9. The method of claim 8, wherein the curable resin composition comprises an epoxy resin.

[10] 9. The method of claim 8, wherein the curable resin composition comprises a bisphenol A type epoxy resin and poly(propylene glycol) diglycidyl ether.

[11] preparing a suspension comprising fibrous or particulate thermoplastic material and flake particles; filtering the suspension to produce a paper product containing the thermoplastic material and the flake particles; hot-pressing the paper product at a temperature equal to or higher than the glass transition temperature of the thermoplastic material; A method for producing a composite member to be used at a predetermined temperature, comprising: The method, wherein the thermoplastic material has a tensile strength in the range of 1 to 30 MPa at the predetermined temperature.

[12] 12. The method of any one of aspects 8 to 11, wherein the composite member has a flexural strength in the range of 100 to 250 MPa, a flexural modulus in the range of 10 to 40 GPa, and a maximum flexural strain in the range of 1 to 2%.

[13] A method according to any one of aspects 8 to 12, wherein the composite member contains the flaked particles in an amount of 5 to 99% by volume based on the total volume of the composite member.

[14] A method according to any one of aspects 8 to 12, wherein the composite material contains the flaked particles in an amount of 50 to 99% by volume based on the total volume of the composite material.

[15] The composite member has a resistance of 300 to 500 J / m 3 15. The method of any one of aspects 8 to 14, wherein the fracture toughness value is in the range of

[16] Aspect 16. The method of any one of aspects 8 to 15, wherein the flaky particles are mica particles. [Effects of the Invention]

[0009] The composite member according to one aspect of the present invention and the composite member obtained by the manufacturing method according to one aspect of the present invention undergo ductile fracture. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a flowchart showing a method for manufacturing a composite member according to the first embodiment. [Figure 2] FIG. 2 is a flowchart showing a method for manufacturing a composite member according to the second embodiment. [Figure 3] FIG. 3 is a diagram schematically showing a cross section of a composite member according to an embodiment. [Figure 4] FIG. 4 shows the tensile stress-tensile strain curve of the cured product of the resin composition used in the examples. [Figure 5] FIG. 5 shows the bending stress-bending strain curve of the composite member produced in the example. [Figure 6] FIG. 6 is a graph showing the relationship between the tensile strength of the cured product of the resin composition used in the examples and the flexural strength of the composite member produced in the examples. [Figure 7] FIG. 7 is a graph showing the relationship between the tensile strength of the cured product of the resin composition used in the examples and the flexural modulus of the composite members produced in the examples. [Figure 8] FIG. 8 is a graph showing the relationship between the tensile strength of the cured product of the resin composition used in the examples and the maximum bending strain of the composite members produced in the examples. [Figure 9] FIG. 9 is a graph showing the relationship between the tensile strength of the cured product of the resin composition used in the examples and the fracture toughness value of the composite member produced in the examples. [Figure 10] FIG. 10 shows cross-sectional SEM images of the composite members of Examples 1 to 4 produced in the working examples. [Figure 11] FIG. 11 shows SEM images of fracture surfaces formed by bending tests of the composite members of Examples 1 to 4 produced in the working examples. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Method for manufacturing composite member (first embodiment)> As shown in FIG. 1, the method for manufacturing a composite member according to the first embodiment includes a step (S11) of preparing a paper product containing flake particles, a step (S12) of impregnating the paper product with a curable resin composition, and a step (S13) of curing the curable resin composition.

[0012] (1) Preparation of paper products (S11) First, the flake particles are mixed with a dispersion medium to prepare a suspension.

[0013] Examples of flake particles that can be used include particles of inorganic materials such as natural mica, synthetic mica, smectite, talc, carbonates, silicates, phosphates, and metals. In this application, the term "flake-like" refers to a particle in which the equivalent circle diameter of the surface (flat surface) with the largest projected area is greater than the maximum length (thickness) in the direction perpendicular to the surface, and can also be referred to as scale-like, plate-like, or thin-plate-like. The flake particles may have a median diameter d of 100 nm to 5,000 μm and an average thickness t of 10 nm to 10 μm. The aspect ratio of the flake particles, i.e., the ratio d / t of the median diameter to the average thickness, may be, for example, 100 or more, and particularly 100 to 10,000. The median diameter d of the flake particles can be measured using a laser diffraction particle size analyzer. The average thickness t of the flaky particles can be determined by measuring the thickness of 30 or more particles from a cross-sectional image of the flaky particles obtained using an SEM or TEM, and calculating the arithmetic mean of the obtained values.

[0014] The dispersion medium may be water, alcohol, or the like.

[0015] The prepared suspension is then paper-spun to produce a paper product. Paper-spun can be performed in accordance with JIS P 8222:2015. Specifically, the suspension is paper-spun using a machine similar to that used in the papermaking industry to obtain a wet mat on a mesh, and the liquid (dispersion medium) contained in the wet mat is removed by drying or the like to obtain a sheet-like paper product.

[0016] In the paper product, the flake particles are arranged overlapping each other and oriented so that the thickness direction of the flake particles is parallel to the thickness direction of the paper product.

[0017] (2) Impregnation (S12) The resulting paper product is impregnated with a curable resin composition. For example, the paper product can be impregnated with the curable resin composition by coating the paper product with the curable resin composition. Impregnation may be promoted by placing the paper product coated with the curable resin composition under reduced pressure or by reducing the viscosity of the curable resin by heating or the like.

[0018] The curable resin composition contains a curable resin such as an epoxy resin, an unsaturated polyester resin, a vinyl ester resin, a phenolic resin, an epoxy acrylate resin, a urethane acrylate resin, a phenoxy resin, an alkyd resin, a urethane resin, a maleimide resin, or a cyanate resin. One type of curable resin may be used alone, or two or more types may be used in combination. The curable resin composition may contain additives such as a polymerization initiator (thermal polymerization initiator, photopolymerization initiator, etc.), a curing agent, a curing accelerator, an antifoaming agent, a surfactant, a flame retardant, a colorant, a pigment, a phosphor, or a mold release agent. The curable resin composition may be heat-curable or photo-curable.

[0019] The curable resin composition is a composition that forms a cured product having a tensile strength in the range of 1 to 30 MPa when cured under the same curing conditions as in the subsequent curing step (S13). By using such a curable resin composition, the composite member obtained by the manufacturing method of this embodiment can have a sufficiently high flexural strength and flexural modulus, while also having a large maximum flexural strain and exhibiting ductile fracture behavior. The cured product of the curable resin composition may have a tensile strength in the range of 1 to 25 MPa or 2 to 24 MPa. The cured product of the curable resin composition may also have a tensile strength in the range of 15 to 30 MPa, 20 to 30 MPa, or 23 to 25 MPa. By using such a curable resin composition, the composite member obtained by the manufacturing method of this embodiment can further have a particularly high fracture toughness value. In conventional techniques, resin compositions that form cured products exhibiting high tensile strength (e.g., 40 MPa or more) are generally used as resin compositions used in the manufacture of filler-reinforced composite members. However, when such materials are used in this embodiment, the composite member does not exhibit ductile fracture behavior and instead undergoes brittle fracture. The tensile strength of the cured product of the curable resin composition can be determined from a tensile stress-tensile strain curve obtained by a tensile test in accordance with JIS C 2151:2019 and ASTM D882. Specifically, the tensile strength is the maximum tensile force recorded when a test piece is pulled until it breaks.

[0020] The amount of curable resin composition impregnated into the paper product may be, for example, such that in the composite member produced by the production method of this embodiment, the volume fraction of the flaky particles based on the volume of the composite member is in the range of 5 to 99 volume %, particularly 40 to 99 volume % or 50 to 99 volume %. By including the flaky particles in such a high volume fraction in the composite member, the composite member can have sufficiently high bending strength and bending modulus.

[0021] (3) Curing (S13) The curable resin composition impregnated into the paper product is cured. Depending on the shape of the composite member to be produced, multiple sheets of the paper product may be stacked and pressure-molded. Curing may be performed by heating, ultraviolet irradiation, or the like, and the curing conditions may be appropriately selected depending on the curable resin composition.

[0022] As a result, a composite member containing a matrix material and flake particles dispersed in the matrix material is obtained. In the composite member obtained by the manufacturing method of this embodiment, the matrix material is a cured product of a curable resin composition. The flake particles are highly oriented so that the thickness direction of the flake particles is parallel to the thickness direction of the composite member.

[0023] <Method for manufacturing composite member (second embodiment)> As shown in FIG. 2, the method for manufacturing a composite member according to the second embodiment includes a step (S21) of preparing a suspension, a step (S22) of making a paper product from the suspension, and a step (S23) of hot-pressing the paper product.

[0024] (1) Preparation of suspension (S21) A suspension is prepared by mixing a fibrous or particulate thermoplastic material and flake particles with a dispersing medium in air or an inert atmosphere such as a nitrogen atmosphere.

[0025] Examples of thermoplastic materials include thermoplastic resins such as polypropylene (PP), polyamide (PA), polyphenylene sulfide (PPS), and polyethersulfone (PES), as well as glass, cellulose, and natural fibers derived from plants such as bamboo and kenaf.

[0026] The thermoplastic material has a tensile strength in the range of 1 to 30 MPa at the operating temperature of the composite member produced by the manufacturing method of this embodiment. By using such a thermoplastic material, the composite member obtained by the manufacturing method of this embodiment can exhibit ductile fracture behavior while maintaining sufficiently high bending strength and bending modulus during use, as well as a large maximum bending strain. The thermoplastic material may have a tensile strength in the range of 1 to 25 MPa or 2 to 24 MPa at the operating temperature of the composite member. Furthermore, the thermoplastic material may have a tensile strength in the range of 15 to 30 MPa, 20 to 30 MPa, or 23 to 25 MPa at the operating temperature of the composite member. By using such a thermoplastic material, the composite member obtained by the manufacturing method of this embodiment can further exhibit particularly high fracture toughness during use. In conventional techniques, thermoplastic materials that exhibit high tensile strength (e.g., 40 MPa or more) at the operating temperature of the composite member are typically used to manufacture filler-reinforced composite members. However, when such materials are used in this embodiment, the composite member does not exhibit ductile fracture behavior but instead undergoes brittle fracture. The tensile strength of a thermoplastic material can be determined from a tensile stress-tensile strain curve obtained by a tensile test in accordance with JIS C 2151:2019 and ASTM D882.

[0027] The fibrous thermoplastic material has an average fiber diameter D of, for example, 0.01 to 1000 μm. fib and an average fiber length L of 0.1 μm to 50 mm. fib The aspect ratio of the fibrous thermoplastic material, i.e., the ratio L fib / D fib The average fiber length L may be, for example, 10 to 10,000. fib The average fiber diameter D can be measured using an optical microscope image. fib is determined by measuring and averaging the diameters (circle equivalent diameters) of 30 or more fibers from a cross-sectional image of the fiber obtained using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0028] The particulate thermoplastic material may have a shape such as flakes, spheres, etc. The flake-shaped thermoplastic material may have a median diameter D of, for example, 1 to 5,000 μm. fl and an average thickness T of 0.1 to 100 μm. fl The aspect ratio of the flaky thermoplastic material, that is, the ratio D fl / T fl The median diameter D of the flaky thermoplastic material may be, for example, 10 to 10,000. fl The average thickness T of the flake-like thermoplastic material can be measured using a laser diffraction particle size distribution analyzer. fl is determined by measuring the thickness of 30 or more particles from a cross-sectional image of the particle obtained using an SEM or TEM and averaging the measured values.

[0029] The spherical thermoplastic material has a median diameter D of, for example, 10 nm to 1,000 μm. sp The spherical thermoplastic material may have a median diameter D sp can be measured using a laser diffraction particle size distribution measuring device.

[0030] Examples of flake particles that can be used include particles of inorganic materials such as natural mica, synthetic mica, smectite, talc, carbonates, silicates, phosphates, and metals. The flake particles may have a median diameter d of 100 nm to 5,000 μm and an average thickness t of 10 nm to 10 μm. The aspect ratio of the flake particles, i.e., the ratio of the median diameter to the average thickness d / t, may be, for example, 100 or more, particularly 100 to 10,000. The median diameter d of the flake particles can be measured using a laser diffraction particle size analyzer. The average thickness t of the flake particles can be determined by measuring the thickness of 30 or more particles from cross-sectional images of the flake particles obtained using SEM or TEM and calculating the arithmetic mean of the obtained values.

[0031] The volume fraction of flake particles V relative to the total volume of the mixed thermoplastic material and flake particles fxThe volume fraction of the flaky particles may be in the range of 5 to 99 volume %, particularly in the range of 40 to 99 volume % or 50 to 99 volume %. By using the flaky particles at a high volume fraction, the composite member produced by the production method of this embodiment can have sufficiently high bending strength and bending modulus.

[0032] The volume fraction of flake particles relative to the total volume of flake particles and thermoplastic particles, V fx and the volume fraction of thermoplastic particles V fy , and the average volume of the flake particles v x , and the average effective volume of the thermoplastic particles v y is expressed by the following formula (1):

number

[0033] The dispersion medium may be water, alcohol, or the like.

[0034] (2) Preparation of paper products (S22) The prepared suspension is then paper-sheeted to produce a paper product containing the thermoplastic material and flake particles. Paper-sheeting can be performed in accordance with JIS P 8222:2015. Specifically, the suspension is paper-sheeted using a paper-sheeting machine similar to that used in the papermaking industry to obtain a wet mat on a mesh, and the liquid (dispersion medium) contained in the wet mat is removed by drying or the like to obtain a sheet-like paper product.

[0035] In the paper product, the flake particles are arranged in an overlapping manner and oriented so that the thickness direction of the flake particles is parallel to the thickness direction of the paper product, with thermoplastic material present between the overlapping flake particles.

[0036] (3) Hot press molding (S23) The paper product is hot-pressed to produce a composite member. Depending on the shape of the composite member to be produced, multiple sheets of paper product may be stacked and hot-pressed. Furthermore, to improve handleability, the stacked paper products may be preliminarily pressed together before hot-pressing. During pressing, the paper product may be heated to a temperature below the melting temperature of the thermoplastic material. Hot-pressing is performed by heating the paper product to a temperature above the glass transition point or melting temperature of the thermoplastic material and below its decomposition temperature. This softens the thermoplastic material and expands to fill the spaces between the flake particles. The thermoplastic material is then cooled to solidify. This molds the paper product, resulting in a composite member containing a matrix material and flake particles dispersed in the matrix material. In the composite member produced by the manufacturing method of this embodiment, the matrix material is a thermoplastic material. The flake particles are highly oriented so that the thickness direction of the flake particles is parallel to the thickness direction of the composite member.

[0037] <Composite materials> 3, the composite material 10 of this embodiment includes a matrix material 2 and flake particles 4 dispersed in the matrix material 2. The composite material 10 can be manufactured by the manufacturing methods of the first and second embodiments described above.

[0038] The composite member 10 may have a plate-like shape. In this application, the term "plate-like" includes not only a flat plate-like shape as shown in Fig. 3, but also a curved plate-like shape having a curved portion.

[0039] The matrix material 2 may be a cured product of the curable resin composition or a thermoplastic material described in the above embodiment. Examples of the curable resin composition, the thermoplastic material, and the material of the flaky particles 4, as well as the shape of the flaky particles 4, have been described in detail in the above embodiment, so further description thereof will be omitted here.

[0040] The composite material 10 may contain the flaky particles 4 in an amount within a range of 5 to 99 volume %, particularly within a range of 40 to 99 volume % or 50 to 99 volume %, based on the total volume of the composite material 10. When the composite material 10 contains the flaky particles 4 at such a high volume fraction, the composite material 10 can have sufficiently high bending strength and bending modulus.

[0041] The flake particles 4 are oriented so that their thickness direction is parallel to the thickness direction of the composite material 10. That is, the flake particles 4 are oriented so that the flat surfaces 4a of the flake particles 4 are parallel to the surface 10a of the composite material 10. This allows the composite material 10 to have sufficiently high bending strength and bending modulus. In this application, "parallel" also includes "substantially parallel," and specifically includes a case where the average angle between two surfaces or directions is 30 degrees or less, preferably 20 degrees or less, more preferably 10 degrees or less, and particularly preferably 5 degrees or less. The average angle between the flat surfaces 4a of the flake particles 4 and the surface 10a of the composite material 10 can be determined, for example, by determining the angles between the flat surfaces 4a of 30 or more flake particles 4 and the surface 10a of the composite material 10 from a cross-sectional SEM image or cross-sectional TEM image of the composite material 10 and averaging them.

[0042] The composite member 10 may have a flexural strength of 100 to 250 MPa, particularly 134 to 199 MPa, a flexural modulus of 10 to 40 GPa, particularly 15 to 30 GPa, and a maximum flexural strain of 1 to 2%, preferably 1 to 1.5%, and particularly 1.26 to 1.29%. According to extensive research by the inventors, a composite member 10 having such mechanical properties undergoes ductile fracture. Therefore, it is suitable for applications requiring both high strength and prevention of fragment shedding upon fracture, such as vehicle exterior panels. The composite member 10 may also have a flexural strength of 150 to 250 MPa, preferably 180 to 220 MPa, and particularly 190 to 210 MPa, a flexural modulus of 20 to 40 GPa, particularly 25 to 35 GPa, and a maximum flexural strain of 1 to 2%, preferably 1 to 1.5%, and particularly 1.28 to 1.3%. According to the inventors' intensive studies, the composite member 10 having such mechanical properties not only undergoes ductile fracture but also has a high fracture toughness value (specifically, 300 to 500 J / m 3 , 400~500J / m 3 , or 450 to 500 J / m 3 Therefore, it can be suitably used in applications that require high toughness in addition to high strength and prevention of fragments falling off when broken.

[0043] The bending strength, bending modulus, maximum bending strain, and fracture toughness of the composite member 10 can be determined from a bending stress-bending strain curve obtained by a three-point bending test in accordance with JIS K 7017: 1999. Specifically, the bending strength is the bending stress applied to the composite member 10 at the maximum load during the test, the bending modulus is the gradient of the stress-strain curve within the elastic limit, the maximum bending strain is the strain of the composite member 10 at the maximum load, and the fracture toughness is the integrated value of the stress-strain curve.

[0044] A composite member 10 having the mechanical properties described above can be manufactured by the manufacturing method of the first or second embodiment described above, but the manufacturing method of the composite member 10 is not limited to these. By selecting an appropriate material as the matrix material 2, that is, a material having a tensile strength within the ranges of 1 to 30 MPa, 1 to 25 MPa, 2 to 24 MPa, 15 to 30 MPa, 20 to 30 MPa, or 23 to 25 MPa, selecting appropriate flake particles, and setting the volume fraction of these particles to appropriate values, it is possible to manufacture the composite member 10 by a method different from the manufacturing method of the first or second embodiment.

[0045] The inventors believe that because the matrix material 2 is a material having a relatively low tensile strength as described above, a moderate shear load is applied to the flake particles when bending stress is applied to the composite member 10, and as a result, the composite member 10 can exhibit ductile fracture behavior while having sufficiently high bending strength and bending modulus.

[0046] The composite member 10 may be further shaped for use, i.e., the composite member 10 may be used as an intermediate material for producing a final product.

[0047] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the present invention as set forth in the claims. [Example]

[0048] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0049] <Production of composite materials> (1) Preparation of resin composition As the hardening agent, the formula (1) [ka] Bisphenol A type epoxy resin (jER828 manufactured by Mitsubishi Chemical Corporation) represented by the formula (2) [ka] Poly(propylene glycol) diglycidyl ether (Denacol EX-931 manufactured by Nagase ChemteX Corporation) represented by the formula (I), 4-methylhexahydrophthalic anhydride (manufactured by DIC Corporation) as a curing agent, and 1,2-dimethylimidazole (manufactured by Shikoku Chemicals Corporation) as a curing accelerator were prepared.

[0050] These materials were mixed in the amounts shown in Table 1. [Table 1]

[0051] Specifically, the measured hard base agent, soft base agent, curing agent, and curing accelerator were mixed at 500 rpm for 3 minutes under atmospheric pressure using a vacuum planetary centrifugal mixer (Thinky Corporation's Awatori Rentaro). The pressure inside the container was then reduced to 1 kPa, and the mixture was mixed at 500 rpm for 2 minutes, then at 1200 rpm for 1 minute, and then at 1500 rpm for 1 minute. This yielded a composition containing an epoxy resin (epoxy resin composition).

[0052] (2) Preparation of paper products White mica particles (diameter 280 μm, average thickness 1 μm, average aspect ratio 280, manufactured by Hubei Zhongtian Mica Products Co., Ltd.) were prepared as flake particles. The diameter of the mica particles was the median diameter d50 measured using a laser diffraction particle size distribution analyzer (Malvern Mastersizer 3000), and the average thickness of the mica particles was determined from SEM images. The white mica particles were added to water and mixed to obtain a suspension.

[0053] 2 L of water was added to the papermaking machine so that the water level was higher than the wire mesh of the papermaking machine. Next, the above suspension was added to the papermaking machine and stirred, and then drained from the bottom of the papermaking machine. As a result, the suspension was filtered through the wire mesh, and a wet mat was formed on the wire mesh.

[0054] A cellulose filter paper was placed on the wet mat, and a stainless steel plate was placed on top of that. A metal roller was applied to the stainless steel plate to compress the wet mat, and the water in the wet mat was absorbed by the filter paper.

[0055] The wet mat was removed from the wire mesh and filter paper and dried in an oven for 4 hours to obtain a sheet-like paper product. A total of five paper products were produced in the same manner for each example.

[0056] (3) Impregnation Each paper product was cut to a size of 50 mm long and 50 mm wide (weight 1.8 g). One paper product was placed in a silicone rubber mold measuring 50 mm long, 50 mm wide, and 20 mm high, and the above-mentioned resin composition was uniformly applied to it. The applied weight of the resin composition in each example was as shown in Table 2. Another paper product was placed on top of it, and another resin composition was applied evenly in the weight shown in Table 2. This process was repeated until the resin composition was applied to five paper products.

[0057] [Table 2]

[0058] The mold containing the five resin composition-coated paper products was placed in a vacuum oven and heated at 80°C for 30 minutes under reduced pressure, thereby impregnating the paper products with the resin composition.

[0059] (4) Hardening The papermaking product impregnated with the resin composition was transferred to a mold measuring 50 mm in length, 50 mm in width, and 10 mm in height, and pressed at 120°C for 90 minutes at a pressure of 5 MPa using a heat press (manufactured by Toyo Seiki Seisaku-sho, Ltd.) to cure the resin composition. This yielded plate-shaped molded articles (composite members) in Examples 1 to 4. In all of the composite members obtained, the volume fraction of the cured resin composition was 40%, and the volume fraction of the white mica particles was 60%.

[0060] <Tensile test of the cured product of the curable resin composition> The resin compositions of Examples 1 to 4 prepared in (1) above were filled into a mold measuring 50 mm in length, 50 mm in width, and 10 mm in height and cured at 120°C for 90 minutes under atmospheric pressure using a heat press. Five dumbbell-shaped test pieces (size 7, thickness 2 mm) were prepared from the resulting cured products according to JIS K 6251:2017 for each example. Tensile tests were performed according to JIS C 2151:2019 and ASTM D882 using a universal mechanical testing machine (Shimadzu Corporation, Autograph AGS-X). The tensile speed was 2 mm / min. The tensile stress-tensile strain curves obtained for each example are shown in Figure 4.

[0061] The tensile strength of the cured resin composition of each example (the maximum tensile force recorded when the test piece was pulled until it broke) was determined from the stress-strain curve in Figure 4. The results are shown in Table 3.

[0062] <Bending test of composite materials> Five test pieces measuring 50 mm in length, 10 mm in width, and 2 mm in thickness were cut from each of the composite members of Examples 1 to 4, and three-point bending tests were performed in accordance with JIS K 7017:1999 using a universal mechanical testing machine (Autograph AGS-X, manufactured by Shimadzu Corporation). The support distance was 32 mm, and the test speed was 1 mm / min. The bending stress-bending strain curves obtained for each example are shown in Figure 5. The composite members of Examples 1 and 2 exhibited brittle fracture behavior, while the composite members of Examples 3 and 4 exhibited ductile fracture behavior.

[0063] The flexural strength (the bending stress applied to the composite member at the maximum load during the test), flexural modulus (the gradient of the stress-strain curve within the elastic limit), maximum flexural strain (the strain of the composite member at the maximum load), and fracture toughness (the value obtained by integrating the stress-strain curve) of the composite member were determined from the stress-strain curve in Figure 5. The results are shown in Table 3. The relationships between the tensile strength of the cured product of the curable resin composition used to prepare the composite member and the flexural strength, flexural modulus, maximum flexural strain, and fracture toughness of the composite member are shown in Figures 6 to 9, respectively.

[0064] [Table 3]

[0065] <Internal structure observation> The cross sections of the composite members of Examples 1 to 4 were observed using a scanning electron microscope (TM3030Plus, manufactured by Hitachi High-Tech Corporation). The obtained SEM images are shown in Figure 10. In the SEM image of Figure 10, the vertical direction is the thickness direction of the composite member, the light-colored areas represent cross sections of mica particles, and the dark-colored areas represent the cured product of the resin composition (matrix material). In all of the composite members of Examples 1 to 4, the mica particles were dispersed in the matrix material and were highly oriented so as to overlap in the thickness direction of the composite member.

[0066] <Fracture surface observation> The fracture surfaces of the composite members fractured in the bending test were observed in the thickness direction of the composite member using an SEM (TM3030Plus manufactured by Hitachi High-Tech Corporation). The obtained SEM images are shown in Figure 11. Many broken mica particles were observed on the fracture surfaces of the composite members of Examples 1 and 2. Many unbroken mica particles were observed on the fracture surfaces of the composite members of Examples 3 and 4.

[0067] These evaluation results showed that by selecting a resin with appropriate tensile strength as the matrix material, composite members can be obtained that have sufficiently high flexural strength and flexural modulus, while also having a large maximum flexural strain and undergoing ductile fracture. Specifically, in Examples 3 and 4, by using a resin composition with a cured tensile strength of 2 to 24 MPa, composite members were obtained that had a sufficiently high flexural strength of 134 to 199 MPa and a sufficiently high flexural modulus of 15 to 30 GPa, while also having a large maximum flexural strain of 1.26 to 1.29%, and also undergoing ductile fracture. In particular, in Example 3, by using a resin composition with a cured tensile strength of 24 MPa, composite members were obtained that had higher flexural strength and higher flexural modulus, while also having a larger maximum flexural strain of 1.29%, and also undergoing ductile fracture, with a maximum flexural strain of 478.7 J / m 3 A composite member exhibiting a particularly high fracture toughness value was obtained. [Explanation of symbols]

[0068] 2 matrix material, 4 flake particles, 4a flat surface of flake particles, 10 composite member, 10a surface of composite member

Claims

1. A composite member comprising a matrix material and flake particles dispersed in the matrix material, The composite material contains the flake particles in an amount of 50 to 99% by volume based on the total volume of the composite material, the matrix material is a cured product of an epoxy resin composition containing a bisphenol A epoxy resin and poly(propylene glycol) diglycidyl ether in a weight ratio of 20:80 to 40:60; the flake particles are mica particles having a median diameter d of 100 nm to 5000 μm, an average thickness t of 10 nm to 10 μm, and a ratio d / t of the median diameter to the average thickness of 100 to 10000; The composite member has a flexural strength in the range of 100 to 250 MPa, a flexural modulus in the range of 10 to 40 GPa, and a maximum flexural strain in the range of 1 to 2%.

2. 300-500J / m ３ 10. The composite member of claim 1, having a fracture toughness value in the range of:

3. Producing a paper product containing flake particles; impregnating the paper product with an epoxy resin composition; curing the epoxy resin composition under predetermined conditions; The method for producing the composite member according to claim 1 or 2, comprising:

4. The method described in claim 3, wherein the epoxy resin composition is a composition that forms a cured product having a tensile strength in the range of 1 to 30 MPa when cured under the specified conditions.

Images