Reinforcing fiber base material and fiber-reinforced composite material

Abstract

The present invention pertains to a reinforcing fiber base material that is provided with one or more reinforcing fiber sheets obtained by pulling and aligning reinforcing fibers in one direction, and that is integrated together by a stitch thread that is made of an amorphous resin material and that satisfies at least one of the following conditions: the tensile elastic modulus of the amorphous resin material is 1 GPa or more at 82°C; and the shrinkage rate of the amorphous resin material is less than 10% when being held at 130°C. The present invention also pertains to a fiber-reinforced composite material manufactured by using said reinforcing fiber base material. A fiber-reinforced composite material according to the present invention has excellent compressive strength in moist-heat environments, suppresses occurrence of microcracks after a cooling-heating cycle, and has excellent durability.

Description

Reinforced fiber substrate and fiber-reinforced composite material

[0001] The present invention relates to a reinforcing fiber substrate for use in aerospace and general industrial applications, and to a fiber-reinforced composite material produced using the same.

[0002] Fiber-reinforced composite materials (FRPs) have excellent weight-saving potential and are widely used in aircraft, sports cars, and other applications. For structural materials that bear loads, in particular, prepregs, which are intermediate substrates made of aligned reinforcing fibers impregnated with a matrix resin, have traditionally been widely used. However, due to the recent demand for high productivity, injection molding methods such as resin transfer molding (RTM) and vacuum-assisted resin transfer molding (VaRTM) have become increasingly popular. Injection molding is a molding method for producing FRP by placing a dry laminate of reinforcing fiber substrates in a mold and injecting, impregnating, and solidifying a liquid matrix resin within the mold.

[0003] When injection molding is used for structural materials, non-crimp fabric (NCF) is often used as the reinforcing fiber substrate, in which one or more layers of unidirectionally aligned reinforcing fiber sheets are laminated and stitched together in the thickness direction with stitch thread. NCF has low waviness of the reinforcing fibers, which allows for high mechanical properties and increases the efficiency of the lamination process. However, when used for structural materials for aircraft, it still lacks compressive strength, durability over long periods of use, and impact resistance compared to prepreg.

[0004] Patent Document 1 discloses a fiber-reinforced composite material that suppresses microcracks by using a fine stitch thread of 30 dtex or less. However, even with this technology, the material still has insufficient resistance to thermal cycles and insufficient compressibility under hot and humid conditions.

[0005] Patent Document 2 discloses a method for producing a fiber-reinforced composite material in which microcracks are suppressed during thermal cycling by achieving a specific relationship between the melting point of the stitch thread and the curing behavior of the matrix resin. However, because the stitch thread is made of a crystalline resin with a low glass transition temperature (Tg) and melting point, the method suffers from insufficient compressibility, particularly under wet heat conditions, and also from insufficient formability, such as resin impregnation and appearance quality, at high temperatures for the reinforcing fiber substrate, depending on the molding conditions.

[0006] Patent Document 3 discloses a reinforcing fiber substrate in which an oil is applied to the surface of a stitch thread to improve adhesion to a matrix resin and suppress microcracks. However, the need for a process to apply an oil to the stitch thread poses a problem in productivity, and the compression characteristics under humid heat may be insufficient depending on the heat resistance of the stitch thread.

[0007] Patent Document 4 discloses a highly durable fiber-reinforced composite material that is excellent in hydrolysis resistance and heat aging resistance by using a highly hydrolysis-resistant stitch thread. However, because a crystalline resin with a high melting point is used, the material lacks thermal cycle resistance.

[0008] Japanese Patent No. 5599407 International Publication No. 2022 / 265727 Japanese Patent Application Laid-Open No. 2022-23119 International Publication No. 2020 / 031834

[0009] The present invention overcomes the drawbacks of the conventional techniques and aims to provide a reinforcing fiber substrate that can stabilize its shape at high temperatures while maintaining excellent productivity, and that simultaneously satisfies mechanical properties that have been difficult to achieve in the past, particularly excellent compressibility under wet heat conditions, and durability during thermal cycles, and a fiber-reinforced composite material using the same.

[0010] In order to solve the above problems, the present invention has the following configuration. [1] A reinforcing fiber substrate comprising one or more constituent elements [A] each formed by unidirectionally aligning reinforcing fibers, and integrated with a constituent element [B], and simultaneously satisfying the following conditions 1 and at least one of conditions 2 and 3: [A]: Reinforcing fiber sheet; [B]: Stitch thread; Condition 1: The constituent element [B] is made of an amorphous resin material; Condition 2: The amorphous resin material constituting the constituent element [B] has a tensile modulus of 1 GPa or more at 82°C; and Condition 3: The shrinkage rate when the constituent element [B] is maintained at 130°C is less than 10%. [2] The reinforcing fiber substrate according to [1], wherein the amorphous resin material constituting the constituent element [B] is an amorphous polyamide. [3] The reinforcing fiber substrate according to [2], wherein the glass transition temperature of the amorphous resin material constituting the constituent element [B] is 140 to 165°C. [4] The reinforcing fiber substrate according to any one of [1] to [3], wherein the fineness of the constituent element [B] is 20 to 60 dtex. [5] The reinforcing fiber substrate according to any one of [1] to [4], wherein a porous material made of a thermoplastic resin is disposed on at least one surface of the component [A]. [6] The thermoplastic resin constituting the porous material is an amorphous polyamide, and the mass per unit area of ​​the porous material w2 [g / m ２ ] and the amount w1 [g / m ] of the component [B] used per unit area of ​​the reinforcing fiber substrate described in [5] ２ [7] A reinforced fiber composite material obtained by impregnating a reinforcing fiber laminate in which a plurality of reinforcing fiber substrates according to any one of [1] to [6] are laminated, with a thermosetting resin and curing the laminate. [8] A linear expansion coefficient α of the cured product of the thermosetting resin is E is 100 x 10 －６ or less, and the linear expansion coefficient α of the amorphous resin material constituting the component [B] is S The reinforced fiber composite material according to [7], which satisfies the relationship of the following formula (2): 2 × α E <α S (2)

[0011] The reinforcing fiber substrate of the present invention and the fiber-reinforced composite material obtained using the same can stabilize the shape of the reinforcing fiber substrate, particularly at high temperatures, while maintaining excellent productivity, and has excellent compressive strength at room temperature and in a humid and hot environment, suppresses the occurrence of microcracks after thermal cycling, and is excellent in durability. Therefore, it is possible to further reduce the weight of structures to which the fiber-reinforced composite material is applied and maintain high mechanical properties. Furthermore, the reinforcing fiber substrate of the present invention can be suitably used for producing fiber-reinforced composite materials by injection molding.

[0012] 1 is a conceptual diagram showing the configuration of a reinforcing fiber substrate; and FIG. 2 is a conceptual diagram showing the configuration of a reinforcing fiber sheet.

[0013] The present invention will be described in detail below with reference to the drawings together with embodiments. The reinforcing fiber substrate of the present invention is formed by laminating one or more reinforcing fiber sheets as component [A] and integrating them with a stitch thread as component [B]. First, component [A] will be described.

[0014] (Component [A]) Component [A] in the present invention is a reinforcing fiber sheet. Component [A] is in the form of a unidirectional sheet obtained by aligning multifilament yarns made of reinforcing fibers in one direction to form a sheet having a predetermined weight per unit area (basis weight). By forming the sheet into a unidirectional sheet, bending of the reinforcing fibers can be suppressed, thereby increasing the compressive strength of a reinforced fiber composite material using the reinforcing fiber substrate of the present invention.

[0015] The unidirectional sheet form can be obtained by arranging the reinforcing fibers so that the fiber axis direction is the same. The aligned reinforcing fibers that make up the unidirectional sheet may or may not be bound and fixed together. If they are not bound and fixed together, they are laminated with another unidirectional sheet as described below while tension is applied in the fiber axis direction, and integrated with a stitch thread. There are no particular restrictions on the method for binding and fixing the aligned reinforcing fibers that make up the unidirectional sheet, and examples include fixing them with binder particles or auxiliary threads. The auxiliary threads may be made of the same material as the component [B] described below.

[0016] The reinforcing fibers used in such a reinforcing fiber sheet are not particularly limited, and examples thereof include glass fibers, carbon fibers, aramid fibers, boron fibers, alumina fibers, and silicon carbide fibers. Two or more of these fibers may be mixed. Carbon fibers are preferred from the viewpoint of obtaining a lightweight, highly rigid fiber-reinforced composite material.

[0017] The weight per unit area of ​​the reinforcing fiber sheet of the present invention, so-called basis weight, is 50 to 800 g / m ２ is preferable, and more preferably 100 to 600 g / m ２ , particularly preferably 150 to 350 g / m ２ By setting the basis weight within this range, a good balance is achieved between lamination efficiency, resin impregnation property, and shaping property.

[0018] (Component [B]) The component [B] in the present invention is a stitch thread. The component [B] must be composed of an amorphous resin material. As described below, the stitch thread stitches and integrates reinforcing fiber sheets to form a reinforcing fiber substrate, and therefore exists continuously in the thickness direction and in-plane direction inside the reinforcing fiber substrate. By using an amorphous resin material with specific properties for the stitch thread of the reinforcing fiber substrate, fracture originating near the stitch thread is less likely to occur, and a fiber-reinforced composite material with excellent durability can be obtained that exhibits excellent compressive strength, particularly in a humid and hot environment, and suppresses the occurrence of microcracks after thermal cycling.

[0019] Here, in the present invention, amorphous refers to a material having a melting enthalpy of less than 5 J / g measured using differential scanning calorimetry at a temperature rise rate of 10°C / min in accordance with JIS K7121 (2012).

[0020] As the amorphous resin material constituting the component [B], amorphous polyamide can be suitably used because it has an excellent balance between heat resistance and durability.

[0021] Examples of such amorphous polyamides include polyamides 4I, 6I, 9I, and 12I, as well as polyamides containing 4,4'-diaminodicyclohexylmethane and / or its derivatives and aromatic or aliphatic dicarboxylic acids as constituent components, which have good compatibility with matrix resins and excellent adhesive properties. Examples of polyamides containing 4,4'-diaminodicyclohexylmethane and / or its derivatives and aromatic or aliphatic dicarboxylic acids as constituent components include "Grilamid" TR90, TR55, TR30, and XE4003 (all manufactured by M-Chemie Japan Co., Ltd.), and "TROGAMIDO" CX7323, CX9701, and CX9704 (all manufactured by Daicel-Evonik Co., Ltd.).

[0022] The amorphous resin material used in component [B] of the present invention preferably has a glass transition temperature (hereinafter referred to as Tg) in the range of 140° C. to 165° C. A fiber-reinforced composite material obtained using a stitch thread (component [B]) made of an amorphous resin material in this range can achieve a better balance between excellent compressive strength under wet heat conditions and suppression of microcracks after thermal cycling.

[0023] The Tg can be measured using DSC in accordance with, for example, JIS K 7121 (2012).

[0024] Furthermore, the component [B] of the present invention simultaneously satisfies the condition 1 that it is made of an amorphous resin material as described above, and at least one of the following conditions 2 and 3. Condition 2: The amorphous resin material constituting the component [B] has a tensile modulus of elasticity at 82°C of 1 GPa or more. Condition 3: The shrinkage rate when the component [B] is maintained at 130°C is less than 10%.

[0025] When component [B] in the present invention is composed of an amorphous resin material having a tensile modulus of 1 GPa or more at 82°C after humidity conditioning, as in condition 2 above, if the tensile modulus is within this range, the fiber-reinforced composite material obtained using the reinforcing fiber substrate of the present invention can exhibit excellent compressive strength, particularly in a humid and hot environment, because the stitch thread does not become a brittle part. Furthermore, by setting the tensile modulus of the amorphous resin material at 82°C after humidity conditioning to 2 GPa or less, stress concentration at the interface with the matrix resin can be effectively suppressed, particularly in a humid and hot environment, and excellent compressive strength can be exhibited, which is preferable.

[0026] The tensile modulus can be measured, for example, by processing the amorphous resin material constituting the component [B] into a dumbbell-shaped resin plate and subjecting it to a tensile test in accordance with JIS K7161 (1994).

[0027] Furthermore, when the component [B] in the present invention is composed of an amorphous resin material having a shrinkage rate of less than 10% in the fiber axis direction when maintained at 130°C as in the above-mentioned condition 3, by being in such a range, the reinforcing fiber substrate of the present invention can suppress disturbance of the orientation of the reinforcing fibers due to dimensional changes in the stitch threads in a high-temperature environment, and therefore the shape of the reinforcing fiber substrate can be stabilized and excellent compressive strength can be exhibited both at room temperature and in a humid and hot environment.

[0028] Here, the shrinkage rate in the fiber axis direction when maintained at 130°C can be calculated by measuring the dimensional change after treating component [B] in a dryer at 130°C, for example, in accordance with the method for measuring dry heat dimensional change of JIS L1013 (2010).

[0029] Furthermore, the fineness of the component [B] in the present invention is preferably 20 to 60 dtex, more preferably 20 to 40 dtex. By having the fineness in this range, it is possible to minimize bending of the reinforcing fibers and improve the impregnation of the resin during injection molding.

[0030] The form of component [B] is not particularly limited, but from the viewpoint of the weaving property and shaping property of the reinforcing fiber substrate, it is preferably composed of a multifilament yarn. Furthermore, the number of filaments contained in such a multifilament yarn is preferably 4 to 20. By keeping the number within this range, the occurrence of microcracks after thermal cycling can be further suppressed, and processability such as shaping property and impregnation property can be improved.

[0031] Furthermore, from the viewpoint of enhancing the impregnation of the matrix resin into the reinforcing fiber substrate, the component [B] is preferably twisted. The number of twists per meter of the stitch yarn is more preferably 100 or more.

[0032] The stitch yarn in the present invention can be produced by known methods such as melt spinning, dry spinning, and wet spinning.

[0033] (Reinforcing fiber substrate) The reinforcing fiber substrate of the present invention is formed by laminating one or more sheets of the component [A] and integrating them with the component [B], and as described above, the component [B] is an amorphous resin material (condition 1), and the amorphous resin material constituting the component [B] has an elastic modulus of 1 GPa or more at 82°C (condition 2) or the shrinkage rate when the component [B] is maintained at 130°C is less than 10% (condition 3).

[0034] FIG. 1 shows a schematic perspective view of one embodiment of the reinforcing fiber substrate of the present invention, in which two or more reinforcing fiber sheets are stacked. Starting from the underside of the reinforcing fiber substrate 1A, the fiber axes of the reinforcing fibers constituting the reinforcing fiber sheets 11, 12, 13, and 14 are stacked in the order of -45°, 90°, +45°, and 0° relative to the longitudinal direction (MD) of the reinforcing fiber substrate 1A, respectively, and stitched and integrated with a stitch thread 2. The layer configuration of the reinforcing fiber substrate of the present invention is not limited to this. It is preferable that the fiber axis directions of the reinforcing fibers constituting adjacent reinforcing fiber sheets in the thickness direction of the reinforcing fiber substrate are different from each other, and it is particularly preferable from the viewpoint of mechanical properties that the fiber axis directions be appropriately selected from 0°, +45°, -45°, and 90°. Furthermore, while FIG. 1 illustrates a configuration in which four reinforcing fiber sheets are stacked, the configuration of the reinforcing fiber substrate of the present invention is not limited to this, and any number of sheets can be stacked. However, from the viewpoint of adaptability to changes in plate thickness and other shapes when applied to structures, it is preferable to set the upper limit to about eight sheets.

[0035] FIG. 2 shows a schematic perspective view of one embodiment of the reinforcing fiber substrate of the present invention, in which one reinforcing fiber sheet is used. The reinforcing fibers constituting the reinforcing fiber sheet 15 are stacked from the underside of the reinforcing fiber substrate 1B, with the fiber axes of the reinforcing fibers at 0° relative to the longitudinal direction (MD) of the reinforcing fiber substrate 1B, and stitched and integrated with a stitch thread 2. When the number of stacked layers is one, it is preferable to include an auxiliary thread 3 to improve the dimensional stability of the substrate. In FIG. 2, the auxiliary thread is arranged on the underside of the reinforcing fiber substrate so that the fiber axis of the auxiliary thread is at 90° relative to the MD, but this is not limited thereto and it is sufficient that the auxiliary thread is arranged at an angle different from the fiber axis of the reinforcing fiber sheet. Glass fiber, carbon fiber, thermoplastic resin fiber, etc. can also be used as the auxiliary thread.

[0036] In the reinforcing fiber substrate of the present invention, as a method of integration using a stitch yarn, tricot knitting, chain knitting, warp knitting using a pattern combining these, weft knitting using a sewing machine, etc. can be applied. Among them, warp knitting, which can achieve both handleability and shaping ability of the reinforcing fiber substrate, is preferred, and tricot knitting is particularly preferred because it can obtain high shaping ability.

[0037] The component [B] per unit area of ​​the reinforcing fiber substrate of the present invention, i.e., the amount w1 (g / m ２ ) is 1 to 10 g / m ２ It is preferable that the density is 1 to 5 g / m ２ It is more preferable that the weight is in this range. When the weight is in this range, the balance between the handleability of the substrate, the impregnation property of the matrix resin, and the compression property of the reinforced fiber composite material is good. The weight per unit area of ​​the stitch thread is determined based on the conditions (stitch pattern, pitch, stitch length, etc.) when stitching the reinforced fiber sheet. ２ It can be calculated from the amount of stitch thread used to obtain a single reinforcing fiber substrate.

[0038] The reinforcing fiber substrate of the present invention preferably has a porous material made of a thermoplastic resin disposed on at least one surface of the component [A], i.e., the reinforcing fiber sheet. This configuration can improve the impact resistance of the fiber-reinforced composite material obtained using the reinforcing fiber substrate of the present invention. Examples of the configuration of the porous material include nonwoven fabric, mat, net, mesh, woven fabric, knitted fabric, short fiber cluster, perforated film, and porous film. In addition, the mass per unit area w2 (g / m) of the porous material can be calculated. ２ ) is 1 to 10 g / m ２ When the content is in this range, a fiber-reinforced composite material having an excellent balance between compressive strength and impact resistance can be obtained.

[0039] The thermoplastic resin constituting the porous material is selected from the group consisting of, for example, polyamide resin, amorphous polyamide resin, polyester resin, polyphenylene sulfide resin, polyetherimide resin, polyethersulfone resin, polyvinyl formal resin, polyetheretherketone resin, polycarbonate resin, polysulfone resin, polyphenylene ether resin, polyimide resin, polyamideimide resin and phenoxy resin.

[0040] Among these, the thermoplastic resin constituting the porous material is preferably an amorphous polyamide, which can achieve a good balance between high levels of impact resistance and compressibility under a humid and hot environment. Examples of amorphous polyamides include polyamides 4I, 6I, 9I, and 12I, and polyamides having 4,4'-diaminodicyclohexylmethane and / or its derivatives and aromatic or aliphatic dicarboxylic acids as constituent components, such as "Grilamid" TR90, TR55, TR30, and XE4003 (all manufactured by M-Chemie Japan Co., Ltd.), and "TROGAMIDO" CX7323, CX9701, and CX9704 (all manufactured by Daicel-Evonik Co., Ltd.).

[0041] In particular, amorphous polyamide is used as the thermoplastic resin constituting the porous material, and the mass per unit area of ​​the porous material, w2 [g / m ２ ] and the amount of stitch thread used per unit area of ​​the reinforcing fiber substrate w1 [g / m ２ ] preferably satisfies the relationship of the following formula 1: 1≦w2 / w1≦5 (1)

[0042] When the ratio of w1 to w2 is within this range, it is possible to simultaneously exhibit high levels of compressibility and impact resistance at room temperature and under moist heat, as well as high levels of impregnation with the matrix resin.

[0043] The reinforcing fiber substrate of the present invention may have a binder resin attached to at least one surface thereof.

[0044] (Fiber-reinforced composite material) The reinforced fiber composite material of the present invention is obtained by impregnating a reinforcing fiber laminate in which one or more sheets of the reinforcing fiber substrate of the present invention are laminated with a thermosetting resin and curing the same. There are no particular limitations on the molding method for the fiber-reinforced composite material, and examples include injection molding methods such as RTM and VaRTM, liquid compression molding, film infusion, and hand lay-up. Among these, the reinforcing fiber substrate of the present invention can be suitably used in injection molding.

[0045] Injection molding is a method in which a reinforced fiber laminate is placed in a mold, a liquid matrix resin is injected into the mold to impregnate the reinforced fiber laminate, and the resin is then cured to obtain a fiber-reinforced composite material. The injection temperature and curing temperature of the matrix resin may or may not be the same and are determined appropriately depending on the size, shape, and resin properties of the molded product. In RTM, the matrix resin is injected under pressure into a reinforced fiber laminate placed in a cavity of the product shape formed in a closed mold. In VaRTM, an open mold and a flexible film (bag) are used, and the reinforced fiber laminate is placed between the rigid open mold and the flexible film, and the interior pressure is reduced to impregnate the matrix resin.

[0046] Examples of the matrix resin used in the reinforced fiber composite material of the present invention include epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, etc. Among these, it is preferable to use epoxy resins, which have excellent mechanical properties, heat resistance, and chemical resistance, in the reinforced fiber composite material of the present invention.

[0047] The linear expansion coefficient α of the cured product of the thermosetting resin used in the fiber-reinforced composite material of the present invention E is 100 x 10 －６ When the temperature is less than or equal to α, residual stress caused by the difference between the molding temperature and the temperature inside the fiber reinforced composite material after demolding can be suppressed. Ｅ and the linear expansion coefficient α of the amorphous resin material constituting the component [B] of the reinforcing fiber substrate of the present invention. Ｓ It is preferable that the relationship of the following formula 2 is satisfied, since microcracks after thermal cycling can be more effectively suppressed. E <α S (2)

[0048] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the descriptions of these examples. Materials and evaluation methods used in these examples and comparative examples are as follows.

[0049] <Materials used in the components of the reinforcing fiber substrate> Component [A]: Reinforcing fiber used in the fiber-reinforced sheet [A]-1 Carbon fiber "TORAYCA (registered trademark)" T800G-24K-71E. Component [B]: Thermoplastic resin material used in the stitch thread [B]-1 Polyamide 6I, [B]-2 Polyamide 6I / 12, [B]-3 "Grilamid (registered trademark)" TR55, [B]-4 "Grilamid (registered trademark)" TR90, [B]-5 Polyethylene terephthalate, [B]-6 Polyamide 12, [B]-7 Polyamide 6 / 12 (50 / 50).

[0050] <Porous Material> In some examples, a nonwoven fabric was used as the porous material. Grilamid (registered trademark) TR90 was used as the thermoplastic resin material constituting the nonwoven fabric. The nonwoven fabric was produced using a melt-blown nonwoven fabric manufacturing device SWMB-T100 (manufactured by Shinwa Kogyo Co., Ltd.).

[0051] <Method for measuring the mass per unit area of ​​porous material: w2> For the nonwoven fabric produced according to the above <Porous material>, the mass per unit area w2 (g / m ２ The nonwoven fabric was wound on a 500 mm wide roll, and 10 samples of 400 mm x 400 mm were taken at 1 m intervals. The weight of each sample was measured using an electronic balance, and the average value divided by the area was calculated as w2 (g / m ２ The obtained w2 (g / m ２ ) are as shown in Tables 1, 2 and 3.

[0052] <Matrix Resin> When injection molding the reinforcing fiber substrate, an amine-cured epoxy resin was used as the matrix resin. The composition of the epoxy resin used was as follows: 70 parts by mass of tetraglycidyldiaminodiphenylmethane type epoxy ("Araldite" (registered trademark) MY-721, manufactured by Huntsman Japan Co., Ltd.), 30 parts by mass of bisphenol F type epoxy ("EPICRON" (registered trademark) 830 (manufactured by DIC Corporation), 59 parts by mass of 4,4'-methylenebis(3-chloro-2,6-diethylaniline) ("Lonzacure" (registered trademark) M-CDEA (manufactured by Lonza)), 25 parts by mass of 4,4'-methylenebis(3,3',5,5'-tetraisopropylaniline) ("Lonzacure" (registered trademark) M-DIPA (manufactured by Lonza)).

[0053] <Method for preparing thermoplastic resin material> [B]-1 and [B]-2 described above in <Materials used in the components of the reinforcing fiber substrate> were prepared by a polycondensation method under pressure conditions using an autoclave. Polyamide 6I ([B]-1) was prepared by using ion-exchanged water as a solvent and an equimolar mixture of isophthalic acid and hexamethylenediamine in an autoclave. The pressure was increased to 1.7 MPa and the mixture was reacted at 260 ° C for 3 hours to obtain amorphous polyamide 6I. Polyamide 6I / 12 ([B]-2) was prepared by blending polyamide 6I and polyamide 12 in a molar ratio of isophthalic acid / hexamethylenediamine / laurolactam = 1 / 1 / 2 so that the copolymerization ratio was 50 / 50. The mixture was then heated to 1.7 MPa in ion-exchanged water as a solvent and reacted at 260 ° C for 5 hours to obtain amorphous polyamide 6I / 12. Polyamide 6 / 12 (50:50) ([B]-7) was prepared by blending polyamide 6 and polyamide 12 at a molar ratio of ε-caprolactam / laurolactam = 1 / 1 so that the copolymerization ratio was 50 / 50, and reacting the mixture in ion-exchanged water as a solvent at a pressure of 1.7 MPa and 260°C for 5 hours to obtain crystalline polyamide 6 / 12 (50:50).

[0054] <Method for Evaluating the Tensile Modulus of Thermoplastic Resin Material Used in Stitch Thread at 82°C> A thermoplastic resin material prepared or purchased according to the above <Method for Preparing Thermoplastic Resin Material> was placed on a stainless steel plate with a 2 mm thick stainless steel spacer, and a stainless steel plate preheated to 250°C was placed on top. The material was then heated and pressurized using a hand press. After cooling to room temperature, the resin material was removed and processed into a 1BA dumbbell-shaped test piece according to JIS K7161 (1994). The processed test piece was subjected to humidity conditioning at room temperature (25°C, 50% RH) for 30 days. The humidity-conditioned test piece was subjected to a resin tensile test at a high temperature (82°C) using an Instron universal testing machine (manufactured by Instron Corporation) with a chuck distance of 58 mm and a test speed of 1 mm / min, to measure the tensile modulus at 82°C. The value measured for the number of samples (n = 8) was used as the tensile modulus.

[0055] <Method for evaluating shrinkage when stitch thread is held at 130°C> A stitch thread prepared according to the above <Method for preparing stitch thread> was cut to a length of 600 mm, and marks were made at 500 mm intervals on a test piece while an initial load of 2.94 mNx (fineness determined in <Method for measuring fineness of stitch thread>) was applied. The test piece was then hung in a hot air oven (manufactured by Espec Corporation) set to 130°C without the initial load, and after leaving it for 30 minutes, it was removed and cooled to room temperature. The initial load was then applied again, and the length between the marks was measured. The shrinkage at 130°C was measured according to the calculation method for dry heat dimensional change (Method B) of JIS L1013 (2010). In this case, the measurement was performed on 5 samples, and the average value was used as the value of the shrinkage when held at 130°C.

[0056] <Method for measuring glass transition temperature (Tg) of thermoplastic resin material> The Tg of a thermoplastic resin material prepared according to the above <Method for preparing thermoplastic resin material> or purchased was measured using a DSC Q2000 (TA Instruments) in accordance with JIS K 7121 (2012) at a heating rate of 10°C per minute.

[0057] <Linear expansion coefficient α of cured matrix resin Ｅ and thermoplastic resin material α ＳMeasurement Method for Matrix Resin: A matrix resin prepared according to the above <Matrix Resin> was poured between aluminum plates sandwiching a 5 mm thick Teflon (registered trademark) spacer and cured for 2 hours in a hot air dryer heated to 180°C to obtain a flat plate made of a cured matrix resin. A thermoplastic resin material prepared or purchased according to the above <Method for Preparing Thermoplastic Resin Material> was placed on a stainless steel plate equipped with a 5 mm thick stainless steel spacer, and a stainless steel plate preheated to 250°C was placed on top and held while heating and pressurizing with a hand press. After cooling to room temperature, the resin material was removed to obtain a flat plate made of a thermoplastic resin material. The linear expansion coefficient of the obtained flat plate was measured in the range of 25°C to 80°C using a TMA Q400 (TA Instruments) in accordance with JIS K 7197 (2012).

[0058] <Method for Producing Stitch Yarn> A multifilament yarn was produced by melt spinning using the thermoplastic resin material used for the stitch yarn: component [B] described in <Materials used for the components of the reinforcing fiber substrate> above.

[0059] <Method for measuring the fineness of stitch thread> The fineness of the stitch thread produced according to the above <Method for producing stitch thread> was measured. The fineness was calculated by measuring the mass of 20 samples with a length of 90 cm according to Method B of JIS L1013 (2010). The fineness of the obtained stitch thread is shown in Tables 1, 2, and 3.

[0060] <Method for producing fiber-reinforced substrate> Two reinforcing fiber sheets in the form of unidirectional sheets were produced by aligning multiple strands of the component [A]-1 described in the above <Materials used in the reinforcing fiber substrate> using a multi-axis loom. These were then stacked in the order of -45° and +45° from the bottom. Next, a stitch thread obtained according to the method described in <Method for producing the stitch thread> was used to penetrate the sheets in the thickness direction using tricot knitting, stitching, and integration to obtain a reinforcing fiber substrate. In some examples, a nonwoven fabric obtained according to the above <Porous material> was placed on the top surface of each reinforcing fiber sheet, and the sheets were stacked in the order of -45°, nonwoven fabric, +45°, and nonwoven fabric from the bottom, and then similarly sewn and integrated.

[0061] In the obtained reinforcing fiber substrate, the basis weight of the reinforcing fiber sheet, the amount of stitch thread used per unit area w1 (g / m ２ ) are as described in Tables 1, 2, and 3.

[0062] <Method for calculating the ratio of the mass per unit area of ​​the porous material to the stitch thread> The mass per unit area w2 (g / m) of the porous material (nonwoven fabric) obtained according to the above <Porous material> and <Method for producing a fiber-reinforced substrate> was calculated. ２ ) was divided by the mass per unit area of ​​the stitch thread w1 to calculate the ratio w2 / w1.

[0063] <Thermal dimensional change rate R of reinforcing fiber substrate at 120 ° C. Ｌ１２０ The reinforcing fiber substrate prepared according to the above <Method for preparing a reinforcing fiber substrate> was cut into a size of 200 mm x 200 mm to prepare a rectangular test piece in which the reinforcing fibers were oriented at +45° / -45°. The length L of the side in the direction in which the stitch thread was oriented (0°) was ＲＴ After measuring, the test piece was placed on a tray covered with nylon film and left to stand for 30 minutes in a hot air oven (manufactured by Espec Corporation) set to 120°C, the same temperature as the resin injection temperature in VaRTM described below. After taking it out, it was cooled to room temperature, and the length L of the side in the direction in which the stitch thread was oriented (0°) was measured. １２０ was measured, and the thermal dimensional change rate R at 120°C was calculated from the following formula (3). Ｌ１２０ The thermal dimensional change rate R (%) at 120°C was calculated and used as an index of the dimensional stability of the reinforcing fiber substrate under high temperature conditions. Measurements were carried out for n = 6, and the average value was taken as the thermal dimensional change rate R (%) at 120°C. Ｌ１２０ (%). R Ｌ１２０ = (L ＲＴ -L １２０ ) / L ＲＴ ×100 (3)

[0064] <Method for Producing Reinforced Fiber Laminate> The reinforcing fiber substrate produced according to the above <Method for Producing Reinforced Fiber Substrate> was cut into 400 mm x 400 mm pieces, and laminates were produced to have the following lamination configurations: Compression after impact (CAI), open-hole compression (OHC), and thermal cycle durability tests: [(+45° / -45° / 0° / 90°)] ２Ｓ , and so on.

[0065] <Method for molding fiber-reinforced composite material: VaRTM> The laminate prepared according to the above <Method for preparing a reinforced fiber laminate> was placed on an aluminum tool plate, the entire body was covered with a polyamide bag film, and the inside of the film was vacuum-suctioned and heated in a hot air dryer set to 120°C. After confirming that the temperature of the laminate had reached 120°C, the resin composition was injected at the pressure differential with atmospheric pressure. After the epoxy resin composition was impregnated, the temperature was raised to 180°C while continuing to reduce the pressure, and the material was thermally cured for 2 hours to obtain a molded product. This molding method is Vacuum-assisted Resin Transfer Molding (VaRTM).

[0066] <Method for Molding Fiber-Reinforced Composite Material: RTM Method> The laminate produced according to the above <Method for Producing Reinforced Fiber Laminate> was placed on the lower mold of a double-sided carbon steel mold, and then the upper mold was closed and pressurized. The mold was heated to 180°C while the interior was evacuated. Next, matrix resin was injected under pressure through the injection hole and then thermally cured for 2 hours to obtain a molded product. The molding temperature and injection pressure are as shown in Tables 1, 2, and 3. This molding method is Resin Transfer Molding (RTM).

[0067] <CAI Test Method> The laminate for CAI prepared according to the above <Method for Preparing Reinforced Fiber Laminate> was heat-cured according to the above <Method for Molding Fiber-Reinforced Composite Material: VaRTM> or <Method for Molding Fiber-Reinforced Composite Material: RTM> to obtain a molded product. A rectangular test piece measuring 150 mm x 100 mm was cut from the obtained molded product, and a drop weight impact of 8 J per mm of test piece thickness was applied to the center of the test piece according to ASTM D7136. The residual compressive strength was then measured according to the test standard ASTM D7137. Measurements were performed on n = 6, and the average value was taken as the CAI strength (MPa).

[0068] <Room Temperature OHC Test Method> The OHC laminate prepared according to the above <Preparation Method of Reinforced Fiber Laminate> was heat-cured according to the above <Forming Method of Fiber Reinforced Composite Material: VaRTM> or <Forming Method of Fiber Reinforced Composite Material: RTM> to obtain a molded product. From the obtained molded product, rectangular test pieces measuring 305 mm x 38 mm were cut out, and a hole with a diameter of 6.35 mm was drilled in the center to prepare test pieces. Compression tests were performed in accordance with the test standard ASTM D6484 (n = 6), and the average value was taken as the room temperature OHC strength (MPa).

[0069] <Heat and Wet OHC Test Method> As in the above <Room Temperature OHC Test Method>, a rectangular test piece measuring 305 mm × 38 mm was prepared by drilling a 6.35 mm hole in the center, and the test piece was immersed in hot water heated to 70° C. for two weeks. The immersion-treated test piece was subjected to a compression test (n=6) in a high-temperature environment of 82° C. in accordance with the test standard ASTM D6484, and the average value was taken as the heat and wet OHC strength (MPa).

[0070] <Method for Testing Thermal Cycle Durability> The laminate for thermal cycle durability testing, prepared according to the above-mentioned <Method for Preparing Reinforced Fiber Laminate>, was thermally cured according to the above-mentioned <Method for Molding Fiber Reinforced Composite Material: VaRTM> or <Method for Molding Fiber Reinforced Composite Material: RTM> to obtain a molded article. Test specimens measuring 80 mm x 80 mm were cut from the resulting molded article and exposed to a humid and hot environment (50°C, 99% RH) for 12 hours. The exposed test specimens were subjected to 2000 consecutive thermal cycles from -55°C to 70°C. A 15-minute temperature hold time was provided after reaching -55°C and 70°C. After the thermal cycles were completed, a cross section of the test specimen was cut out and observed at 200x magnification using a VHX6000, and the number of cracks that had occurred was counted.

[0071] <Surface Quality Evaluation Method> The laminate for CAI prepared according to the above <Method for preparing a reinforced fiber laminate> was heat-cured according to the above <Method for molding a fiber reinforced composite material: VaRTM> or <Method for molding a fiber reinforced composite material: RTM> to obtain a molded product. The surface quality of the obtained molded product was evaluated according to the following criteria. C: Surface voids, damage to the stitch thread surface present B: No surface voids, damage to the stitch thread surface present A: No surface voids, no damage to the stitch thread surface

[0072] <Method for measuring impregnation time and fiber volume content> When resin was injected into a laminate for CAI prepared according to the above <Method for preparing a reinforced laminate> according to the above <Method for molding a fiber-reinforced composite material: VaRTM> or <Method for molding a fiber-reinforced composite material: RTM>, the time it took for the resin to reach the suction hole from the injection hole was defined as the impregnation time (minutes). The fiber volume content (Vf) of the molded product was calculated by dividing the weight of the CF residue after decomposition by the weight of the test piece before decomposition according to the nitric acid decomposition method described in JIS K7075 (1991), to give Vf (%).

[0073] Example 1 A stitch thread (component [B]) made of PA6I and having a fineness of 75 dtex was produced according to the above-mentioned <Method for preparing thermoplastic resin material> and <Method for producing stitch thread>. The tensile modulus of PA6I at 82°C was evaluated according to the <Method for evaluating the tensile modulus of thermoplastic resin material used in stitch thread at 82°C>, and the result was 1.3 GPa.

[0074] Using the prepared stitch thread and "TORAYCA (registered trademark)" T800G-24K-71E as reinforcing fiber, a reinforcing fiber substrate in the form of a so-called biaxial NCF was prepared in which the fiber axes of the aligned carbon fibers of the reinforcing fiber sheet (constituent element [A]) were laminated in the order of -45° and +45° according to <Method for preparing fiber-reinforced substrate>. The amount w1 of the stitch thread used per unit area was 8 g / m ２ Next, a reinforced fiber laminate was produced according to <Method for producing reinforced fiber laminate>, and molded articles for CAI evaluation, OHC evaluation, in-plane shear evaluation, and thermal cycle durability test were produced at a curing temperature of 180°C according to the above <Method for molding fiber reinforced composite material: VaRTM>.

[0075] The prepared reinforcing fiber substrate was evaluated according to the above-mentioned <Method for measuring the thermal dimensional change rate RL120 of a reinforcing fiber substrate at 120°C>. Ｌ１２０ The coefficient of linear expansion of the cured matrix resin was 0%, indicating excellent dimensional stability under high temperature conditions. Ｅ and thermoplastic resin material α Ｓ α was measured according to the measurement method Ｅ is 30 x 10－６ , α Ｓ is 80x10 －６ It was.

[0076] The molded article was evaluated according to the CAI test method, room temperature OHC test method, moist heat OHC test method, and heat cycle durability test method. The CAI strength was 190 MPa, the room temperature OHC strength was 280 MPa, and the moist heat OHC strength was 240 MPa, demonstrating excellent compressive properties, especially under moist heat conditions. Furthermore, the number of cracks after the heat cycle durability test was excellent, at only one.

[0077] The surface quality of the molded article was evaluated according to the above-mentioned <Surface Quality Evaluation Method>, and was rated as good, with an A rating. The impregnation time measured according to the above-mentioned <Method for Measuring Impregnation Time and Fiber Volume Content> was 5 minutes, indicating excellent impregnation properties. The Vf of this molded article was 57.0%.

[0078] Examples 2 to 6, 8, and 10: Reinforced fiber substrates and reinforced fiber laminates were prepared in the same manner as in Example 1, except that the type of resin material constituting the stitch thread, the stitch thread fineness, and the amount of stitch thread used per unit area of ​​the reinforcing fiber substrate (w1) were changed as shown in Tables 1 and 2 (data are shown in Tables 1 and 2). Fiber-reinforced composite materials were then prepared using VaRTM in the same manner as in Example 1, and the CAI strength, thermal cycle durability, and room temperature and humid heat OHC were evaluated for each example. The results showed that excellent physical properties were obtained, particularly in terms of OHC strength under humid heat conditions, and that high levels of crack resistance after thermal cycles were also achieved. Furthermore, the impregnation times for each example were 4.0 to 15.0 minutes, demonstrating excellent impregnation performance using VaRTM. Furthermore, the surface quality of the molded articles was excellent.

[0079] Examples 7 and 9: Reinforced fiber substrates and reinforced fiber substrates were prepared in the same manner as in Example 1, except that the type of resin material constituting the stitch thread, the stitch thread fineness, and the amount of stitch thread used per unit area of ​​the reinforcing fiber substrate (w1) were changed as shown in Tables 1 and 2 (data shown in Tables 1 and 2). Reinforced fiber composite materials were then prepared according to the above-mentioned <Fiber-reinforced composite material molding method: RTM>, and the CAI strength, thermal cycle durability, and room temperature and humid heat OHC were evaluated for each example. As a result, excellent physical properties were obtained, particularly in terms of OHC strength under humid heat environments, and high levels of crack resistance after thermal cycles were also achieved. Furthermore, the impregnation time for each example was 3.0 minutes, demonstrating excellent impregnation even in RTM. Furthermore, the surface quality of the molded products was good.

[0080] (Examples 11 and 12) The nonwoven fabric prepared according to the above <Porous material> was placed on top of the reinforcing fiber sheet as described in <Method for preparing fiber-reinforced substrate>, and the layers were stacked in the order of -45°, nonwoven fabric, +45°, nonwoven fabric, and stitched together with stitch thread to prepare a reinforcing fiber substrate (data shown in Table 2). The mass per unit area w2 of the nonwoven fabric and the amount of stitch thread used per unit area w1 of the reinforcing fiber substrate, measured according to the above <Method for measuring the mass per unit area of ​​porous material: w2>, are shown in Table 2, and the w2 / w1 ratio was 0.75 and 6.

[0081] Using the prepared reinforcing fiber substrate, a reinforcing fiber laminate was prepared in the same manner as in Example 1. Next, fiber-reinforced composite materials were prepared using VaRTM in the same manner as in Example 1, and the CAI strength, thermal cycle durability, and room temperature and humid heat OHC of each example were evaluated. As a result, high CAI strength and OHC strength in a humid heat environment, as well as crack resistance after thermal cycles, were obtained, resulting in a balance between impact resistance, compression properties in a humid heat environment, and durability. Furthermore, the surface quality of the molded article was good.

[0082] (Examples 13 and 14) Reinforced fiber substrates were produced in the same manner as in Examples 11 and 12, except that the configurations of the stitch yarn and nonwoven fabric were changed as shown in Table 2 (data are shown in Table 2). At this time, w2 / w1 was set to 1.5 and 4, in the range of 1 to 5.

[0083] Using the prepared reinforcing fiber substrate, a reinforcing fiber laminate was produced in the same manner as in Example 1. Next, fiber-reinforced composite materials were produced using VaRTM in the same manner as in Example 1, and CAI strength, cold-heat cycle durability, and room temperature and humid heat OHC were evaluated for each example. As a result, high CAI strength, particularly high humid heat OHC strength, and crack resistance after cold-heat cycles were obtained. Furthermore, the impregnation time was 6.0 to 8.0 minutes, demonstrating high impregnation in VaRTM. In other words, impact resistance, compression characteristics under humid heat environments, durability, and impregnation were all achieved at particularly high levels. Furthermore, the surface quality of the molded products was good.

[0084] Comparative Example 1: The thermoplastic resin material constituting component [B] was a crystalline resin, PA6 / 12 (50:50). The tensile modulus at 82°C was evaluated to be 0.3 GPa, which was outside the range of Condition 2. A fiber-reinforced composite material was produced using the components shown in Table 3 in the same manner as in Example 1, and its CAI strength, thermal cycle durability, and room temperature and moist heat OHC were evaluated. After the thermal cycle durability test, the number of cracks was one, indicating excellent durability. However, the moist heat OHC was 210 MPa, which was insufficient. Furthermore, the stitch thread on the surface of the molded product adhered to the mold during molding, resulting in scattered damage to the stitch thread surface. The surface quality of the molded product was rated B.

[0085] Comparative Example 2: A fiber-reinforced composite material was prepared in the same manner as in Comparative Example 1, except that it was prepared by RTM. The CAI strength, thermal cycle durability, and room temperature and wet heat OHC were evaluated. The number of cracks after the thermal cycle durability test was one, indicating excellent durability, but the wet heat OHC was insufficient at 210 MPa. Furthermore, because the matrix resin was injected at a temperature above the melting point of the stitch thread, voids were observed near the surface stitch thread, and further, scattered damage was observed on the stitch thread surface due to adhesion of the stitch to the mold. As a result, the surface quality of the molded product was rated C, which is low.

[0086] Comparative Example 3: The thermoplastic resin material constituting component [B] was PA6I / 12, an amorphous resin. The tensile modulus at 82°C was evaluated to be 0.7 GPa, which was outside the range of Condition 2. A fiber-reinforced composite material was produced using the components shown in Table 3 in the same manner as in Comparative Example 1, and its CAI strength, thermal cycle durability, and room temperature and moist heat OHC were evaluated. After the thermal cycle durability test, the number of cracks was 0, indicating excellent durability. However, the moist heat OHC was 200 MPa, which was insufficient. The surface quality of the molded article was rated B.

[0087] Comparative Example 4: The thermoplastic resin material constituting component [B] was PA12, a crystalline resin. The tensile modulus at 82°C was evaluated to be 0.5 GPa, which was outside the range of Condition 2. A fiber-reinforced composite material was produced using the components shown in Table 3 in the same manner as in Comparative Example 1, and its CAI strength, thermal cycle durability, and room temperature and moist heat OHC were evaluated. The surface quality of the molded product was rated high at A, but its moist heat OHC was insufficient at 225 MPa. Furthermore, the number of cracks after the thermal cycle durability test was 10, indicating insufficient durability.

[0088] Comparative Example 5: The thermoplastic resin material constituting component [B] was polyethylene terephthalate, a crystalline polyester resin. The tensile modulus at 82°C was evaluated to be 0.8 GPa, which was outside the range of Condition 2. A fiber-reinforced composite material was produced using the components shown in Table 3 in the same manner as in Comparative Example 1, and its CAI strength, thermal cycle durability, and room temperature and moist heat OHC were evaluated. The surface quality of the molded product was rated high at A, but its moist heat OHC was insufficient at 225 MPa. Furthermore, the number of cracks after the thermal cycle durability test was 50, indicating insufficient durability.

[0089]

[0090]

[0091]

[0092] The fiber-reinforced substrate of the present invention has excellent impregnation properties in resin injection molding, and the fiber-reinforced composite material obtained by combining it with a matrix resin can achieve high levels of both compressive strength in a hot and humid environment and crack resistance after thermal cycling, and therefore can be suitably used for aircraft components, particularly large primary structural components.

[0093] Specifically, it can be preferably used for many structural materials, such as aircraft components such as fuselages, main wings, tails, moving surfaces, fairings, cowls, doors, seats, and interior materials, spacecraft components such as motor cases and main wings, satellite components such as structures and antennas, automobile components such as outer panels, chassis, aerodynamic components, and seats, railway vehicle components such as structures and seats, and ship components such as hulls and seats.In particular, the fiber-reinforced substrate of the present invention achieves a high level of both compressive strength under wet heat and cold cycles and high crack resistance, and also exhibits good impregnation properties in resin injection molding, making it suitable for use in aircraft components, particularly large primary structural components.

[0094] 1A Reinforced fiber substrate 1B Reinforced fiber substrate 2 Stitch thread 3 Auxiliary thread 11 Reinforced fiber sheet (-45 degrees) 12 Reinforced fiber sheet (90 degrees) 13 Reinforced fiber sheet (+45 degrees) 14 Reinforced fiber sheet (0 degrees) 15 Reinforced fiber sheet

Claims

1. A reinforcing fiber substrate comprising one or more sheets of component [A] formed by aligning reinforcing fibers in one direction, and integrated with component [B], and simultaneously satisfying the following conditions 1 and at least one of conditions 2 and 3: [A]: Reinforcing fiber sheet [B]: Stitch thread Condition 1: Component [B] is made of an amorphous resin material Condition 2: The tensile modulus of elasticity at 82°C of the amorphous resin material constituting component [B] is 1 GPa or more Condition 3: The shrinkage rate when component [B] is maintained at 130°C is less than 10% 2. The reinforcing fiber substrate according to claim 1, wherein the amorphous resin material constituting component [B] is an amorphous polyamide.

3. The reinforcing fiber substrate according to claim 2, wherein the amorphous resin material constituting component [B] has a glass transition temperature of 140 to 165°C.

4. The reinforcing fiber substrate according to claim 1, wherein the fineness of component [B] is 20 to 60 dtex.

5. The reinforcing fiber substrate according to claim 1, wherein a porous material made of a thermoplastic resin is disposed on at least one surface of the component [A].

6. The thermoplastic resin constituting the porous material is amorphous polyamide, and the mass per unit area of the porous material, w2 [g / m ２ ] and the amount w1 [g / m ] of the component [B] used per unit area of the reinforcing fiber substrate according to claim 5 ２ 6. The reinforcing fiber substrate according to claim 5, wherein the relationship between w2 and w1 is expressed by the following formula (1): 1≦w2 / w1≦5 (1) 7. A reinforced fiber composite material obtained by impregnating a reinforced fiber laminate in which a plurality of reinforcing fiber substrates according to any one of claims 1 to 6 are laminated, with a thermosetting resin and curing the same.

8. Linear expansion coefficient α of the cured product of the thermosetting resin E is 100 x 10 －６ or less, and the linear expansion coefficient α of the amorphous resin material constituting the component [B] is S The reinforced fiber composite material according to claim 7, which satisfies the relationship of the following formula (2): 2 × α E <α S (2)

Images