Prepregs, preforms, and fiber-reinforced plastic molded products

Abstract

Provided is a prepreg in which 5 to 65 parts by weight of a sheet-like fiber base material is impregnated with 35 to 95 parts by weight of a resin, in which the sheet-like fiber base material comprises more than 50% by weight and 99% by weight or less of discontinuous carbon fibers (A) and 1% by weight or more and less than 50% by weight of discontinuous organic fibers (B) both dispersed uniformly, the prepreg satisfying any one of the following requirements 1 to 3. Requirement 1: the resin is a thermoplastic resin (C), and the difference between the melting point Tmb (°C) of the organic fibers (B) and the melting point Tmc (°C) of the thermoplastic resin (C) (i.e., Tmb-Tmc) is 20 to 200°C; requirement 2: the resin is a heat-curable resin (D) and the difference between the melting point Tmb (°C) of the organic fibers (B) and the curing temperature Tmd (°C) of the heat-curable resin (D) (i.e., Tmb-Tmd) is 20 to 400°C: and requirement 3: the organic fibers (B) do not have a melting point.　A prepreg having excellent moldability, mechanical properties and impact strength, a preform, and a fiber-reinforced resin molded article are provided.

Description

Technical Field

[0001] The present invention relates to a prepreg, a preform and a fiber-reinforced resin molded article.

Background Art

[0002] In recent years, fiber-reinforced resins excellent in lightweight properties and strength have been used for various industrial applications. Further, due to good shapeability for complex shapes and good productivity, development of pressing materials such as sheet molding compound (SMC) and injection materials such as pellets as materials using discontinuous reinforcing fibers is also active.

[0003] Further, as another form of discontinuous fiber-reinforced resin, there are a fiber-reinforced resin in which reinforcing fibers dispersed in a single fiber state are bonded to each other at a large number of contact points by a resin, and a porous fiber-reinforced resin in which voids are formed with the reinforcing fibers serving as a support (Patent Documents 1 and 2). These have excellent moldability and mechanical properties due to the dispersion state of reinforcing fibers and the porous structure.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problem to be Solved by the Invention

[0005] However, although fiber-reinforced resins as disclosed in Patent Documents 1 and 2 have excellent mechanical properties, there has been a problem that fibers break upon impact, resulting in insufficient impact strength.

[0006] The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a fiber-reinforced resin having excellent moldability, mechanical properties and impact strength.

Means for Solving the Problem

[0007] The present invention, which solves the above problems, has the following configuration. [1] A prepreg comprising 5 to 65 parts by weight of a sheet-like fibrous base material in which discontinuous carbon fibers (A) in an amount of more than 50% by weight and 99% by weight or less and discontinuous organic fibers (B) in an amount of 1% by weight or more and less than 50% by weight is uniformly dispersed, and in which 35 to 95 parts by weight of resin is impregnated, wherein any of the following conditions 1 to 3 are met. Condition 1: The resin is a thermoplastic resin (C), and the difference between the melting point Tmb (°C) of the organic fiber (B) and the melting point Tmc (°C) of the thermoplastic resin (C) (Tmb-Tmc) is 20-200°C. Condition 2: The resin is a thermosetting resin (D), and the difference between the melting point Tmb (°C) of the organic fiber (B) and the curing temperature Tmd (°C) of the thermosetting resin (D) (Tmb-Tmd) is 20-400°C. Condition 3: The organic fiber (B) has no melting point. [2] The prepreg according to [1], wherein the resin expands with an average out-of-plane expansion rate of 250-800% when softened. [3] The basis weight of the sheet-like fibrous material is 10 to 200 g / m² 2 The prepreg described in [1] or [2]. [4] The prepreg according to any one of [1] to [3], wherein the coefficient of variation (CV) of the basis weight is 0.1 to 10%. [5] The prepreg according to any one of [1] to [4], wherein the sheet-like fibrous base material further comprises 0.1 to 10% by weight of a binder resin (E). [6] The prepreg according to any one of [1] to [5], wherein the sheet-like fibrous base material is a papermaking base material. [7] The prepreg according to any one of [1] to [6], wherein the sheet-like fibrous base material has a content of 60 to 80% by weight of discontinuous carbon fibers (A) and a content of 20 to 40% by weight of discontinuous organic fibers (B). [8] The prepreg according to any one of [1] to [7], wherein the average fiber length of the carbon fiber (A) is 1 to 15 mm. [9] The prepreg according to any one of [1] to [8], wherein the average fiber length of the organic fiber (B) is 4 to 20 mm.

[10] The prepreg according to any one of [1] to [9], wherein the organic fiber (B) is a fiber made of a resin selected from polyester resin, polyaryl ether ketone resin, aromatic polyamide resin and polyarylene sulfide resin.

[11] The prepreg according to any one of [1] to

[10] , wherein the diameter of the organic fiber (B) is 15 to 50 μm.

[12] The prepreg according to any one of [1] to

[11] , wherein the tensile strength of the organic fiber (B) is 1 to 6 GPa.

[13] The prepreg according to any one of [1] to

[12] , wherein the tensile elongation at break of the organic fiber (B) is 2.5 to 100%.

[14] In condition 1, the difference (Tmb-Tmc) between the melting point Tmb (°C) of the organic fiber (B) and the melting point Tmc (°C) of the thermoplastic resin (C) is 50 to 160°C, the prepreg according to any one of [1] to

[13] .

[15] The prepreg according to any one of [1] to

[14] , wherein the thermoplastic resin (C) in condition 1 is selected from polyolefin resin, polyamide resin and polyarylene sulfide resin.

[16] The prepreg according to any one of [1] to

[15] , wherein the resin impregnation rate of the prepreg is 80 to 100%.

[17] Maximum tensile strength σ of the prepreg Max and minimum value σ Min The ratio (σ Max / σ Min A prepreg as described in any of [1] to

[16] , wherein ) is 1 to 2. A preform comprising at least one laminated prepreg as described in any of

[18] [1] to

[17] . A fiber-reinforced resin molded product obtained by molding the preforms described in

[19] and

[18] . [Effects of the Invention]

[0008] According to the present invention, prepregs, preforms, and fiber-reinforced resin molded articles having excellent moldability, mechanical properties, and impact strength can be obtained. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing the cross-sectional structure of the prepreg of the present invention. [Figure 2] This is a schematic diagram showing the cross-sectional structure of the fiber-reinforced resin molded product of the present invention. [Modes for carrying out the invention]

[0010] The present invention will be described below with reference to the drawings as appropriate for ease of understanding, but the present invention is not limited to these drawings.

[0011] The prepreg of the present invention comprises discontinuous carbon fibers (A), discontinuous organic fibers (B), and a resin. In this specification, the carbon fibers (A) and organic fibers (B) contained in the prepreg are collectively referred to as "reinforcement fibers" or simply "fibers." Examples of resins impregnated into the sheet-like fibrous substrate include thermoplastic resins and thermosetting resins. In the present invention, thermoplastic resins and thermosetting resins may be blended, in which case the resin impregnating the sheet-like fibrous substrate is the resin that accounts for more than 50% by weight of the components constituting the resin. For example, if the resin that accounts for more than 50% by weight of the components constituting the resin is a thermoplastic resin, the resin impregnated into the sheet-like fibrous substrate is referred to as a thermoplastic resin.

[0012] The prepreg of the present invention can be used as a structural material itself, or as a base material for molding fiber-reinforced resin molded articles. Therefore, when referring to the mechanical properties of a prepreg in this specification, the mechanical properties of a fiber-reinforced resin molded article using that prepreg may also be referred to at the same time.

[0013] Figure 1 is a schematic diagram showing the cross-sectional structure of one embodiment of the prepreg of the present invention. As shown in Figure 1, the prepreg of the present invention contains carbon fibers 2, organic fibers 3, and resin 4.

[0014] The prepreg in this embodiment is made by impregnating 5 to 65 parts by weight of a sheet-like fibrous base material, in which discontinuous carbon fibers (A) in an amount of more than 50% by weight and 99% by weight or less, and discontinuous organic fibers (B) in an amount of 1% by weight or more and less than 50% by weight, with 35 to 95 parts by weight of resin. Carbon fibers (A) have excellent rigidity and strength, and by including more than 50% by weight and 99% by weight or less of carbon fibers (A) in the sheet-like fibrous base material, the reinforcing effect derived from carbon fibers (A) can be sufficiently achieved, thereby providing excellent rigidity and strength. Organic fibers (B) have relatively good ductility compared to carbon fibers (A) and are less likely to break under impact. Therefore, for a prepreg containing organic fibers (B) to break under impact, it is necessary for the organic fibers (B) to break the resin or pull out of the resin, thus providing the prepreg with excellent impact strength. By having an organic fiber (B) content of 1% by weight or more in the sheet-like fibrous base material, the reinforcing effect derived from the organic fiber (B) can be sufficiently achieved, and excellent impact strength can be provided. By having an organic fiber (B) content of less than 50% by weight, the relative content of carbon fiber (A) to organic fiber (B) becomes larger, making it possible to achieve both the excellent rigidity and strength provided by carbon fiber (A) and the excellent impact strength provided by organic fiber (B).

[0015] The carbon fiber (A) content in the sheet-like fibrous base material is preferably 60 to 80% by weight, and the organic fiber (B) content is preferably 20 to 40% by weight. A prepreg with an organic fiber (B) content of 20% by weight or more allows for superior impact strength. On the other hand, a prepreg with an organic fiber (B) content of 40% by weight or less allows for the maintenance of excellent expandability and provides superior moldability.

[0016] Furthermore, the uniform dispersion of reinforcing fibers allows them to have numerous contact points, forming a network structure. As a result, the load applied to the prepreg is dispersed through the resin and contact points, and the carbon fibers (A) bear the load, exhibiting excellent mechanical properties. In addition, for the material to break under impact, it is necessary for the organic fibers (B) to break the resin or to be pulled out of the resin at numerous contact points, thus enabling the material to exhibit excellent impact strength. Moreover, by impregnating the sheet-like fibrous substrate in which carbon fibers (A) and organic fibers (B) are dispersed with resin, the reinforcing effect of the reinforcing fibers can be fully realized.

[0017] Examples of carbon fibers (A) include PAN-based, rayon-based, lignin-based, and pitch-based carbon fibers. These fibers may also be surface-treated. Surface treatments include bonding a metal as a conductor, as well as treatment with coupling agents, sizing agents, binding agents, and additives. These fibers may be used individually or in combination of two or more types. Furthermore, they may be used in combination with metal fibers such as aluminum, brass, and stainless steel, or inorganic fibers such as graphite fibers, glass fibers, silicon carbide fibers, and silicon nitride fibers. Among these, PAN-based, pitch-based, and rayon-based carbon fibers, which have excellent specific strength and specific rigidity, are preferred from the viewpoint of weight reduction. In addition, a combination of carbon fibers and glass fibers is preferable from the viewpoint of balancing mechanical properties and economic efficiency. From the viewpoint of improving conductivity, carbon fibers coated with metals such as nickel, copper, or ytterbium can also be used. Among these, PAN-based carbon fibers, which have excellent mechanical properties such as strength and elastic modulus, are more preferably used.

[0018] Examples of organic fibers (B) include polyolefin resins such as polyethylene and polypropylene, polyamide resins such as nylon 6, nylon 66, and aromatic polyamides, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and liquid crystal polyester, polyaryl ether ketone resins such as polyether ketones, polyether sulfone, polyarylene sulfide, and fluororesin. Two or more of these may be used in combination. In particular, from the viewpoint of suppressing fiber breakage during impact, it is preferable that the organic fiber (B) of the present invention be selected from polyester resins, aromatic polyamide resins, polyaryl ether ketone resins, and polyarylene sulfide resins.

[0019] In the present invention, the average fiber length of the carbon fiber (A) is preferably 1 to 15 mm. An average fiber length of 1 mm or more of the carbon fiber (A) allows for sufficient reinforcement, thereby imparting excellent mechanical properties to the prepreg. On the other hand, an average fiber length of 15 mm or less of the carbon fiber (A) makes it less prone to bending in the prepreg, allowing for excellent moldability due to its discontinuous nature while maintaining high mechanical properties. More preferably, the average fiber length of the carbon fiber (A) is 2 to 13 mm.

[0020] Furthermore, the average fiber length of the organic fiber (B) is preferably 4 to 20 mm. When the average fiber length of the organic fiber (B) is 4 mm or more, the organic fiber (B) has many contact points with other fibers and resin, resulting in many instances of resin fracture or extraction of the organic fiber (B) from the resin during impact, thus exhibiting excellent impact strength. On the other hand, when the average fiber length of the organic fiber (B) is 20 mm or less, it does not cause deterioration of dispersibility, and a homogeneous prepreg can be obtained. The average fiber length of the organic fiber (B) is more preferably 6 to 15 mm.

[0021] The average fiber length of the reinforcing fibers can be calculated by removing the resin components by methods such as burning or leaching, randomly selecting 400 fibers from the remaining reinforcing fibers, measuring their lengths to the nearest 100 μm, and then averaging their lengths.

[0022] In the present invention, the diameter of the organic fiber (B) is preferably 15 to 50 μm. In the prepreg of the present invention, since the discontinuous organic fiber (B) is uniformly dispersed, the load is borne by the organic fiber, which exists as a single fiber rather than a fiber bundle. Therefore, if the diameter of the organic fiber (B) is 15 μm or more, the load-bearing capacity of the organic fiber (B) increases sufficiently with increasing cross-sectional area, and the breakage of the single organic fiber due to load during impact can be sufficiently suppressed, thereby providing the prepreg with excellent impact strength. If the diameter of the organic fiber (B) is 50 μm or less, the number of organic fibers per unit volume of organic fiber (B) can be sufficiently large, resulting in a large number of resin fractures or organic fiber (B) being pulled out of the resin during impact, thereby providing the prepreg with excellent impact strength.

[0023] In the present invention, the tensile strength of the organic fiber (B) is preferably 1 to 6 GPa. By keeping it within this range, the breakage of the organic fiber (B) during impact can be sufficiently suppressed, and the prepreg can be given excellent impact strength.

[0024] The tensile elongation at break of the organic fiber (B) of the present invention is preferably 2.5 to 100%. A tensile elongation of 2.5% or more sufficiently suppresses the fracture of the organic fiber (B) during impact, providing excellent impact strength. A tensile elongation of 100% or less suppresses the elongation of the organic fiber (B) during impact, allowing it to bear a sufficient load, also providing excellent impact strength. The tensile elongation at break of the organic fiber (B) is preferably 2.5 to 30%, more preferably 2.5 to 15%. The tensile elongation at break (%) of the organic fiber (B) can be determined by the following method. A tensile test was performed on a single organic fiber in a room under standard conditions (20°C, 65%RH) with a gripping distance of 250 mm and a tensile speed of 300 mm / min. The length of the fiber at break was measured (however, if the fiber broke near the chuck, it was treated as a chuck break and excluded from the data). The result was calculated to two decimal places using the following formula, and the second decimal place was rounded off. The average value of n=3 data points from this measurement was taken as the tensile elongation at break.

[0025] Tensile elongation at break (%) = [(Length at break (mm) - 250) / 250] × 100 In the prepreg of the present invention, if the sheet-like fiber base material is 5 parts by weight or more and the resin is 95 parts by weight or less, the reinforcing effect derived from the reinforcing fibers can be sufficiently achieved, and excellent mechanical properties can be exhibited. On the other hand, if the sheet-like fiber base material is 65 parts by weight or less and the resin is 35 parts by weight or more, the reinforcing fibers can be sufficiently bonded together by the resin, and the reinforcing effect of the reinforcing fibers can be sufficiently achieved. The prepreg of the present invention is made by impregnating a sheet-like fiber base material with resin, and the impregnation rate is preferably 80 to 100%. Within this range, the prepreg can be used without impairing the moldability and mechanical properties of the prepreg, which are the effects of the present invention.

[0026] Furthermore, the prepreg of the present invention satisfies any of the following conditions 1 to 3. Condition 1: The resin is a thermoplastic resin (C), and the difference between the melting point Tmb (°C) of the organic fiber (B) and the melting point Tmc (°C) of the thermoplastic resin (C) (Tmb-Tmc) is 20-200°C. Condition 2: The resin is a thermosetting resin (D), and the difference between the melting point Tmb (°C) of the organic fiber (B) and the curing temperature Tmd (°C) of the thermosetting resin (D) (Tmb-Tmd) is 20-400°C. Condition 3: The organic fiber (B) has no melting point. Under condition 1, i.e., when the resin is a thermoplastic resin (C), a (Tmb-Tmc) of 20-200°C allows the thermoplastic resin (C) to be softened without melting the organic fibers (B) during resin impregnation, resulting in a prepreg in which the organic fibers (B) remain in a fibrous state within the thermoplastic resin (C). Organic fibers (B) are resistant to breakage, and for the fiber-reinforced resin to break under impact, it is necessary for the organic fibers (B) to break or be pulled out of the thermoplastic resin at the point of contact between the fibers. Therefore, the presence of organic fibers (B) in a fibrous state provides excellent impact strength. A (Tmb-Tmc) of 30-180°C is preferable, and a more preferable of 50-160°C. This allows the thermoplastic resin (C) to be sufficiently softened within a temperature range that does not melt the organic fibers (B) during molding, thus enabling the production of a prepreg with excellent impact strength without compromising productivity or moldability.

[0027] Under condition 2, i.e., when the resin is a thermosetting resin (D), a (Tmb-Tmd) of 20-400°C allows the thermosetting resin (D) to be softened and then cured without melting the organic fibers (B) during resin impregnation, resulting in a prepreg in which the organic fibers (B) remain in fibrous form within the thermosetting resin (D), thereby imparting excellent impact strength to the prepreg. A (Tmb-Tmd) of 30-380°C is preferable, and a 50-350°C is more preferable. This allows the thermosetting resin (D) to be sufficiently softened and cured within a temperature range that does not melt the organic fibers (B) during molding, thus enabling the acquisition of a prepreg with excellent impact strength without compromising productivity or moldability.

[0028] Condition 3, that is, the organic fiber (B) having no melting point, allows for the prepreg to be obtained in which the organic fiber (B) does not melt during molding and remains in a fibrous state within the resin, resulting in a prepreg with excellent impact strength. Examples of organic fibers (B) having no melting point include aramid fibers.

[0029] Thermoplastic resins (C) include polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), and liquid crystal polyester; polyolefins such as polyethylene (PE), polypropylene (PP), and polybutylene; polyarylene sulfides such as polyoxymethylene (POM), polyamide (PA), and polyphenylene sulfide (PPS); polyketone (PK), polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyethernitrile (PEN), and fluoropolymers such as polytetrafluoroethylene; and liquid crystal polymers (L). Examples of thermoplastic resins include crystalline resins such as "CP," amorphous resins such as "styrene-based resins, polycarbonate (PC), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyphenylene ether (PPE), polyimide (PI), polyamide-imide (PAI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone, and polyarylate (PAR)," as well as phenolic resins, phenoxy resins, and thermoplastic elastomers such as polystyrene-based, polyolefin-based, polyurethane-based, polyester-based, polyamide-based, polybutadiene-based, polyisoprene-based, fluoropolymer-based, and acrylonitrile-based resins, and copolymers and modified versions thereof. Among these, amorphous resins such as polycarbonate and styrene-based resins are preferred from the viewpoint of surface appearance, polyetheretherketone is preferred from the viewpoint of continuous use temperature, and fluoropolymer-based resins are preferred from the viewpoint of chemical resistance. In the prepreg of the present invention, under condition 1, the thermoplastic resin (C) is preferably selected from polyolefin resin, polyamide resin, and polyarylene sulfide resin. Specifically, polyolefin is preferred from the viewpoint of lightness, polyamide is preferred from the viewpoint of strength, and polyarylene sulfide is preferred from the viewpoint of heat resistance.

[0030] Examples of thermosetting resins (D) include unsaturated polyester resins, vinyl ester resins, epoxy resins, phenolic resins, acrylic resins, urea resins, melamine resins, thermosetting polyimide resins, copolymers and modified versions thereof, and resins blended therefrom.

[0031] Furthermore, the resin may contain impact-enhancing agents such as elastomers or rubber components, other fillers, or additives, to the extent that it does not impair the objectives of the present invention. Examples of fillers and additives include inorganic fillers, flame retardants, conductivity imparters, nucleating agents, ultraviolet absorbers, antioxidants, vibration damping agents, antibacterial agents, insecticides, deodorants, color inhibitors, heat stabilizers, mold release agents, antistatic agents, plasticizers, lubricants, colorants, pigments, dyes, foaming agents, antifoaming agents, or coupling agents.

[0032] The prepreg of the present invention exhibits a springback phenomenon when the resin softens, due to the restorative force of the fibers in the sheet-like fibrous substrate. In other words, the prepreg has out-of-plane expandability. Preferably, the prepreg of the present invention expands with an average out-of-plane expansion rate of 250-800% when the resin softens. An average expansion rate of 250% or more allows the expanded fiber-reinforced resin molded product to contain sufficient voids, thereby providing excellent lightweight properties. On the other hand, an average expansion rate of 800% or less allows the expanded fiber-reinforced resin molded product to possess sufficient mechanical properties. The average expansion rate is calculated as (thickness of the expanded fiber-reinforced resin molded product [mm]) / (thickness of the prepreg before expansion [mm]) × 100 [%], and is the arithmetic mean of the expansion rates measured at five randomly selected locations. The term "softening of the resin" refers to the time when, if the resin is a thermoplastic resin (C), it is heated for 5 minutes at a temperature 20°C higher than the melting point of the thermoplastic resin (C), and when, if the resin is a thermosetting resin (D), it is heated for 1 minute at a temperature 30°C lower than the curing temperature of the thermosetting resin (D).

[0033] The basis weight of the sheet-like fibrous base material of the present invention is 10 to 200 g / m². 2 Preferably, it is 10 g / m². 2When the value is equal to or higher than the above range, tearing during handling of the sheet-like fiber base material and resin impregnation is suppressed, and a prepreg excellent in moldability and mechanical properties can be obtained. On the other hand, 200 g / m 2 When the value is equal to or lower than the above range, resin can be easily impregnated, and a prepreg excellent in moldability and mechanical properties can be obtained. Further, it is preferable that the coefficient of variation (CV) of basis weight, which indicates variation in basis weight of the sheet-like fiber base material, is 0.1 to 10%. In the production process of the sheet-like fiber base material, a coefficient of variation (CV) of basis weight of 0.1% or more can practically occur. When the coefficient of variation (CV) of basis weight is less than 0.1%, this means that the average value of basis weight is very large, and variation in basis weight is less likely to appear. When the coefficient of variation (CV) of basis weight is 0.1% or more, an excessive increase in the average value of basis weight is suppressed, resin can be easily impregnated, and a prepreg excellent in moldability and mechanical properties can be obtained. On the other hand, when the coefficient of variation (CV) of basis weight is 10% or less, this means that carbon fibers (A) and organic fibers (B) are sufficiently uniformly dispersed. Portions with a relatively small amount of carbon fibers (A) become fragile portions in terms of strength and rigidity, and portions with a relatively small amount of organic fibers (B) are prone to fiber breakage and become fragile portions in terms of impact strength. Therefore, when carbon fibers (A) and organic fibers (B) are uniformly dispersed, there are no local fragile portions, and the prepreg can achieve both excellent mechanical properties and impact strength. The coefficient of variation of basis weight is calculated from each basis weight w of five 1 cm-square sheet-like fiber base materials i (i=1 to 5) and the average value W thereof by the following formula.

[0034] [Formula]

[0035] The sheet-like fibrous substrate of the present invention preferably contains 0.1 to 10% by weight of binder resin (E). By including 0.1% by weight or more of binder resin (E), the fibers in the sheet-like fibrous substrate can be sufficiently bound together, suppressing tearing during handling and resin impregnation, and resulting in a prepreg with excellent moldability and mechanical properties. By including 10% by weight or less of binder resin (E), the weight content of binder resin (E) relative to the reinforcing fibers becomes relatively small, allowing the prepreg to achieve both excellent lightness and mechanical properties.

[0036] The sheet-like fiber substrate of the present invention is preferably a papermaking substrate. By being a papermaking substrate in which fibers are dispersed in water during papermaking, carbon fibers (A) and organic fibers (B) can be uniformly mixed and dispersed, resulting in a prepreg that has no localized weak points and can achieve both excellent mechanical properties and impact strength.

[0037] The prepreg of the present invention has a maximum tensile strength σ Max and minimum value σ Min The ratio (σ Max / σ Min It is preferable that the ratio of tensile strengths is 1 to 2. A ratio of tensile strengths of 2 or less means that the tensile strength of the prepreg is highly isotropic, which suppresses the propagation of cracks in the weaker direction during impact and provides the prepreg with excellent impact strength.

[0038] The tensile strength of the prepreg is determined by cutting a test specimen from the prepreg and measuring its tensile properties according to ISO 527-3 (1995). The test specimen is measured in four directions: +45 degrees, -45 degrees, and 90 degrees, with any direction designated as 0 degrees. The number of measurements for each direction should be n=5 or more, and the average value of all measurement results is taken as the tensile strength. The maximum value of the tensile strength in each measurement direction is σ Max Let the minimum value be σ Min Let's assume that.

[0039] The prepreg of the present invention can be used as a preform. Here, a preform is made by laminating at least one sheet of the prepreg of the present invention, and there are no particular restrictions on its form. Means for producing a preform include, for example, laminating the prepreg before preheating, and laminating the prepreg after preheating. Here, preheating refers to the process of heating the prepreg to above its melting point or softening point before subjecting it to molding. In other words, laminating the prepreg after heat treatment means heating each prepreg individually or partially individually, and then laminating the prepregs that are above their melting point or softening point. The resulting laminate also corresponds to the preform of the present invention. The amount of lamination and size of the preform can be appropriately adjusted according to the desired shape of the molded product.

[0040] Another aspect of the present invention is a fiber-reinforced resin molded article obtained by molding the preform of the present invention.

[0041] The fiber-reinforced resin molded articles of the present invention can typically be produced by heat molding the preform of the present invention.

[0042] Figure 2 is a schematic diagram showing the cross-sectional structure of one embodiment of the fiber-reinforced resin molded article of the present invention. As shown in Figure 2, one embodiment 6 of the fiber-reinforced resin molded article of the present invention includes carbon fibers 2, organic fibers 3, and resin 4, as well as voids 5.

[0043] Examples of heat molding methods for obtaining the fiber-reinforced resin molded articles of the present invention include autoclave molding, press molding, and oven molding. They may also be combined with other materials to form part of a component. By being molded from the preform of the present invention, the fiber-reinforced resin molded articles of the present invention can exhibit excellent mechanical properties and impact strength. [Examples]

[0044] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0045] (1) Measurement of the weight content of sheet-like fiber base material and resin in prepregs Prepregs are manufactured by laminating resin sheets and fiber mats. The basis weight (Wr) of the resin sheet is calculated as follows: 2 ) and number of layers Nr, basis weight Wf (g / m²) of carbon fibers in the fiber mat 2 ) and the basis weight of organic fibers Wo (g / m 2 The weight content of the sheet-like fiber base material and the weight content of the resin in the prepreg were calculated from the number of layers (Nm) of the fiber mat and the number of layers of the fiber mat using the following formula. Weight content (parts by weight) of sheet-like fiber base material = {(Wf × Nm) + (Wo × Nm)} / {(Wf × Nm) + (Wo × Nm) + (Wr × Nr)} × 100 Resin weight content (parts by weight) = (Wr × Nr) / {(Wf × Nm) + (Wo × Nm) + (Wr × Nr)} × 100 (2) Measurement of prepreg density ρ A test specimen was cut from the prepreg, and the apparent density of the prepreg was measured according to JIS K 7222 (2005). The dimensions of the test specimen were 100 mm in length and 100 mm in width. The length, width, and thickness of the test specimen were measured with a micrometer, and the volume V (mm³) of the test specimen was calculated from the obtained values. 3 The mass M (g) of the cut-out test piece was calculated. The density ρ of the prepreg was calculated by substituting the obtained mass M and volume V into the following equation. ρ(g / cm 3 )=10 3 ×M / V (3) Charpy impact test of fiber-reinforced resin molded products Test specimens were cut from fiber-reinforced resin molded products, and the Charpy impact strength of the fiber-reinforced resin molded products was measured according to JIS K 7111 (2006). The test specimens were cut to a length of 80 ± 2 mm, a width of 10.0 ± 0.2 mm, and a thickness of 4.0 ± 0.2 mm. Edgewise impact testing was performed using specimens without notches. The number of measurements was n=3, and the arithmetic mean was taken as the impact strength.

[0046] (4) Bending test of prepreg Test specimens were cut from the prepreg, and their bending strength and flexural modulus were measured according to ISO 178 method (1993). Test specimens were prepared in four directions: +45°, -45°, and 90°, with any given direction defined as 0°. For each direction, n=3 measurements were taken, and the arithmetic mean values ​​were used as the bending strength and flexural modulus.

[0047] [Average out-of-plane expansion coefficient of prepreg] The out-of-plane expansion coefficient of the prepreg was determined using the following formula, based on the thickness of the prepreg before expansion (before heating) and the thickness of the porous structure after the resin was softened and expanded. Note that softening the resin means heating the prepreg at a temperature 20°C above the melting point of the thermoplastic resin (C) for 5 minutes if the resin is a thermoplastic resin (C), and heating the prepreg at a temperature 30°C below the curing temperature of the thermosetting resin (D) for 1 minute if the resin is a thermosetting resin (D). (Out-of-plane expansion rate of prepreg) = (Thickness of porous structure after expansion [mm]) / (Thickness of prepreg before expansion [mm]) × 100 [%] The average out-of-plane expansion rate of the prepreg was calculated as the arithmetic mean of the out-of-plane expansion rates of the prepreg measured at five randomly selected locations.

[0048] (5) Material of the test specimen [Carbon fiber] A continuous carbon fiber with a total of 12,000 strands was obtained by spinning, calcining, and surface oxidation treatment from a copolymer mainly composed of polyacrylonitrile. The properties of this continuous carbon fiber were as follows. Single fiber diameter: 7 μm Density: 1.8g / cm 3 Tensile strength: 4,600 MPa Tensile modulus: 220 GPa Tensile elongation at break: 2.1% [PET fiber 1] Polyester fiber (Toray Industries, Inc. "Tetron" (registered trademark) 1700T-288F-702C, melting point 260℃, fiber diameter 23μm, density 1.38g / cm³) 3A tensile strength of 14% was used for the fracture.

[0049] [PET fiber 2] Polyester fiber (Toray Industries, Inc. "Tetron" (registered trademark), melting point 260℃, fiber diameter 7μm, density 1.38g / cm³) 3 A tensile strength of 46% was used.

[0050] [PET fiber 3] Polyester fiber (Toray Industries, Inc. "Tetron" (registered trademark), melting point 260℃, fiber diameter 10μm, density 1.38g / cm³) 3 A tensile strength of 42% was used.

[0051] [PET fiber 4] Polyester fiber (Toray Industries, Inc. "Tetron" (registered trademark), melting point 260℃, fiber diameter 18μm, density 1.38g / cm³) 3 A tensile strength of 36.5% was used.

[0052] [LCP ​​fiber] Liquid crystal polyester fiber (Toray Industries, Inc. "Siberas" (registered trademark) 1700T-288F, melting point 330℃, fiber diameter 23μm, density 1.39g / cm³) 3 A tensile strength of 2.8% was used.

[0053] [Aramid fiber] Para-aramid fiber (Toray Industries, Inc.'s "Kevlar" (registered trademark), fiber diameter 12 μm, density 1.44 g / cm³) 3 A tensile strength of 3.6% was used.

[0054] [Resin sheet 1] This material consists of 80% by mass of unmodified polypropylene resin (Prime PolyPro® J105G, manufactured by Prime Polymer Co., Ltd.) and 20% by mass of acid-modified polypropylene resin (Admer® QB510, manufactured by Mitsui Chemicals, Inc.), with a basis weight of 150 g / m². 2 A resin sheet 1 was prepared. The density of the obtained resin sheet 1 was 0.92 g / cm³. 3 The melting point was 165°C.

[0055] [Resin sheet 2] This material consists of 80% by mass of unmodified polypropylene resin (Prime PolyPro® J105G, manufactured by Prime Polymer Co., Ltd.) and 20% by mass of acid-modified polypropylene resin (Admer® QB510, manufactured by Mitsui Chemicals, Inc.), with a basis weight of 200 g / m². 2 A resin sheet 2 was prepared. The density of the obtained resin sheet 2 was 0.92 g / cm³. 3 The melting point was 165°C.

[0056] [Resin sheet 3] Polyetherketone (Arkema's "Kepstan" (registered trademark) 6003) with a basis weight of 150 g / m² 2 A resin sheet 3 was fabricated. The melting point of the obtained resin sheet 2 was 305°C.

[0057] [Resin sheet 4] 30 parts by mass of “jER” (registered trademark) 828 (manufactured by Mitsubishi Chemical Corporation), 35 parts by mass of “jER” (registered trademark) 1001, and 35 parts by mass of “jER” (registered trademark) 154 were added to a kneader, and the temperature was raised to 150°C while kneading. A transparent viscous liquid was obtained by kneading at 150°C for 1 hour. After the viscous liquid was cooled to 60°C while kneading, 3.7 parts by mass of DYCY7 (manufactured by Mitsubishi Chemical Corporation) as a curing agent, 3 parts by mass of DCMU99 (manufactured by Hodogaya Chemical Co., Ltd.) as a curing accelerator, and 3 parts by mass of “Matsumoto Microsphere” (registered trademark) M (manufactured by Matsumoto Oil & Pharmaceutical Co., Ltd.) as particles were added, and the mixture was kneaded at 60°C for 30 minutes to prepare an epoxy resin composition. A basis weight of 150 g / m² was obtained from this epoxy resin composition. 2 A resin sheet 4 was prepared. The curing temperature of the obtained resin sheet 4 was 165°C.

[0058] [Fiber Mat 1] Carbon fiber and PET fiber 1 were cut to lengths of 6 mm and 13 mm, respectively, to obtain chopped carbon fiber and chopped PET fiber 1. A dispersion with a concentration of 0.1% by mass was prepared consisting of water and a surfactant (Nacalai Tex Co., Ltd., polyoxyethylene lauryl ether (trade name)), and a fiber mat was manufactured using the dispersion, chopped carbon fiber, and chopped PET fiber 1. The manufacturing apparatus for the fiber mat is a cylindrical container with a diameter of 1,000 mm and an opening cock at the bottom of the container that serves as a dispersion tank. An agitator is attached to the opening on the top surface of the dispersion tank, and the chopped carbon fiber, chopped PET fiber 1, and dispersion can be introduced through the opening. The papermaking substrate was dried in a drying oven at 200°C for 30 minutes to obtain a web. This web was stacked to obtain fiber mat 1. The average fiber lengths of the carbon fiber and PET fiber 1 in the fiber mat were 6 mm and 13 mm, respectively, and the basis weight of the carbon fiber was 72 g / m². 2 The basis weight of PET fiber 1 is 28 g / m². 2 That was the case.

[0059] [Fiber Mat 2] Fiber mat 2 was obtained in the same manner as fiber mat 1, except that PET fiber 1 in fiber mat 1 was replaced with LCP fiber. The average fiber lengths of carbon fiber and LCP fiber in the fiber mat were 6 mm and 13 mm, respectively, and the basis weight of the carbon fiber was 72 g / m². 2 The basis weight of the LCP fiber is 28 g / m 2 That was the case.

[0060] [Fiber Mat 3] Fiber mat 3 was obtained in the same manner as fiber mat 1, except that PET fiber 1 in fiber mat 1 was replaced with PET fiber 2. The average fiber lengths of carbon fiber and PET fiber 2 in the fiber mat were 6 mm and 13 mm, respectively, and the basis weight of the carbon fiber was 72 g / m². 2 The basis weight of PET fiber 2 is 28 g / m². 2 That was the case.

[0061] [Fiber Mat 4] Fiber mat 4 was obtained in the same manner as fiber mat 1, except that PET fiber 1 in fiber mat 1 was replaced with PET fiber 3. The average fiber lengths of carbon fiber and PET fiber 3 in the fiber mat were 6 mm and 13 mm, respectively, and the basis weight of the carbon fiber was 72 g / m². 2 The basis weight of PET fiber 3 is 28 g / m². 2 That was the case.

[0062] [Fiber Mat 5] Fiber mat 5 was obtained in the same manner as fiber mat 1, except that PET fiber 1 in fiber mat 1 was replaced with PET fiber 4. The average fiber lengths of carbon fiber and PET fiber 4 in the fiber mat were 6 mm and 13 mm, respectively, and the basis weight of the carbon fiber was 72 g / m². 2 The basis weight of PET fiber 4 is 28 g / m². 2 That was the case.

[0063] [Fiber Mat 6] Fiber mat 6 was obtained in the same manner as fiber mat 2, except that the carbon fibers in fiber mat 2 were cut to a length of 0.5 mm. The average fiber lengths of the carbon fibers and LCP fibers in the fiber mat were 0.5 mm and 13 mm, respectively, and the basis weight of the carbon fibers was 72 g / m². 2 The basis weight of the LCP fiber is 28 g / m 2 That was the case.

[0064] [Fiber Mat 7] Fiber mat 7 was obtained in the same manner as fiber mat 2, except that the carbon fibers in fiber mat 2 were cut to a length of 20 mm. The average fiber lengths of the carbon fibers and LCP fibers in the fiber mat were 20 mm and 13 mm, respectively, and the basis weight of the carbon fibers was 72 g / m². 2 The basis weight of the LCP fiber is 28 g / m 2 That was the case.

[0065] [Fiber Mat 8] Fiber mat 8 was obtained in the same manner as fiber mat 2, except that the LCP fibers in fiber mat 2 were cut to a length of 2 mm. The average fiber lengths of the carbon fibers and LCP fibers in the fiber mat were 6 mm and 2 mm, respectively, and the basis weight of the carbon fibers was 72 g / m². 2 The basis weight of the LCP fiber is 28 g / m 2 That was the case.

[0066] [Fiber Mat 9] Fiber mat 9 was obtained in the same manner as fiber mat 2, except that the LCP fibers in fiber mat 2 were cut to a length of 30 mm. The average fiber lengths of the carbon fibers and LCP fibers in the fiber mat were 6 mm and 30 mm, respectively, and the basis weight of the carbon fibers was 72 g / m². 2 The basis weight of the LCP fiber is 28 g / m 2 That was the case.

[0067] [Fiber Mat 10] Fiber mat 10 was obtained in the same manner as fiber mat 1, except that PET fiber 1 in fiber mat 1 was replaced with aramid fiber. The average fiber lengths of carbon fiber and aramid fiber in the fiber mat were 6 mm and 13 mm, respectively, and the basis weight of the carbon fiber was 72 g / m². 2 The basis weight of the aramid fiber is 28 g / m². 2 That was the case.

[0068] [Fiber Mat 11] Fiber mat 11 was obtained in the same manner as fiber mat 2, except that the chopped LCP fibers were left with some of their original thickness remaining. The average fiber lengths of the carbon fibers and LCP fibers in the fiber mat were 6 mm and 13 mm, respectively, and the basis weight of the carbon fibers was 72 g / m². 2 The basis weight of the LCP fiber is 28 g / m 2 That was the case.

[0069] [Fiber Mat 12] Fiber mat 12 was obtained in the same manner as fiber mat 2, except that the ratio of chopped carbon fibers and chopped LCP fibers added to the dispersion tank was changed. The average fiber lengths of the carbon fibers and LCP fibers in the fiber mat were 6 mm and 13 mm, respectively, and the basis weight of the carbon fibers was 84 g / m². 2 The basis weight of the LCP fiber is 16g / m 2 That was the case.

[0070] [Fiber Mat 13] Fiber mat 13 was obtained in the same manner as fiber mat 2, except that the ratio of chopped carbon fibers and chopped LCP fibers added to the dispersion tank was changed. The average fiber lengths of the carbon fibers and LCP fibers in the fiber mat were 6 mm and 13 mm, respectively, and the basis weight of the carbon fibers was 63 g / m². 2 The basis weight of the LCP fiber is 37 g / m 2 That was the case.

[0071] [Fiber Mat 14] Fiber mat 14 was obtained in the same manner as fiber mat 2, except that the ratio of chopped carbon fibers and chopped LCP fibers added to the dispersion tank was changed. The average fiber lengths of the carbon fibers and LCP fibers in the fiber mat were 6 mm and 13 mm, respectively, and the basis weight of the carbon fibers was 56 g / m². 2 The basis weight of the LCP fiber is 44 g / m 2 That was the case.

[0072] [Fiber Mat 15] Fiber mat 15 was obtained in the same manner as fiber mat 2, except that the ratio of chopped carbon fibers and chopped LCP fibers added to the dispersion tank was changed. The average fiber lengths of the carbon fibers and LCP fibers in the fiber mat were 6 mm and 13 mm, respectively, and the basis weight of the carbon fibers was 51 g / m². 2 The basis weight of the LCP fiber is 49 g / m 2 That was the case.

[0073] [Fiber Mat 16] Fiber mat 16 was obtained in the same manner as fiber mat 2, except that the ratio of chopped carbon fibers and chopped LCP fibers added to the dispersion tank was changed. The average fiber lengths of the carbon fibers and LCP fibers in the fiber mat were 6 mm and 13 mm, respectively, and the basis weight of the carbon fibers was 39 g / m². 2 The basis weight of the LCP fiber is 61 g / m 2 That was the case.

[0074] [Fiber Mat 17] Carbon fibers were cut to a length of 6 mm to obtain chopped carbon fibers. A dispersion with a concentration of 0.1% by mass was prepared consisting of water and a surfactant (Nacalai Tex Co., Ltd., polyoxyethylene lauryl ether (trade name)), and a fiber mat was manufactured using the dispersion and the chopped carbon fibers. The manufacturing apparatus for the fiber mat is a cylindrical container with a diameter of 1,000 mm and an opening cock at the bottom of the container that serves as a dispersion tank. An agitator is attached to the opening on the top surface of the dispersion tank, and chopped carbon fibers and the dispersion can be introduced through the opening. The papermaking substrate was dried in a drying oven at 200°C for 30 minutes to obtain a web. This web was stacked to obtain a fiber mat 17. The average fiber length of the carbon fibers in the fiber mat was 6 mm, and the basis weight was 90 g / m². 2 That was the case.

[0075] [Fiber Mat 18] Similar to fiber mat 17, with a basis weight of 110g / m². 2 A fiber mat 18 was obtained.

[0076] (Example 1) A laminate was fabricated by arranging fiber mat 1 and resin sheet 1 in the order of [resin sheet 1 / fiber mat 1 / resin sheet 1 / fiber mat 1 / resin sheet 1 / fiber mat 1 / resin sheet 1 / fiber mat 1 / resin sheet 1 / fiber mat 1 / resin sheet 1]. Then, a prepreg was obtained by going through the following steps (A) to (C). (A) Place the laminate in a press molding die cavity preheated to 180°C and close the die. (B) Apply a pressure of 3 MPa and hold it for 5 minutes, then cool the cavity temperature to 50°C while maintaining the pressure. (C) Open the mold and remove the prepreg.

[0077] Subsequently, a fiber-reinforced resin molded product was obtained by following the steps (D) to (F) below. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 1. The impact strength was higher compared to Comparative Example 1. (D) Place the prepreg in the same press molding die cavity as (A) which has been preheated to 180°C, fasten the die and hold for 5 minutes, then release the die and insert a metal spacer at its end to adjust the thickness of the fiber-reinforced resin molded product to 4.0 mm. (E) Re-tighten the mold cavity and cool the cavity temperature to 50°C while maintaining the pressure. (F) Open the mold and remove the fiber-reinforced resin molded product.

[0078] (Example 2) A prepreg and a fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that fiber mat 1 was replaced with fiber mat 2. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 1. Compared to Example 1, organic fiber (B) with higher tensile strength was used, resulting in particularly high impact strength.

[0079] (Example 3) A prepreg and fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that fiber mat 1 was replaced with fiber mat 2, resin sheet 1 was replaced with resin sheet 3, and the preheating temperature in process (A) was 350°C, the pressure in process (B) was 10 MPa, and the holding time was 10 minutes. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 1. Even when a resin with a higher melting point than in Example 2 was used, the product exhibited particularly high impact strength, similar to Example 2.

[0080] (Example 4) The resin sheet 1 in Example 1 was replaced with resin sheet 4, and a prepreg was obtained by going through the following steps (A) to (C). (A) Place the laminate in a press molding die cavity preheated to 60°C and close the die. (B) Apply a pressure of 5 MPa and hold it for 90 minutes. (C) Open the mold and remove the prepreg.

[0081] Subsequently, a fiber-reinforced resin molded product was obtained by following the steps (D) to (F) below. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 1. When the resin was changed from Example 2 to a thermosetting resin, the product exhibited particularly high impact strength, similar to Example 2. (D) Place the prepreg in a press molding die cavity preheated to 60°C, apply a pressure of 5 MPa and hold for 5 minutes, then release the die and insert a metal spacer at its end to adjust the thickness of the fiber-reinforced resin molded product to 4.0 mm. (E) Re-close the mold cavity and, while maintaining the pressure, heat the mold to 150°C and cure for 90 minutes. (F) Open the mold and remove the fiber-reinforced resin molded product.

[0082] (Example 5) A prepreg and a fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that fiber mat 1 was replaced with fiber mat 10. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 1. The impact strength was higher than that of Comparative Example 1. Comparing Example 2 and Example 5, Example 2 showed particularly high impact strength due to the use of organic fibers (B) with a larger diameter.

[0083] (Example 6) A prepreg and a fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that fiber mat 1 was replaced with fiber mat 11. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 1. The impact strength was higher than that of Comparative Example 1. Comparing Example 2 and Example 6, Example 2 had a smaller coefficient of variation in the basis weight of the fiber mat and particularly high impact strength.

[0084] (Example 7) A prepreg and a fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that fiber mat 1 was replaced with fiber mat 12. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 1. The impact strength was higher than that of Comparative Example 1. Comparing Example 2 and Example 7, Example 2 had a higher content of organic fiber (B) and therefore had particularly high impact strength.

[0085] (Example 8) Except for replacing fiber mat 1 with fiber mat 13, the same process as in Example 1 was followed to obtain a prepreg and a fiber-reinforced resin molded product. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 1. Comparing Example 2 and Example 8, Example 8 had a higher content of organic fiber (B) and exhibited particularly high impact strength.

[0086] (Example 9) Except for replacing fiber mat 1 with fiber mat 14, the same process as in Example 1 was followed to obtain a prepreg and a fiber-reinforced resin molded product. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 1. However, in Example 9, the content of organic fiber (B) was high, and the fiber-reinforced resin molded product did not expand well to a thickness of 4 mm, so the impact strength of the fiber-reinforced resin molded product was not evaluated.

[0087] (Example 10) Except for replacing fiber mat 1 with fiber mat 15, the same process as in Example 1 was followed to obtain a prepreg and a fiber-reinforced resin molded product. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 1. However, in Example 10, the content of organic fiber (B) was high, and the fiber-reinforced resin molded product did not expand well to a thickness of 4 mm, so the impact strength of the fiber-reinforced resin molded product was not evaluated.

[0088] (Example 11) A prepreg and a fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that fiber mat 1 was replaced with fiber mat 6. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 2. The impact strength was higher compared to Comparative Example 1. Comparing Example 2 and Example 11, Example 2 had a larger average fiber length of carbon fiber (A), and particularly high flexural modulus and flexural strength.

[0089] (Example 12) Except for replacing fiber mat 1 with fiber mat 7, the same process as in Example 1 was followed to obtain a prepreg and a fiber-reinforced resin molded product. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 2. The impact strength was higher compared to Comparative Example 1. Comparing Example 2 and Example 12, Example 2 had a smaller average fiber length of carbon fiber (A), and particularly high flexural modulus and flexural strength.

[0090] (Example 13) A prepreg and a fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that fiber mat 1 was replaced with fiber mat 8. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 2. The impact strength was higher than that of Comparative Example 1. Comparing Example 2 and Example 13, Example 2 had a larger average fiber length of organic fiber (B) and particularly high impact strength.

[0091] (Example 14) A prepreg and a fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that fiber mat 1 was replaced with fiber mat 9. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 2. The impact strength was higher than that of Comparative Example 1. Comparing Example 2 and Example 14, Example 2 had a smaller average fiber length of organic fiber (B) and particularly high impact strength.

[0092] (Example 15) A prepreg and a fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that fiber mat 1 was replaced with fiber mat 3. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 2. The impact strength was higher than that of Comparative Example 1. Comparing Example 1 and Example 15, Example 1 had a larger diameter and tensile strength of organic fiber (B), and therefore a particularly high impact strength.

[0093] (Example 16) A prepreg and a fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that fiber mat 1 was replaced with fiber mat 4. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 2. The impact strength was higher than that of Comparative Example 1. Comparing Example 1 and Example 16, Example 1 had a larger diameter and tensile strength of organic fiber (B), and therefore a particularly high impact strength.

[0094] (Example 17) A prepreg and a fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that fiber mat 1 was replaced with fiber mat 5. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 2. The impact strength was higher than that of Comparative Example 1. Comparing Example 16 and Example 17, Example 17 had a larger diameter of organic fiber (B) and therefore a particularly high impact strength.

[0095] (Comparative Example 1) A prepreg and fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that a laminate was prepared in which the fiber mat 17 and resin sheet 2 were arranged in the order of [resin sheet 2 / fiber mat 3 / resin sheet 2 / fiber mat 3 / resin sheet 2 / fiber mat 3 / resin sheet 2]. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 2.

[0096] (Comparative Example 2) A prepreg and a fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that fiber mat 1 was replaced with fiber mat 18. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 2.

[0097] (Comparative Example 3) A prepreg and a fiber-reinforced resin molded product were obtained by following the same process as in Example 1, except that fiber mat 1 was replaced with fiber mat 16. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 2. However, in Comparative Example 3, the fiber-reinforced resin molded product did not expand well to a thickness of 4 mm, so the impact strength of the fiber-reinforced resin molded product was not evaluated.

[0098] (Comparative Example 4) A prepreg and a fiber-reinforced resin molded product were obtained by following the same process as in Example 3, except that fiber mat 2 was replaced with fiber mat 1. The properties of the obtained prepreg and fiber-reinforced resin molded product are shown in Table 2.

[0099] [Table 1]

[0100] [Table 2] [Explanation of Symbols]

[0101] 1 Prepreg 2. Carbon fiber (A) 3. Organic fibers (B) 4 resin 5 void 6. Fiber-reinforced resin molded products

Claims

1. A prepreg comprising 5 to 65 parts by weight of a sheet-like fibrous base material in which discontinuous carbon fibers (A) at a concentration of 60% to 80% by weight and discontinuous organic fibers (B) at a concentration of 20% to 40% by weight is uniformly dispersed, and impregnated with 35 to 95 parts by weight of resin, wherein the diameter of the organic fibers (B) is 15 to 50 μm, and the prepreg satisfies any of the following conditions 1 to 3. Condition 1: The resin is a thermoplastic resin (C), and the difference between the melting point Tmb (°C) of the organic fiber (B) and the melting point Tmc (°C) of the thermoplastic resin (C) (Tmb - Tmc) is 20 to 200°C. Condition 2: The resin is a thermosetting resin (D), and the difference between the melting point Tmb (°C) of the organic fiber (B) and the curing temperature Tmd (°C) of the thermosetting resin (D) (Tmb - Tmd) is between 20 and 400°C. Condition 3: The organic fiber (B) has no melting point.

2. The prepreg according to claim 1, wherein the resin expands with an average out-of-plane expansion rate of 250 to 800% when softened.

3. The basis weight of the aforementioned sheet-like fibrous base material is 10 to 200 g / m². ２ The prepreg according to claim 1.

4. The prepreg according to claim 3, wherein the coefficient of variation (CV) of the basis weight is 0.1 to 10%.

5. The prepreg according to claim 1, wherein the sheet-like fibrous base material further comprises 0.1 to 10% by weight of a binder resin (E).

6. The prepreg according to claim 1, wherein the sheet-like fibrous base material is a papermaking base material.

7. The prepreg according to claim 1, wherein the average fiber length of the carbon fiber (A) is 1 to 15 mm.

8. The prepreg according to claim 1, wherein the average fiber length of the organic fiber (B) is 4 to 20 mm.

9. The prepreg according to claim 1, wherein the organic fiber (B) is a fiber made of a resin selected from polyester resin, polyaryletherketone resin, aromatic polyamide resin, and polyarylene sulfide resin.

10. The prepreg according to claim 1, wherein the tensile strength of the organic fiber (B) is 1 to 6 GPa.

11. The prepreg according to claim 1, wherein the tensile elongation at break of the organic fiber (B) is 2.5 to 100%.

12. The prepreg according to claim 1, wherein, in condition 1, the difference (Tmb - Tmc) between the melting point Tmb (°C) of the organic fiber (B) and the melting point Tmc (°C) of the thermoplastic resin (C) is 50 to 160°C.

13. The prepreg according to claim 1, wherein in condition 1, the thermoplastic resin (C) is selected from polyolefin resin, polyamide resin, and polyarylene sulfide resin.

14. The prepreg according to claim 1, wherein the resin impregnation rate of the prepreg is 80 to 100%.

15. The maximum value σ of the tensile strength of the aforementioned prepreg Ｍａｘ and minimum value σ Ｍｉｎ The ratio (σ Ｍａｘ / σ Ｍｉｎ The prepreg according to claim 1, wherein ) is 1 to 2.

16. A preform comprising at least one laminated prepreg according to claim 1.

17. A fiber-reinforced resin molded article obtained by molding the preform described in claim 16.

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