Fiber-reinforced resin manufacturing method

Abstract

The present invention provides a fiber-reinforced resin which has excellent tensile shear bonding strength and is able to be integrated with another structural member with high productivity by means of thermal welding, thereby being suitable as a structural material. The present invention is a fiber-reinforced resin which contains constituents (A), (B) and (C), while having a multilayer structure that is composed of a thermosetting resin layer that is formed of (B) a thermosetting resin, a thermoplastic resin layer that is formed of (C) a thermoplastic resin, and a mixed layer that is present between the thermoplastic resin layer and the thermosetting resin layer, while being obtained by mixing the thermoplastic resin (C) and the thermosetting resin (B), in such a manner that the thermoplastic resin layer is present in the surface. With respect to this fiber-reinforced resin, at least some of (A) reinforcing fibers are present in the mixed layer. (A) Reinforcing fibers (B) Thermosetting resin (C) Thermoplastic resin

Description

[Technical Field]

[0001] The present invention relates to a fiber-reinforced resin, an integrally molded product, and a method for producing the fiber-reinforced resin. [Background technology]

[0002] Fiber-reinforced composite materials, which combine thermosetting or thermoplastic resins as a matrix with reinforcing fibers such as carbon fiber or glass fiber, are lightweight yet offer excellent mechanical properties such as strength and rigidity, as well as heat and corrosion resistance. Therefore, they have been applied in numerous fields, including aerospace, automobiles, railway vehicles, ships, civil engineering and construction, and sporting goods. However, these fiber-reinforced composite materials are not suitable for the production of complex-shaped parts and structures in a single molding process. For these applications, components made from the fiber-reinforced composite material must first be fabricated and then integrated with other components. Mechanical joining methods, such as those using bolts, rivets, and screws, and adhesives, are commonly used to integrate fiber-reinforced composite materials made from reinforcing fibers and thermosetting resins with other components. Mechanical joining methods require pre-processing of the joints, such as drilling holes, which lengthens the manufacturing process and increases production costs. Furthermore, drilling holes reduces the strength of the material. Bonding methods that use adhesives require a bonding process that includes preparing the adhesive and applying the adhesive, as well as a curing process, which lengthens the manufacturing process and poses the problem of not being able to achieve satisfactory reliability in terms of adhesive strength.

[0003] Fiber-reinforced composite materials using a thermoplastic resin as a matrix can be integrated with other components using the above-mentioned methods, and can also be joined by welding, which has the potential to shorten the time required to join components. However, when mechanical properties in high-temperature, high-humidity environments and excellent chemical resistance are required, such as in aircraft structural components, there is a problem that the heat resistance and chemical resistance are insufficient compared to fiber-reinforced composite materials made of thermosetting resin and reinforcing fibers.

[0004] Here, Patent Document 1 discloses a method of joining a fiber-reinforced composite material made of a thermosetting resin and reinforcing fibers with an adhesive.

[0005] Patent Document 2 discloses a method for integrating a member made of a thermoplastic resin with a member made of a fiber-reinforced composite material made of a thermosetting resin. That is, the method discloses a method in which the reinforcing fibers are exposed on the surface of a composite material made of reinforcing fibers and a cured thermosetting resin, and a thermoplastic resin is welded to the surface to obtain a composite of a thermosetting resin and a thermoplastic resin bonded together by the reinforcing fibers.

[0006] Furthermore, Patent Document 3 discloses a method for producing fiber-reinforced resin in which a thermoplastic resin adhesive layer is formed on the surface of a composite material made of a thermosetting resin and reinforcing fibers, and discloses a method for obtaining thermal weldability of the composite material via the thermoplastic resin.

[0007] Non-Patent Document 1 discloses a fiber-reinforced composite material in which a film or prepreg made of a thermoplastic resin that is easily compatible with the thermosetting resin is disposed on the surface layer of a prepreg made of reinforcing fibers and a thermosetting resin. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2018-161801 [Patent Document 2] Japanese Patent Application Publication No. 4-294128 [Patent Document 3] Patent No. 3906319 [Non-patent literature]

[0009] [Non-Patent Document 1] InvestigatIon on Energy Director-less Ultrasonic Welding of Polyetherimide (PEI)- to Epoxy-based Composites. (Composites Part B: Engineering Volume 173, 15 September 2019) Summary of the Invention [Problem to be solved by the invention]

[0010] However, the technique disclosed in Patent Document 1 is a method of joining fiber-reinforced composite materials made of reinforcing fibers and thermosetting resins together with an adhesive, and does not solve fundamental problems such as the lengthening of the adhesive manufacturing process and the reliability of adhesive strength.

[0011] The method described in Patent Document 2 requires a step of exposing the reinforcing fiber portion on the surface of the cured thermosetting resin after curing the thermosetting resin in the composite, and there are many issues with the production stability of this step and the quality stability due to resin degradation.

[0012] In the method described in Patent Document 3, although thermal welding is achieved via a thermoplastic resin, the bonding strength at the interface between the thermoplastic resin and the thermosetting resin is weak, and depending on the materials used, the interface may become defective and reduce strength.

[0013] In Non-Patent Document 1, a thermoplastic resin is formed on the surface of a thermosetting resin, but the improvement in strength due to the compatibility between the thermosetting resin and the thermoplastic resin is limited, and a high bonding strength equivalent to that of a structural adhesive is not achieved.

[0014] Therefore, an object of the present invention is to provide a fiber reinforced resin that exhibits excellent bonding strength when thermally welded to the same or different members. [Means for solving the problem]

[0015] In order to solve this problem, the prepreg of the present invention has the following configuration: That is, the present invention is a fiber-reinforced resin containing components [A], [B], and [C], which has a laminate structure consisting of a thermosetting resin layer made of a [B] thermosetting resin, a thermoplastic resin layer made of a [C] thermoplastic resin, and a mixed layer present between the thermoplastic resin layer and the thermosetting resin layer and formed by mixing the [C] thermoplastic resin and the [B] thermosetting resin, such that the thermoplastic resin layer is present on the surface, and at least a portion of the [A] reinforcing fibers is present in the mixed layer. [A] Reinforced fiber [B] Thermosetting resin [C]Thermoplastic resin [Effects of the Invention]

[0016] The fiber-reinforced resin of the present invention can be thermally welded to the same or different types of components, thereby shortening the time required for the joining process compared to conventional fiber-reinforced composite materials made of thermosetting resin and reinforcing fibers, and enabling the rapid molding of structural components. Furthermore, the integrated molded products obtained by joining the fiber-reinforced resin to components exhibit excellent bonding strength and have excellent mechanical properties as structural materials, and can be used in a wide range of applications such as aircraft structural components, automobile structural components, and electronic device housings, thereby significantly reducing the molding time and molding costs of products. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross-sectional schematic view of a mixed layer of a fiber-reinforced resin according to the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] The fiber-reinforced resin of the present invention will be described below with reference to the drawings as appropriate, but the drawings are used for convenience to facilitate understanding of the present invention and do not limit the present invention in any way. In this specification, a cross section of a fiber-reinforced resin refers to a cross section cut parallel to the thickness direction, unless otherwise specified.

[0019] <Fiber reinforced resin> The fiber-reinforced resin of the present invention comprises reinforcing fibers of component [A], a thermosetting resin of component [B], and a thermoplastic resin of component [C], and has a laminate structure consisting of a thermosetting resin layer made of the thermosetting resin [B], a thermoplastic resin layer made of the thermoplastic resin [C], and a mixed layer present between the thermoplastic resin layer and the thermosetting resin layer, the mixed layer being a mixture of the thermoplastic resin [C] and the thermosetting resin [B], such that the thermoplastic resin layer is present on the surface, and at least a part of the reinforcing fibers [A] is present in the mixed layer.

[0020] Examples of the reinforcing fibers of the component [A] used in the present invention include glass fibers, carbon fibers, metal fibers, aromatic polyamide fibers, polyaramid fibers, alumina fibers, silicon carbide fibers, boron fibers, and basalt fibers. These may be used alone or in combination of two or more types as appropriate. These reinforcing fibers may be surface-treated. Examples of surface treatments include metal deposition treatment, treatment with a coupling agent, treatment with a sizing agent, and treatment with an additive. These reinforcing fibers also include conductive reinforcing fibers. Carbon fibers are preferably used as reinforcing fibers because of their low specific gravity, high strength, and high elastic modulus.

[0021] Commercially available carbon fibers include "TORAYCA (registered trademark)" T800G-24K, "TORAYCA (registered trademark)" T800S-24K, "TORAYCA (registered trademark)" T700G-24K, "TORAYCA (registered trademark)" T700S-24K, "TORAYCA (registered trademark)" T300-3K, and "TORAYCA (registered trademark)" T1100G-24K (all manufactured by Toray Industries, Inc.).

[0022] The form of the reinforcing fibers in the fiber-reinforced resin can be appropriately selected from a form in which reinforcing fiber bundles formed by gathering reinforcing fibers are arranged in one direction, a form in which reinforcing fiber bundles arranged in one direction are further laminated, a woven form, etc. However, to obtain a fiber-reinforced resin that is lightweight and has a higher level of durability, it is preferable that the reinforcing fiber bundles be in the form of long fibers (fiber bundles) arranged in one direction or continuous fibers such as a woven fabric. In this case, the reinforcing fiber bundle may be composed of multiple fibers of the same form or multiple fibers of different forms. The number of reinforcing fibers constituting one reinforcing fiber bundle is usually 300 to 60,000, but considering the production of the substrate, it is preferably 300 to 48,000, more preferably 1,000 to 24,000. The range may be a combination of any of the above upper and lower limits.

[0023] The reinforcing fibers of component [A] preferably have a strand tensile strength of 5.5 GPa or more, as measured in accordance with the resin-impregnated strand test method of JIS R7608 (2007), because this results in a fiber-reinforced resin with excellent bond strength in addition to tensile strength. It is even more preferable for the strand tensile strength to be 5.8 GPa or more. The bond strength referred to here refers to the tensile shear bond strength determined in accordance with ISO4587:1995 (JIS K6850 (1994)) and the out-of-plane tensile bond strength determined in accordance with ASTM D7291-07.

[0024] Examples of thermosetting resins used in component [B] include unsaturated polyester resins, vinyl ester resins, epoxy resins, phenolic resins, urea resins, melamine resins, polyimide resins, cyanate ester resins, bismaleimide resins, benzoxazine resins, copolymers or modified products thereof, and resins obtained by blending at least two of these. Among these, epoxy resins are preferred because of their excellent mechanical properties, heat resistance, and adhesion to reinforcing fibers.

[0025] In the fiber-reinforced resin of the present invention, the thermosetting resin of component [B] exists as a cured product. When the fiber-reinforced resin is subjected to differential scanning calorimetry under an inert gas atmosphere, if the area of ​​the peak appearing as an exothermic reaction (residual heat) is 50 J / g or less, the thermosetting resin of component [B] can be determined to be substantially a cured product.

[0026] Examples of the base resin of the epoxy resin include bisphenol type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD ​​type epoxy resin, and bisphenol S type epoxy resin; brominated epoxy resins such as tetrabromobisphenol A diglycidyl ether; epoxy resins having a biphenyl skeleton, epoxy resins having a naphthalene skeleton, epoxy resins having a dicyclopentadiene skeleton; novolac type epoxy resins such as phenol novolac type epoxy resin and cresol novolac type epoxy resin; Examples of epoxy resins include glycidyl amine type epoxy resins such as phenol, N,N,O-triglycidyl-p-aminophenol, N,N,O-triglycidyl-4-amino-3-methylphenol, N,N,N',N'-tetraglycidyl-4,4'-methylenedianiline, N,N,N',N'-tetraglycidyl-2,2'-diethyl-4,4'-methylenedianiline, N,N,N',N'-tetraglycidyl-m-xylylenediamine, N,N-diglycidylaniline, and N,N-diglycidyl-o-toluidine; resorcinol diglycidyl ether; and triglycidyl isocyanurate.

[0027] Furthermore, by including 40 to 100 parts by mass of a glycidylamine-type epoxy resin containing three or more glycidyl groups per 100 parts by mass of the total epoxy resin contained in the epoxy resin, a cured product with high heat resistance can be obtained. Examples of glycidylamine-type epoxy resins containing three or more glycidyl groups include N,N,O-triglycidyl-m-aminophenol, N,N,O-triglycidyl-p-aminophenol, N,N,O-triglycidyl-4-amino-3-methylphenol, N,N,N',N'-tetraglycidyl-4,4'-methylenedianiline, N,N,N',N'-tetraglycidyl-2,2'-diethyl-4,4'-methylenedianiline, and N,N,N',N'-tetraglycidyl-m-xylylenediamine.

[0028] Furthermore, when the thermosetting resin of component [B] is an epoxy resin having one or more of the structures of diphenyl ether, diphenylmethane, and 2,2-diphenylpropane, the compatibility between the thermosetting resin of component [B] and the thermoplastic resin of component [C] is improved, the strength of the interface between the mixed layer and the thermosetting resin layer is improved, and the bonding strength when formed into an integrated molded product is excellent, which is preferable.

[0029] Examples of epoxy resins having the above structure include diglycidyl ether diphenyl ether, which has a diphenyl ether structure; bisphenol F type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, N,N,N',N'-tetraglycidyl-4,4'-methylenedianiline, N,N,N',N'-tetraglycidyl-2,2'-diethyl-4,4'-methylenedianiline, which have a diphenylmethane structure; and bisphenol A type epoxy resin, which has a 2,2-diphenylpropane structure.

[0030] Examples of the curing agent for the epoxy resin include dicyandiamide, aromatic amine compounds, phenol novolac resins, cresol novolac resins, polyphenol compounds, imidazole derivatives, tetramethylguanidine, thiourea-added amines, carboxylic acid hydrazides, carboxylic acid amides, and polymercaptans.

[0031] In particular, the use of aromatic amine curing agents as epoxy resin curing agents can produce epoxy resin cured products with good heat resistance. Examples of aromatic amine compounds include diaminodiphenylsulfone, diaminobenzanilide, diaminobenzophenone, diaminodiphenylmethane, and the like, as well as their isomers and adducts with aliphatic hydrocarbons and halogen groups.

[0032] The thermoplastic resin of component [C] is not particularly limited, and examples thereof include polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, and liquid crystal polyester; polyolefins such as polyethylene, polypropylene, and polybutylene; styrene-based resins; urethane resins; polyoxymethylene; polyamides such as polyamide 6 and polyamide 66; polycarbonate; polymethyl methacrylate; polyvinyl chloride; polyphenylene sulfide; polyphenylene ether; modified polyphenylene ether; polyimide; polyamideimide; polyetherimide; polysulfone; modified polysulfone; polyethersulfone; polyarylene ether ketones such as polyketone, polyether ketone, polyether ether ketone, and polyether ketone ketone; polyarylate; polyether nitrile; phenolic resins; and phenoxy resins. These thermoplastic resins may also be copolymers or modified versions of the above-mentioned resins, or resins obtained by blending two or more of these resins. Among these, polyetherimide, polyethersulfone, and polysulfone are preferred because they have high compatibility with thermosetting resins, improve the strength of the interface between the mixed layer and the thermoplastic resin layer, and provide excellent bonding strength when formed into an integrally molded product.

[0033] The weight-average molecular weight of the thermoplastic resin of component [C] is preferably 10,000 g / mol or more and 40,000 g / mol or less. When the weight-average molecular weight is 10,000 g / mol or more, the thermoplastic resin has excellent heat resistance and mechanical properties, thereby exhibiting excellent bonding strength at room temperature and in high-temperature environments. When the weight-average molecular weight is 40,000 g / mol or less, the compatibility with the thermosetting resin is increased, improving the interfacial strength between the mixed layer and the thermoplastic resin layer, thereby exhibiting excellent bonding strength.

[0034] The fiber-reinforced resin of the present invention has a laminated structure consisting of a "thermosetting resin layer" made of [B] a thermosetting resin, a "thermoplastic resin layer" made of [C] a thermoplastic resin, and a "mixed layer formed by mixing the thermoplastic resin and the thermosetting resin" present between the thermoplastic resin layer and the thermosetting resin layer, with the thermoplastic resin layer being present on the surface, and at least a portion of the [A] reinforcing fibers being present in the mixed layer.

[0035] In the present invention, the term "mixed layer" refers to a layer in which the thermoplastic resin [C] is mixed with the thermosetting resin [B] before curing, and then the thermosetting resin [B] before curing is cured. The presence of such a mixed layer can be determined by observing the resin region in the fiber-reinforced resin using microscopic infrared spectroscopy (microscopic IR). For example, in an absorption spectrum obtained by microscopic IR, the peaks originating from the thermosetting resin of component [B] and the peaks originating from the thermoplastic resin of component [C] can be distinguished, and the region where the peaks of each resin are mixed between the two components can be defined as a mixed layer. Note that, as the peaks originating from each resin, it is preferable to select characteristic peaks possessed by each resin, and it is more preferable to avoid peaks commonly possessed by both resins.

[0036] Therefore, it is preferable that the thermosetting resin before curing that forms the mixed layer and the thermoplastic resin of component [C] are compatible with each other, and it is more preferable to select a combination such that, for example, the Relative Energy Difference Number in terms of the Hansen Solubility Parameter is within 1.0. As a specific example, when an epoxy resin is selected as the thermosetting resin of component [B], examples of the thermoplastic resin of component [C] include polysulfone, polyethersulfone, and polyetherimide.

[0037] The thickness of the mixed layer is not particularly limited, but is preferably 10 μm to 500 μm, and more preferably 20 μm to 200 μm from the viewpoint of ensuring a stable mixed layer.

[0038] In the present invention, the presence of at least a portion of the reinforcing fibers [A] in the mixed layer reinforces the mixed layer with the reinforcing fibers, and when the mixed layer is thermally welded to another member via the component [C], high bonding strength is exhibited. A volume fraction of the reinforcing fibers [A] present in the mixed layer of 10% to 80% is preferred because higher bonding strength is exhibited. A volume fraction of the reinforcing fibers [A] present in the mixed layer of 30% to 70% is even more preferred.

[0039] In the present invention, the presence of reinforcing fibers in the mixed layer means that the reinforcing fibers are observed in a state where they are contained in the mixed layer in a cross section perpendicular to the fiber axis direction of the reinforcing fibers in the fiber-reinforced resin.

[0040] <Method of manufacturing fiber reinforced resin> The fiber reinforced resin of the present invention may, for example, be (1) A prepreg containing an uncured thermosetting resin and [A] reinforcing fibers (2) [C] A prepreg containing a resin mixture of a thermoplastic resin and an uncured thermosetting resin and [A] reinforcing fibers. (3) [C] Film made of thermoplastic resin and arranging the laminated laminated sheets so that a film made of a thermoplastic resin [C] is present on the surface, and then applying heat and pressure to cure the uncured thermosetting resin to form a thermosetting resin [B].

[0041] (1) A prepreg containing an uncured thermosetting resin and the reinforcing fibers [A] can be produced by impregnating a reinforcing fiber bundle in which the reinforcing fibers [A] are aligned in one direction or a woven fabric of the reinforcing fibers [A] with the uncured thermosetting resin by a known method. Alternatively, such a prepreg may be commercially available.

[0042] (2) A prepreg containing a resin mixture of [C] thermoplastic resin and uncured thermosetting resin and [A] reinforcing fibers can be produced by kneading the thermoplastic resin [C] and the uncured thermosetting resin to obtain a resin mixture and then processing the mixture into a film, and then impregnating a reinforcing fiber bundle in which the reinforcing fibers [A] are aligned in one direction or a woven fabric of the reinforcing fibers [A] with the resin mixture. Alternatively, one side of a prepreg made of a thermosetting resin obtained in the same manner as in (1) may be impregnated with the resin mixture, or the reinforcing fibers may be first impregnated with the resin mixture and then impregnated with the uncured thermosetting resin to form a prepreg.

[0043] (3) The film made of the thermoplastic resin [C] can be produced by molding the thermoplastic resin [C] into a film by a known method, but commercially available products can also be used.

[0044] <Integrated molded product> The fiber-reinforced resin of the present invention can be used to efficiently produce an integrated molded product by heat welding another component (adherend) via the thermoplastic resin layer of the component [C]. The adherend is not particularly limited as long as it can be heat-welded to the component [C], and examples include components containing a thermoplastic resin, metal components with a thermoplastic resin disposed on the surface, and micro-fabricated components with a thermoplastic resin embedded in the surface. The adherend may also be the fiber-reinforced resin of the present invention. In other words, it is also possible to bond the thermoplastic resin layers of the fiber-reinforced resin of the present invention to each other to produce an integrated molded product. The means for heat-welding the fiber-reinforced resin and the adherend is not particularly limited, and examples include vibration welding, ultrasonic welding, laser welding, resistance welding, induction welding, insert injection molding, and outsert injection molding.

[0045] The strength of the bond in the integrally molded product can be evaluated based on ISO4587:1995 (JIS K6850(1994)) and ASTM D7291-07. The tensile shear bond strength measured based on ISO4587:1995 is preferably 20 MPa or more, more preferably 25 MPa or more, when the test environment temperature is 23°C. For applications requiring mechanical properties in high-temperature environments, the bond strength evaluated based on ISO4587:1995 is preferably 10 MPa or more, more preferably 13 MPa or more, when the test environment temperature is 80°C. The higher the tensile shear bond strength, the better. There is no particular upper limit, but for a typical integrally molded product made of fiber-reinforced resin, the upper limit of the tensile shear bond strength at a test environment temperature of 23°C or 80°C is 200 MPa. Furthermore, the out-of-plane tensile bond strength measured based on ASTM D7291-07 is preferably 30 MPa or more, more preferably 35 MPa or more. [Example]

[0046] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. The unit "parts" used in the composition ratios means parts by mass unless otherwise noted. Furthermore, measurements of various properties were carried out in an environment of 23°C and 50% relative humidity unless otherwise noted.

[0047] <Materials used in Examples and Comparative Examples> [Reinforcing fiber for component [A]] T800: Carbon fiber ("TORAYCA (registered trademark)" T800S-24K, manufactured by Toray Industries, Inc., strand tensile strength: 5.9 GPa) T700: Carbon fiber ("TORAYCA (registered trademark)" T700S-24K, manufactured by Toray Industries, Inc., strand tensile strength: 4.9 GPa).

[0048] [Epoxy resin composition serving as component [B] (thermosetting resin)] 50 parts by mass of tetraglycidyldiaminodiphenylmethane ("Araldite" (registered trademark) MY721; manufactured by Huntsman Advanced Materials; epoxy equivalent: 113 (g / eq.)), 50 parts by mass of bisphenol A-type epoxy resin ("jER" (registered trademark) 825; manufactured by Mitsubishi Chemical Corporation; epoxy equivalent: 175 (g / eq.)), and 45.1 parts by mass of 4,4'-diaminodiphenyl sulfone (Seikacure S; manufactured by Wakayama Seika Kogyo Co., Ltd.) as a curing agent were charged into a kneading device and kneaded under heating at a temperature of 100°C or less, thereby obtaining epoxy resin composition B-1.

[0049] 100 parts by mass of a biphenyl-type epoxy resin ("jER" (registered trademark) YX4000, manufactured by Mitsubishi Chemical Corporation; epoxy equivalent: 186 (g / eq.)) and 33.3 parts by mass of 4,4'-diaminodiphenyl sulfone (Seikacure S, manufactured by Wakayama Seika Kogyo Co., Ltd.) as a curing agent were placed in a kneading device and kneaded under heating at a temperature of 100°C or less, thereby obtaining an epoxy resin composition B-2.

[0050] [Thermoplastic resin layer] The thermoplastic resin that will be the following component [C] was melt-formed into a film having a thickness of 50 μm. PEI: Polyetherimide (ULTEM® 1010 manufactured by SABIC, weight average molecular weight 47,000 g / mol) PES1: Polyethersulfone ("Sumikaexcel" (registered trademark) PES5003P, manufactured by Sumitomo Chemical Co., Ltd., weight-average molecular weight 47,300 g / mol) PES2: Polyethersulfone (Virantage 10700RFP, manufactured by Solvay, weight average molecular weight 21,000 g / mol).

[0051] [Film before hardening that will become the mixed layer] 50 parts by mass of an epoxy resin composition and 50 parts by mass of a thermoplastic resin were each placed in a kneading device in the combinations shown in Table 1, and then heated and kneaded at a temperature of 80°C to obtain a resin mixture.The mixture was then coated onto release paper using a knife coater to produce a pre-cured film that would become the mixed layer.

[0052] [Prepreg] The prepregs were produced by the following four methods. The composition of the materials used in each example is as shown in Table 1.

[0053] Prepreg [I] (thermosetting resin layer): An epoxy resin composition was applied to a prepreg sheet with a resin weight of 50 g / m using a knife coater. 2 This resin film was coated on a release paper with [A] reinforcing fibers (weight per unit area: 193 g / m) aligned in one direction. 2 The laminate was placed on both sides of the laminated sheet and impregnated with the epoxy resin composition while being heated and pressurized using heat rolls to obtain prepreg [I].

[0054] Prepreg [II] (mixed layer + thermosetting resin layer): Unidirectionally aligned [A] reinforced fiber (weight 193 g / m 2 ) from one side of the uncured film (basis weight 50 g / m 2 ) was impregnated under heat and pressure, and a resin film (basis weight 50 g / m) made of an epoxy resin composition was then applied from the other side. 2 ) was impregnated to obtain prepreg [II].

[0055] Prepreg [III] (mixed layer + thermosetting resin layer): Unidirectionally aligned [A] reinforced fiber (weight 100 g / m2 ) from one side of the uncured film (basis weight 100 g / m 2 ) was impregnated under heat and pressure, and a resin film (basis weight 50 g / m) made of an epoxy resin composition was then applied from the other side. 2 ) was impregnated to obtain prepreg [III].

[0056] Prepreg [IV] (mixed layer + thermosetting resin layer): Unidirectionally aligned [A] reinforced fiber (weight 50 g / m 2 ) from one side of the uncured film (basis weight 100 g / m 2 ) was impregnated under heat and pressure, and a resin film (basis weight 50 g / m) made of an epoxy resin composition was then applied from the other side. 2 ) was impregnated to obtain prepreg [IV].

[0057] <Evaluation of properties of fiber-reinforced resin and integrally molded products> (1) Confirmation of the mixed layer The fiber-reinforced resins prepared in each of the Examples and Comparative Examples were embedded in an embedding resin so that the surface cut perpendicular to the fiber axis direction of the reinforcing fibers 2 served as the observation surface, as shown in FIG. 1 , and the observation surface was mirror-polished to prepare a cross-sectional sample. As shown in FIG. 1 , in the cross-sectional sample (fiber-reinforced resin 1) of the object to be observed, microscopic IR spectra were obtained for the portion corresponding to component [C] (thermoplastic resin layer 3), the portion corresponding to component [B] (thermosetting resin layer 4), and the portion corresponding to mixed layer 5. In the obtained absorption spectra, the imide group peak derived from polyetherimide, the thermoplastic resin used in the Examples and Comparative Examples, was observed between 1705 and 1745 cm . -1 The sulfonyl group peak derived from polyethersulfone was observed at 1280-1380 cm -1 These peak heights and the peak heights at 1460-1540 cm -1 The height of the peak derived from the aromatic ring observed in the sample was compared with the height of the peak derived from the aromatic ring observed in the sample. When the height of the peak derived from the aromatic ring was set to 1, the region where the reference peak height derived from the thermoplastic resin was 0.1 or more and 5.0 or less was determined to be a mixed layer.

[0058] (2) Measurement method for tensile shear bond strength Tabs were attached to the integrally molded articles prepared in each Example and Comparative Example in accordance with ISO4587:1995 (JIS K6850(1994)), and the articles were cut to a width of 25 mm to obtain the target test specimens. The obtained test specimens were dried in a vacuum oven for 24 hours, and the tensile shear bond strength was measured at environmental temperatures of 23°C and 80°C in accordance with ISO4587:1995 (JIS K6850(1994)). The test results were evaluated as follows: (a) Tensile shear bond strength at 23°C 28MPa or more:A 25MPa or more but less than 28MPa: B 20MPa or more but less than 25MPa: C Less than 20 MPa: D (fail) (b) Tensile shear bond strength at 80°C 16MPa or more:A 13MPa or more but less than 16MPa: B 10MPa or more but less than 13MPa: C Less than 10 MPa: D (fail).

[0059] (3) Out-of-plane tensile bond strength measurement method The integrally molded articles prepared in each Example and Comparative Example were ground into spool shapes with an outer diameter of 25 mm, an inner diameter of 19 mm, and a gauge length of 6.4 mm to obtain the desired test specimens. The obtained test specimens were dried in a vacuum oven for 24 hours, and the out-of-plane tensile bond strength was measured according to ASTM D7291-07. The test results were evaluated as follows: 40MPa or more:A 35MPa or more but less than 40MPa: B 30MPa or more but less than 35MPa: C Less than 30 MPa: D (fail).

[0060] (4) Method for measuring the thickness of the mixed layer For the mixed layer region determined in (1), the distance between the boundary line between regions 3 and 5 and the boundary line between regions 4 and 5 shown in Figure 1 was measured at 100 points every 5 μm, and the average value was calculated as the thickness of the mixed layer.

[0061] (5) Measurement method for volume fraction of reinforcing fibers In the cross-sectional sample prepared in (1), the mixed layer region was identified using the method in (1) in an arbitrary 100 μm square observation area, and the reinforcing fiber and mixed layer region were binarized to determine the areas of both regions, and the volume fraction of the reinforcing fiber was calculated using the following formula. Volume fraction of reinforcing fiber = Area of ​​reinforcing fiber / (Area of ​​reinforcing fiber + Area of ​​mixed layer region) <Examples and Comparative Examples> [Examples 1 to 5] Six prepregs [I] were cut to a specified size, and two prepregs [II] were cut to the same shape, for a total of eight pieces. The axial direction of the reinforcing fibers was defined as 0°, and the direction perpendicular to the axis was defined as 90°, with the [0° / 90°] 2s Prepregs were laminated in a structure of (the symbol s indicates mirror symmetry) with the outermost layer being prepreg [II]. Here, prepreg [II] was laminated so that the resin composition that would become the mixed layer was on the outermost surface. Thermoplastic resin films were laminated on both outermost surfaces. This laminate was set in a press molding die, and while maintaining this shape, a pressure of 0.6 MPa was applied using a press and heated at 180°C for 120 minutes to obtain a fiber-reinforced resin for evaluating tensile shear bond strength. Component [C] was located on the surface of the fiber-reinforced resin.

[0062] The prepared fiber-reinforced resin was cut into two pieces, 250 mm wide and 92.5 mm long, with the axial direction of the reinforcing fibers (0° direction) as the length direction of the test piece, and then dried in a vacuum oven for 24 hours. The two panels were then overlapped, with the 0° direction as the length direction, so that the joining surface was a 12.5 mm long range from the end of the two panels. The overlapping surfaces were welded together by applying a pressure of 3 MPa at 290°C and holding for 1 minute, yielding an integrated molded product for evaluating tensile shear bond strength.

[0063] A total of 75 prepregs were prepared: 73 prepregs [I] cut to a specified size and two prepregs [II] cut to the same shape. The 75 prepregs were stacked so that all had the same reinforcing fiber direction, with the outermost layer being prepreg [II]. Prepreg [II] was stacked so that the resin composition that would form the mixed layer was on the outermost surface. A thermoplastic resin film was laminated on both outermost surfaces. This laminated prepreg was placed in a press mold, and while maintaining its shape, it was pressed under 0.6 MPa and heated at 180°C for 120 minutes to obtain a fiber-reinforced resin for evaluating out-of-plane tensile bond strength and confirming the mixed layer. Component [C] was located on the surface of the fiber-reinforced resin.

[0064] The resulting fiber-reinforced resin was cut into two rectangular pieces, 250 mm wide and 125 mm long, with the axial direction of the reinforcing fibers (0° direction) as the length direction of the test piece, and then dried in a vacuum oven for 24 hours. The two panels were then stacked with the same reinforcing fiber axial direction, and the joint surfaces were welded together by applying a pressure of 3 MPa at 290°C and holding for 1 minute to obtain an integrated molded product for evaluating the out-of-plane tensile bond strength. The evaluation results for the physical properties of the fiber-reinforced resin and the integrated molded product are shown in Table 1.

[0065] [Example 6] Except for changing all prepregs [II] to prepregs [III], a fiber reinforced resin and an integrally molded product were produced in the same manner as in Example 1. The evaluation results of the physical properties of the fiber reinforced resin and the integrally molded product are shown in Table 1.

[0066] [Example 7] Except for changing all prepregs [II] to prepregs [IV], a fiber reinforced resin and an integrally molded product were produced in the same manner as in Example 1. The evaluation results of the physical properties of the fiber reinforced resin and the integrally molded product are shown in Table 1.

[0067] In Examples 1 to 7, a peak derived from imide groups or a peak derived from sulfonyl groups was strongly observed on the surface of the obtained fiber-reinforced resin, but no peak derived from imide groups or a peak derived from sulfonyl groups was observed in the central part where the prepreg [I] was laminated. Furthermore, a peak derived from imide groups or a peak derived from sulfonyl groups was observed near the outermost layer where the fiber bundles were located (corresponding to the outermost layer side of the prepreg [II]), but its height was almost the same as that of the peak derived from aromatic rings, and its relative height was lower than that observed on the surface, confirming that the thermosetting resin and the thermoplastic resin were mixed.

[0068] [Comparative Example 1] A fiber reinforced resin and an integrally molded product were produced in the same manner as in Example 1, except that all prepregs [II] in Example 1 were changed to prepregs [I]. The evaluation results of the physical properties of the fiber reinforced resin and the integrally molded product are shown in Table 1.

[0069] The resulting fiber-reinforced resin exhibited no peaks derived from imide or sulfonyl groups near the outermost fiber bundle layer, indicating the presence of a mixed layer containing reinforcing fibers. The resulting fiber-reinforced resin had a tensile shear bond strength of 4 MPa and decomposed easily, resulting in the thermoplastic resin film peeling off.

[0070] Comparative Example 2 In Comparative Example 1, a pre-cured film (basis weight 50 g / m) was applied to both sides of the laminate of prepregs (all [I]) to form a mixed layer. 2 ) was attached to the sheet, and then thermoplastic resin films were laminated on both sides. A fiber-reinforced resin was produced by treating this laminate in the same manner as in Example 1. Table 1 shows the evaluation results of the physical properties of the fiber-reinforced resin and the integrally molded product.

[0071] Near the outermost layer of the fiber-reinforced resin where the fiber bundles are located, no peaks derived from imide groups or sulfonyl groups were observed, and a mixed layer containing reinforcing fibers could not be confirmed. The tensile shear bond strength of the resulting fiber-reinforced resin was 12 MPa, and it broke in the mixed layer. Although it exhibited a bond strength comparable to that of a general adhesive, it was insufficient for structural bonding.

[0072] [Table 1]

[0073] From the above results, in the examples, high bonding strength equivalent to structural bonding can be achieved with heat welding in just a few minutes. This fundamentally solves the problem of conventional adhesive bonding, which is the lengthening of manufacturing processes such as the bonding process, including adhesive preparation and application, and the curing process. Furthermore, although the fiber-reinforced resin of the present invention uses a thermosetting resin and a thermoplastic resin, a mixed layer is formed between the two resins, which avoids concerns about layer separation. [Explanation of symbols]

[0074] 1: Fiber reinforced resin 2: Reinforced fiber 3: Thermoplastic resin layer 4: Thermosetting resin layer 5: Mixed layer

Claims

1. (1) Prepreg containing uncured thermosetting resin and [A] reinforcing fiber (2) [C] A prepreg containing a resin mixture of a thermoplastic resin and an uncured thermosetting resin and [A] reinforcing fibers (3) [C] Film made of thermoplastic resin [C] a film made of a thermoplastic resin is present on the surface, (1) A prepreg containing an uncured thermosetting resin and [A] reinforcing fibers, (2) A prepreg containing a resin mixture of [C] thermoplastic resin and uncured thermosetting resin and [A] reinforcing fibers, (3) A film made of [C] thermoplastic resin, in that order, or (3) A method for producing a fiber-reinforced resin, comprising: arranging a film made of [C] a thermoplastic resin; (2) a prepreg containing a resin mixture of [C] a thermoplastic resin and an uncured thermosetting resin and [A] reinforcing fibers; and (1) a prepreg containing an uncured thermosetting resin and [A] reinforcing fibers in that order; and curing the uncured thermosetting resin by heating and pressurizing to form [B] a thermosetting resin.

2. The method for producing a fiber-reinforced resin according to claim 1, wherein the thermosetting resin [B] is an epoxy resin.

3. The method for producing a fiber-reinforced resin according to claim 1 or 2, wherein the thermoplastic resin [C] is a resin selected from the group consisting of polysulfone, polyethersulfone, and polyetherimide.

4. The method for producing a fiber-reinforced resin according to claim 2, wherein the epoxy resin comprises an epoxy resin having one or more structures of diphenyl ether, diphenylmethane, or 2,2-diphenylpropane.

5. The method for producing a fiber-reinforced resin according to any one of claims 1 to 4, wherein the weight average molecular weight of the thermoplastic resin [C] is 10,000 g / mol or more and 40,000 g / mol or less.

6. The method for producing a fiber-reinforced resin according to any one of claims 1 to 5, wherein the [A] reinforcing fibers are arranged in one direction or are woven.

7. The method for producing a fiber-reinforced resin according to any one of claims 1 to 6, wherein the reinforcing fiber [A] has a strand tensile strength of 5.5 GPa or more.

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