Prepreg, fiber-reinforced resin molded body, and manufacturing method thereof

Abstract

To obtain a fiber-reinforced resin molded body in which a thermosetting resin layer and a thermoplastic resin layer are firmly bonded together as much as possible independently of the type of resin.SOLUTION: There is provided a prepreg, comprising: a reinforcing fiber (A); a thermosetting resin (B); and a thermoplastic resin (C), in which a thermoplastic resin layer mainly composed of the thermoplastic resin (C) is in contact with a thermosetting resin layer mainly composed of the thermosetting resin (B), wherein the thermoplastic resin layer constitutes at least one surface of the prepreg, and a surface of the thermoplastic resin layer in contact with the thermosetting resin layer is a modified surface.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a prepreg having a fiber-reinforced thermosetting resin layer and a thermoplastic resin layer, a fiber-reinforced resin molded article molded using the prepreg, and methods for producing the same. [Background technology]

[0002] Fiber-reinforced composite materials, which are made by combining reinforcing fibers with thermosetting resins, are lightweight, have excellent mechanical properties, dimensional stability, and the like, and are therefore used in a wide range of fields, such as aircraft and other transportation equipment, electrical and electronic equipment, sporting goods, and building materials. Such fiber-reinforced composite materials are sometimes used with a thermoplastic resin member bonded to their surface. Therefore, attempts have been made to provide a thermoplastic resin layer on the surface of a fiber-reinforced composite material and to weld a thermoplastic resin member via the thermoplastic resin layer.

[0003] As one example, Non-Patent Document 1 describes a technique in which a film of thermoplastic resin having a relatively high affinity with thermosetting resin is placed on an uncured prepreg, which is a precursor of a fiber-reinforced composite material, and a mixed layer in which the thermosetting resin of the prepreg and the thermoplastic resin of the film are mixed is formed at the interface, thereby bonding the prepreg and the film to form a thermoplastic resin layer. Patent Document 1 also describes a technique in which a thin thermoplastic resin film is laminated on the surface layer of a thermosetting resin prepreg and allowed to co-flow, thereby forming a thermoplastic resin layer on the surface layer of the fiber-reinforced thermosetting resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2004 / 060658 [Non-patent literature]

[0005] [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]

[0006] However, when applied to aircraft components, etc., further improvements in the bonding strength during welding are required, and in particular, technology that can be applied even to combinations where the affinity between the thermosetting resin layer and the thermoplastic resin layer is low is required.

[0007] An object of the present invention is to obtain a fiber-reinforced resin molded article in which a thermosetting resin layer and a thermoplastic resin layer are firmly bonded together as much as possible independently of the type of resin. [Means for solving the problem]

[0008] The present invention relates to a prepreg comprising reinforcing fibers (A), a thermosetting resin (B), and a thermoplastic resin (C), in which a thermoplastic resin layer mainly composed of the thermoplastic resin (C) is in contact with a thermosetting resin layer mainly composed of the thermosetting resin (B), wherein the thermoplastic resin layer constitutes at least one surface of the prepreg, and the surface of the thermoplastic resin layer in contact with the thermosetting resin layer is a modified surface. [Effects of the Invention]

[0009] By using the prepreg of the present invention, it is possible to obtain a fiber-reinforced resin molding in which a thermosetting resin layer and a thermoplastic resin layer are firmly bonded together. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a cross section perpendicular to the plane direction in one embodiment of the prepreg of the present invention. [Figure 2] 1 is a schematic diagram showing the layer structure of the preforms produced in Example 1 and Comparative Example 2. FIG. [Figure 3] FIG. 2 is a schematic diagram showing the layer structure of the preforms produced in Example 2 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] The prepreg of the present invention will be described in detail below.

[0012] The prepreg of the present invention contains reinforcing fibers (A), a thermosetting resin (B), and a thermoplastic resin (C). A thermoplastic resin layer primarily composed of the thermoplastic resin (C) is in contact with a thermosetting resin layer primarily composed of the thermosetting resin (B), and the thermoplastic resin layer constitutes at least one surface of the prepreg. The thermoplastic resin layer and the thermosetting resin layer are both continuous layers and are in contact with each other. Here, the thermosetting resin layer contains the thermosetting resin (B) and reinforcing fibers (A). The thermoplastic resin layer also contains the thermoplastic resin (C) and, depending on the embodiment, optionally a portion of the reinforcing fibers (A). In other words, the thermosetting resin layer may contain reinforcing fibers (A) in addition to the thermosetting resin (B), and the thermoplastic resin layer may contain reinforcing fibers (A) in addition to the thermoplastic resin (C). Therefore, in this specification, the thermoplastic resin layer is referred to as a layer primarily composed of the thermoplastic resin (C), and the thermosetting resin layer is referred to as a layer primarily composed of the thermosetting resin (B).

[0013] The thermoplastic resin layer of the prepreg of the present invention has a chemically modified surface in contact with the thermosetting resin layer. The modification is a process for improving the adhesion between the thermoplastic resin layer and the thermosetting resin layer by adding specific functional groups to the surface. Examples of the modification include dry processes such as ultraviolet irradiation, plasma treatment, and corona discharge, and wet processes such as chemical treatment. From the viewpoint of simplicity, dry treatment is preferred. The modification generates functional groups such as carboxyl groups and hydroxyl groups on the surface of the thermoplastic resin layer in contact with the thermosetting resin layer. The generated functional groups improve the affinity with the thermosetting resin (B). Alternatively, the functional groups generated during curing of the prepreg react with the thermosetting resin (B), improving the bonding strength between the thermoplastic resin layer and the thermosetting resin layer of the resulting fiber-reinforced resin molded product (hereinafter sometimes simply referred to as the "molded product").

[0014] An example of an index of the amount of functional groups is the oxygen atom concentration. The oxygen atom concentration of the modified surface of the thermoplastic resin layer is preferably 15 atom% or more, more preferably 20 atom% or more, and even more preferably 25 atom% or more. By setting the oxygen atom concentration within such a range, the bonding strength of both the thermoplastic resin layer and the thermosetting resin layer of the molded article obtained as a molded product is improved. Here, the oxygen atom concentration in this specification is a value measured using an X-ray photoelectron spectrometer.

[0015] An example of an indicator of affinity is the water contact angle. The water contact angle on the modified surface of the thermosetting resin layer is preferably 60° or less, more preferably 50° or less, and even more preferably 40° or less. By setting the water contact angle within this range, the bonding strength of both the thermoplastic resin layer and the thermosetting resin layer of the molded article obtained as a molded product is improved. Here, the water contact angle is a value measured by the sessile drop method, in which a droplet of pure water is dropped on the modified surface of the thermoplastic resin sheet immediately after modification in a direction perpendicular to the surface of the thermoplastic resin film, and the angle formed by the droplet with the thermoplastic resin sheet when the droplet lands is measured.

[0016] When the treatment is carried out by ultraviolet irradiation, the oxygen atom concentration and the water contact angle can be controlled by, for example, the irradiation time during the treatment.

[0017] As shown in FIG. 1, the prepreg of the present invention preferably has an uneven structure at the interface between the thermoplastic resin layer and the thermosetting resin layer. Having an uneven structure at the interface between the thermoplastic resin layer and the thermosetting resin layer increases the area of ​​the interface between the thermoplastic resin layer and the thermosetting resin layer, thereby enhancing the effect of modifying the thermoplastic resin layer. Specifically, the roughness average length RSm in a cross section perpendicular to the surface direction is preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 60 μm or less. Furthermore, the roughness average height Rc in the same cross section is preferably 3.5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. Here, the roughness average length RSm and the roughness average height Rc are values ​​determined from the cross-sectional curve formed by the interface in accordance with JIS B0601 (2001). The roughness average length RSm and the roughness average height Rc are measured, for example, within an arbitrary 500 μm square area in a cross-sectional image obtained using an optical microscope or X-ray CT.

[0018] The thermoplastic resin layer of the prepreg of the present invention preferably contains at least a portion of the reinforcing fibers (A). It is also preferable that at least a portion of the reinforcing fibers (A) straddle the boundary between the thermoplastic resin layer and the thermosetting resin layer and contact both resin layers. Referring to FIG. 1, reinforcing fibers 1A and 1B, which are part of the reinforcing fibers (A), contact both the thermosetting resin layer and the thermoplastic resin layer at a portion of their cross section. While the explanation here is based on a specific cross section using FIG. 1, some reinforcing fibers (A) can be said to be in contact with both resin layers even if they are not in contact with both resin regions at a specific cross section, as long as they are in contact with both resin layers somewhere along their entire length. The reinforcing fibers (A) present at the boundary surface chemically and / or physically bond with the thermosetting resin (B) and the thermoplastic resin (C), thereby improving the adhesion between the thermosetting resin layer and the thermoplastic resin layer of the resulting molded article. In the prepreg of the present invention, functional groups are introduced into the thermoplastic resin layer by modification, and the introduced functional groups improve the affinity between the reinforcing fibers (A) and the thermoplastic resin (C). Alternatively, the bond between the reinforcing fiber (A) and the thermoplastic resin (C) is strengthened by the reaction between the functional group generated when the prepreg is cured and the functional group on the surface of the reinforcing fiber (A).

[0019] When reinforcing fibers (A) are present in the thermoplastic resin layer of the prepreg of the present invention, the reinforcing fibers (A) are preferably unevenly distributed on the side of the thermoplastic resin layer that contacts the thermosetting resin layer. Specifically, the reinforcing fibers are preferably distributed in an area of ​​10% or more of the average thickness of the thermoplastic resin layer from the surface that contacts the thermosetting resin layer, more preferably 20% or more, and even more preferably 30% or more. By setting the reinforcing fibers in such a range, the aforementioned reinforcing fibers (A) can be chemically and / or physically bonded to the thermosetting resin (B) and the thermoplastic resin (C), thereby further improving the adhesion between the thermosetting resin layer and the thermoplastic resin layer. On the other hand, the thermoplastic resin layer of the prepreg of the present invention can be heat-sealed when a molded article is produced, as described below. From the viewpoint of heat welding, it is better for the surface of the thermoplastic resin layer not to contain reinforcing fibers, as this allows the resin to flow more easily and allows for easier welding. Therefore, it is preferable that the reinforcing fibers (A) are distributed in an area that is less than 80% of the average thickness of the thermoplastic resin layer from the surface in contact with the thermosetting resin layer, more preferably less than 70%, and even more preferably less than 60%.

[0020] Examples of the reinforcing fiber (A) include glass fibers made of E-glass, C-glass, S-glass, D-glass, etc.; polyacrylonitrile-based, rayon-based, lignin-based, and pitch-based carbon fibers; metal fibers made of stainless steel, iron, gold, silver, aluminum, and alloys thereof; aromatic polyamide fibers; polyaramid fibers; alumina fibers; silicon carbide fibers; boron fibers; and ceramic fibers. These may be used alone or in combination of two or more. Metal fibers, glass fibers, and carbon fibers are preferred as the reinforcing fiber (A) from the viewpoints of high strength and high elastic modulus. Among these, carbon fibers, which have a low specific gravity and excellent specific strength and specific rigidity, are preferred from the viewpoint of lightweight construction. Polyacrylonitrile-based carbon fibers are particularly preferred because they can achieve low production costs.

[0021] The form of the reinforcing fiber (A) may be a continuous fiber form, such as a strand consisting of a large number of filaments, a cloth such as a plain weave, satin weave, or twill weave composed of such strands, a strand in which a large number of filaments are arranged in one direction (unidirectional strand), or a unidirectional cloth composed of such unidirectional strands. Note that "continuous fiber" refers to a linear fiber having a length of 10 mm or more, and in a prepreg, it is preferably a fiber having a length from one end to the opposite end. From the viewpoint of exhibiting high mechanical properties, continuous fiber reinforcing fibers are preferably used. Furthermore, the form of the reinforcing fiber (A) may be a fiber-dispersed form in which strands and / or single fibers of the reinforcing fiber are dispersed in a planar form, such as a chopped strand mat, a papermaking mat, a carding mat, or an airlaid mat. From the viewpoint of shape-forming ability, the fiber-dispersed form is preferred.

[0022] Examples of the thermosetting resin (B) that forms the thermosetting resin layer include unsaturated polyester, vinyl ester, epoxy, phenol (resol type), urea-melamine, polyimide, copolymers and modified products thereof, and resins obtained by blending at least two of these. From the viewpoint of improving impact resistance and toughness, a thermoplastic resin or rubber component may be added to the thermosetting resin (B).

[0023] The thermosetting resin (B) particularly suitable for the present invention is an epoxy resin, which is generally used in combination with a curing agent and a curing catalyst. Epoxy resins whose precursors are amines, phenols, or compounds having a carbon-carbon double bond are particularly preferred. Specifically, epoxy resins whose precursors are amines include various isomers of tetraglycidyldiaminodiphenylmethane, triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, and triglycidylaminocresol. Epoxy resins whose precursors are phenols include bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, phenol novolac epoxy resin, and cresol novolac epoxy resin. Epoxy resins whose precursors are compounds having a carbon-carbon double bond include, but are not limited to, alicyclic epoxy resins. Brominated epoxy resins, which are obtained by brominating these epoxy resins, can also be used. Epoxy resins whose precursors are aromatic amines, such as tetraglycidyldiaminodiphenylmethane, are most suitable for the present invention due to their excellent heat resistance and adhesion to the reinforcing fibers (A).

[0024] Epoxy resins are preferably used in combination with epoxy curing agents. Any compound having an active group capable of reacting with an epoxy group can be used as the epoxy curing agent. Compounds having an amino group, an acid anhydride group, or an azide group are preferred. Specifically, dicyandiamide, various isomers of diaminodiphenyl sulfone, and aminobenzoic acid esters are suitable. Specifically, dicyandiamide is preferably used because it provides excellent prepreg storage stability. Furthermore, various isomers of diaminodiphenyl sulfone are most suitable for the present invention because they provide cured products with good heat resistance.

[0025] The thermoplastic resin (C) forming the thermoplastic resin layer is not particularly limited, and examples thereof include polyester resins such as polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, polytrimethylene terephthalate (PTT) resin, polyethylene naphthalate (PENp) resin, and liquid crystal polyester; polyolefin resins such as polyethylene (PE) resin, polypropylene (PP) resin, and polybutylene resin; styrene resins; and urethane resins, as well as polyoxymethylene (POM) resin, polyamide (PA) resin, polycarbonate (PC) resin, polymethyl methacrylate (PMMA) resin, and polyvinyl chloride (PVC) resin. Examples of such a resin include polyarylene sulfide (PAS) resins such as polyphenylene sulfide (PPS) resin, polyethersulfone (PES) resin, polyamideimide (PAI) resin, polyetherimide (PEI) resin, polysulfone (PSU) resin, modified PSU resin, polyketone (PK) resin, polyetherketone (PEK) resin, polyetheretherketone (PEEK) resin, polyetherketoneketone (PEKK) resin, polyarylate (PAR) resin, polyethernitrile (PEN) resin, thermoplastic polyimide (PI) resin, polyphenylene ether (PPE) resin, modified PPE resin, and polyamide (PA) resin. From the viewpoint of heat resistance and chemical resistance, polyarylketone resins such as polyketone (PK) resin, polyetheretherketone (PEEK) resin, and polyetherketoneketone (PEKK) are preferred. These thermoplastic resins may be copolymers or modified products of the above-mentioned thermoplastic resins, and / or resins in which two or more types are blended, and may further contain other fillers or additives as appropriate depending on the application, etc., as long as the object of the present invention is not impaired. For example, a flame retardant may be added to enhance the flame retardancy of the thermoplastic resin.

[0026] The prepreg of the present invention can be produced by the following methods, etc. Each method will be described below.

[0027] The first manufacturing method includes a modification step of modifying at least one surface of a sheet made of a thermoplastic resin (C), and a lamination step of laminating a sheet made of the modified thermoplastic resin (C) onto a prepreg containing reinforcing fibers (A) and a thermosetting resin (B) so that the modified surface is in contact with the prepreg containing reinforcing fibers (A) and a thermosetting resin (B). The form of the thermoplastic resin sheet is not particularly limited, but examples include a resin film and a nonwoven fabric. The first manufacturing method can be easily carried out because it only requires modifying a thermoplastic resin sheet made of a thermoplastic resin (C) and laminating it with an uncured thermosetting resin.

[0028] The second manufacturing method includes a modification step of modifying at least one surface of a sheet made of a thermoplastic resin (C), an impregnation step 1 of impregnating the reinforcing fibers (A) with the sheet made of the modified thermoplastic resin (C) with the modified surface facing the reinforcing fibers (A), and an impregnation step 2 of impregnating the reinforcing fibers (A) with a thermosetting resin (B) from the side opposite to the thermoplastic resin (C). The order of the impregnation steps 1 and 2 does not matter.

[0029] In the second manufacturing method, the interface between the thermoplastic resin layer and the thermosetting resin layer has an uneven structure, and a structure in which the reinforcing fibers (A) are present across the interface between the thermoplastic resin layer and the thermosetting resin layer and in contact with both resin layers is preferable. The method of impregnating the thermoplastic resin or thermosetting resin is not particularly limited. In batch production, a thermoplastic or thermosetting resin sheet is placed on a reinforcing fiber sheet in which reinforcing fibers are arranged, and the sheet is impregnated by heating and pressurizing with a press. In continuous operation, the reinforcing fibers are continuously drawn out, and a thermosetting or thermoplastic resin sheet is placed on top of it, and the sheet is impregnated by heating and pressurizing with a nip roll. By adjusting the impregnation amount by the heating temperature, pressure, impregnation time, etc., the roughness average length RSm, roughness average height Rc, and the distribution of reinforcing fibers in the thermoplastic resin layer can be controlled.

[0030] The fiber-reinforced resin molding of the present invention can be produced by laminating the prepreg of the present invention, either alone or with other prepregs, to form a preform, and then pressurizing and heating the preform to cure it. Examples of pressurizing and heating methods include press molding, autoclave molding, bagging, tape wrapping, and internal pressure molding. The heating temperature is preferably above the melting point of the thermoplastic resin (C) if it is a crystalline resin, or above the glass transition temperature if it is an amorphous resin. The melting point and glass transition temperature can be measured using a differential scanning calorimeter (DSC) according to JIS K 7121 (2012). By doing this, even in the first manufacturing method, there is no uneven structure at the boundary between the thermoplastic resin layer and the thermosetting resin layer at the prepreg stage, and even if there is no reinforcing fiber (A) that straddles the boundary between the thermoplastic resin layer and the thermosetting resin layer and comes into contact with both resin layers, the thermoplastic resin layer can flow during curing, so it is possible to impart an uneven structure to the boundary between the thermoplastic resin layer and the thermosetting resin layer, or to create a structure in which there is reinforcing fiber (A) that straddles the boundary between the thermoplastic resin layer and the thermosetting resin layer and comes into contact with both resin layers.

[0031] When molding a molded article, it is preferable to use a preform in which the thermoplastic resin layer of the prepreg of the present invention is laminated so as to form the surface of the molded article, whereby the thermoplastic resin layer functions as a welding layer in the molded article and can be welded to the same or different members by known welding means such as hot plate welding, vibration welding, ultrasonic welding, laser welding, resistance welding, and induction heating welding. [Example]

[0032] The present invention will be described in more detail below with reference to examples.

[0033] 1. Materials used in the Examples and Comparative Examples <Reinforced fiber (A)> A polymer containing polyacrylonitrile as the main component was spun and calcined to obtain continuous carbon fibers with a total of 12,000 filaments. The continuous carbon fibers were then subjected to electrolytic surface treatment and dried in heated air at 120°C to obtain carbon fibers. The properties of the carbon fibers were as follows:

[0034] Density: 1.80g / cm 3 Single fiber diameter: 7 μm Tensile strength: 4.9GPa Tensile modulus: 230GPa <Thermosetting resin (B)> 50 parts by mass of bisphenol A epoxy resin ("jER" (registered trademark) 825 (manufactured by Mitsubishi Chemical Corporation)), 50 parts by mass of tetraglycidyldiaminodiphenylmethane ("Sumiepoxy" (registered trademark) ELM434 (manufactured by Sumitomo Chemical Co., Ltd.)), and 8 parts by mass of polyethersulfone ("Sumikaexcel" (registered trademark) PES5003P (manufactured by Sumitomo Chemical Co., Ltd.)) were added and mixed under heat to dissolve the polyethersulfone. Next, while continuing to mix, the temperature was lowered to 100°C or less, and 45 parts by mass of 4,4'-diaminodiphenylsulfone (Seikacure S (manufactured by Wakayama Seika Kogyo Co., Ltd.)) was added and stirred to obtain thermosetting resin (B).

[0035] <Thermosetting resin film> The obtained thermosetting resin (B) was coated on release paper using a knife coater to prepare a thermosetting resin film.

[0036] <Thermosetting prepreg> The carbon fibers are aligned in one direction and drawn out as a continuous reinforced fiber sheet, with a weight of 190 g / m 2 The basis weight was adjusted to 50g / m 2 The thermosetting resin film was placed on both sides of a reinforcing fiber sheet aligned in one direction, and the reinforcing fiber sheet was impregnated with the thermosetting resin film while being heated and pressurized using a heat roll set at 60°C, thereby obtaining a thermosetting prepreg.

[0037] <Thermoplastic resin film> A thermoplastic resin film 1 having a thickness of 100 μm was prepared using a polyether ketone ketone resin (KEPSTAN (registered trademark) 6002, manufactured by Arkema, melting point 305° C.).

[0038] <Modified thermoplastic resin film> Thermoplastic resin film 1 was irradiated with ultraviolet light-ozone modifier (Novascan PSD Pro Series UV / Ozone system, manufactured by Novascan) for 10 minutes to obtain modified thermoplastic resin film 2.

[0039] 2. Evaluation Method (Evaluation method 1) Measurement of oxygen atom concentration in thermoplastic resin film The oxygen atomic concentration of the thermoplastic resin film was measured using an X-ray photoelectron spectrometer (PHI Quantera II, manufactured by ULVAC-PHI, Inc.) The oxygen atomic concentration was measured on the modified surface for modified thermoplastic resin films, and on either surface for untreated films.

[0040] (Evaluation Method 2) Measurement of Water Contact Angle of Thermoplastic Resin Film The water contact angle of the thermoplastic resin film was measured using the sessile drop method. A droplet of pure water was dropped onto the surface of a dry thermoplastic resin film in a direction perpendicular to the surface of the thermoplastic resin film. An image of the drop landing was taken with a microscope, and the angle between the thermoplastic resin film and the droplet was measured from the image, which was taken as the water contact angle. For modified thermoplastic resin films, the measurement was made on the modified surface, and for untreated thermoplastic resin films, the measurement was made on either surface.

[0041] (Evaluation method 3) Cross-sectional observation of the boundary surface between the thermoplastic resin layer and the thermosetting resin layer of the prepreg The uneven structure of the prepreg was observed by taking photographs of the boundary surface between the thermoplastic resin layer and the thermosetting resin layer at a magnification of 500x using a laser microscope (Keyence VHX-5000). Cross-sectional observations were performed at 10 locations, and in each of the obtained cross-sectional images, the RSm and Rc of the cross-sectional curve formed by the boundary surface between the thermoplastic resin layer and the thermosetting resin layer were measured in a 500 μm square area based on JIS B0601 (2001), and the average values ​​were used as the RSm and Rc of the boundary surface between the thermoplastic resin layer and the thermosetting resin layer.

[0042] (Evaluation method 4) Single lap shear (SLS) test of joint The molded bodies obtained in each Example and Comparative Example were cut into 100 mm x 25 mm pieces using a diamond cutter so that the 0° direction of the surface fibers was aligned with the long side, and then dried in a vacuum oven for 24 hours. The cut molded bodies were then overlapped so that the welding layers were in contact with each other with a lap length of 12.5 mm. Thermoplastic resin film 1 was inserted into the lap and fixed with a jig. A bonded body was then obtained by ultrasonic welding using a HiQ DIALOG 20 / 6200 ultrasonic welder manufactured by Harman Ultrasonics Japan, with an amplitude of 31.9 μm (single amplitude), an oscillation time of 0.7 s, and a surface pressure of 2 MPa. The resulting bonded body was evaluated for bond strength at an ambient temperature of 23°C in accordance with ISO 4587:1995 (JIS K 6850 (1994)). Five samples were tested for each sample, and the average bond strength of the five samples was taken as the bond strength. Based on the measurement results, the bond strength was evaluated as follows: 〇: Bond strength is 30 MPa or more △: Bond strength is 15 MPa or more and less than 30 MPa ×: Bond strength is less than 15 MPa.

[0043] 3. Preparation of prepreg and fiber-reinforced resin molding Example 1 190g / m as a continuous reinforced fiber sheet with carbon fibers aligned in one direction 2The carbon fiber sheet was impregnated with the thermoplastic resin film 2 by sandwiching the laminate of the reinforcing fiber sheet and the thermoplastic resin film 2 between release films and applying pressure at 360°C and 0.5 MPa for 1 minute in a press molding machine. The carbon fiber sheet was then impregnated with the thermoplastic resin film 2. The laminate was then transferred to a different press molding machine and cooled and pressed at 40°C and 0.5 MPa until the laminate cooled, producing an intermediate. The surface of the obtained intermediate opposite to the surface impregnated with the thermoplastic resin film 2 was coated with a film having a basis weight of 60 g / m. 2 The thermosetting resin film was laminated on the carbon fiber sheet, and the laminate was sandwiched between release films. The laminate was then pressed at 120°C and 0.5 MPa for 5 minutes in a press molding machine, thereby impregnating the carbon fiber sheet with the thermosetting resin film and producing a prepreg having a thermoplastic resin layer and a thermosetting resin layer.

[0044] Next, seven rectangular sheets of a predetermined size were cut out from the thermosetting prepreg and one from the prepreg having a thermoplastic resin layer and a thermosetting resin layer. As shown in Figure 2, the direction of the long side of the rectangular cut-out sheet was set to 0°, and seven thermosetting prepregs were stacked so that the fiber direction was [90° / 0° / 90° / 90° / 0° / 90° / 0°]. One prepreg having a thermoplastic resin layer and a thermosetting resin layer was stacked on the surface of the 90° layer so that the fiber direction was 0°, thereby obtaining a preform.

[0045] Next, the preform was heated in an autoclave at 180°C for 2 hours while applying a surface pressure of 0.6 MPa to cure the thermosetting resin, thereby obtaining a molded product. The obtained molded product had a welding layer made of PEKK resin formed on its surface. The obtained molded product was ultrasonically welded using the method described above to obtain a bonded product. The SLS test results of the obtained bonded product, the surface condition of the thermoplastic resin film used, and the evaluation results of the cross section of the prepreg having a thermoplastic resin layer and a thermosetting resin layer are shown in Table 1 (the same is shown in Table 1 for the following examples).

[0046] Example 2 The modified thermoplastic resin film 2 was laminated onto the thermosetting prepreg with the modified surface facing the prepreg, thereby producing a prepreg having a thermoplastic resin layer and a thermosetting resin layer.

[0047] Next, seven rectangular sheets of a specified size were cut out from the thermosetting prepreg and one from the prepreg having a thermoplastic resin layer and a thermosetting resin layer. As shown in Figure 3, the direction of the long side of the rectangular cut-out sheet was set to 0°, and seven thermosetting prepreg sheets were laminated so that the fiber direction was [90° / 0° / 90° / 90° / 0° / 90° / 0°]. One prepreg sheet having a thermoplastic resin layer and a thermosetting resin layer was laminated on the surface of the 90° layer side so that the fiber direction was 0°.

[0048] Next, the preform was heated in an autoclave at 180°C for 2 hours while applying a surface pressure of 0.6 MPa to harden the thermosetting resin, thereby obtaining a molded product. The molded product thus obtained had a welding layer made of PEKK resin on its surface. The molded product thus obtained was ultrasonically welded using the method described above to obtain a bonded product.

[0049] (Comparative Example 1) A molded article was obtained in the same manner as in Example 2, except that the modified thermoplastic resin film 2 used in producing the prepreg having a thermoplastic resin layer and a thermosetting resin layer was replaced with unmodified thermoplastic resin film 1. The obtained molded article had low affinity between the thermosetting resin layer and the thermoplastic resin layer, and they were easily peeled off.

[0050] (Comparative Example 2) A molded article was obtained in the same manner as in Example 1, except that the modified thermoplastic resin film 2 used in producing a prepreg having a thermoplastic resin layer and a thermosetting resin layer was replaced with unmodified thermoplastic resin film 1. The molded article obtained had a welding layer made of PEKK resin formed on its surface. The molded article obtained was ultrasonically welded using the method described above to obtain a bonded article.

[0051] [Table 1] [Explanation of symbols]

[0052] 1: Reinforced fiber (A) 1A, 1B: Reinforced fiber (A) in contact with both the thermoplastic resin layer and the thermosetting resin layer 2: Thermosetting resin layer mainly composed of thermosetting resin (B) 3: Thermoplastic resin layer mainly composed of thermoplastic resin (C) 4: Interface between thermoplastic resin layer and thermosetting resin layer 5: Prepreg having a thermoplastic resin layer and a thermosetting resin layer 6: Thermosetting prepreg (90°) 7: Thermosetting prepreg (0°) 8:Thermoplastic resin layer 9: Thermosetting resin layer 10: Thermoplastic resin film

Claims

1. A prepreg comprising reinforcing fibers (A), a thermosetting resin (B), and a thermoplastic resin (C), in which a thermoplastic resin layer mainly composed of the thermoplastic resin (C) is in contact with a thermosetting resin layer mainly composed of the thermosetting resin (B), wherein the thermoplastic resin layer constitutes at least one surface of the prepreg, and the surface of the thermoplastic resin layer in contact with the thermosetting resin layer is a modified surface.

2. 2. The prepreg according to claim 1, wherein the modified surface is a surface modified by at least one treatment selected from the group consisting of ultraviolet irradiation, plasma treatment, and corona discharge.

3. 2. The prepreg according to claim 1, wherein the oxygen atom concentration of the modified surface is 15 atom % or more.

4. The prepreg according to claim 1 , wherein the boundary surface between the thermoplastic resin layer and the thermosetting resin layer has an uneven structure.

5. 5. The prepreg according to claim 4, wherein in a cross section perpendicular to the plane direction, the cross-sectional curve formed by the boundary surface has a roughness average length RSm defined in JIS B0601 (2001) of 100 μm or less and a roughness average height Rc of 3.5 μm or more.

6. The prepreg according to claim 1, wherein at least a portion of the reinforcing fibers (A) is contained in the thermoplastic resin layer.

7. The prepreg according to claim 6, wherein at least a portion of the reinforcing fibers (A) straddles the boundary surface between the thermoplastic resin layer and the thermosetting resin layer and contacts both resin layers.

8. 7. The prepreg according to claim 6, wherein the reinforcing fibers (A) are distributed in a region of 10% or more and less than 80% of the average thickness of the thermoplastic resin layer from the surface in contact with the thermosetting resin layer.

9. A fiber-reinforced resin molding obtained by molding a preform containing the prepreg according to any one of claims 1 to 8.

10. A method for producing a prepreg comprising reinforcing fibers (A), a thermosetting resin (B), and a thermoplastic resin (C), wherein a thermoplastic resin layer containing the thermoplastic resin (C) as a main component and a thermosetting resin layer containing the thermosetting resin (B) as a main component are in contact with each other, the method comprising: A modification step of chemically modifying at least one surface of a sheet made of a thermoplastic resin (C); and a lamination step of laminating a sheet made of the modified thermoplastic resin (C) onto a prepreg containing reinforcing fibers (A) and a thermosetting resin (B) so that the modified surface is in contact with the prepreg containing the reinforcing fibers (A) and the thermosetting resin (B); A method for producing a prepreg having the above structure.

11. A method for producing a prepreg comprising reinforcing fibers (A), a thermosetting resin (B), and a thermoplastic resin (C), the prepreg being formed by adjoining a thermoplastic resin layer mainly composed of the thermoplastic resin (C) and a thermosetting resin layer mainly composed of the thermosetting resin (B), the method comprising: A modification step of chemically modifying at least one surface of a sheet made of a thermoplastic resin (C); and an impregnation step 1 of impregnating the sheet made of the modified thermoplastic resin (C) into the reinforcing fibers (A) with the modified surface facing the reinforcing fibers (A); an impregnation step 2 in which the thermosetting resin (B) is impregnated into the reinforcing fibers (A) from the side opposite to the thermoplastic resin (C); A method for producing a prepreg having the above structure.

12. The method for producing a prepreg according to claim 10 or 11, wherein the modification is at least one treatment selected from the group consisting of ultraviolet irradiation, plasma treatment, and corona discharge.

13. The method for producing a prepreg according to claim 10 or 11, wherein the sheet made of the modified thermoplastic resin (C) has a water contact angle of 60° or less.

14. A method for producing a fiber-reinforced resin molded body, comprising heating a preform containing the prepreg according to any one of claims 1 to 8 to cure the thermosetting resin (B).

15. The method for producing a fiber-reinforced resin molded body according to claim 14, wherein the heating temperature is not less than the melting point when the thermoplastic resin (C) is a crystalline resin, and not less than the glass transition temperature when the thermoplastic resin (C) is an amorphous resin.

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