Steel plate-fiber-reinforced resin composite and method for manufacturing steel plate-fiber-reinforced resin composite

Abstract

To realize both a further improvement of adhesiveness between a steel plate and an FRP and prevention of corrosion due to water.SOLUTION: A steel plate-fiber reinforced resin composite of the present invention comprises a steel plate member, a first adhesive layer mainly composed of a resin composition made of two different materials, a second adhesive layer mainly composed of a resin having a tensile modulus of elasticity of 500 MPa or more at 25°C, and a fiber reinforced resin layer composed of a fiber reinforced resin containing reinforcing fibers in a matrix resin, wherein the resin composition of the first adhesive layer contains a phenoxy resin and a polyester elastomer in a mass ratio range of 20:80 to 80:20, and in elastic modulus phase images of multiple and arbitrary 10 μm square regions obtained by observing the resin composition of the first adhesive layer with an AFM equipped with a probe having a tip radius of 10 nm under an atmosphere at 25°C, an area ratio of the areas forming a phase separation structure due to the phenoxy resin and the polyester elastomer is 1 area % or less of a total observation area.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] This invention relates to a steel plate-fiber-reinforced resin composite and a method for manufacturing a steel plate-fiber-reinforced resin composite. [Background technology]

[0002] In the transportation equipment industry, including automobiles and aircraft, development of composite materials combining metal materials and fiber-reinforced plastics (FRP) has been underway to achieve both weight reduction and improved safety. When using FRP alone as a component, there are challenges in using existing manufacturing equipment designed for metal components, as well as issues with FRP's processability, compressive strength, brittleness, and cost. Therefore, the combination of metal components and FRP is expected to solve these problems, and many of these combinations have a structure in which metal plates and FRP are bonded together. By combining metal components and FRP in this way, it is possible to develop superior materials that cannot be achieved with either metal component or FRP alone.

[0003] Conventionally, to bond metal components and FRP, it is common to use adhesives, as shown in, for example, Patent Documents 1 and 2 below. However, when using adhesives, the process must include steps for applying the adhesive and drying the adhesive, which complicates the manufacturing process of the composite material. Therefore, from the viewpoint of simplifying the manufacturing process, it is considered preferable to bond FRP to metal components without using adhesives.

[0004] On the other hand, phenoxy resin is known as a resin that exhibits excellent adhesion to metal materials such as steel plates and can be easily compounded with metal materials by heat compression bonding. By using FRP with such phenoxy resin as the matrix resin, it becomes possible to directly heat-compress the FRP onto metal materials (see, for example, Patent Document 3 below). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2010-89394 [Patent Document 2] Special Publication No. 2012-515667 [Patent Document 3] Japanese Patent Publication No. 2019-151106 [Overview of the project] [Problems that the invention aims to solve]

[0006] The inventors conducted further studies with the aim of achieving both further improvement in the adhesion between the metal member and the FRP, and further improvement in the corrosion resistance of the composite material formed by combining the metal member and the FRP. In the case of a composite material of a metal member and an FRP, from the perspective of corrosion resistance, there is a problem of electrolytic corrosion (also called galvanic corrosion) that occurs when carbon-reinforced fibers are directly in contact with the metal member in CFRP, which uses carbon-reinforced fibers as the reinforcing fibers of the FRP.

[0007] To prevent such electrochemical corrosion, it was thought that a bonding resin layer could be provided between the metal member and the CFRP to prevent direct contact between the metal member and the carbon-reinforced fibers. However, as a result of the inventors' investigation, it was found that there were cases in which electrochemical corrosion occurred even when a bonding resin layer was provided between the metal member and the CFRP. As a result of further investigation by the inventors regarding this point, it was found that electrochemical corrosion occurred as a result of the carbon-reinforced fibers and the metal member being electrically connected via water that had permeated the bonding resin layer.

[0008] Furthermore, it was found that even when FRP other than CFRP is composited with metal components via an adhesive resin layer, if water can penetrate the adhesive resin layer, various corrosive factors can reach the metal components along with the water, potentially making it difficult to improve corrosion resistance.

[0009] Based on the above findings, the inventors have found that there is room for further improvement in composites of metal members and FRP, specifically in terms of preventing corrosion caused by water permeability of the adhesive resin layer.

[0010] Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to provide a steel plate-fiber-reinforced resin composite and a method for manufacturing a steel plate-fiber-reinforced resin composite that can achieve both further improvement of adhesion between the steel plate and FRP and prevention of corrosion caused by water. [Means for solving the problem]

[0011] In order to solve the above problems, the inventors conducted diligent studies and concluded that, from the perspective of adhesion, it is possible to further improve adhesion by providing an adhesive resin layer that has both shear peel strength and vertical peel strength. In addition, from the perspective of preventing corrosion caused by water, the inventors conceived that by making the adhesive resin layer a two-layer structure and providing an adhesive resin layer with excellent waterproofing properties along with the above-mentioned adhesive resin layer, it is possible to prevent water from penetrating between the steel plate and the FRP. Based on the above findings, the gist of the present invention is as follows:

[0012] (1) A steel plate member made of a steel plate or a molded body of the steel plate; a first adhesive layer located on at least a part of the surface of the steel plate member and mainly composed of two different resin compositions; a second adhesive layer located on at least a part of the surface of the first adhesive layer and mainly composed of a resin having a tensile modulus of elasticity of 500 MPa or more at 25°C; and a fiber-reinforced resin layer located on at least a part of the surface of the second adhesive layer and composed of a fiber-reinforced resin containing reinforcing fibers in a matrix resin, wherein the resin composition of the first adhesive layer is a phenoxy resin and polyester ela A steel plate-fiber-reinforced resin composite comprising a phenoxy resin and a polyester elastomer in a mass ratio (phenoxy resin: polyester elastomer) within the range of 20:80 to 80:20, wherein, in elastic modulus phase image images obtained by observing the resin composition of the first adhesive layer with an atomic force microscope (AFM) equipped with a probe with a tip radius of 10 nm in an atmosphere of 25°C, the area ratio of regions forming a phase separation structure due to the phenoxy resin and the polyester elastomer is 1 area % or less of the total observed area. (2) The steel plate-fiber-reinforced resin composite according to (1), wherein the reinforcing fibers in the fiber-reinforced resin layer are conductive, and at least one of the first adhesive layer or the second adhesive layer further contains a non-conductive substance, or further has a resin layer containing a non-conductive substance between the second adhesive layer and the fiber-reinforced resin layer and on at least a part of the surface of the second adhesive layer. (3) The non-conductive material has an electrical resistivity of 1 × 10 6 The steel plate-fiber-reinforced resin composite according to (2), wherein the composite is at least one selected from insulating particles, glass particles, glass fibers, or aramid fibers having a density of Ω·m or greater. (4) The steel sheet-fiber-reinforced resin composite according to (1) or (2), wherein the resin composition of the first adhesive layer has a glass transition temperature of 60°C or less, a tensile modulus of elasticity at 25°C of 2500 MPa or less, and a tensile elongation at break of 5% or more. (5) The resin composition of the first adhesive layer contains the phenoxy resin and the polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 20:80 to 60:40, as described in (1) or (2). (6) The steel plate-fiber-reinforced resin composite according to (5), wherein the resin composition of the first adhesive layer contains the phenoxy resin and the polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 25:75 to 50:50. (7) The steel plate-fiber-reinforced resin composite according to (1) or (2), wherein, when viewed in plan from above the fiber-reinforced resin layer, the first adhesive layer and the second adhesive layer are the same size, and the fiber-reinforced resin layer is smaller in size than the first adhesive layer. (8) The steel plate-fiber-reinforced resin composite according to (1) or (2), wherein the second adhesive layer is provided so as to cover the surface and sides of the first adhesive layer. (9) The steel plate-fiber-reinforced resin composite according to (1) or (2), wherein the phenoxy resin contained in the first adhesive layer is a phenoxy resin having a bisphenol A skeleton. (10) The matrix resin of the fiber-reinforced resin layer is a steel plate-fiber-reinforced resin composite according to (1) or (2), with phenoxy resin as the main component. (11) The steel plate-fiber-reinforced resin composite according to (10), wherein the matrix resin of the fiber-reinforced resin layer is mainly composed of a phenoxy resin having a bisphenol A skeleton. (12) The steel plate-fiber-reinforced resin composite according to (1) or (2), wherein the reinforcing fibers in the fiber-reinforced resin layer are carbon-reinforced fibers. (13) The steel plate-fiber-reinforced resin composite according to (1) or (2), wherein the resin of the second adhesive layer is a phenoxy resin. (14) The steel plate-fiber-reinforced resin composite according to (13), wherein the resin of the second adhesive layer is a phenoxy resin having a bisphenol A skeleton. (15) The steel plate is a steel plate-fiber-reinforced resin composite according to (1) or (2), having a tensile strength of 1500 MPa or more. (16) A method for manufacturing a steel plate-fiber reinforced resin composite having a steel plate member made of a steel plate or a formed body of the steel plate, a first adhesive layer located on at least a part of the surface of the steel plate member and mainly composed of two different resin compositions, a second adhesive layer located on at least a part of the surface of the first adhesive layer, and a fiber reinforced resin layer located on at least a part of the surface of the second adhesive layer and composed of a fiber reinforced resin containing reinforcing fibers in a matrix resin. The method includes overlaying a first adhesive layer mainly composed of two different resin compositions on at least a part of the surface of the steel plate, overlaying a second adhesive layer mainly composed of a resin having a tensile elastic modulus of 500 MPa or more at 25°C on at least a part of the surface of the first adhesive layer, and overlaying a fiber reinforced resin layer composed of a fiber reinforced resin containing reinforcing fibers in a matrix resin on at least a part of the surface of the second adhesive layer, and thermocompression bonding the first adhesive layer, the second adhesive layer, and the fiber reinforced resin layer to the steel plate. The resin composition of the first adhesive layer contains a phenoxy resin and a polyester elastomer in a mass ratio (phenoxy resin: polyester elastomer) within the range of 20:80 to 80:20. In the elastic modulus phase image obtained by observing the resin composition of the first adhesive layer with an atomic force microscope (AFM) equipped with a probe having a tip radius of 10 nm in an atmosphere at 25°C, the area ratio of the portions forming a phase separation structure due to the phenoxy resin and the polyester elastomer is 1 area% or less of the total observed area. A method for manufacturing a steel plate-fiber reinforced resin composite. (17) A method for producing a steel plate-fiber-reinforced resin composite comprising: a steel plate member made of a steel plate or a molded body of the steel plate; a first adhesive layer located on at least a part of the surface of the steel plate member and mainly composed of two different resin compositions; a second adhesive layer located on at least a part of the surface of the first adhesive layer; and a fiber-reinforced resin layer located on at least a part of the surface of the second adhesive layer and composed of a fiber-reinforced resin containing reinforcing fibers in a matrix resin, wherein the steel plate is press-molded to form a molded body of the steel plate; the first adhesive layer, mainly composed of two different resin compositions, is superimposed on at least a part of the surface of the molded body of the steel plate; the second adhesive layer, mainly composed of a resin having a tensile modulus of elasticity of 500 MPa or more at 25°C, is superimposed on at least a part of the surface of the first adhesive layer; and the matrix resin is located on at least a part of the surface of the second adhesive layer. A method for manufacturing a steel plate-fiber-reinforced resin composite, comprising stacking fiber-reinforced resin layers composed of fiber-reinforced resin containing reinforcing fibers in a steel resin, and heat-pressing the first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer onto a molded steel plate, wherein the resin composition of the first adhesive layer contains phenoxy resin and polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 20:80 to 80:20, and observing the resin composition of the first adhesive layer with an atomic force microscope (AFM) equipped with a probe with a tip radius of 10 nm in an atmosphere of 25°C, the area ratio of regions forming a phase separation structure due to the phenoxy resin and polyester elastomer in multiple arbitrary 10 μm square regions of elastic modulus phase image images is 1 area % or less of the total observed area. (18) A method for manufacturing a steel plate-fiber reinforced resin composite having a steel plate member made of a steel plate or a formed body of the steel plate, a first adhesive layer located on at least a part of the surface of the steel plate member and mainly composed of two different resin compositions, a second adhesive layer located on at least a part of the surface of the first adhesive layer, and a fiber reinforced resin layer located on at least a part of the surface of the second adhesive layer and composed of a fiber reinforced resin containing reinforcing fibers in a matrix resin. At least a part of the surface of the steel plate is overlaid with a first adhesive layer mainly composed of two different resin compositions, at least a part of the surface of the first adhesive layer is overlaid with a second adhesive layer mainly composed of a resin having a tensile elastic modulus of 500 MPa or more at 25°C, and at least a part of the surface of the second adhesive layer is overlaid with a fiber reinforced resin layer composed of a fiber reinforced resin containing reinforcing fibers in a matrix resin to form a laminate. The laminate is processed using a press molding machine having a heated mold, and the steel plate is formed into a formed body while thermocompression bonding the first adhesive layer, the second adhesive layer, and the fiber reinforced resin layer to the steel plate. The resin composition of the first adhesive layer contains a phenoxy resin and a polyester elastomer in a mass ratio (phenoxy resin: polyester elastomer) within the range of 20:80 to 80:20. By observing the resin composition of the first adhesive layer with an atomic force microscope (AFM) equipped with a probe having a tip radius of 10 nm in an atmosphere at 25°C, in the elastic modulus phase image of a plurality of arbitrary 10 μm square regions obtained, the area ratio of the portions forming the phase separation structure due to the phenoxy resin and the polyester elastomer is 1 area% or less of the total observation area. A method for manufacturing a steel plate-fiber reinforced resin composite.

Advantages of the Invention

[0013] As described above, according to the present invention, it is possible to provide a steel plate-fiber reinforced resin composite and a method for manufacturing the steel plate-fiber reinforced resin composite in which both further improvement in adhesion between the steel plate and the FRP and prevention of corrosion caused by water are achieved.

Brief Description of the Drawings

[0014] [Figure 1A] This is a schematic explanatory diagram showing an example of a steel plate-fiber-reinforced resin composite according to an embodiment of the present invention. [Figure 1B] This is a schematic explanatory diagram showing an example of a steel plate-fiber-reinforced resin composite according to the same embodiment. [Figure 1C] This is a schematic explanatory diagram showing an example of a steel plate-fiber-reinforced resin composite according to the same embodiment. [Figure 1D] This is a schematic explanatory diagram showing an example of a steel plate-fiber-reinforced resin composite according to the same embodiment. [Figure 2] This is a schematic diagram illustrating an example of the structure of the second adhesive layer according to the same embodiment. [Figure 3] This is a schematic diagram illustrating an example of the structure of the second adhesive layer according to the same embodiment. [Figure 4] This is a schematic diagram illustrating another example of a steel plate-fiber-reinforced resin composite according to the same embodiment. [Figure 5A] This flowchart shows an example of the process for manufacturing a steel plate-fiber-reinforced resin composite according to the same embodiment. [Figure 5B] This flowchart shows another example of the process for manufacturing a steel plate-fiber-reinforced resin composite according to the same embodiment. [Figure 5C] This flowchart shows another example of the process for manufacturing a steel plate-fiber-reinforced resin composite according to the same embodiment. [Figure 6A] This figure shows an example of an AFM elastic modulus phase image of the first adhesive layer corresponding to an embodiment of the present invention. [Figure 6B] This figure shows an example of an AFM elastic modulus phase image of the first adhesive layer corresponding to an embodiment of the present invention. [Figure 6C] This figure shows an example of an AFM elastic modulus phase image of the first adhesive layer corresponding to an embodiment of the present invention. [Figure 7] This is a schematic diagram illustrating the shape of the test specimen used in the three-point bending test. [Figure 8] This is a schematic diagram illustrating the method of the three-point bending test. [Modes for carrying out the invention]

[0015] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. In this specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant descriptions will be omitted.

[0016] (Regarding steel plate-fiber-reinforced resin composites) First, with reference to Figures 1A to 1D, the steel plate-fiber-reinforced resin composite according to an embodiment of the present invention will be described in detail. Figures 1A to 1D are schematic explanatory diagrams showing an example of the steel plate-fiber-reinforced resin composite according to this embodiment.

[0017] <About the overall structure of the steel plate-fiber-reinforced resin composite> As schematically shown in Figure 1A, the steel plate-fiber-reinforced resin composite 1 according to this embodiment comprises a steel plate member 10 made of a steel plate, a first adhesive layer 20 located on at least a portion of the surface of the steel plate member 10, a second adhesive layer 30 located on at least a portion of the surface of the first adhesive layer 20, and a fiber-reinforced resin layer 40 located on at least a portion of the surface of the second adhesive layer 30.

[0018] In Figure 1A, the first adhesive layer 20, the second adhesive layer 30, and the fiber-reinforced resin layer 40 are shown as being provided on a part of one surface of the steel plate member 10. However, the first adhesive layer 20, the second adhesive layer 30, and the fiber-reinforced resin layer 40 may be provided on the entire surface of one surface of the steel plate member 10.

[0019] Furthermore, the first adhesive layer 20, the second adhesive layer 30, and the fiber-reinforced resin layer 40 may be provided on both sides of the steel plate member 10, as schematically shown in Figure 1B. Moreover, the steel plate-fiber-reinforced resin composite 1 according to this embodiment may have a sandwich structure, as schematically shown in Figure 1C, in which the fiber-reinforced resin layer 40 is sandwiched between two second adhesive layers 30, these two second adhesive layers 30 are further sandwiched between two first adhesive layers 20, and these two first adhesive layers 20 are further sandwiched between two steel plate members 10.

[0020] Furthermore, in the steel plate-fiber-reinforced resin composite 1 according to this embodiment, the steel plate member 10 is not limited to a plate shape as schematically shown in Figures 1A to 1C, but may be composed of a molded steel plate, as schematically shown in Figure 1D. The specific shape of the molded steel plate can be any shape, and may have a complex shape, such as a vehicle panel used in an automobile.

[0021] The following sections will describe in detail the steel plate member 10, the first adhesive layer 20, the second adhesive layer 30, and the fiber-reinforced resin layer 40 in the steel plate-fiber-reinforced resin composite 1.

[0022] <Regarding the steel plate member 10> In the following section, we will explain in detail the case where the steel plate member 10 is constructed using a steel plate as the base material. The detailed material, shape, and thickness of the steel plate member 10 according to this embodiment are acceptable as long as it can be formed by pressing or other processing, and a thin plate shape is preferred. Examples of materials for such a steel plate member 10 include iron and iron-based alloys including stainless steel. The material of the steel plate member 10 is preferably an iron material and an iron-based alloy, and more preferably an iron material with a higher elastic modulus compared to other metal types. Examples of such iron materials include cold-rolled steel sheets for general use, deep drawing, or ultra-deep drawing, which are standardized by Japanese Industrial Standards (JIS) as thin plate-shaped steel sheets used in automobiles, cold-rolled high-tensile steel sheets for workability in automobiles, hot-rolled steel sheets for general use and processing, hot-rolled steel sheets for automobile structures, and hot-rolled high-tensile steel sheets for workability in automobiles. Carbon steel, alloy steel, and high-tensile steel used for general structural and machine structural purposes can also be cited as iron materials, not limited to thin plate shapes. The components of such steel materials may include, for example, one or more of the following elements in addition to Fe and C: Si, Mn, S, P, Al, N, Cr, Mo, Ni, Cu, Ca, Mg, Ce, Hf, La, Zr, and Sb. One or more of these additive elements can be appropriately selected to obtain the desired material strength and formability, and their content can also be adjusted as appropriate.

[0023] Furthermore, it is preferable that the various steel materials described above have a tensile strength of 1500 MPa or more.

[0024] Furthermore, the steel material may be subjected to any surface treatment. Here, surface treatments include, for example, various plating treatments such as zinc plating and aluminum plating, chemical conversion treatments such as chromate treatment and non-chromate treatment, and physical surface roughening treatments such as sandblasting or chemical surface roughening treatments such as chemical etching. In addition, alloying of the plating or multiple types of surface treatments may be applied. It is preferable that the surface treatment is performed for the purpose of providing rust prevention.

[0025] The steel plate member 10 according to this embodiment may be plated with various types of plating. Such plating improves the corrosion resistance of the steel plate member 10. In particular, if the steel plate member 10 is made of steel, plating is more preferable. Various known types of plating can be used, such as zinc-based plating. For example, hot-dip galvanized steel sheets, alloyed hot-dip galvanized steel sheets, Zn-Al-Mg alloy plated steel sheets, aluminum plated steel sheets, electro-galvanized steel sheets, electro-Zn-Ni alloy plated steel sheets, etc. can be used as plated steel sheets (steel materials).

[0026] Furthermore, to improve adhesion with the first adhesive layer 20, it is preferable to treat the surface of the steel plate member 10 with a primer. Preferred primers for this treatment include, for example, silane coupling agents and triazine thiol derivatives. Examples of silane coupling agents include epoxy-based silane coupling agents, amino-based silane coupling agents, and imidazole silane compounds. Examples of triazine thiol derivatives include 6-diallylamino-2,4-dithiol-1,3,5-triazine, 6-methoxy-2,4-dithiol-1,3,5-triazine monosodium, 6-propyl-2,4-dithiolamino-1,3,5-triazine monosodium, and 2,4,6-trithiol-1,3,5-triazine.

[0027] Furthermore, in order to improve adhesion with the first adhesive layer 20, a chemical conversion treatment layer (not shown) containing at least one element selected from the group consisting of Cr, P, Si, and Zr may be further provided on the surface of the steel plate member 10. By providing such a chemical conversion treatment layer, the adhesion between the steel plate member 10 and the first adhesive layer 20 will be further improved.

[0028] In this embodiment, the explanation focuses on steel materials, but it is also possible to use titanium, aluminum, magnesium, or alloys thereof instead of steel. Examples of alloys include Ti-based alloys, Al-based alloys, and Mg alloys.

[0029] <Regarding the first adhesive layer 20> Next, the first adhesive layer 20 of the steel plate-fiber-reinforced resin composite 1 according to this embodiment will be described in detail.

[0030] The first adhesive layer 20 according to this embodiment is a layer located on at least a portion of the surface of the steel plate member 10, as schematically shown in Figures 1A to 1D. This first adhesive layer 20 mainly consists of two different resin compositions.

[0031] Here, if a hard resin is used, the resulting composite material will have excellent shear peel strength, and if a soft resin is used, the resulting composite material will have excellent vertical peel strength. Therefore, in the first adhesive layer 20 according to this embodiment, a mixture of two different resin compositions is used: a hard resin component that has excellent shear peel strength and a soft resin component that has excellent vertical peel strength. This makes it possible to realize an adhesive layer that has excellent shear peel strength and vertical peel strength, and further improvement in adhesion can be achieved in the steel plate-fiber-reinforced resin composite 1 according to this embodiment.

[0032] Specifically, in the first adhesive layer 20 according to this embodiment, phenoxy resin is used as the hard resin component, and polyester elastomer is used as the soft resin component. In other words, the resin composition of the first adhesive layer 20 according to this embodiment has phenoxy resin and polyester elastomer as essential components.

[0033] The shear peel strength and vertical peel strength, which are the focus of this invention, are inherently in a trade-off relationship. Phenoxy resin is a resin with excellent adhesive properties, but it is also a hard resin. Therefore, while it has excellent shear peel strength, its vertical peel strength is low. In other words, when the inventors verified the mechanical properties of a steel plate-fiber-reinforced resin composite sample, they found that when phenoxy resin was used alone, vertical peel strength was low, resulting in delamination in the vertical direction. On the other hand, polyester elastomer has lower shear peel strength than phenoxy resin, but it is a soft resin. Therefore, while it has excellent vertical peel strength, its shear peel strength is low. In other words, when the inventors verified the mechanical properties of a steel plate-fiber-reinforced resin composite sample, they found that when polyester elastomer was used alone, shear peel strength was low, resulting in delamination in the shear direction.

[0034] However, we discovered that by blending phenoxy resin and polyester elastomer in an appropriate ratio, it is possible to achieve excellent balance between shear peel strength and vertical peel strength, which are typically in a trade-off relationship.

[0035] While thermoplastic elastomers include olefin-based, polyurethane-based, and polyamide-based types, polyester elastomers are selected due to their compatibility with phenoxy resins, heat resistance, and flexibility.

[0036] Here, phenoxy resin has a molecular structure very similar to epoxy resin, and is an amorphous thermoplastic resin that is linear, contains hydroxyl groups, and has repeating units composed of ether groups, and exhibits excellent shear peel strength. Such phenoxy resin will be described in more detail below, but those having a bisphenol skeleton are preferred, and in particular, phenoxy resin having a bisphenol A skeleton is preferred.

[0037] Furthermore, the bisphenol A skeleton preferably accounts for 50% or more of the polymer chains constituting the phenoxy resin, and most preferably, the phenoxy resin is composed solely of the bisphenol A skeleton. By using a phenoxy resin having a bisphenol A skeleton, it is possible to further improve the adhesion between the steel plate member 10 and the first adhesive layer 20, and the adhesion between the first adhesive layer 20 and the second adhesive layer 30. Various types of phenoxy resins can be used, but examples of such phenoxy resins include Phenotot YP-50, YP-50S, and YP-70 manufactured by Nippon Steel Chemical & Material Co., Ltd., and PKHC and PKHH manufactured by Gabriel Phenoxies Co., Ltd.

[0038] Furthermore, the phenoxy resin used is preferably one with a mass-average molecular weight (Mw) of 20,000 to 100,000 and a hydroxyl group equivalent (g / eq) of 50 to 750, or one with a glass transition temperature (Tg) of 65°C to 150°C, preferably 70°C to 150°C. Moreover, the phenoxy resin used is preferably one that has a melt viscosity of 3000 Pa·s or less at any temperature within the range of 160 to 250°C, more preferably one that has a melt viscosity in the range of 90 Pa·s to 2900 Pa·s, and even more preferably one that has a melt viscosity in the range of 100 Pa·s to 2800 Pa·s.

[0039] Furthermore, polyester elastomers are thermoplastic polyester block copolymers exhibiting rubber-like elasticity, containing hard segments (crystalline phase) and soft segments (amorphous phase) as constituent units in their molecular structure, and possessing excellent vertical peel strength. Such polyester elastomers are broadly classified into polyester-polyether type and polyester-polyester type based on the combination of hard and soft segments.

[0040] While various types of polyester elastomers can be used, polyester-polyether type polyester elastomers are particularly preferred. This is presumably because the chemical structure of the polyether component (e.g., polytetramethylene glycol) constituting the soft segment of polyester-polyether type elastomers is similar to that of phenoxy resins, and they readily mix with phenoxy resins in a wide range of mixing ratios without phase separation. Examples of such polyester elastomers include Perprene P-type manufactured by Toyobo Co., Ltd. and Hytrel manufactured by Toray DuPont.

[0041] Furthermore, the polyester elastomer used preferably has a melting point in the range of 120°C to 250°C, and more preferably in the range of 130°C to 240°C. Moreover, the polyester elastomer used preferably has a melt viscosity of 3000 Pa·s or less at any temperature within the range of 120 to 250°C, more preferably in the range of 90 Pa·s to 2900 Pa·s, and even more preferably in the range of 100 Pa·s to 2800 Pa·s.

[0042] Furthermore, it is preferable to use a polyester elastomer polymerized in a ratio of hard segment components to soft segment components (hard segment component / soft segment component, hard / soft ratio) within the range of 1 / 99 to 50 / 50. Having a hard / soft ratio within this range allows for more uniform mixing with the phenoxy resin.

[0043] On the other hand, as mentioned earlier, if the resin composition constituting the first adhesive layer 20 does not contain phenoxy resin, the first adhesive layer 20 cannot exhibit excellent shear peel strength. Also, if the resin composition constituting the first adhesive layer 20 does not contain polyester elastomer, the first adhesive layer 20 cannot exhibit excellent vertical peel strength.

[0044] Here, in the resin composition constituting the first adhesive layer 20, the mass ratio of phenoxy resin to polyester elastomer (phenoxy resin:polyester elastomer) is set within the range of 20:80 to 80:20. When the mass ratio of phenoxy resin to polyester elastomer is within the above range, and the phenoxy resin and polyester elastomer are uniformly mixed as described in detail below, the resin composition constituting the first adhesive layer 20 will have excellent shear peel strength and vertical peel strength. As a result, the steel plate-fiber-reinforced resin composite 1 according to this embodiment can achieve superior vertical peel strength while maintaining shear peel strength. Note that if the mass ratio of phenoxy resin in the resin composition is less than 20, the polyester elastomer will be in excess, causing the shear peel strength to decrease too much, and if the blending ratio of phenoxy resin exceeds 80, it will be in excess, causing the vertical peel strength to decrease too much. In either case, it will be impossible to achieve both shear peel strength and vertical peel strength in the resin composition. The mass ratio of phenoxy resin to polyester elastomer is preferably in the range of 20:80 to 60:40, and more preferably in the range of 25:75 to 50:50. By increasing the proportion of polyester elastomer compared to phenoxy resin in this way, it becomes possible to achieve a better balance between shear peel strength and vertical peel strength. As a result, it becomes possible to achieve strength equivalent to or greater than that of the individual components (i.e., shear peel strength of phenoxy resin alone, and vertical peel strength of polyester elastomer alone).

[0045] The mass ratio of phenoxy resin to polyester elastomer in the first adhesive layer 20 constituting the steel plate-fiber-reinforced resin composite 1 according to this embodiment can be measured as follows. First, the second adhesive layer 30 and the fiber-reinforced resin layer 40 are peeled off from the steel plate-fiber-reinforced resin composite 1 to expose the first adhesive layer 20. Then, the exposed first adhesive layer 20 is scraped off. This is dissolved in a deuterated solvent and analyzed using a nuclear magnetic resonance (NMR) spectrometer. 13The 13C NMR spectrum is measured. From the ratio of the integral value of the aromatic carbon of the phenol ether in the phenoxy resin (around 155 ppm) to the integral value of the carbonyl carbon of the polyester elastomer (around 165 ppm), which can be measured in this spectrum, the mass ratio of the phenoxy resin to the polyester elastomer can be calculated.

[0046] Furthermore, in the first adhesive layer 20 according to this embodiment, it is not sufficient for phenoxy resin and polyester elastomer to simply be present; it is required that the phenoxy resin and polyester elastomer be uniformly mixed with each other. If the mixing state of the two is non-uniform (for example, if phase separation occurs and a sea-island-like domain structure is formed), when shear load or peel load is applied, the load will concentrate on the non-uniform parts, and high adhesive strength will not be achieved. However, by uniformly mixing the two, it is possible to achieve both the high shear adhesive strength of phenoxy resin and the excellent vertical adhesive strength of polyester elastomer.

[0047] In this embodiment, as an indicator to confirm whether the phenoxy resin and polyester resin are uniformly mixed, we focus on the size of the phase separation structure caused by the phenoxy resin and polyester elastomer in the elastic modulus phase image obtained by using an atomic force microscope (AFM).

[0048] Here, a phase separation structure refers to a distinct spotted or striped pattern observed in elastic modulus phase images obtained by AFM under specific conditions, as detailed below, when sea-island or co-continuous structures are present.

[0049] More specifically, in the first adhesive layer 20 according to this embodiment, the area ratio of the areas forming the phase separation structure is 1 area % or less of the total observed area in the elastic modulus phase image images of multiple arbitrary 10 μm square regions obtained by observing the surface of the resin composition using an atomic force microscope (AFM) equipped with a tip radius of 10 nm in an atmosphere of 25°C. On the other hand, if the area ratio of the areas forming the phase separation structure exceeds 1 area % of the total observed area, it means that the phenoxy resin and the polyester elastomer are in phase separation, and it is not possible to achieve both excellent shear peel strength and excellent vertical peel strength.

[0050] Here, the above-mentioned elastic modulus phase image can be observed using an atomic force microscope (AFM). Specifically, after smoothing the surface of the adhesive resin composition using a cryomicrotome (-40°C), the image can be observed by scanning in tapping mode using a Bruker-AXS Dimension Icon AFM equipped with a Bruker-AXS NCHV probe (tip radius of curvature 10 nm, spring constant 42 N / m).

[0051] When the resin composition according to this embodiment is observed in any 10 μm × 10 μm area using the method described above, a uniform image without light and shadow due to the difference in elastic modulus between the phenoxy resin and the polyester elastomer is obtained, and the distinct spotted or striped patterns (phase separation structure) seen in cases of sea-island or co-continuous structures are hardly observed, or not observed at all. More specifically, in the total area of ​​any multiple 10 μm square observation areas in multiple samples, the area percentage of locations where the above-mentioned phase separation structure is observed is 1 area % or less of the total area of ​​the observation areas. Preferably, the area percentage of locations where such phase separation structure is observed is 0.1 area % or less, and more preferably 0 area % (i.e., a state in which no phase separation structure is observed at all).

[0052] Furthermore, AFM observation should be performed on at least two samples at 10 or more locations (20 or more fields of view). Preferably, AFM observation should be performed on 5 or more samples at 10 or more locations (50 or more fields of view), and more preferably, on 10 samples at 10 or more locations (100 or more fields of view).

[0053] The mixing conditions for the phenoxy resin and polyester elastomer required to achieve the phase separation structure described above will be explained in more detail below.

[0054] Furthermore, it is preferable that the resin composition constituting the first adhesive layer 20 has a glass transition temperature of 60°C or less, a tensile modulus of elasticity at 25°C of 2500 MPa or less, and a tensile elongation at break of 5% or more. By having the resin composition exhibit the above physical properties, the first adhesive layer 20 can exhibit superior adhesion between the steel plate member 10 and the second adhesive layer 30, while also exhibiting superior shear peel strength and vertical peel strength.

[0055] Furthermore, while there is no specific lower limit for the glass transition temperature of the resin composition, due to the limitations of available materials, it is practically around -60°C. Similarly, while there is no specific lower limit for the tensile modulus at 25°C, due to the limitations of available materials, it is practically around 1 MPa. Moreover, while there is no specific upper limit for the tensile elongation at 25°C, due to the limitations of available materials, it is practically around 800%.

[0056] Here, the glass transition temperature of a resin composition can be measured by various known methods, and for example, it can be determined by measuring the resin composition of interest using a differential scanning calorimetry (DSC). In addition, the tensile modulus and tensile elongation at 25°C can be measured using a universal material testing machine.

[0057] In addition to the phenoxy resin and polyester elastomer described above, the resin composition according to this embodiment may contain various optional components. Preferred optional components include, for example, thermoplastic resins such as polyvinyl chloride, polystyrene, ABS resin, acrylic resin, polyethylene, polypropylene, polycarbonate, polyphenylene ether, polyamides such as nylon 6 and nylon 610, polyacetal, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyphenyl sulfone, polysulfone, polyarylate, polyetherimide, polyetheretherketone, polyphenylene sulfide, polyamideimide, and polyimide. The resin composition may further contain optional components such as flame retardants, inorganic fillers, colorants, antioxidants, UV inhibitors, plasticizers, crosslinking agents, and solvents, depending on the purpose.

[0058] In this case, the total mass ratio of phenoxy resin and polyester elastomer to the total mass of resin components in the resin composition is preferably 70% by mass or more, and more preferably 90% by mass or more. If the total mass ratio of phenoxy resin and polyester elastomer is less than 70% by mass, it may be difficult to achieve the desired properties.

[0059] The thickness of the first adhesive layer 20 in this embodiment is preferably, for example, 20 to 500 μm. Having the first adhesive layer 20 with such a thickness makes it possible to further improve the adhesion between the steel plate member 10 and the fiber-reinforced resin layer 40.

[0060] Here, the thickness of the first adhesive layer 20 is measured by embedding the sample of interest in the resin, cutting out a cross-section, polishing it to create an observation surface, and then observing this observation surface with a scanning electron microscope (SEM). If the sample of interest is thin, the cross-section may be enlarged by oblique cutting before measuring the thickness.

[0061] Furthermore, if the first adhesive layer 20 and the second adhesive layer 30 do not contain a non-conductive substance as described later, the boundary line between the first adhesive layer 20 and the second adhesive layer 30 may not be clearly visible. In such cases, a micro-hardness tester (for example, the Dynamic Ultra-Micro Hardness Tester DUH-211 manufactured by Shimadzu Corporation) can be used to perform point analysis in the thickness direction to identify the hardness distribution, and the thickness can be determined from this hardness distribution by focusing on the position where the hardness indicated by the analysis results changes.

[0062] <Regarding the second adhesive layer 30> Next, the second adhesive layer 30 of the steel plate-fiber-reinforced resin composite 1 according to this embodiment will be described in detail.

[0063] As schematically shown in Figures 1A to 1D, the second adhesive layer 30 in this embodiment is located on at least a portion of the surface of the first adhesive layer 20 as described above, and functions as a waterproof resin layer to prevent water from penetrating into the first adhesive layer 20.

[0064] The presence of such a second adhesive layer 30 prevents water from penetrating the first adhesive layer 20 and various corrosive factors from reaching the steel plate member 10. Furthermore, the presence of such a second adhesive layer 30 prevents electrical connection between the steel plate member 10 and the carbon fiber resin via water, even if the fiber-reinforced resin layer 40 contains carbon fiber resin as reinforcing fibers, thereby preventing the occurrence of electrolytic corrosion.

[0065] The second adhesive layer 30 is made primarily of a resin having a tensile modulus of 500 MPa or more at 25°C, thereby enabling the second adhesive layer 30 itself to exhibit excellent waterproofing properties, and thus contributing to the corrosion resistance described above. Furthermore, "main component" refers to a component that is present in 50 parts by mass or more out of 100 parts by mass of the total resin components.

[0066] Here, the tensile modulus of the resin reflects the relationship between the measurement temperature (25°C in the above case) and the glass transition temperature of the resin. A high value of the tensile modulus indicates that the glass transition temperature of the resin is higher than the measurement temperature. The higher the value of the tensile modulus, the higher the glass transition temperature of the resin tends to be. A high glass transition temperature means that the molecular motion of the molecules constituting the resin decreases, making it less permeable to water molecules.

[0067] By making the second adhesive layer 30 primarily composed of a resin having the tensile modulus described above, the second adhesive layer 30 itself exhibits excellent waterproofing properties, thereby providing the aforementioned effect of contributing to corrosion resistance.

[0068] If the tensile modulus at 25°C is less than 500 MPa, the waterproofing properties described above cannot be achieved, and the corrosion resistance cannot be improved.

[0069] Furthermore, the tensile modulus of the main component resin in the second adhesive layer 30 at 25°C is preferably 1200 MPa or more, and more preferably 1800 MPa or more. Also, the tensile modulus of the main component resin in the second adhesive layer 30 at 25°C is preferably less than 3000 MPa. By having the tensile modulus of the main component resin at 25°C be 3000 MPa or less, it is possible to further improve the waterproofing of the second adhesive layer 30, and even when the steel plate-fiber-reinforced resin composite 1 is processed, the resin can follow the processing and prevent peeling associated with the processing. The tensile modulus of the main component resin at 25°C is more preferably less than 2400 MPa.

[0070] Examples of resins that have the tensile modulus described above and can be used as the main component of the second adhesive layer 30 include polyamide resins, polypropylene resins, thermoplastic polyester resins, and phenoxy resins. Among these, it is particularly preferable to use a phenoxy resin having a bisphenol A skeleton.

[0071] Even when used in the second adhesive layer 30, the bisphenol A skeleton preferably accounts for 50% or more of the polymer chains constituting the phenoxy resin, and most preferably, the phenoxy resin is composed solely of the bisphenol A skeleton. By using a phenoxy resin having a bisphenol A skeleton, it is possible to further improve the adhesion between it and the first adhesive layer 20. Various types of phenoxy resins can be used, but examples of such phenoxy resins include Phenotot YP-50, YP-50S, and YP-70 manufactured by Nippon Steel Chemical & Material Co., Ltd., and PKHC and PKHH manufactured by Gabriel Phenoxies Co., Ltd.

[0072] Furthermore, when used in the second adhesive layer 30, the phenoxy resin used is preferably one with a mass-average molecular weight (Mw) of 20,000 to 100,000 and a hydroxyl group equivalent (g / eq) of 50 to 750, or a glass transition temperature (Tg) of 65°C to 150°C, preferably 70°C to 150°C. Moreover, the phenoxy resin used is preferably one that has a melt viscosity of 3000 Pa·s or less at any temperature in the range of 160 to 250°C, more preferably one that has a melt viscosity in the range of 90 Pa·s to 2900 Pa·s, and even more preferably one that has a melt viscosity in the range of 100 Pa·s to 2800 Pa·s.

[0073] The thickness of the second adhesive layer 30 in this embodiment is preferably, for example, 20 to 500 μm. Having the second adhesive layer 30 with such a thickness makes it possible to further improve the adhesion between the steel plate member 10 and the fiber-reinforced resin layer 40.

[0074] Furthermore, it is more preferable that the thickness of the second adhesive layer 30 satisfies the above-mentioned range and is greater than or equal to the thickness of the first adhesive layer 20. Moreover, it is even more preferable that the ratio of the thickness of the second adhesive layer to the thickness of the first adhesive layer 20 (second adhesive layer / first adhesive layer) is within the range of 1 to 25. By having the thicknesses of the first adhesive layer 20 and the second adhesive layer 30 within the above-mentioned range, the balance between the waterproofness and adhesion exhibited by the steel plate-fiber-reinforced resin composite 1 becomes more favorable.

[0075] The thickness of the second adhesive layer 30 can be measured in the same manner as the first adhesive layer 20.

[0076] Here, in order to further suppress the prevention of water penetration into the first adhesive layer 20 by the second adhesive layer 30, it is preferable that the second adhesive layer 30 has structural features such as those shown in Figure 2 or Figure 3. A brief explanation follows with reference to Figures 2 and 3. Figures 2 and 3 are schematic explanatory diagrams showing an example of the structure of the second adhesive layer according to this embodiment.

[0077] For example, as illustrated in Figure 2, when the steel plate-fiber-reinforced resin composite 1 is viewed from above the fiber-reinforced resin layer 40, the first adhesive layer 20 and the second adhesive layer 30 are the same size, and the fiber-reinforced resin layer 40 may be smaller than the first adhesive layer 20. In other words, the steel plate-fiber-reinforced resin composite 1 according to this embodiment may have a so-called terrace structure, as illustrated in Figure 2. With such a structure, the possibility of the surface of the first adhesive layer 20 being exposed to water is reduced, eliminating the water penetration path to the first adhesive layer 20, and further improving the corrosion resistance of the steel plate-fiber-reinforced resin composite 1.

[0078] Furthermore, as illustrated in Figure 3, for example, the second adhesive layer 30 may be provided so as to cover the surface and sides of the first adhesive layer 20. This further reduces the possibility of the surface of the first adhesive layer 20 being exposed to water, thereby further improving the corrosion resistance of the steel plate-fiber-reinforced resin composite 1. In the case of the covering state illustrated in Figure 3, the size of the fiber-reinforced resin layer 40 (size when viewed from above in a plan view) is not particularly limited and may be smaller than the second adhesive layer 30, the same size as the second adhesive layer 30, or larger than the second adhesive layer 30.

[0079] In the steel plate-fiber-reinforced resin composite 1 according to this embodiment, the reinforcing fibers present in the fiber-reinforced resin layer 40 may be conductive. In this case as well, in order to prevent the occurrence of electrochemical corrosion, it is preferable that at least one of the first adhesive layer 20 or the second adhesive layer 30 further contains a non-conductive substance. By having at least one of the first adhesive layer 20 or the second adhesive layer 30 further contain a non-conductive substance in addition to the resin described above, it is possible to reliably prevent electrical connection between the steel plate member 10 and the fiber-reinforced resin layer 40.

[0080] Furthermore, in the steel plate-fiber-reinforced resin composite 1 according to this embodiment, if the reinforcing fibers present in the fiber-reinforced resin layer 40 are conductive, the steel plate-fiber-reinforced resin composite 1 according to this embodiment may have a structure as illustrated in Figure 4. Figure 4 is a schematic explanatory diagram showing another example of the steel plate-fiber-reinforced resin composite according to this embodiment.

[0081] In other words, in the steel plate-fiber-reinforced resin composite 1 according to this embodiment, if the reinforcing fibers present in the fiber-reinforced resin layer 40 are conductive, a resin layer 50 containing a non-conductive substance may be further provided between the second adhesive layer 30 and the fiber-reinforced resin layer 40, and on at least a portion of the surface of the second adhesive layer 30. By providing such a resin layer 50, it is possible to reliably prevent electrical connection between the steel plate member 10 and the fiber-reinforced resin layer 40. The thickness of the resin layer 50 according to this embodiment is preferably, for example, about 190 to 210 μm.

[0082] Here, the non-conductive material mentioned above includes, for example, glass particles and glass fibers (electrical resistivity of glass: 1 × 10⁻⁶). 10 ~1 × 10 14 Ω·m), aramid fiber (electrical resistivity: 1 × 10⁻¹⁰) 12 ~1 × 10 14 Ω·m), or electrical resistivity of 1 × 10⁻⁶. 6 At least one of the insulating particles having an electrical resistivity of Ω·m or more can be mentioned. By incorporating such a nonconductive material into at least one of the first adhesive layer 20 or the second adhesive layer 30, or into the resin layer 50, it is possible to reliably ensure insulation between the steel plate member 10 and the fiber-reinforced resin layer 40. Here, the electrical resistivity is 1 × 10⁻⁶. 6 Examples of insulating particles with a density of Ω·m or greater include glass particles, polyester particles, polyamide particles, and rubber particles.

[0083] <Regarding the fiber-reinforced resin layer 40> Next, the fiber-reinforced resin layer 40 of the steel plate-fiber-reinforced resin composite 1 according to this embodiment will be described in detail.

[0084] The fiber-reinforced resin layer 40 according to this embodiment is a layer located on at least a portion of the surface of the second adhesive layer 30, as schematically shown in Figures 1A to 1D. This fiber-reinforced resin layer 40 is composed of a fiber-reinforced resin containing reinforcing fibers in the matrix resin.

[0085] As the matrix resin described above, various known thermoplastic resins and thermosetting resins can be used, but it is preferable to use a resin mainly composed of phenoxy resin, and more preferable to use a resin mainly composed of phenoxy resin having a bisphenol A skeleton. Here, "main component" means a component that is present in 50 parts by mass or more of 100 parts by mass of the total resin components. Note that "resin components" include thermoplastic resins and thermosetting resins, but do not include non-resin components such as crosslinking agents.

[0086] Furthermore, various known reinforcing fibers can be used as the reinforcing fibers, such as glass-reinforced fibers, carbon-reinforced fibers, and resin-reinforced fibers using high-strength resins such as aramid fibers. In this case, it is more preferable to use glass-reinforced fibers or carbon-reinforced fibers as the reinforcing fibers.

[0087] These matrix resins and carbon-reinforced fibers will be described in more detail below.

[0088] The average thickness of the fiber-reinforced resin layer 40 according to this embodiment is preferably in the range of 0.1 to 3.0 mm. By setting the average thickness of the fiber-reinforced resin layer 40 within the above range, a good balance of processability and strength can be achieved for the steel plate-fiber-reinforced resin composite 1. The average thickness of the fiber-reinforced resin layer 40 is more preferably 0.2 mm or more, even more preferably 0.3 mm or more, and even more preferably 0.5 mm or more. On the other hand, the average thickness of the fiber-reinforced resin layer 40 is more preferably 2.8 mm or less, even more preferably 2.5 mm or less, and even more preferably 2.0 mm or less.

[0089] ≪About Matrix Resin≫ The matrix resin of the fiber-reinforced resin layer 40 according to this embodiment is the resin that constitutes the fiber-reinforced resin layer 40. The type of resin of such matrix resin is not particularly limited, and either a thermoplastic resin or a thermosetting resin can be used, but preferably a thermoplastic resin that has good flexural strength and excellent processability is used. For example, the resin component of the matrix resin contains 50 parts by mass or more, 60 parts by mass or more, 70 parts by mass or more, 80 parts by mass or more, or 90 parts by mass or more of thermoplastic resin per 100 parts by mass of the resin component. Alternatively, the matrix resin may contain only a thermoplastic resin.

[0090] The types of thermoplastic resins that can be used as the matrix resin are not particularly limited, but for example, one or more can be selected from phenoxy, polyolefins and their acid-modified products, polypropylene, polystyrene, polymethyl methacrylate, AS resin, ABS resin, thermoplastic aromatic polyesters such as polyethylene terephthalate and polybutylene terephthalate, polycarbonate, polyimide, polyamide, polyamide-imide, polyetherimide, polyethersulfone, polyphenylene ether and its modified products, polyphenylene sulfide, polyoxymethylene, polyarylate, polyether ketone, polyether ether ketone, polyether ketone ketone, and nylon.

[0091] As the thermoplastic resin used for the matrix resin, it is more preferable to use phenoxy resin, which has a molecular structure very similar to epoxy resin, as described above. Due to the similarity of its molecular structure to epoxy resin, phenoxy resin has heat resistance comparable to epoxy resin. Therefore, by using phenoxy resin as the matrix resin, it is possible to achieve both heat resistance and processability in the steel plate-fiber-reinforced resin composite 1. Furthermore, as described above, since phenoxy resin is used in the first adhesive layer 20, by appropriately setting the resin components of the second adhesive layer 30 and using phenoxy resin as the matrix resin of the fiber-reinforced resin layer 40, it is possible to further improve the adhesion between the first adhesive layer 20 and the fiber-reinforced resin layer 40.

[0092] Furthermore, it is possible to create a crosslinkable resin composition (i.e., a cured resin composition) by incorporating a crosslinking agent such as an acid anhydride, isocyanate, or caprolactam into a resin composition containing phenoxy resin. Since the heat resistance of the crosslinkable resin composition is improved by utilizing the secondary hydroxyl groups contained in the phenoxy resin in the crosslinking reaction, it is advantageous for application to components used in higher-temperature environments.

[0093] Furthermore, the resin composition for forming the matrix resin (including the crosslinkable resin composition) may contain, to the extent that it does not impair its adhesiveness or physical properties, other additives such as natural rubber, synthetic rubber, elastomers, various inorganic fillers, solvents, extender pigments, colorants, antioxidants, UV inhibitors, flame retardants, flame retardant aids, etc.

[0094] ≪About carbon-reinforced fibers≫ The fiber-reinforced resin layer 40 according to this embodiment contains reinforcing fibers, and as described above, it is preferable to use carbon-reinforced fibers as such reinforcing fibers. The presence of carbon-reinforced fibers improves the strength compared to a resin layer consisting only of matrix resin. The carbon-reinforced fibers according to this embodiment are not particularly limited, and pitch-based carbon-reinforced fibers or PAN-based carbon-reinforced fibers can be used. The carbon-reinforced fibers may consist of only one type of carbon-reinforced fiber, or two or more types of carbon-reinforced fibers.

[0095] The carbon-reinforced fiber content (fiber volume content Vf) of the fiber-reinforced resin layer 40 is not particularly limited, but from the viewpoint of sufficiently reinforcing the fiber-reinforced resin layer 40 and ensuring processability, it is preferably 10% by volume or more and 70% by volume or less. If the carbon-reinforced fiber content is less than 10% by volume, the fiber-reinforced resin layer 40 may not be sufficiently reinforced. On the other hand, if the carbon-reinforced fiber content exceeds 70% by volume, it is undesirable from a cost perspective, and furthermore, it may become difficult to impregnate the fiber-reinforced resin layer 40 with carbon-reinforced fibers. The carbon-reinforced fiber content in the fiber-reinforced resin layer 40 is preferably 15% by volume or more, 20% by volume or more, or 30% by volume or more, and also 65% by volume or less, 60% by volume or less, or 55% by volume or less.

[0096] The measurement method of the content Vf (volume %) of carbon reinforcing fibers in the fiber reinforced resin layer 40 can be carried out as follows. More specifically, using a knife or a cutting machine, etc., the fiber reinforced resin layer 40 is peeled off from the steel plate-fiber reinforced resin composite 1 to obtain a test piece for measuring the content of carbon reinforcing fibers. Measure the absolute dry mass (W3) of the test piece (the peeled fiber reinforced resin layer 40). Next, immerse the test piece in 20% hydrochloric acid to dissolve the matrix resin, and measure the absolute dry mass (W4) of the carbon reinforcing fibers obtained as a residue. After measurement, the content Wf (mass %) of carbon reinforcing fibers based on mass = (W4 / W3)×100 is obtained, and the density ρ3 (g / cm 3 ) of the test piece and the density ρ4 (g / cm 3 ) of the carbon reinforcing fibers are used to calculate the content Vf (volume %) of carbon reinforcing fibers in the fiber reinforced resin layer 40 = Wf×(ρ3 / ρ4).

[0097] As described above, the fiber reinforced resin layer 40 included in the steel plate-fiber reinforced resin composite 1 according to the present embodiment has been described in detail.

[0098] As described above, the steel plate-fiber reinforced resin composite 1 according to the present embodiment is lightweight, not only excellent in shear peel strength and vertical peel strength, but also has excellent corrosion resistance. In addition, the steel plate-fiber reinforced resin composite 1 according to the present embodiment is also excellent in workability, so it can be used for various applications. Such a steel plate-fiber reinforced resin composite 1 is particularly preferably used for automotive members.

[0099] (Regarding the manufacturing method of the metal-fiber reinforced resin composite) Hereinafter, the manufacturing method of the steel plate-fiber reinforced resin composite according to the present embodiment will be described in detail with reference to FIGS. 5A to 5C. FIGS. 5A to 5C are flowcharts showing an example of the flow of the manufacturing method of the steel plate-fiber reinforced resin composite according to the present embodiment.

[0100] Hereinafter, paying attention to the steel plate-fiber reinforced resin composite having the structure shown in FIGS. 1A to 1D, its manufacturing method will be described. In such a manufacturing method, first, preparation of a steel plate member, a first adhesive layer, a second adhesive layer, and a fiber reinforced resin layer is carried out.

[0101] <Preparation of E plate components> The steel sheet material used for steel sheet components typically contains C, Si, Mn, P, S, Al, and N, with the remainder being Fe and impurities. Alternatively, some of the remaining Fe may be replaced with other elements. Preferably, a slab having the desired composition is hot-rolled, pickled, and then cold-rolled to obtain a cold-rolled steel sheet. If necessary, the obtained cold-rolled steel sheet may be heat-treated (annealing, quenching, etc.) under any atmosphere to obtain the desired structure. When a zinc-based plating layer is to be applied to the surface, the zinc-based plating can be formed by known methods, with the plating adhesion amount ranging from 5 to 90 g / m² depending on the application. 2 You can select from the options as appropriate. The thickness of the steel plate component can also be selected as appropriate; for example, 0.1 to 3.5 mm is acceptable.

[0102] Prior to the subsequent heat-compression bonding process, it is preferable to degrease the surface of the steel plate member with an alkaline degreasing agent or the like as a pretreatment to improve the adhesion between the steel plate and the resin film. Alternatively, as an additional pretreatment, an aqueous solution containing water-dispersed silica may be applied to the steel plate member using a bar coater or the like, and then dried in a hot air oven at a plate temperature of approximately 120-180°C.

[0103] <Preparation of the resin sheet for the first adhesive layer> A resin composition for the first adhesive layer is prepared by mixing a phenoxy resin, a polyester elastomer, and optional components, including a non-conductive substance, as needed. In this process, the desired resin composition is achieved by appropriately selecting and controlling various conditions related to the preparation of the resin composition (such as the mixing ratio of raw materials). The phenoxy resin is a resin containing hydroxyl groups and in which repeating units are formed by ether groups. The polyester elastomer is a thermoplastic polyester block copolymer containing hard segments (crystalline phase) containing polyester units and soft segments (amorphous phase) containing polyether and / or polyester units as constituent units. There are no particular restrictions on the method of mixing the phenoxy resin, polyester elastomer, and other components; generally known methods can be used.

[0104] For example, one method involves dissolving and mixing the phenoxy resin and polyester elastomer in a mixer-type stirrer at a temperature range of 15 to 40°C using an organic solvent that is a good solvent for the phenoxy resin and polyester elastomer to form a varnish. Another method involves melting and kneading the materials at a temperature at which both the phenoxy resin and polyester elastomer melt, preferably at the higher of the glass transition temperature of the phenoxy resin or the melting point of the polyester elastomer, plus approximately 20°C. If the kneading temperature is too high, there is a concern that the performance will deteriorate due to thermal degradation or decomposition of the resin. If the temperature is such that neither the phenoxy resin nor the polyester elastomer melts, the mixing of the two will be uneven, and the desired resin properties cannot be obtained. When melting and kneading, it is preferable to use a twin-screw extruder as the kneading device. A twin-screw extruder is a screw extruder with screws that rotate in the same direction. The screws may be a full-flight screw with an elliptical two-bladed screw shape or a kneading disc, which may be used individually or in combination as appropriate.

[0105] A resin sheet for the first adhesive layer is prepared by processing the resin composition obtained by the above method into a sheet. There are no particular restrictions on the method of sheet formation, and generally known methods can be used. Examples of such methods include melt extrusion molding, solution casting molding, and calendering. Among these, the method of forming a sheet from a resin composition melted and kneaded in a twin-screw extruder by melt extrusion molding is preferable from the standpoint of environmental impact because it does not contain organic solvents and does not require a separate drying process.

[0106] <Preparation of the resin sheet for the second adhesive layer> A resin composition for the second adhesive layer is prepared by mixing a resin having a tensile modulus of 500 MPa or more at 25°C, and optional components such as non-conductive substances as needed.

[0107] Such preparations can be carried out, for example, by using an organic solvent that is a good solvent for the resin to be used, dissolving and mixing it in a mixer-type stirrer at a temperature range of 15 to 40°C to form a varnish, or by melting and kneading it at a temperature at which the resin melts, preferably at a temperature of about the melting point of the resin + 20°C. When melting and kneading, it is preferable to use a twin-screw extruder as the kneading apparatus.

[0108] A resin sheet for the second adhesive layer is prepared by processing the resin composition obtained by the above method into a sheet. There are no particular restrictions on the method of sheet formation, and generally known methods can be used. Examples of such methods include melt extrusion molding, solution casting molding, and calendering. Among these, the method of forming a sheet from a resin composition melted and kneaded in a twin-screw extruder by melt extrusion molding is preferable from the standpoint of environmental impact because it does not contain organic solvents and does not require a separate drying process.

[0109] Furthermore, when forming a resin layer 50 as shown in Figure 4, the resin composition to be formed can be prepared by mixing the resin to be used with a non-conductive substance in the same manner as described above.

[0110] <Preparation of the fiber-reinforced resin layer> A predetermined binder resin for the fiber-reinforced resin layer (e.g., phenoxy resin) is heated above its glass transition temperature to form a resin sheet, for example, with a thickness of about 10 to 150 μm. These resin sheets and reinforcing fiber substrates (e.g., carbon-reinforced fiber substrates) are alternately laminated to form a laminate, and the resulting laminate is heated and pressurized above the glass transition temperature of the resin to heat-seal the resin, thereby producing a material for the fiber-reinforced resin layer. Alternatively, the predetermined binder resin may be pulverized, and the classified powder may be powder-coated onto the reinforcing fiber substrate under predetermined conditions in an electrostatic field. The powder-coated reinforcing fiber substrates are then laminated and heat-sealed. The thickness of the resin sheet, the thickness of the reinforcing fiber substrate, or the number of layers can be changed depending on the desired average thickness and reinforcing fiber content of the fiber-reinforced resin layer. The heating and pressurizing conditions can also be set appropriately; for example, heating and pressurizing at a temperature of 180 to 240°C and a pressure of 1 to 5 MPa for 1 to 30 minutes is sufficient.

[0111] <Formation of steel plate-fiber-reinforced resin composite> Using the steel plate members prepared as described above, the resin sheet for the first adhesive layer, the material for the second adhesive layer, and the fiber-reinforced resin layer, a steel plate-fiber-reinforced resin composite is formed using one of the methods shown in Figures 5A to 5C.

[0112] For example, in the example shown in Figure 5A, the first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer (more specifically, the resin sheet for the first adhesive layer, the resin sheet for the second adhesive layer, and the material for the fiber-reinforced resin layer) are superimposed on the surface of the steel plate member prepared as described above (step S101), and then the first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer are heat-pressed onto the steel plate (step S103).

[0113] In the example shown in Figure 5B, first, the steel plate prepared as described above is press-molded to form a steel plate molded body having the desired shape (step S111). The steel plate molded body obtained in this way functions as a steel plate member. Subsequently, the first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer (more specifically, the resin sheet for the first adhesive layer, the resin sheet for the second adhesive layer, and the material for the fiber-reinforced resin layer) are layered on the surface of the steel plate molded body (step S113), and then the first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer are heat-pressed onto the steel plate molded body (step S115).

[0114] Furthermore, in the example shown in Figure 5C, first, the first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer (more specifically, the resin sheet for the first adhesive layer, the resin sheet for the second adhesive layer, and the material for the fiber-reinforced resin layer) are layered on the surface of the steel plate prepared as described above to form a laminate (step S121). Then, using a press molding machine with a heated mold, the laminate is processed into the desired shape while the first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer are heat-pressed together (step S123). In other words, in the example shown in Figure 5C, the so-called hot pressing method (also called the hot stamping method) is used to process the laminate into the desired shape and to heat-press the first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer together. This method makes it possible to simultaneously perform the molding process of the steel plate and the heat-pressing process of the first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer, thus making it possible to form a steel plate-fiber-reinforced resin composite very easily.

[0115] By this method, it is possible to form the steel plate-fiber-reinforced resin composite according to this embodiment.

[0116] The heat-sealing conditions can also be set as appropriate; for example, heating and pressurizing at a temperature of 200-300°C and a pressure of 1-5 MPa for 1-30 minutes is sufficient.

[0117] The method for manufacturing the steel plate-fiber-reinforced resin composite according to this embodiment has been described in detail above. [Examples]

[0118] The steel plate-fiber-reinforced resin composite according to the present invention will be described in detail below with reference to examples and comparative examples. Note that the following examples are merely examples of the steel plate-fiber-reinforced resin composite according to the present invention, and the steel plate-fiber-reinforced resin composite according to the present invention is not limited to the examples below.

[0119] Regarding the preparation of the steel plate component 10: [Creation of cold-rolled steel sheets] A slab consisting of the chemical components shown in Table 1 below (the remainder being Fe and impurities) was hot-rolled and pickled, then cold-rolled to obtain a cold-rolled steel sheet with a thickness of 1.4 mm. Next, the prepared cold-rolled steel sheet was annealed in a continuous annealing apparatus under conditions that resulted in a maximum plate temperature of 820°C. The gas atmosphere in the annealing furnace during the annealing process was an N2 atmosphere containing 1.0 volume% H2. The cold-rolled steel sheet that underwent the annealing process will be referred to as "CR" below.

[0120] [Table 1]

[0121] Furthermore, JIS No. 5 test specimens were cut from cold-rolled steel sheets made using the above steel grades A to C, perpendicular to the rolling direction, and their strength was measured by tensile tests at room temperature. As noted in the remarks in Table 1, steel grade A had a tensile strength of 980 MPa or more and less than 1180 MPa, so its material was defined as "980 class". Steel grade B had a tensile strength of 440 MPa or more and less than 590 MPa, so it was defined as "440 class". Steel grade C had a tensile strength of 270 MPa or more and less than 440 MPa, so it was defined as "270 class".

[0122] Furthermore, for steel grades A and B in Table 1, cold-rolled steel sheets with a thickness of 1.4 mm were prepared by annealing them in a continuous hot-dip galvanizing apparatus with an annealing process, under conditions where the maximum plate temperature reached in the annealing process was 820°C, and then hot-dip galvanizing in the plating process. The gas atmosphere in the annealing furnace during the annealing process was an N2 atmosphere containing 1.0 volume% H2.

[0123] Three types of plated steel sheets were used as the components of the plating bath in the plating process: Zn-0.2%Al (hereinafter referred to as "GI"), Zn-0.09%Al (hereinafter referred to as "GA"), and Zn-1.5%Al-1.5%Mg (hereinafter referred to as "Zn-Al-Mg"). In the case of using a molten plating bath with Zn-0.09%Al plating (GA), the steel sheet was immersed in the molten plating bath, and while withdrawing the steel sheet from the plating bath, N2 gas was blown from a slit nozzle and gas wiping was performed to adjust the amount of coating. Then, the sheet was heated to a temperature of 480°C using an induction heater to alloy it and diffuse the Fe in the steel sheet into the plating layer.

[0124] For the amount of plating deposited on one side of a plated steel sheet, GA is 45 g / m². 2 For plating other than GA, the rate is 60g / m². 2 That's what I decided.

[0125] Furthermore, JIS No. 5 test specimens were cut from various plated steel sheets made using the above-mentioned steel grades A and B, perpendicular to the rolling direction, and tensile tests were performed at room temperature to measure their strength. As a result, for all types of plating, as noted in the remarks in Table 1, plated steel sheets derived from steel grade A had a tensile strength of 980 MPa or more and less than 1180 MPa, and were therefore defined as "980 class." Plated steel sheets derived from steel grade B had a tensile strength of 440 MPa or more and less than 590 MPa, and were therefore defined as "440 class."

[0126] Furthermore, for steel sheet C mentioned above, the obtained cold-rolled steel sheet was subjected to hot press heating using a furnace heating method, followed by hot pressing. During furnace heating, the furnace atmosphere was set to 910°C and the air-heat ratio to 1.1. After the steel sheet temperature reached 900°C, the steel sheet was quickly removed from the furnace. After hot pressing, the steel sheet was cooled to 650°C. After cooling, the steel sheet was sandwiched using a flat die equipped with a water-cooling jacket and hot pressed to produce a hot-pressed molded body. Even in areas where the cooling rate was slow during hot pressing, the sheet was cooled to approximately 360°C, the starting point of martensitic transformation, at a cooling rate of 50°C / second or more, and then quenched. Finally, the scale of the hot-pressed molded body was removed by shot blasting.

[0127] A hot-pressed body made using steel plate C in this manner will be referred to as "HS" below. Since the tensile strength of such a hot-pressed body, measured in a JIS No. 5 test specimen, was 1500 MPa or higher, its material was defined as "1500 class".

[0128] [Method for evaluating the resin composition constituting the first adhesive layer] (Glass transition temperature) The measurements were performed in accordance with JIS K7121:2012 (Method for measuring transition temperatures of plastics). If two transition temperatures were measured, the lower value was adopted as the glass transition temperature.

[0129] (Tensile modulus, tensile elongation at fracture) Measurements were performed in accordance with JIS K6251:2017 (Vulcanized rubber and thermoplastic rubber - Method for determining tensile properties). A dumbbell-shaped No. 5 specimen was used. However, the tensile modulus was determined in accordance with JIS K7161 (Plastics - Method for determining tensile properties). Each measurement was performed at 25°C using an AND Corporation Tensilon universal tester RTF-2410, and the physical properties of phenoxy resin alone (Comparative Example 1) were measured in accordance with JIS K7161.

[0130] (Observation of elastic modulus phase image using AFM) After smoothing the cross-section (approximately 3 mm in diameter) of the resin pellet using a cryomicrotome (-40°C), an arbitrary 10 μm × 10 μm area was scanned in tapping mode using a Bruker-AXS Dimension Icon AFM equipped with a Bruker-AXS NCHV probe (tip radius of curvature 10 nm, spring constant 42 N / m) in a 25°C atmosphere.

[0131] Furthermore, when observing the elastic modulus phase image, observations were performed on 10 arbitrary fields of view for each resin pellet sampled at a stage when the manufacturing conditions were stable, using 10 separate resin pellets, and the area ratio of spots or striped patterns (phase separation structure) caused by phenoxy resin and polyester elastomer was calculated.

[0132] <Method for preparing the resin composition constituting the first adhesive layer> [Resin composition 1] Pellets of phenoxy resin having a bisphenol A skeleton (product name: Phenotot YP50S, manufactured by Nippon Steel Chemical & Material Co., Ltd.) and pellets of polyester elastomer (product name: Hytrel BD406, manufactured by Toray DuPont Co., Ltd.) were weighed in a mass ratio of 80 / 20 using an electronic balance and mixed for 15 minutes at a rotation of 30 rpm and oscillation of 30 rpm using a rocking mixer (manufactured by Aichi Electric Co., Ltd., RM-10(S)). The mixed pellets were put into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (manufactured by Toshiba Machine Co., Ltd., TEM26SS, L / D approx. 50, cylinder setting temperature 200℃, rotation speed 220 rpm), and melt-kneaded under operating conditions of a discharge rate of 12 kg / h to obtain resin composition 1. The evaluation results of the obtained resin composition 1 are shown in Table 2 below.

[0133] In addition, in the "AFM Elastic Modulus Phase Image" column (sometimes abbreviated as "AFM") in Table 2 below, a score of "OK" indicates that the area ratio of the phase separation structure was 1 area % or less, or not observed at all, while a score of "NG" indicates that the area ratio of the phase separation structure was greater than 1 area %.

[0134] [Resin composition 2] Pellets of phenoxy resin having a bisphenol A skeleton (product name: Phenotot YP50S, manufactured by Nippon Steel Chemical & Material Co., Ltd.) and pellets of polyester elastomer (product name: Hytrel BD406, manufactured by Toray DuPont Co., Ltd.) were weighed in a mass ratio of 67 / 33 using an electronic balance and mixed for 15 minutes at a rotation of 30 rpm and oscillation of 30 rpm using a rocking mixer (manufactured by Aichi Electric Co., Ltd., RM-10(S)). The mixed pellets were fed into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (manufactured by Toshiba Machine Co., Ltd., TEM26SS, L / D approx. 50, cylinder setting temperature 220°C, rotation speed 220 rpm), and melt-kneaded under operating conditions of discharge rate 12 kg / h to obtain resin composition 2. The evaluation results of the obtained resin composition 2 are shown in Table 2 below, and the observation results of the elastic modulus phase image by AFM are shown in Figure 6A.

[0135] [Resin composition 3] Pellets of phenoxy resin having a bisphenol A skeleton (product name: Phenotot YP50S, manufactured by Nippon Steel Chemical & Material Co., Ltd.) and pellets of polyester elastomer (product name: Hytrel BD406, manufactured by Toray DuPont Co., Ltd.) were weighed in a mass ratio of 60 / 40 using an electronic balance and mixed for 15 minutes at a rotation of 30 rpm and oscillation of 30 rpm using a rocking mixer (manufactured by Aichi Electric Co., Ltd., RM-10(S)). The mixed pellets were put into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (manufactured by Toshiba Machine Co., Ltd., TEM26SS, L / D approx. 50, cylinder setting temperature 200℃, rotation speed 220 rpm), and melt-kneaded under operating conditions of discharge rate 12 kg / h to obtain resin composition 3. The evaluation results of the obtained resin composition 3 are shown in Table 2 below.

[0136] [Resin composition 4] Pellets of phenoxy resin having a bisphenol A skeleton (product name: Phenotot YP50S, manufactured by Nippon Steel Chemical & Material Co., Ltd.) and pellets of polyester elastomer (product name: Hytrel BD406, manufactured by Toray DuPont Co., Ltd.) were weighed in a mass ratio of 40 / 60 using an electronic balance and mixed for 15 minutes at a rotation of 30 rpm and oscillation of 30 rpm using a rocking mixer (manufactured by Aichi Electric Co., Ltd., RM-10(S)). The mixed pellets were put into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (manufactured by Toshiba Machine Co., Ltd., TEM26SS, L / D approx. 50, cylinder setting temperature 200℃, rotation speed 220 rpm), and melt-kneaded under operating conditions of discharge rate 12 kg / h to obtain resin composition 4. The evaluation results of the obtained resin composition 4 are shown in Table 2 below.

[0137] [Resin composition 5] Pellets of phenoxy resin having a bisphenol A skeleton (product name: Phenotot YP50S, manufactured by Nippon Steel Chemical & Material Co., Ltd.) and pellets of polyester elastomer (product name: Hytrel BD406, manufactured by Toray DuPont Co., Ltd.) were weighed out in a mass ratio of 33 / 67 using an electronic balance, and mixed for 15 minutes at a rotation of 30 rpm and oscillation of 30 rpm using a rocking mixer (manufactured by Aichi Electric Co., Ltd., RM-10(S)). The mixed pellets were put into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (manufactured by Toshiba Machine Co., Ltd., TEM26SS, L / D approx. 50, cylinder setting temperature 200℃, rotation speed 220 rpm), and melt-kneaded under operating conditions of discharge rate 12 kg / h to obtain resin composition 5. The evaluation results of the obtained resin composition 5 are shown in Table 2 below.

[0138] In some cases, various non-conductive substances were further mixed with the above-mentioned resin to prepare a resin composition 5 containing non-conductive substances. The non-conductive substances used are as follows:

[0139] • Electrical resistivity is 1 × 10⁻⁶ 6 Insulating particles with a mass of Ω·m or greater (in Table 3 below, "1 × 10⁻¹⁰") 6 This is abbreviated as "the above particles." Micropearl GS-L200, manufactured by Sekisui Chemical Co., Ltd. • Electrical resistivity is 1 × 10⁻⁶ 6 Insulating particles with a diameter less than Ω·m (in Table 3 below, "1 × 10⁻¹⁰") 6 Abbreviated as "less than particles". ): Ishihara Sangyo Co., Ltd. Typeque CR-95 • Glass particles: Unibeads SPL-200 manufactured by Unitika Ltd. • Glass fiber: Manufactured by Nitto Boseki Co., Ltd., Glass cloth WEA7628 127 S236 FE • Aramid fiber: Manufactured by Nitto Boseki Co., Ltd., Aramid Cloth K281

[0140] [Resin composition 6] Pellets of phenoxy resin having a bisphenol A skeleton (product name: Phenotot YP50S, manufactured by Nippon Steel Chemical & Material Co., Ltd.) and pellets of polyester elastomer (product name: Hytrel BD406, manufactured by Toray DuPont Co., Ltd.) were weighed in a mass ratio of 20 / 80 using an electronic balance and mixed for 15 minutes at a rotation of 30 rpm and oscillation of 30 rpm using a rocking mixer (manufactured by Aichi Electric Co., Ltd., RM-10(S)). The mixed pellets were fed into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (manufactured by Toshiba Machine Co., Ltd., TEM26SS, L / D approx. 50, cylinder setting temperature 200℃, rotation speed 220 rpm), and melt-kneaded under operating conditions of a discharge rate of 12 kg / h to obtain resin composition 6. The evaluation results of the obtained resin composition 6 are shown in Table 2 below.

[0141] [Resin composition 7] Pellets of phenoxy resin having a bisphenol A skeleton (product name: Phenotot YP50S, manufactured by Nippon Steel Chemical & Material Co., Ltd.), pellets of polyester elastomer (product name: Hytrel BD406, manufactured by Toray DuPont Co., Ltd.), a phenolic antioxidant (product name: Adeka Stab AO-80, manufactured by ADEKA Corporation), and a phosphite antioxidant (product name: Adeka Stab PEP-36, manufactured by ADEKA Corporation) were weighed out in a mass ratio of 33 / 67 / 0.1 / 0.1 using an electronic balance, and mixed for 15 minutes at a rotation of 30 rpm and oscillation of 30 rpm using a rocking mixer (manufactured by Aichi Electric Co., Ltd., RM-10(S)). The mixed pellets were fed into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (Toshiba Machine Co., Ltd. TEM26SS, L / D approximately 50, cylinder setting temperature 200°C, rotation speed 220 rpm), and melt-kneaded under operating conditions of a discharge rate of 12 kg / h to obtain resin composition 7. The evaluation results of the obtained resin composition 7 are shown in Table 2 below.

[0142] [Resin composition 8] Resin composition 8 was obtained in the same manner as resin composition 1, except that 100 parts by mass of phenoxy resin (product name: Phenotot YP50S, manufactured by Nippon Steel Chemical & Material Co., Ltd.) was used and polyester elastomer was not included. The evaluation results of the obtained resin composition 8 are shown in Table 2 below.

[0143] [Resin composition 9] Resin composition 9 was obtained in the same manner as in Resin Example 1, except that 100 parts by mass of polyester elastomer (product name: Hytrel BD406, manufactured by Toray DuPont Co., Ltd.) was used and phenoxy resin was not added. The evaluation results of the obtained resin composition 9 are shown in Table 2 below, and the observation results of the elastic modulus phase image by AFM are shown in Figure 6B.

[0144] [Resin composition 10] Pellets of phenoxy resin having a bisphenol A skeleton (product name: Phenotot YP50S, manufactured by Nippon Steel Chemical & Material Co., Ltd.) and pellets of polyethylene terephthalate (product name: NEH-2070, manufactured by Unitika Ltd.) were weighed in a 50 / 50 mass ratio using an electronic balance and mixed for 15 minutes at a rotation of 30 rpm and oscillation of 30 rpm using a rocking mixer (manufactured by Aichi Electric Co., Ltd., RM-10(S)). The mixed pellets were fed into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (manufactured by Toshiba Machine Co., Ltd., TEM26SS, L / D approximately 50, cylinder setting temperature 280°C, rotation speed 220 rpm), and melt-kneaded under operating conditions of a discharge rate of 12 kg / h to obtain resin composition 10. The evaluation results of the obtained resin composition 10 are shown in Table 2 below, and the observation results of the elastic modulus phase image by AFM are shown in Figure 6C.

[0145] [Table 2]

[0146] Figure 6B shows that the polyester elastomer BD406 used in the above resin composition contains components other than polyester elastomer, which are presumed to be additives. Figure 6A, which shows a mixture of approximately 30% polyester elastomer BD406 and approximately 70% phenoxy resin YP50S, shows that despite the addition of a large amount of phenoxy resin, it exhibits almost the same appearance as Figure 6B, which is polyester elastomer alone, indicating that no phase separation structure attributable to either component is observed. The white spots in Figures 6A and 6B are presumed to be the additive components mentioned above. In addition, although large vertical stripes are slightly observed in Figure 6A, these stripes are patterns created when the sample was scraped and are not due to a phase separation structure.

[0147] Figure 6C shows an example where polyethylene terephthalate, which is a polyester-based resin, is mixed with phenoxy resin instead of polyester elastomer. It can be seen that even though they are both polyester-based resins, polyethylene terephthalate, which does not contain soft segments (amorphous phase) containing polyether and / or polyester units in its constituent units, has low compatibility with phenoxy resin and undergoes phase separation.

[0148] <Method for producing a resin sheet that will serve as the first adhesive layer> [Resin composition 1] A resin sheet with a thickness of 0.05 to 0.10 mm was prepared using the above resin composition 1 with a 37t automatic press. Molding conditions: Pressed at 200°C and 1 MPa for 3 minutes, followed by degassing three times, and then pressed again at 200°C and 8 MPa for 5 minutes, and cooled to 60°C while under pressure.

[0149] [Resin composition 2] A resin sheet with a thickness of 0.05 to 0.10 mm was prepared using the above resin composition 2 with a 37t automatic press. Molding conditions: Pressed at 200°C and 1 MPa for 3 minutes, followed by degassing three times, and then pressed again at 200°C and 8 MPa for 5 minutes, and cooled to 60°C while under pressure.

[0150] [Resin composition 3] A resin sheet with a thickness of 0.05 to 0.10 mm was prepared using the above resin composition 3 with a 37t automatic press. Molding conditions: Pressed at 200°C and 1 MPa for 3 minutes, followed by degassing three times, and then pressed again at 200°C and 8 MPa for 5 minutes, and cooled to 60°C while under pressure.

[0151] [Resin composition 4] A resin sheet with a thickness of 0.05 to 0.10 mm was prepared using the above resin composition 4 with a 37t automatic press. Molding conditions: Pressed at 200°C and 1 MPa for 3 minutes, followed by degassing three times, and then pressed again at 200°C and 8 MPa for 5 minutes, and cooled to 60°C while under pressure.

[0152] [Resin composition 5] A resin sheet with a thickness of 0.02 to 0.50 mm was prepared using the above resin composition 5 with a 37t automatic press. Molding conditions: Pressed at 200°C and 1 MPa for 3 minutes, followed by degassing three times, and then pressed again at 200°C and 8 MPa for 5 minutes, and cooled to 60°C while under pressure.

[0153] [Resin composition 6] A resin sheet with a thickness of 0.05 to 0.10 mm was prepared using a 37t automatic press machine. Molding conditions: Pressed at 200°C and 1 MPa for 3 minutes, followed by degassing three times. Then, pressed again at 200°C and 8 MPa for 5 minutes, and cooled to 60°C while under pressure.

[0154] [Resin composition 7] A 37t automatic press was used to create resin sheets with a thickness of 0.05 to 0.10 mm made from the above resin composition 7. The molding conditions were: press at 200°C and 1 MPa for 3 minutes, followed by degassing three times, and then press again at 200°C and 8 MPa for 5 minutes, after which the sheet was cooled to 60°C while under pressure.

[0155] [Resin composition 8] A resin sheet with a thickness of 0.05 to 0.10 mm was prepared using the above resin composition 8 with a 37t automatic press. Molding conditions: Pressed at 200°C and 1 MPa for 3 minutes, followed by degassing three times. Then, pressed again at 200°C and 8 MPa for 5 minutes, and cooled to 60°C while under pressure.

[0156] [Resin composition 9] A resin sheet with a thickness of 0.05 to 0.10 mm was prepared using the above resin composition 9 with a 37t automatic press. Molding conditions: Pressed at 200°C and 1 MPa for 3 minutes, followed by degassing three times. Then, pressed again at 200°C and 8 MPa for 5 minutes, and cooled to 60°C while under pressure.

[0157] [Resin composition 10] A resin sheet with a thickness of 0.05 to 0.10 mm was prepared using the above resin composition 10 with a 37t automatic press. Molding conditions: Pressed at 280°C and 1 MPa for 3 minutes, followed by degassing three times. Then, under molding conditions: Pressed at 200°C and 8 MPa for 5 minutes, and cooled to 60°C while under pressure.

[0158] <Method for preparing the resin composition constituting the second adhesive layer> [Resin composition A] 100 parts by mass of phenoxy resin (product name: Phenotot YP50S, manufactured by Nippon Steel Chemical & Material Co., Ltd.) was used. These pellets were fed into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (Toshiba Machine Co., Ltd. TEM26SS, L / D approximately 50, cylinder setting temperature 200°C, rotation speed 220 rpm), and melt-kneaded under operating conditions of a discharge rate of 12 kg / h to obtain resin composition A. The tensile modulus of the obtained resin composition A was measured in the same manner as for the resin composition that would become the first adhesive layer, and the results are shown in Table 3 below.

[0159] [Resin composition B] Pellets of phenoxy resin having a bisphenol A skeleton (product name: Phenotot YP50S, manufactured by Nippon Steel Chemical & Material Co., Ltd.) and pellets of polyester elastomer (product name: Hytrel BD406, manufactured by Toray DuPont Co., Ltd.) were weighed in a mass ratio of 60 / 40 using an electronic balance and mixed for 15 minutes at a rotation of 30 rpm and oscillation of 30 rpm using a rocking mixer (manufactured by Aichi Electric Co., Ltd., RM-10(S)). The mixed pellets were fed into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (manufactured by Toshiba Machine Co., Ltd., TEM26SS, L / D approx. 50, cylinder setting temperature 200℃, rotation speed 220 rpm), and melt-kneaded under operating conditions of a discharge rate of 12 kg / h to obtain resin composition B. The measurement results of the tensile modulus of the obtained resin composition B are shown in Table 3 below.

[0160] [Resin composition C] Pellets of phenoxy resin having a bisphenol A skeleton (product name: Phenotot YP50S, manufactured by Nippon Steel Chemical & Material Co., Ltd.) and pellets of copolymerized polyamide (product name: Grillon C CR9, manufactured by M-Scheme Japan Co., Ltd.) were weighed in a mass ratio of 40 / 60 using an electronic balance and mixed for 15 minutes at a rotation of 30 rpm and oscillation of 30 rpm using a rocking mixer (manufactured by Aichi Electric Co., Ltd., RM-10(S)). The mixed pellets were fed into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (manufactured by Toshiba Machine Co., Ltd., TEM26SS, L / D approx. 50, cylinder setting temperature 200℃, rotation speed 220 rpm), and melt-kneaded under operating conditions of a discharge rate of 12 kg / h to obtain resin composition C. The measurement results of the tensile modulus of the obtained resin composition C are shown in Table 3 below.

[0161] [Resin composition D] 100 parts by mass of copolymerized polyamide (product name: Grillon C CR9, manufactured by M-Scheme Japan Co., Ltd.) was used. These pellets were fed into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (Toshiba Machine Co., Ltd. TEM26SS, L / D approximately 50, cylinder setting temperature 200°C, rotation speed 220 rpm), and melt-kneaded under operating conditions of a discharge rate of 12 kg / h to obtain resin composition D. The tensile modulus of the obtained resin composition D was measured in the same manner as for the resin composition that would become the first adhesive layer, and the results are shown in Table 3 below.

[0162] [Resin composition E] Pellets of polyester elastomer (product name: Hytrel BD406, manufactured by Toray DuPont Co., Ltd.) and pellets of copolymerized polyamide (product name: Grillon C CR9, manufactured by M-Scheme Japan Co., Ltd.) were weighed in a mass ratio of 40 / 60 using an electronic balance and mixed for 15 minutes at a rotation of 30 rpm and oscillation of 30 rpm using a rocking mixer (manufactured by Aichi Electric Co., Ltd., RM-10(S)). The mixed pellets were fed into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (manufactured by Toshiba Machine Co., Ltd., TEM26SS, L / D approx. 50, cylinder setting temperature 200℃, rotation speed 220 rpm), and melt-kneaded under operating conditions of discharge rate 12 kg / h to obtain resin composition E. The measurement results of the tensile modulus of the obtained resin composition E are shown in Table 3 below.

[0163] [Resin composition F] 100 parts by mass of polyester elastomer (product name: Hytrel BD406, manufactured by Toray DuPont Co., Ltd.) was used. These pellets were fed into the hopper of a twin-screw extruder with a screw diameter of 26 mm and rotating in the same direction (Toshiba Machine Co., Ltd. TEM26SS, L / D approximately 50, cylinder setting temperature 200°C, rotation speed 220 rpm), and melt-kneaded under operating conditions of a discharge rate of 12 kg / h to obtain resin composition F. The tensile modulus of the obtained resin composition F was measured in the same manner as for the resin composition that would become the first adhesive layer, and the results are shown in Table 3 below.

[0164] In some cases, various non-conductive substances were further mixed with the resin to prepare a resin composition containing non-conductive substances. The non-conductive substances used were the same as those described above.

[0165] <Method for producing a resin sheet that will serve as the second adhesive layer> A 37t automatic press was used to create resin sheets with thicknesses ranging from 0.02 to 0.50 mm from each resin composition. The molding conditions were: 200°C, 1 MPa for 3 minutes, followed by degassing three times. Then, the sheets were pressed again at 200°C, 8 MPa for 5 minutes, and cooled to 60°C while under pressure.

[0166] [Table 3]

[0167] <Method for producing a resin sheet that will form the resin layer> Using the resin composition 8 shown in Table 2 above and the non-conductive substances described above, a resin sheet to be the resin layer was prepared in the same manner as the method for preparing the resin sheet to be the first adhesive layer.

[0168] Regarding the fabrication of fiber-reinforced resin layers: (Phenoxycarbon fiber reinforced polymer, gravity fiber reinforced polymer, aramid fiber reinforced polymer) The powder, obtained by crushing and classifying "Phenotote YP-50S," a bisphenol A type phenoxy resin manufactured by Nippon Steel Chemical & Material Co., Ltd., with an average particle size D50 of 80 μm, was powder coated onto a carbon fiber reinforced fiber substrate (SA-3203, manufactured by Sakai Obex Co., Ltd.), a glass fiber reinforced fiber substrate (Glass Cloth WEA7628 127 S236 FE, manufactured by Nitto Boseki Co., Ltd.), or an aramid fiber reinforced fiber substrate (Aramid Cloth K281, manufactured by Nitto Boseki Co., Ltd.) under conditions of a static charge of 70 kV and a spray air pressure of 0.32 MPa. Subsequently, the powder-coated reinforced fiber substrates were laminated, and this laminate was heat-fused with resin by pressing it in a press heated to 240°C at 3 MPa for 5 minutes, thereby producing phenoxy resin CFRP layer forming material, phenoxy resin GFRP layer forming material, and phenoxy resin AFRP layer forming material with a thickness of 1.0 mm or 1.6 mm and a Vf (fiber volume content) of 60%.

[0169] The average particle size of the pulverized and classified phenoxy resin was measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EX, manufactured by Nikkiso Co., Ltd.), determining the particle size at which the cumulative volume reached 50% based on volume.

[0170] (Post-bake phenoxy CFRP) Bisphenol A type phenoxy resin "YP-50S" manufactured by Nippon Steel Chemical & Material Co., Ltd., crystalline epoxy resin "YSLV-80XY" manufactured by Nippon Steel Chemical & Material Co., Ltd., and acid anhydride "BISDA" manufactured by SABIC Corporation were each pulverized and classified to obtain powders with an average particle size D50 of 80 μm. Of these powders, 44 parts by mass of YP-50S, 17 parts by mass of YSLV-80XY, and 39 parts by mass of BISDA were prepared and mixed in a rocking mixer. The resulting mixed powder was powder coated onto a carbon fiber reinforced fiber substrate (SA-3202I, manufactured by Sakai Obex Co., Ltd.) under electrostatic conditions of a charge of 70 kV and a spray air pressure of 0.32 MPa. Subsequently, the powder-coated reinforced fiber substrates were laminated, and this laminate was pressed at 5 MPa for 10 minutes in a press heated to 200°C. The laminate was then removed at a demolding temperature of 200°C to produce a cross-linked phenoxy resin CFRP layer material with a thickness of 1.0 mm and a Vf (fiber volume content) of 60%.

[0171] (Epoxy CFRP) A material for forming epoxy resin CFRP layers with a thickness of 1.0 mm or 1.6 mm was prepared by laminating the required number of general-purpose PAN-based carbon fiber prepregs (Toray Industries, Inc. P6343B-05P, Vf (fiber volume content) 47%) and molding them in an autoclave at 130°C, 5 atm, and for 2 hours.

[0172] Regarding the formation method of steel plate-fiber-reinforced resin composites Next, the first adhesive layer, second adhesive layer, (resin layer), and fiber-reinforced resin layer were layered sequentially on a steel plate, and a metal-FRP composite material sample was fabricated by pressing it for 3 minutes at 3 MPa in a press machine with a flat die heated to 240°C. The combinations of the first adhesive layer, second adhesive layer, resin layer, and fiber-reinforced resin layer used are shown in Table 4 below.

[0173] ≪Evaluation Method≫ [Three-point bending test] 1. Preparation of three-point bending test specimens A 275mm x 820mm test piece was cut from the fabricated steel plate, and 80mm x 800mm test pieces were cut from the fabricated first adhesive layer, second adhesive layer, (resin layer), and fiber-reinforced resin layer. Next, each layer was laminated so that it was positioned in the center of the cut steel plate, and a steel plate-FRP composite was fabricated as a composite sample by pressing it for 3 minutes at a pressure of 3MPa in a press machine with a flat die heated to 250°C. When resin composition 10 was used as the first adhesive layer, the pressing was performed at 280°C. Furthermore, the fabricated composite sample was processed in a bending press machine to produce a hat-shaped steel plate-FRP composite molded sample.

[0174] However, for the sample using steel grade C, the obtained cold-rolled steel sheet was first subjected to hot press heating using a furnace heating method, followed by hot pressing. During furnace heating, the furnace atmosphere was set to 910°C and the air-heat ratio to 1.1. After the steel sheet temperature reached 900°C, the steel sheet was quickly removed from the furnace. After hot pressing, the steel sheet was cooled to 650°C. After cooling, the steel sheet was sandwiched between flat dies equipped with a water-cooling jacket and hot-pressed to produce a hat-shaped hot-pressed body. Even in areas where the cooling rate was slow during hot pressing, the material was cooled to approximately 360°C, the starting point of martensitic transformation, at a cooling rate of 50°C / second or more, and then quenched. Next, the scale of the hot-pressed body was removed by shot blasting. Then, a first adhesive layer, a second adhesive layer, a resin layer, and a fiber-reinforced resin layer were laminated onto the hat-shaped molded body after shot blasting. A steel plate-FRP composite was then fabricated as a composite sample by pressing it for 3 minutes at a pressure of 3 MPa in a press machine with a flat die heated to 250°C.

[0175] Furthermore, using only 275mm x 820mm steel plates that do not have the first adhesive layer, second adhesive layer, (resin layer), and fiber-reinforced resin layer laminated, a hat-shaped steel plate molded sample was prepared by processing it with a bending press in the same manner as described above.

[0176] Subsequently, a three-point bending test specimen was fabricated by butting the flanges of the fabricated steel plate-FRP composite molded sample (upper) and the steel plate molded body (lower), and then spot welding the flanges together, resulting in a shape schematically shown in Figure 7. The spot welding was performed at 30 mm intervals along the length of the flange. When fabricating the test specimen, the upper composite molded body and the lower metal plate molded body were made from the same steel plate, and the three-point bending test specimen was constructed.

[0177] 2. Three-point bending test method As shown in Figure 8, the above-mentioned test specimen was supported at two support points (distance between support points: 700 mm). The center of the distance between the support points was designated as the load point, and a force was applied to the load point by moving an indenter vertically downwards. A three-point bending test was performed by measuring the load applied to the indenter at the load point. The movement speed of the indenter at the load point was set to 0.83 mm / s. The maximum load applied to the indenter at the load point was then measured.

[0178] In addition, the delamination area ratio of the steel plate / FRP interface was measured at positions 150 mm to the left and right of the center of the bent portion of the above test specimen. Based on the obtained delamination area ratio, the "delamination state" was evaluated as an evaluation index for the degree of composite bonding between the steel plate and FRP. The delamination area ratio was defined as the ratio of the delamination area at the interface between the steel plate and the first or second adhesive layer in a 300 mm length section (300 mm length x 300 mm width) centered on the central load point (bent deformation portion) within the 800 mm length x 300 mm width CFRP bonded section.

[0179] For comparison, the maximum load during the three-point bending test was also measured for three-point bending test specimens using steel plate molded bodies for both the upper and lower molded bodies (i.e., test specimens combining molded bodies that do not use the first adhesive layer, second adhesive layer, resin layer, or fiber-reinforced resin layer; hereinafter referred to as "steel plate test specimens"), in the same manner as described above.

[0180] The maximum load of the three-point bending test specimen was divided by the maximum load of the steel plate test specimen to relativize the maximum load of the three-point bending test specimen and use this as the "stiffening effect evaluation". The evaluation criteria for the "stiffening effect evaluation" are as follows: A score of "C" or higher was considered a pass.

[0181] ◇Evaluation Criteria A:1.10 times or more B: 1.05 times or more and less than 1.10 times C: Over 1.00x and less than 1.05x D: 1.00 times or less

[0182] Furthermore, the maximum load of the three-point bending test specimen itself was also evaluated as an "absolute strength evaluation." The evaluation criteria for the "absolute strength evaluation" are as follows:

[0183] ◇Evaluation Criteria A:30kN or more B: 25kN or more and less than 30kN C: 15kN or more and less than 25kN D: 10kN or more and less than 15kN E: Less than 10kN

[0184] Furthermore, the evaluation criteria for the "detachment state" are as follows: A score of "B" or higher was considered acceptable.

[0185] ◇Evaluation Criteria A: Less than 50% B: 50% or more but less than 70% C: 70% or more

[0186] [Corrosion resistance test] A composite sample was prepared by layering a steel plate with a 70mm wide x 150mm long coating or film layer in the center, and then pressing the first adhesive layer, second adhesive layer, (resin layer), and fiber-reinforced resin layer so that the composite section of the steel plate and the first adhesive layer, second adhesive layer, (resin layer), and fiber-reinforced resin layer measured 50mm wide x 100mm long. After degreasing, surface preparation, and zinc phosphate treatment, electrodeposition coating was applied to this composite sample. For sample No. 44 below, a terrace structure was adopted in which the first and second adhesive layers protruded approximately 2mm beyond the fiber-reinforced resin layer.

[0187] Degreasing was performed by spraying an 18 g / l aqueous solution of a degreasing agent (product name: Fine Cleaner E2083) manufactured by Nippon Parkerizing Co., Ltd. at 40°C for 120 seconds, followed by rinsing with water. Next, the degreased cold-rolled steel sheet was immersed in a 0.5 g / l aqueous solution of a surface conditioning agent (product name: Preparen XG) manufactured by Nippon Parkerizing Co., Ltd. at room temperature for 60 seconds. Subsequently, it was immersed in a zinc phosphate treatment agent (product name: Palbond L3065) manufactured by Nippon Parkerizing Co., Ltd. for 120 seconds, rinsed with water, and dried to obtain a chemically treated steel sheet. After that, a 15 μm electrodeposition coating (product name: Powernics) manufactured by Nippon Paint Co., Ltd. was applied, and the sheet was baked in an oven at 170°C for 20 minutes. This was used as a sample.

[0188] A cycle corrosion test (CCT) was performed using the prepared samples. The CCT mode was conducted in accordance with the neutral salt spray cycle test of JIS H8520:1999. The sample was placed in the testing machine with the FRP side as the evaluation surface, so that salt water was sprayed onto the evaluation surface. Corrosion resistance was evaluated by visually observing the appearance of the sample after 240 cycles and determining the maximum width of red rust. A smaller width of red rust indicates better corrosion resistance. In addition, since red rust occurs near the edges of the first and second adhesive layers attached to the steel plate, the corrosion width occurring from the edges of the resin layer was measured. The location with the largest corrosion width among the corrosion widths from the entire edge of the resin layer was evaluated as the maximum corrosion width. The evaluation criteria are as follows. A score of "D" or higher was judged as passing.

[0189] ◇Evaluation Criteria A: Maximum corrosion width is less than 2 mm B: Maximum corrosion width is more than 2mm and less than 4mm C: Maximum corrosion width is more than 4mm and less than 6mm D: Maximum corrosion width is greater than 6mm but less than or equal to 8mm. E: Maximum corrosion width exceeds 8 mm

[0190] The results obtained are summarized in Table 5 below.

[0191] [Table 4]

[0192] [Table 5]

[0193] As is clear from Tables 4 and 5 above, the examples of the present invention showed excellent evaluation results in the corrosion resistance test and the three-point bending test, while the comparative examples of the present invention showed test results that were unsatisfactory in at least one of the corrosion resistance test or the three-point bending test.

[0194] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention.

[0195] The embodiments disclosed herein are illustrative and not restrictive in all respects. The embodiments described above may be omitted, replaced, or modified in various ways without departing from the appended claims, the technical scope of the invention as described later, and the spirit thereof. For example, the constituent elements of the embodiments described above can be combined in any way without impairing their effects. Furthermore, such any combination will naturally yield the effects and benefits of each constituent element in the combination, as well as other effects and benefits that will be obvious to those skilled in the art from the description herein.

[0196] Furthermore, the effects described herein are merely descriptive or illustrative, and not limiting. In other words, the technology according to the present invention may produce other effects that will be apparent to those skilled in the art from the description herein, in addition to or instead of the effects described above.

[0197] Furthermore, the following configurations also fall within the technical scope of the present invention. (1) A steel plate member made of a steel plate or a molded body of said steel plate, A first adhesive layer located on at least a portion of the surface of the steel plate member, comprising a resin composition mainly composed of two different materials, A second adhesive layer located on at least a portion of the surface of the first adhesive layer, and mainly composed of a resin having a tensile modulus of 500 MPa or more at 25°C, A fiber-reinforced resin layer located on at least a portion of the surface of the second adhesive layer, and composed of a fiber-reinforced resin containing reinforcing fibers in the matrix resin, Equipped with, The resin composition of the first adhesive layer contains phenoxy resin and polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 20:80 to 80:20. A steel plate-fiber-reinforced resin composite, wherein, in elastic modulus phase image images obtained by observing the resin composition of the first adhesive layer with an atomic force microscope (AFM) equipped with a probe with a tip radius of 10 nm in an atmosphere of 25°C, the area ratio of regions forming a phase separation structure due to the phenoxy resin and the polyester elastomer is 1 area % or less of the total observed area. (2) The reinforcing fibers in the fiber-reinforced resin layer are electrically conductive, The steel sheet-fiber-reinforced resin composite according to (1), wherein at least one of the first adhesive layer or the second adhesive layer further comprises a non-conductive substance. (3) The reinforcing fibers in the fiber-reinforced resin layer are electrically conductive, The steel plate-fiber-reinforced resin composite according to (1), further comprising a resin layer containing a non-conductive substance located between the second adhesive layer and the fiber-reinforced resin layer, and located on at least a portion of the surface of the second adhesive layer. (4) The nonconductive material has an electrical resistivity of 1 × 10 6 The steel plate-fiber-reinforced resin composite according to (2) or (3), wherein the composite is at least one selected from insulating particles, glass particles, glass fibers, or aramid fibers having a density of Ω·m or greater. (5) The steel sheet-fiber-reinforced resin composite according to any one of (1) to (4), wherein the resin composition of the first adhesive layer has a glass transition temperature of 60°C or less, a tensile modulus of elasticity at 25°C of 2500 MPa or less, and a tensile elongation at break of 5% or more. (6) The steel plate-fiber-reinforced resin composite according to any one of (1) to (5), wherein the resin composition of the first adhesive layer contains the phenoxy resin and the polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 20:80 to 60:40. (7) The steel plate-fiber-reinforced resin composite according to any one of (1) to (6), wherein the resin composition of the first adhesive layer contains the phenoxy resin and the polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 25:75 to 50:50. (8) When viewed from above in a plan view of the fiber-reinforced resin layer, A steel plate-fiber-reinforced resin composite according to any one of (1) to (7), wherein the first adhesive layer and the second adhesive layer are the same size, and the fiber-reinforced resin layer is smaller in size than the first adhesive layer. (9) The steel plate-fiber-reinforced resin composite according to any one of (1) to (7), wherein the second adhesive layer is provided so as to cover the surface and sides of the first adhesive layer. (10) The steel plate-fiber-reinforced resin composite according to any one of (1) to (9), wherein the phenoxy resin contained in the first adhesive layer is a phenoxy resin having a bisphenol A skeleton. (11) The steel plate-fiber-reinforced resin composite according to any one of (1) to (10), wherein the matrix resin of the fiber-reinforced resin layer is mainly composed of phenoxy resin. (12) The steel plate-fiber-reinforced resin composite according to any one of (1) to (11), wherein the matrix resin of the fiber-reinforced resin layer is mainly composed of a phenoxy resin having a bisphenol A skeleton. (13) The steel plate-fiber-reinforced resin composite according to any one of (1) to (12), wherein the reinforcing fibers of the fiber-reinforced resin layer are carbon-reinforced fibers. (14) The steel plate-fiber-reinforced resin composite according to any one of (1) to (13), wherein the resin of the second adhesive layer is a phenoxy resin. (15) The steel plate-fiber-reinforced resin composite according to any one of (1) to (14), wherein the resin of the second adhesive layer is a phenoxy resin having a bisphenol A skeleton. (16) The steel plate is a steel plate-fiber-reinforced resin composite according to any one of (1) to (15), having a tensile strength of 1500 MPa or more. A manufacturing method for producing a steel plate-fiber-reinforced resin composite described in any one of (17)(1) to (16), A first adhesive layer, mainly composed of two different resin compositions, is superimposed on at least a portion of the surface of a steel plate; a second adhesive layer, mainly composed of a resin with a tensile modulus of elasticity of 500 MPa or more at 25°C, is superimposed on at least a portion of the surface of the first adhesive layer; and a fiber-reinforced resin layer, composed of a fiber-reinforced resin containing reinforcing fibers in a matrix resin, is superimposed on at least a portion of the surface of the second adhesive layer. The first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer are heat-pressed onto the steel plate. The resin composition of the first adhesive layer contains phenoxy resin and polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 20:80 to 80:20. A method for producing a steel plate-fiber-reinforced resin composite, wherein, in elastic modulus phase image images obtained by observing the resin composition of the first adhesive layer with an atomic force microscope (AFM) equipped with a probe with a tip radius of 10 nm in an atmosphere of 25°C, the area ratio of regions forming a phase separation structure due to the phenoxy resin and the polyester elastomer is 1 area % or less of the total observed area. A manufacturing method for producing a steel plate-fiber-reinforced resin composite described in any one of (18)(1) to (16), After press-forming the steel plate to form a steel plate body, A first adhesive layer, mainly composed of two different resin compositions, is superimposed on at least a portion of the surface of the molded steel plate; a second adhesive layer, mainly composed of a resin having a tensile modulus of 500 MPa or more at 25°C, is superimposed on at least a portion of the surface of the first adhesive layer; and a fiber-reinforced resin layer, composed of a fiber-reinforced resin containing reinforcing fibers in a matrix resin, is superimposed on at least a portion of the surface of the second adhesive layer. The first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer are heat-pressed onto the molded steel plate. The resin composition of the first adhesive layer contains phenoxy resin and polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 20:80 to 80:20. A method for producing a steel plate-fiber-reinforced resin composite, wherein, in elastic modulus phase image images obtained by observing the resin composition of the first adhesive layer with an atomic force microscope (AFM) equipped with a probe with a tip radius of 10 nm in an atmosphere of 25°C, the area ratio of regions forming a phase separation structure due to the phenoxy resin and the polyester elastomer is 1 area % or less of the total observed area. A manufacturing method for producing a steel plate-fiber-reinforced resin composite described in any one of (19)(1) to (16), A laminate is formed by layering a first adhesive layer, mainly composed of two different resin compositions, onto at least a portion of the surface of a steel plate; layering a second adhesive layer, mainly composed of a resin with a tensile modulus of elasticity of 500 MPa or more at 25°C, onto at least a portion of the surface of the first adhesive layer; and layering a fiber-reinforced resin layer, composed of a fiber-reinforced resin containing reinforcing fibers in a matrix resin, onto at least a portion of the surface of the second adhesive layer. The laminate is processed using a press molding machine having a heated mold, and the first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer are heat-pressed onto the steel plate to form a molded body. The resin composition of the first adhesive layer contains phenoxy resin and polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 20:80 to 80:20. A method for producing a steel plate-fiber-reinforced resin composite, wherein, in elastic modulus phase image images obtained by observing the resin composition of the first adhesive layer with an atomic force microscope (AFM) equipped with a probe with a tip radius of 10 nm in an atmosphere of 25°C, the area ratio of regions forming a phase separation structure due to the phenoxy resin and the polyester elastomer is 1 area % or less of the total observed area. [Explanation of Symbols]

[0198] 1. Steel plate-fiber-reinforced resin composite 10 Steel plate members 20 1st adhesive layer 30 Second adhesive layer 40 Fiber-reinforced resin layer 50 resin layer

Claims

1. A steel plate member made of a steel plate or a molded body of said steel plate, A first adhesive layer located on at least a portion of the surface of the steel plate member, comprising a resin composition mainly composed of two different materials, A second adhesive layer located on at least a portion of the surface of the first adhesive layer, and mainly composed of a resin having a tensile modulus of elasticity of 500 MPa or more at 25°C, A fiber-reinforced resin layer located on at least a portion of the surface of the second adhesive layer, and composed of a fiber-reinforced resin containing reinforcing fibers in the matrix resin, Equipped with, The resin composition of the first adhesive layer contains a phenoxy resin and a polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 20:80 to 80:

20. A steel plate-fiber-reinforced resin composite, wherein, in elastic modulus phase image images obtained by observing the resin composition of the first adhesive layer with an atomic force microscope (AFM) equipped with a probe with a tip radius of 10 nm in an atmosphere of 25°C, the area ratio of regions forming a phase separation structure due to the phenoxy resin and the polyester elastomer is 1 area % or less of the total observed area.

2. The reinforcing fibers in the fiber-reinforced resin layer are conductive, and The steel sheet-fiber-reinforced resin composite according to claim 1, wherein at least one of the first adhesive layer or the second adhesive layer further contains a non-conductive substance, or further comprises a resin layer containing a non-conductive substance between the second adhesive layer and the fiber-reinforced resin layer, and on at least a portion of the surface of the second adhesive layer.

3. The aforementioned non-conductive material has an electrical resistivity of 1 × 10⁻⁶. ６ The steel plate-fiber-reinforced resin composite according to claim 2, wherein the composite is at least one selected from insulating particles, glass particles, glass fibers, or aramid fibers having an impedance of Ω·m or greater.

4. The steel plate-fiber-reinforced resin composite according to claim 1 or 2, wherein the resin composition of the first adhesive layer has a glass transition temperature of 60°C or less, a tensile modulus of elasticity at 25°C of 2500 MPa or less, and a tensile elongation at break of 5% or more.

5. The steel plate-fiber-reinforced resin composite according to claim 1 or 2, wherein the resin composition of the first adhesive layer contains the phenoxy resin and the polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 20:80 to 60:

40.

6. The steel plate-fiber-reinforced resin composite according to claim 5, wherein the resin composition of the first adhesive layer contains the phenoxy resin and the polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 25:75 to 50:

50.

7. When viewed from above in a plan view of the fiber-reinforced resin layer, The steel plate-fiber-reinforced resin composite according to claim 1 or 2, wherein the first adhesive layer and the second adhesive layer are of the same size, and the fiber-reinforced resin layer is smaller in size than the first adhesive layer.

8. The steel plate-fiber-reinforced resin composite according to claim 1 or 2, wherein the second adhesive layer is provided so as to cover the surface and sides of the first adhesive layer.

9. The steel plate-fiber-reinforced resin composite according to claim 1 or 2, wherein the phenoxy resin contained in the first adhesive layer is a phenoxy resin having a bisphenol A skeleton.

10. The steel plate-fiber-reinforced resin composite according to claim 1 or 2, wherein the matrix resin of the fiber-reinforced resin layer is mainly composed of phenoxy resin.

11. The steel plate-fiber-reinforced resin composite according to claim 10, wherein the matrix resin of the fiber-reinforced resin layer mainly comprises a phenoxy resin having a bisphenol A skeleton.

12. The steel plate-fiber-reinforced resin composite according to claim 1 or 2, wherein the reinforcing fibers in the fiber-reinforced resin layer are carbon-reinforced fibers.

13. The steel plate-fiber-reinforced resin composite according to claim 1 or 2, wherein the resin of the second adhesive layer is a phenoxy resin.

14. The steel plate-fiber-reinforced resin composite according to claim 13, wherein the resin of the second adhesive layer is a phenoxy resin having a bisphenol A skeleton.

15. The steel plate-fiber-reinforced resin composite according to claim 1 or 2, wherein the steel plate has a tensile strength of 1500 MPa or more.

16. A method for producing a steel plate-fiber-reinforced resin composite comprising: a steel plate member made of a steel plate or a molded body of said steel plate; a first adhesive layer located on at least a portion of the surface of the steel plate member and mainly composed of two different resin compositions; a second adhesive layer located on at least a portion of the surface of the first adhesive layer; and a fiber-reinforced resin layer located on at least a portion of the surface of the second adhesive layer and composed of a fiber-reinforced resin containing reinforcing fibers in a matrix resin, wherein the method comprises: A first adhesive layer, mainly composed of two different resin compositions, is superimposed on at least a portion of the surface of a steel plate; a second adhesive layer, mainly composed of a resin having a tensile modulus of 500 MPa or more at 25°C, is superimposed on at least a portion of the surface of the first adhesive layer; and a fiber-reinforced resin layer, composed of a fiber-reinforced resin containing reinforcing fibers in a matrix resin, is superimposed on at least a portion of the surface of the second adhesive layer. The first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer are heat-pressed onto the steel plate. The resin composition of the first adhesive layer contains a phenoxy resin and a polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 20:80 to 80:

20. A method for producing a steel plate-fiber-reinforced resin composite, wherein, in elastic modulus phase image images obtained by observing the resin composition of the first adhesive layer with an atomic force microscope (AFM) equipped with a probe with a tip radius of 10 nm in an atmosphere of 25°C, the area ratio of regions forming a phase separation structure due to the phenoxy resin and the polyester elastomer is 1 area % or less of the total observed area.

17. A method for producing a steel plate-fiber-reinforced resin composite comprising: a steel plate member made of a steel plate or a molded body of said steel plate; a first adhesive layer located on at least a portion of the surface of the steel plate member and mainly composed of two different resin compositions; a second adhesive layer located on at least a portion of the surface of the first adhesive layer; and a fiber-reinforced resin layer located on at least a portion of the surface of the second adhesive layer and composed of a fiber-reinforced resin containing reinforcing fibers in a matrix resin, wherein the method comprises: After press-forming the steel plate to form a steel plate body, A first adhesive layer, mainly composed of two different resin compositions, is superimposed on at least a portion of the surface of the molded steel plate; a second adhesive layer, mainly composed of a resin having a tensile modulus of 500 MPa or more at 25°C, is superimposed on at least a portion of the surface of the first adhesive layer; and a fiber-reinforced resin layer, composed of a fiber-reinforced resin containing reinforcing fibers in a matrix resin, is superimposed on at least a portion of the surface of the second adhesive layer. The first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer are heat-pressed onto the molded steel plate. The resin composition of the first adhesive layer contains a phenoxy resin and a polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 20:80 to 80:

20. A method for producing a steel plate-fiber-reinforced resin composite, wherein, in elastic modulus phase image images obtained by observing the resin composition of the first adhesive layer with an atomic force microscope (AFM) equipped with a probe with a tip radius of 10 nm in an atmosphere of 25°C, the area ratio of regions forming a phase separation structure due to the phenoxy resin and the polyester elastomer is 1 area % or less of the total observed area.

18. A method for producing a steel plate-fiber-reinforced resin composite comprising: a steel plate member made of a steel plate or a molded body of said steel plate; a first adhesive layer located on at least a portion of the surface of the steel plate member and mainly composed of two different resin compositions; a second adhesive layer located on at least a portion of the surface of the first adhesive layer; and a fiber-reinforced resin layer located on at least a portion of the surface of the second adhesive layer and composed of a fiber-reinforced resin containing reinforcing fibers in a matrix resin, wherein the method comprises: A laminate is formed by layering a first adhesive layer, mainly composed of two different resin compositions, onto at least a portion of the surface of a steel plate; layering a second adhesive layer, mainly composed of a resin with a tensile modulus of 500 MPa or more at 25°C, onto at least a portion of the surface of the first adhesive layer; and layering a fiber-reinforced resin layer, composed of a fiber-reinforced resin containing reinforcing fibers in a matrix resin, onto at least a portion of the surface of the second adhesive layer. The laminate is processed using a press molding machine having a heated mold, and the first adhesive layer, the second adhesive layer, and the fiber-reinforced resin layer are heat-pressed onto the steel plate to form a molded body. The resin composition of the first adhesive layer contains a phenoxy resin and a polyester elastomer in a mass ratio (phenoxy resin:polyester elastomer) within the range of 20:80 to 80:

20. A method for producing a steel plate-fiber-reinforced resin composite, wherein, in elastic modulus phase image images obtained by observing the resin composition of the first adhesive layer with an atomic force microscope (AFM) equipped with a probe with a tip radius of 10 nm in an atmosphere of 25°C, the area ratio of regions forming a phase separation structure due to the phenoxy resin and the polyester elastomer is 1 area % or less of the total observed area.

Images