Layered body and fused body using same

Abstract

The purpose of the present invention is to provide a layered body in which fiber-reinforced thermoplastic resin base materials are layered, with which fusion stability can be improved without separately using conductive particles or a susceptor of a dissimilar material. Specifically provided is a layered body obtained by layering a plurality of fiber-reinforced thermoplastic resin base materials, said layered body being characterized in that: the fiber-reinforced thermoplastic resin base materials are obtained by impregnating a thermoplastic resin into conductive reinforcing fibers aligned in parallel; amongst the plurality of fiber-reinforced thermoplastic resin base materials, the orientation direction of a fiber-reinforced thermoplastic resin base material L(1) constituting one surface layer and the orientation direction of a fiber-reinforced thermoplastic resin base material L(2) which is adjacent to the fiber-reinforced thermoplastic resin base material L(1) and is the second layer from the one surface layer are different from each other, and the orientation direction of the fiber-reinforced thermoplastic resin base material L(2) and the orientation direction of a fiber-reinforced thermoplastic resin base material L(3) which is the third layer from the one surface layer are different from each other; and when the total number of the fiber-reinforced thermoplastic resin base materials is k (where k is a natural number of 3 or more), the electrical conductivity C(1), in the thickness direction, of the fiber-reinforced thermoplastic resin base material L(1) constituting the one surface layer and the electrical conductivity C(k), in the thickness direction, of the fiber-reinforced thermoplastic resin base material L(k) constituting the other surface layer have the relationship in formula (1).

Description

Laminate and welded body using same

[0001] The present invention relates to a laminate made of a fiber-reinforced thermoplastic resin having excellent heating characteristics during induction heating and good moldability, and a welded article using the same.

[0002] Plastic composite materials, which consist of reinforcing fibers and a matrix resin, are lighter than metal-based or ceramic-based composite materials, and are available in a wide variety of materials, with remarkable technological progress. Such plastic composite materials are used as molded products, including components for electrical and electronic devices, precision machinery, construction materials, automotive components, home appliances, household goods, sporting goods, medical instruments, and aircraft and space equipment components.

[0003] The main reinforcing fibers used in plastic composite materials are organic aramid fibers, or inorganic fibers such as glass and carbon fibers, due to their high strength, high elastic modulus, and excellent heat resistance. Inorganic fibers have a low specific gravity and are lightweight, and carbon fibers in particular are used as reinforcing fibers in plastic composite materials because they have excellent properties such as heat resistance, corrosion resistance, and chemical resistance in addition to their mechanical properties of high strength and high elasticity.

[0004] On the other hand, thermoplastic resins have attracted attention as matrix resins because of their moldability and ease of post-processing by welding. To commercialize thermoplastic resin-based composite materials using thermoplastic resins as the matrix resin, technological developments are underway to weld two or more thermoplastic resin-based composite materials together.

[0005] For example, a method has been disclosed in which two fiber-reinforced resin laminates are stacked on top of each other and a susceptor is sandwiched between them to absorb the magnetic field and uniformly heat the interface between the two fiber-reinforced resin laminates, thereby welding them together (see Patent Document 1).

[0006] Furthermore, a method has been disclosed in which, when induction welding a thermoplastic resin composite material, conductive particles are filled between the substrates that make up a fiber-reinforced resin laminate to increase electrical conductivity and make it easier to heat (see Patent Document 2).

[0007] International Publication No. WO 2012 / 158293 International Publication No. WO 2016 / 017553

[0008] However, the technology described in Patent Document 1 can efficiently weld the interface of a unidirectional laminate by using a susceptor in high-frequency induction heating, but there are concerns about the impact on physical properties because different materials are used.

[0009] Furthermore, with the technology described in Patent Document 2, it is difficult to spray the conductive particles in the same state every time, and there are concerns about the stability of quality.

[0010] The present invention is intended to solve the problems associated with the above-mentioned conventional technology, and aims to provide a laminate in which fiber-reinforced thermoplastic resin substrates are laminated, which can improve welding stability without using a separate susceptor or conductive particles made of a different material.

[0011] In order to solve the above problems, the present invention mainly has any one of the following configurations. [1] A laminate in which a plurality of fiber-reinforced thermoplastic resin substrates are laminated, wherein the fiber-reinforced thermoplastic resin substrate is obtained by impregnating electrically conductive reinforcing fibers aligned in parallel with a thermoplastic resin, and the plurality of fiber-reinforced thermoplastic resin substrates are different in the orientation direction of the fiber-reinforced thermoplastic resin substrate L (1) constituting one surface layer and the orientation direction of the fiber-reinforced thermoplastic resin substrate L (2) adjacent to the one surface layer. The orientation direction of the fiber-reinforced thermoplastic resin substrate L (2) and the orientation direction of the fiber-reinforced thermoplastic resin substrate L (3) are different from each other, and further, when the total number of the fiber-reinforced thermoplastic resin substrates is k (where k is a natural number of 3 or more), the electrical conductivity C (1) in the thickness direction of the fiber-reinforced thermoplastic resin substrate L (1) constituting one surface layer and the electrical conductivity C (k) in the thickness direction of the fiber-reinforced thermoplastic resin substrate L (k) constituting the other surface layer are expressed by the following formula (1).

[0012]

[0013] [2] A laminate in which a plurality of fiber-reinforced thermoplastic resin substrates are laminated, wherein the fiber-reinforced thermoplastic resin substrate is a laminate in which electrically conductive reinforcing fibers aligned in parallel are impregnated with a thermoplastic resin, and the plurality of fiber-reinforced thermoplastic resin substrates have a fiber-reinforced thermoplastic resin substrate L (1) constituting one surface layer and a fiber-reinforced thermoplastic resin substrate L (2) in the second layer from the one surface layer adjacent to the fiber-reinforced thermoplastic resin substrate L (1). The orientation direction of the fiber-reinforced thermoplastic resin substrate L (2) and the orientation direction of the fiber-reinforced thermoplastic resin substrate L (3) in the third layer from the one surface layer are different from each other. are different from each other, and further, the total number of the fiber reinforced thermoplastic resin substrates is k (where k is a natural number of 3 or more), and the maximum value of the thickness direction electrical conductivity C(n) (where n is a natural number such that 1 ≦ n ≦ k) of each fiber reinforced thermoplastic resin substrate is C(max) and the minimum value is C(min), C(max) exists from the fiber reinforced thermoplastic resin substrate L(1) to the fiber reinforced thermoplastic resin substrate L([k / 2]), and C(min) exists from the fiber reinforced thermoplastic resin substrate L([k / 2] + 1) to the fiber reinforced thermoplastic resin substrate L(k), and C(max) and C(min) have the relationship of formula (2).

[0014]

[0015] [3] The fiber reinforced thermoplastic resin substrate layer A consisting of the fiber reinforced thermoplastic resin substrate L (1) constituting one surface layer and the fiber reinforced thermoplastic resin substrate L (2) constituting the second layer from the one surface layer has an electrical conductivity C (A) in the thickness direction, and the fiber reinforced thermoplastic resin substrate L (k) constituting the other surface layer and the fiber reinforced thermoplastic resin substrate L (k-1) constituting the second layer from the other surface layer. The laminate according to [1], wherein the electrical conductivity C (B) in the thickness direction of the fiber reinforced thermoplastic resin substrate layer B consisting of the fiber reinforced thermoplastic resin substrate L (k-1) constituting the second layer is expressed by the formula (3).

[0016]

[0017] [4] The laminate according to any one of [1] to [3], wherein the regression line of the electrical conductivity of the plurality of fiber-reinforced thermoplastic resin substrates has a negative slope from the fiber-reinforced thermoplastic resin substrate L(1) to the fiber-reinforced thermoplastic resin substrate L(k). [5] The laminate according to any one of [1] to [4], wherein the thickness of the fiber-reinforced thermoplastic resin substrate is 0.05 mm to 0.5 mm. [6] The laminate according to any one of [1] to [5], wherein a resin layer having a thickness of 1 to 50 μm is provided on at least one surface of the laminate. [7] A welded body obtained by stacking and welding a plurality of the laminates according to any one of [1] to [6], or a welded body obtained by stacking and welding a laminate according to any one of [1] to [6] with another material, wherein the fiber-reinforced thermoplastic resin substrate L(1) forms a weld interface in the laminate. [8] The welded body according to [7], wherein the welding is performed by induction heating.

[0018] Regarding [k / 2] in the expressions "fiber reinforced thermoplastic resin substrate L([k / 2])" and "fiber reinforced thermoplastic resin substrate L([k / 2]+1)", the symbol [_] means a Gauss symbol, and [k / 2] means the maximum integer value not exceeding k / 2.

[0019] Further, the range expressed by "C (max) is present in the fiber reinforced thermoplastic resin substrate L (1) to the fiber reinforced thermoplastic resin substrate L ([k / 2])" also includes L (1) and L ([k / 2]), and C (max) means that the fiber reinforced thermoplastic resin substrate L (1) or the fiber reinforced thermoplastic resin substrate L ([k / 2]). Similarly, the range expressed by "C (min) is present in the fiber reinforced thermoplastic resin substrate L ([k / 2] + 1) to the fiber reinforced thermoplastic resin substrate L (k)" also includes L ([k / 2] + 1) and L (k), and C (min) means that the fiber reinforced thermoplastic resin substrate L ([k / 2] + 1) or the fiber reinforced thermoplastic resin substrate L (k).

[0020] The present invention provides a laminate comprising a plurality of fiber-reinforced thermoplastic resin substrates, the fiber-reinforced thermoplastic resin substrates being formed by impregnating parallel, electrically conductive reinforcing fibers with a thermoplastic resin. In the laminate, the orientation direction of a fiber-reinforced thermoplastic resin substrate L(1) constituting one surface layer is different from the orientation direction of a fiber-reinforced thermoplastic resin substrate L(2) adjacent to the fiber-reinforced thermoplastic resin substrate L(1), and the orientation direction of a fiber-reinforced thermoplastic resin substrate L(2) adjacent to the fiber-reinforced thermoplastic resin substrate L(2) is different from the orientation direction of a fiber-reinforced thermoplastic resin substrate L(3) in a third layer. Furthermore, when the total number of fiber-reinforced thermoplastic resin substrates is k (where k is a natural number greater than or equal to 3), the electrical conductivity C(1) of the fiber-reinforced thermoplastic resin substrate L(1) constituting one surface layer of the laminate and the electrical conductivity C(k) of the fiber-reinforced thermoplastic resin substrate L(k) constituting the other surface layer of the laminate satisfy the relationship shown in Equation (1).

[0021]

[0022] According to the present invention, the difference in welding characteristics between the front and back of the laminate can be increased. Therefore, by arranging the fiber-reinforced thermoplastic resin substrate L(1) having a high electrical conductivity on the side farther from the coil during induction heating, it is possible to reliably heat the fiber-reinforced thermoplastic resin substrate L(1) farther from the coil while preventing excessive heating of the fiber-reinforced thermoplastic resin substrate L(k) closer to the coil.

[0023] Further, in the present invention, there is provided a laminate in which a plurality of fiber-reinforced thermoplastic resin substrates are laminated, and the fiber-reinforced thermoplastic resin substrate is obtained by impregnating electrically conductive reinforcing fibers aligned in parallel with a thermoplastic resin, and the plurality of fiber-reinforced thermoplastic resin substrates are such that the orientation direction of the fiber-reinforced thermoplastic resin substrate L (1) constituting one surface layer and the orientation direction of the fiber-reinforced thermoplastic resin substrate L (2) in the second layer from the one surface layer adjacent to the fiber-reinforced thermoplastic resin substrate L (1) are different from each other, and the orientation direction of the fiber-reinforced thermoplastic resin substrate L (2) and the orientation direction of the fiber-reinforced thermoplastic resin substrate L (3) in the third layer from the one surface layer are different from each other. Furthermore, when the total number of the fiber reinforced thermoplastic resin substrates is k (where k is a natural number of 3 or more), and the maximum value of the thickness direction electrical conductivity C (n) (where n is a natural number such that 1 ≦ n ≦ k) of each fiber reinforced thermoplastic resin substrate is C (max) and the minimum value is C (min), C (max) exists from the fiber reinforced thermoplastic resin substrate L (1) to the fiber reinforced thermoplastic resin substrate L ([k / 2]), and C (min) exists from the fiber reinforced thermoplastic resin substrate L ([k / 2] + 1) to the fiber reinforced thermoplastic resin substrate L (k), and C (max) and C (min) satisfy the relationship of formula (2). A similar effect can be achieved by making it so.

[0024]

[0025] Thus, according to the present invention, it is possible to provide a laminate having fiber-reinforced thermoplastic resin substrates with excellent induction heating properties, and when such a laminate is induction heated, the surfaces to be welded can be welded more reliably and easily without using different materials that affect the physical properties.

[0026] Fig. 1 is a schematic diagram of a laminate showing one embodiment of the present invention. Fig. 2 is a schematic diagram of one embodiment of the present invention, showing a method for laminating a plurality of fiber-reinforced thermoplastic resin substrates that constitute the laminate. Fig. 3 is a schematic diagram of another embodiment of the present invention, showing a method for laminating a plurality of fiber-reinforced thermoplastic resin substrates that constitute the laminate. Fig. 4 is an example of a cross-sectional observation photograph used when measuring the electrical conductivity of a laminate. Fig. 5 is a diagram showing measurement points when measuring electrical conductivity.

[0027] The laminate according to the present invention is a laminate 10 in which a plurality of fiber-reinforced thermoplastic resin substrates 1 are stacked, as shown in Fig. 1, and the fiber-reinforced thermoplastic resin substrate 1 is formed by impregnating parallel, electrically conductive reinforcing fibers with a thermoplastic resin. The fiber-reinforced thermoplastic resin substrates are configured such that the orientation direction of the fiber-reinforced thermoplastic resin substrate L(1) constituting one surface layer is different from the orientation direction of the fiber-reinforced thermoplastic resin substrate L(2) in the second layer from the surface layer adjacent to the fiber-reinforced thermoplastic resin substrate L(1), and the orientation direction of the fiber-reinforced thermoplastic resin substrate L(2) is different from the orientation direction of the fiber-reinforced thermoplastic resin substrate L(3) in the third layer from the surface layer.

[0028] In the present invention, when the total number of fiber-reinforced thermoplastic resin substrates contained in the laminate is k (where k is a natural number of 3 or more), the electrical conductivity C (1) in the thickness direction of the fiber-reinforced thermoplastic resin substrate L (1) constituting one surface layer and the electrical conductivity C (k) in the thickness direction of the fiber-reinforced thermoplastic resin substrate L (k) constituting the other surface layer are preferably in the relationship of formula (1).

[0029]

[0030] Further, in the laminate according to the present invention, the total number of fiber-reinforced thermoplastic resin substrates is k (where k is a natural number of 3 or more), and the maximum value of the thickness direction electrical conductivity C (n) (where n is a natural number such that 1 ≦ n ≦ k) of each fiber-reinforced thermoplastic resin substrate is C (max) and the minimum value is C (min), C (max) exists from the fiber-reinforced thermoplastic resin substrate L (1) to the fiber-reinforced thermoplastic resin substrate L ([k / 2]), and C (min) exists from the fiber-reinforced thermoplastic resin substrate L ([k / 2] + 1) to the fiber-reinforced thermoplastic resin substrate L (k), and it is preferable that C (max) and C (min) have the relationship of formula (2).

[0031]

[0032] In the present invention, the electrical conductivity C (1) and the electrical conductivity C (k) satisfy the relationship of the above formula (1), and C (max) is present from the fiber reinforced thermoplastic resin substrate L (1) to the fiber reinforced thermoplastic resin substrate L ([k / 2]), and C (min) is present from the fiber reinforced thermoplastic resin substrate L ([k / 2] + 1) to the fiber reinforced thermoplastic resin substrate L (k), and it is more preferable that C (max) and C (min) satisfy the relationship of the above formula (2).

[0033] [Reinforcing fiber] The reinforcing fiber used in the fiber-reinforced thermoplastic resin substrate is a continuous fiber. Continuous fiber refers to a state in which the reinforcing fiber is substantially continuous in the fiber length direction in the fiber-reinforced thermoplastic resin substrate. Note that a substantially continuous state includes not only a state in which the reinforcing fiber is completely uninterrupted in the fiber-reinforced thermoplastic resin substrate, but also a state in which the reinforcing fiber is cut as an individual reinforcing fiber due to a cut in part of the substrate, but the reinforcing fiber is present in the length direction of the substrate as a whole, throughout the entire substrate. The reinforcing fibers are aligned in parallel and arranged in one direction in the fiber-reinforced thermoplastic resin substrate.

[0034] The reinforcing fibers used in the present invention have electrical conductivity, which allows the fiber-reinforced thermoplastic resin substrate to be heated by resistance heating.

[0035] Examples of reinforcing fibers include carbon fibers, metal fibers, and inorganic fibers. Among these, carbon fibers include, for example, polyacrylonitrile (PAN)-based carbon fibers made from PAN fibers, pitch-based carbon fibers made from petroleum tar or petroleum pitch, cellulose-based carbon fibers made from viscose rayon or cellulose acetate, vapor-grown carbon fibers made from hydrocarbons, and graphitized fibers thereof. Among these carbon fibers, PAN-based carbon fibers are preferably used because of their excellent balance between strength and elastic modulus.

[0036] Examples of metal fibers include fibers made of metals such as iron, gold, silver, copper, aluminum, brass, and stainless steel. Examples of inorganic fibers include fibers made of inorganic materials such as silicon carbide.

[0037] These reinforcing fibers are often expected to function as reinforcing materials, so it is desirable that they exhibit high mechanical properties, and it is more preferable to use carbon fibers.

[0038] [Bundle of reinforcing fibers] The reinforcing fibers of the present invention are preferably handled in the form of a bundle of a plurality of fibers. The number of single fibers contained in one bundle is not limited, but the number of reinforcing fiber bundles is preferably 3,000 to 24,000, and more preferably 12,000 to 24,000.

[0039] [Reinforced fiber sheet] A plurality of bundles of reinforcing fibers are prepared and aligned in parallel in one direction to form a reinforcing fiber sheet. At the time of forming the reinforcing fiber sheet, the sheet has not yet been impregnated with the thermoplastic resin described below.

[0040] [Fiber-reinforced thermoplastic resin substrate] The fiber-reinforced thermoplastic resin substrate is a so-called unidirectional prepreg, which is obtained by impregnating a reinforcing fiber sheet with a thermoplastic resin.

[0041] [Thermoplastic resin] Examples of the thermoplastic resin (matrix resin) used in the fiber-reinforced thermoplastic resin substrate according to the present invention include: (i) polyester-based resins such as polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, polytrimethylene terephthalate (PTT) resin, polyethylene naphthalate (PEN) resin, and liquid crystal polyester resin; (ii) polyolefin-based resins such as polyethylene (PE) resin, polypropylene (PP) resin, and polybutylene resin; (iii) styrene-based resins; (iv) polyoxymethylene (POM) resin, polyamide (PA) resin, polycarbonate (PC) resin, polymethylene methacrylate (PMMA) resin, and polyvinyl chloride (PV) resin. C) resins, polyphenylene sulfide (PPS) resins, polyphenylene ether (PPE) resins, modified PPE resins, polyimide (PI) resins, polyamideimide (PAI) resins, polyetherimide (PEI) resins, polysulfone (PSU) resins, modified PSU resins, polyethersulfone resins, polyketone (PK) resins, polyarylene ether ketone resins (PAEK), polyarylate (PAR) resins, polyethernitrile (PEN) resins, phenolic resins, phenoxy resins, polytetrafluoroethylene resins, and other fluorine-based resins, as well as (v) resins selected from thermoplastic elastomers such as polyurethane resins, polybutadiene resins, and polyisoprene resins. In particular, from the viewpoints of mechanical properties and heat resistance, thermoplastic resins selected from polyphenylene sulfide resins (PPS), polyarylene ether ketone resins (PAEK), polyethersulfone resins (PES), polyetherimide (PEI), and liquid crystal polymers (LCPs) are more preferably used.

[0042] Preferred examples of the polyarylene ether ketone resin (PAEK) include polyether ketone (PEK), polyether ether ketone (PEEK), polyether ether ketone ketone (PEEKK), polyether ketone ketone (PEKK), polyether ketone ether ketone ketone (PEKEKK), polyether ether ketone ether ketone (PEEKEK), polyether ether ether ketone (PEEEK), and polyether diphenyl ether ketone (PEDEK), as well as copolymers, modified products, and blends of two or more of these resins.

[0043] [Fillers and Additives] When the reinforcing fibers are impregnated with the thermoplastic resin, the thermoplastic resin may further contain fillers, various additives, etc., as required.

[0044] As the filler, any filler generally used as a resin filler can be used, thereby providing a fiber-reinforced thermoplastic resin substrate, a laminate, a welded body, and a molded product using the same. It is possible to further improve the strength, rigidity, heat resistance, and dimensional stability.

[0045] Examples of fillers include fibrous inorganic fillers such as glass fiber, carbon fiber, potassium titanate whisker, zinc oxide whisker, aluminum borate whisker, aramid fiber, alumina fiber, silicon carbide fiber, ceramic fiber, asbestos fiber, gypsum fiber, and metal fiber; and non-fibrous inorganic fillers such as wollastonite, zeolite, sericite, kaolin, mica, talc, clay, pyrophyllite, bentonite, montmorillonite, asbestos, aluminosilicate, alumina, silicon oxide, magnesium oxide, zirconium oxide, titanium oxide, iron oxide, calcium carbonate, magnesium carbonate, dolomite, calcium sulfate, barium sulfate, magnesium hydroxide, calcium hydroxide, aluminum hydroxide, glass beads, ceramic beads, boron nitride, silicon carbide, and silica. Two or more of these fillers may be contained. Furthermore, these fillers may be hollow. Furthermore, the montmorillonite may be treated with a coupling agent such as an isocyanate compound, an organic silane compound, an organic titanate compound, an organic borane compound, or an epoxy compound. Furthermore, the montmorillonite may be an organically modified montmorillonite in which interlayer ions are cation-exchanged with an organic ammonium salt. Furthermore, as long as the fibrous filler is made of discontinuous fibers, it can be given functionality without impairing the reinforcing effect of the continuous reinforcing fibers.

[0046] Examples of various additives include antioxidants and heat stabilizers (hindered phenols, hydroquinones, phosphites and their substitution products, copper halides, iodine compounds, etc.), weathering agents (resorcinols, salicylates, benzotriazoles, benzophenones, hindered amines, etc.), release agents and lubricants (aliphatic alcohols, aliphatic amides, aliphatic bisamides, bisurea, polyethylene wax, etc.), pigments (cadmium sulfide, phthalocyanine, carbon black, etc.), dyes (nigrosine, aniline black, etc.), plasticizers (octyl p-oxybenzoate, N- butylbenzenesulfonamide, etc.), antistatic agents (alkyl sulfate-type anionic antistatic agents, quaternary ammonium salt-type cationic antistatic agents, nonionic antistatic agents such as polyoxyethylene sorbitan monostearate, betaine-type amphoteric antistatic agents, etc.), flame retardants (melamine cyanurate, hydroxides such as magnesium hydroxide and aluminum hydroxide, ammonium polyphosphate, brominated polystyrene, brominated polyphenylene oxide, brominated polycarbonate, brominated epoxy resin, or combinations of these brominated flame retardants with antimony trioxide, etc.), etc. Two or more of these may be blended.

[0047] [Method for producing a fiber-reinforced thermoplastic resin substrate] A fiber-reinforced thermoplastic resin substrate can be obtained by impregnating parallel reinforcing fibers with a thermoplastic resin. Examples of resin impregnation methods include the film method, in which a film-like thermoplastic resin is melted and pressurized to impregnate a reinforcing fiber bundle with the thermoplastic resin; the comingle method, in which a fibrous thermoplastic resin is blended with a reinforcing fiber bundle, and then the fibrous thermoplastic resin is melted and pressurized to impregnate the reinforcing fiber bundle with the thermoplastic resin; the powder method, in which a powdered thermoplastic resin is dispersed into the gaps between the fibers in the reinforcing fiber bundle, and then the powdered thermoplastic resin is melted and pressurized to impregnate the reinforcing fiber bundle with the thermoplastic resin; and the pultrusion method, in which a reinforcing fiber bundle is immersed in the molten thermoplastic resin and pressurized to impregnate the reinforcing fiber bundle with the thermoplastic resin. The pultrusion method is preferred from the viewpoint of easily producing a wide variety of fiber-reinforced thermoplastic resin substrates with various thicknesses, fiber volume contents, etc., while the powder method is preferred from the viewpoint of producing fiber-reinforced thermoplastic resin substrates with good fiber dispersion and resin impregnation properties.

[0048] The fiber-reinforced thermoplastic resin substrate is prepared, for example, in a long length and stored in a roll.

[0049] [Method for Producing Laminate] The laminate of the present invention is obtained, for example, by unwinding a fiber-reinforced thermoplastic resin substrate from a roll, cutting out a required number of sheets of the required length, and laminating them.

[0050] Next, a specific method for laminating substrates so that the orientation direction of the reinforcing fibers differs between substrates in the laminate will be described with reference to FIGS. 2 and 3 . For example, as shown in FIG. 2 , each fiber-reinforced thermoplastic resin substrate 1 is pulled out from a roll by a predetermined length and cut in a direction intersecting the orientation direction of the reinforcing fibers. Then, as shown in FIG. 2 , the fiber-reinforced thermoplastic resin substrates cut to a predetermined length are sequentially laminated while being appropriately rotated so that the reinforcing fibers of the fiber-reinforced thermoplastic resin substrate face the desired orientation direction. On the other hand, as shown in FIG. 3 , when the fiber-reinforced thermoplastic resin substrate is cut from the roll, it may be cut so that the laminate has a desired shape and fiber orientation direction. That is, each fiber-reinforced thermoplastic resin substrate 1 is cut not only in a direction intersecting the orientation direction of the reinforcing fibers, but also in a direction at ±45° or ±90° to the orientation direction of the reinforcing fibers. In this case, the cut fiber-reinforced thermoplastic resin substrates can be laminated without being rotated.

[0051] The laminate obtained in this manner is preferably integrated by applying heat and / or pressure. Examples of methods for applying heat and / or pressure include a press molding method in which the laminated fiber reinforced thermoplastic resin substrate is placed in a mold or on a press plate as described above, and then the mold or press plate is closed and pressurized, a vacuum press method in which press molding is performed with the inside of the mold or the entire press machine reduced in pressure, an autoclave molding method in which the laminated fiber reinforced thermoplastic resin substrate is placed in an autoclave and pressurized and heated as described above, a bagging molding method in which the laminated molding material is wrapped in a film or the like as described above, and heated in an oven while reducing the inside pressure and pressurizing at atmospheric pressure, a wrapping tape method in which tape is wrapped around the laminated fiber reinforced thermoplastic resin substrate as described above while applying tension and heated in an oven, and an internal pressure molding method in which the laminated fiber reinforced thermoplastic resin substrate is placed in a mold as described above, and a gas or liquid is injected into a core also placed in the mold to pressurize it.

[0052] [Electrical Conductivity] Electrical conductivity is an index for evaluating the ease with which a material transmits electrical energy. Electrical conductivity is a physical quantity that indicates the ability of a material to transmit electric current, and is usually expressed in units of S / m. In the laminate according to the present invention, even when impregnated with a thermoplastic resin, the electrical conductivity of the reinforcing fibers is dominant, so it is possible to change the electrical conductivity of the laminate by changing the reinforcing fibers.

[0053] [Method for Measuring Electrical Conductivity] The method for measuring the electrical conductivity of the laminate according to the present invention will be described below.

[0054] A test specimen obtained by polishing a cross section perpendicular to the orientation of the reinforcing fibers in the laminate is placed on the microscope stage and connected to a DC voltage / current source / monitor with electrodes formed on the top and bottom surfaces of the specimen. One of the voltage terminals is connected to a probe, and while a constant current is applied in the thickness direction of the specimen, the probe is scanned across the side of the specimen from the top edge to the bottom edge. The resistance of the specimen is measured from the distance traveled and the voltage drop. The probe is oriented perpendicular (horizontally) to the thickness direction of the specimen (the lamination direction of the fiber-reinforced thermoplastic resin substrate) as shown in Figure 4. Two measurement points are used for each substrate, as shown in Figure 5. The resistivity of each substrate is calculated from the difference between the upper and lower ends of the substrate, as shown in a and b in Figure 5. When measuring the electrical conductivity of multiple fiber-reinforced thermoplastic resin substrates, the resistivity is calculated from the difference between the upper and lower ends of the multiple substrates being measured, as shown in a and d in Figure 5. The electrical conductivity is calculated by calculating the reciprocal of the resistivity.

[0055] [Preparation of fiber-reinforced thermoplastic resin substrates with different electrical conductivities] The electrical conductivity can be controlled, for example, by using a fiber-reinforced thermoplastic resin substrate in which notches are made in the reinforcing fibers or by using a fiber-reinforced thermoplastic resin substrate in which the surface oxygen concentration of the reinforcing fibers is adjusted.

[0056] Examples of methods for obtaining a slit substrate in which reinforcing fibers are cut include, for example, preparing the aforementioned reinforcing fiber sheet by aligning the reinforcing fibers in one direction to prepare a preliminary substrate, and then cutting the substrate manually or with a cutter to form a reinforcing fiber sheet. Alternatively, when impregnating the aforementioned reinforcing fiber sheet with resin to prepare a fiber-reinforced thermoplastic resin substrate, methods include making the slits by pressing a rotary blade roller or mold with blades arranged in predetermined positions against the reinforcing fiber sheet or substrate, or by irradiating the reinforcing fiber sheet or substrate with a laser to make the slits. Methods using manual work or a cutting machine are suitable for simple slits, while press-cutting is suitable for mass production in consideration of production efficiency, and laser methods are suitable for selecting and cutting specific locations in the substrate.

[0057] When using a rotary blade roller, the roller may be directly carved to provide the desired blades, but it is preferable to wrap a sheet-like mold with blades carved into a flat plate and arranged in the desired positions around a magnetic roller, etc., since this facilitates blade replacement. By using such a rotary blade roller, even small cuts (specifically, cut lengths of 1 mm or less, for example) can be inserted well. After making the cuts, the cut base material may be further thermocompressed with a roller or the like to fill and fuse the resin in the cut portions, improving handleability.

[0058] The electrical conductivity can be controlled by making the incisions in a direction transverse to the reinforcing fibers. It is also preferable to make incisions in a direction parallel to the reinforcing fibers in order to improve formability. When making both incisions in a substrate containing reinforcing fibers and resin oriented in one direction, it is generally preferable to carry out the steps of inserting incisions transverse to the reinforcing fibers and inserting incisions parallel to the reinforcing fibers separately. By separating the steps in this way, it becomes easier to manufacture an incised substrate with consistent quality.

[0059] The method for inserting the incisions in the direction transverse to the reinforcing fibers and the incisions in the direction parallel to the reinforcing fibers does not necessarily have to be the same method, and they may be inserted by different methods. In addition, either the incisions in the direction transverse to the reinforcing fibers or the incisions in the direction parallel to the reinforcing fibers may be inserted first, and the order is not particularly limited. In addition, each may be performed multiple times.

[0060] It is preferable that the incisions transverse to the reinforcing fibers and the incisions parallel to the reinforcing fibers are basically inserted in separate steps as described above, but they may be inserted simultaneously if the incision insertion methods are different or if the blades of the rotary blade roller allow for the insertion of parallel incisions and transverse incisions simultaneously.

[0061] As a method for adjusting the surface oxygen concentration of the reinforcing fibers in a fiber-reinforced thermoplastic resin substrate, a method of performing an oxidation treatment on the reinforcing fibers before impregnating them with a thermoplastic resin can be mentioned. By performing the oxidation treatment on the reinforcing fibers, oxygen-containing functional groups are introduced onto the surface, and as a result, the surface oxygen concentration can be adjusted.

[0062] As the oxidation treatment method, gas phase oxidation, liquid phase oxidation and liquid phase electrolytic oxidation are used, but liquid phase electrolytic oxidation, which is an electrical surface treatment, is preferably used from the viewpoint of high productivity and uniform treatment.

[0063] Electrolytes used in liquid-phase electrolytic oxidation include acidic and alkaline electrolytes. Examples of acidic electrolytes include solutions or dispersions of inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, boric acid, and carbonic acid; organic acids such as acetic acid, butyric acid, oxalic acid, acrylic acid, and maleic acid; and salts such as ammonium sulfate and ammonium hydrogen sulfate. Among these, sulfuric acid and nitric acid, which exhibit strong acidity, are preferred. Examples of alkaline electrolytes include aqueous solutions of hydroxides such as sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, and barium hydroxide; aqueous solutions of carbonates such as sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, and ammonium carbonate; aqueous solutions of bicarbonates such as sodium bicarbonate, potassium bicarbonate, magnesium bicarbonate, calcium bicarbonate, barium bicarbonate, and ammonium bicarbonate; and aqueous solutions of ammonia, tetraalkylammonium hydroxide, and hydrazine.

[0064] After the electrical surface treatment step, it is also preferable to carry out a water washing step in which unnecessary electrolytic treatment solution is washed away with water, and a drying step in which the water is dried.

[0065] The reinforcing fibers are preferably subjected to an oxidation treatment so that the surface oxygen concentration (O / C) measured by X-ray photoelectron spectroscopy is less than 0.2. When the carbon fiber surface has functional groups containing oxygen atoms, such as hydroxyl groups or carboxyl groups, the conductive path of the carbon fiber is obstructed and the electrical conductivity decreases. When the O / C is 0.2 or more, the amount of functional groups is large, so the electrical conductivity is likely to decrease. Therefore, the O / C is preferably less than 0.2, and more preferably 0.1 or less.

[0066] [Lamination of fiber-reinforced thermoplastic resin substrates with different electrical conductivities] In the laminate according to the present invention, the fiber-reinforced thermoplastic resin substrates are laminated so that the surface layer and the back layer basically have different electrical conductivities. Specifically, when the total number of fiber-reinforced thermoplastic resin substrates is k (where k is a natural number of 3 or more), the electrical conductivity C (1) in the thickness direction of the fiber-reinforced thermoplastic resin substrate L (1) constituting one surface layer and the electrical conductivity C (k) in the thickness direction of the fiber-reinforced thermoplastic resin substrate L (k) constituting the other surface layer are preferably selected and laminated as appropriate so as to satisfy the relationship of formula (1).

[0067]

[0068] This allows for a greater difference in welding characteristics between the front and back of the laminate. Therefore, when welding laminates of the present invention to each other or to other components by induction heating, the fiber-reinforced thermoplastic resin substrate with higher electrical conductivity is positioned farther from the coil, preventing excessive heating of the fiber-reinforced thermoplastic resin substrate closer to the coil while more reliably heating the fiber-reinforced thermoplastic resin substrate farther from the coil, facilitating welding. If the electrical conductivity C(1) of one surface layer is less than 1.5 times the electrical conductivity C(k) of the other surface layer, the difference in electrical conductivity between the two surface layers becomes small, which can result in insufficient heating of the welding surface during induction heating or excessive heating of the surface opposite the welding surface, resulting in poor welding. The magnification is preferably 2x or more, more preferably 3x or more.

[0069] Further, in the present invention, in order to exhibit a similar effect, when the maximum value of the electrical conductivity C (n) (where n is a natural number such that 1 ≦ n ≦ k) in the thickness direction of each fiber reinforced thermoplastic resin substrate is C (max) and the minimum value is C (min), C (max) is present from the fiber reinforced thermoplastic resin substrate L (1) to the fiber reinforced thermoplastic resin substrate L ([k / 2]), and C (min) is present from the fiber reinforced thermoplastic resin substrate L ([k / 2] + 1) to the fiber reinforced thermoplastic resin substrate L (k). It may also be laminated so as to be present.

[0070] By doing so, it is possible to make the maximum value C(max) and minimum value C(min) of the electrical conductivity in the thickness direction of each layer constituting the laminate satisfy the relationship defined by formula (2), thereby improving the welding characteristics when induction heating is performed on the front and back of the laminate.

[0071]

[0072] Furthermore, when welding laminates according to the present invention to each other or to other components using induction heating, by arranging the layer with high electrical conductivity on the side farther from the coil, it is possible to reliably heat the fiber-reinforced thermoplastic resin substrate farther from the coil while preventing excessive heating of the fiber-reinforced thermoplastic resin substrate located near the coil, making welding easy and reliable.

[0073] In order to more reliably heat layers that require sufficient heating during induction heating and to prevent layers that require less heating from being excessively heated, thereby further improving weldability, it is desirable to control C(max) to be at least two times, more preferably at least three times, C(min).

[0074] In addition, it is also preferable that the laminate according to the present invention satisfies both the relationships defined by the above formulas (1) and (2).

[0075] In the laminate according to the present invention, in any of the above embodiments, when the fiber-reinforced thermoplastic resin substrates are laminated, the orientation directions of the fiber-reinforced thermoplastic resin substrate L(1) constituting one surface layer and the fiber-reinforced thermoplastic resin substrate L(2) adjacent to the fiber-reinforced thermoplastic resin substrate L(1) in the second layer from the surface layer are different from each other, and the orientation directions of the fiber-reinforced thermoplastic resin substrate L(2) and the fiber-reinforced thermoplastic resin substrate L(3) in the third layer from the surface layer are also different from each other. In this case, the orientation directions of the fiber-reinforced thermoplastic resin substrate L(1) on the surface layer side and the fiber-reinforced thermoplastic resin substrate L(3) in the third layer are the same. In this way, if the orientation directions of the reinforcing fibers constituting the fiber-reinforced thermoplastic resin substrates are different between adjacent substrates in at least the third layer from the surface layer, which will be arranged far from the coil during induction heating, the number of intersections between the reinforcing fibers increases, making it easier for electricity to pass through. In other words, the electrical conductivity near the surface layer, which will be arranged far from the coil during induction heating, can be increased.

[0076] [Preferred embodiment] The laminate according to the present invention has a fiber reinforced thermoplastic resin substrate layer A consisting of a fiber reinforced thermoplastic resin substrate L (1) constituting one surface layer and a fiber reinforced thermoplastic resin substrate L (2) constituting the second layer from the one surface layer. The electrical conductivity C (A) in the thickness direction of the fiber reinforced thermoplastic resin substrate layer A, and the fiber reinforced thermoplastic resin substrate L (k) constituting the other surface layer and the fiber reinforced thermoplastic resin substrate L (k-1) constituting the second layer from the other surface layer. The electrical conductivity C (B) in the thickness direction of the fiber reinforced thermoplastic resin substrate layer B consisting of the fiber reinforced thermoplastic resin substrate L (k-1) preferably satisfies the relationship of formula (3).

[0077]

[0078] In this way, the electrical conductivity C(A) of the two fiber-reinforced thermoplastic resin substrate layers on one surface layer side (the surface layer side that will be placed farther from the coil during induction heating) and the electrical conductivity C(B) of the two fiber-reinforced thermoplastic resin substrate layers on the other surface layer side (the surface layer side that will be placed closer to the coil during induction heating) satisfy the above-mentioned relationship, thereby enabling more reliable induction heating of the desired location. Specifically, when the electrical conductivity C(A) is 1.5 times or more than the electrical conductivity C(B), the difference in welding characteristics between the front and back of the laminate is more reliably increased, thereby more reliably preventing heating near the surface layer on the coil side, where excessive heating is not desirable during induction heating. Furthermore, the magnification of the above formula (3) is preferably 2 times or more, more preferably 3 times or more. That is, C(A) is preferably 2 times or more, more preferably 3 times or more, of C(B).

[0079] Furthermore, in the laminate according to the present invention, when the relationship between the electrical conductivity of each fiber reinforced thermoplastic resin substrate and position is graphed from the fiber reinforced thermoplastic resin substrate L1 constituting one surface layer to the fiber reinforced thermoplastic resin substrate L(k) constituting the other surface layer, it is preferable that the regression line has a negative slope. Note that the regression line in the present invention is obtained by simple linear regression, and the simple linear regression model is expressed as y = mx + c, that is, as a linear function. y: dependent variable x: independent variable m: slope c: y-intercept The slope m and y-intercept c are obtained by the following formula.

[0080]

[0081]

[0082] n: number of data.

[0083] In addition, when configuring so that the electrical conductivity value decreases from L(1) to L(k), a region where the electrical conductivity is temporarily constant in the thickness direction of the substrate may be provided, and the overall electrical conductivity value may be configured to decrease from L(1) to L(k). Also, as long as the regression line of the electrical conductivity of the fiber-reinforced thermoplastic resin substrate has a negative slope from L(1) to L(k), there may be a region where the electrical conductivity value increases locally from L(1) to L(k).

[0084] The negative slope of the regression line means that there is no region where the electrical conductivity is substantially higher than that of L(k), which prevents localized heating inside the laminate during induction heating and the resulting resin deterioration, and enables the laminate to have one surface layer made of L(1) that is most susceptible to heating.

[0085] In the present invention, the thickness of the fiber-reinforced thermoplastic resin substrate is preferably 0.05 to 0.5 mm. If the thickness is 0.05 mm or more, the strength of the welded body obtained using the laminate of the present invention and its molded article can be improved. 0.07 mm or more is more preferable. On the other hand, if the thickness is 0.5 mm or less, it is easier to impregnate the reinforcing fibers with the thermoplastic resin. 0.4 mm or less is more preferable, and 0.3 mm or less is even more preferable.

[0086] In the present invention, it is also a preferred embodiment to form a resin layer having a thickness of 1 to 50 μm on the surface layer of the fiber-reinforced thermoplastic resin substrate constituting at least one surface of the laminate. By forming a resin layer, the weld strength of the welded body can be more easily expressed without impairing the mechanical properties of the fiber-reinforced thermoplastic resin substrate during welding. Such a resin layer may be formed on only one surface of the laminate, or may be formed on both surfaces. From the viewpoint of adhesion, it is preferable that a resin layer is formed on at least the welding surface. Such a resin layer may be composed of the same type of thermoplastic resin as the matrix resin constituting the fiber-reinforced thermoplastic resin substrate, or may be composed of a thermoplastic resin different from the matrix resin. From the viewpoint of adhesion, the same type of resin is preferable.

[0087] A plurality of laminates according to the present invention can be prepared, stacked, and welded together to form a welded body. Alternatively, a welded body can be obtained by stacking a laminate according to the present invention on a different material and welding them together. In the process of obtaining a welded body, at least one welding surface is the fiber-reinforced thermoplastic resin substrate L(1) of the laminate according to the present invention, and an induction coil is provided on the side of the fiber-reinforced thermoplastic resin substrate L(k) to perform induction heating. This can increase the welding temperature at the interface between the laminates or the interface between the laminate and another material located away from the induction coil, thereby improving welding stability. Furthermore, in this case, since the electrical conductivity satisfies the relationship of the above formula (1), heating and melting of the fiber-reinforced thermoplastic resin substrate L(k) can be suppressed.

[0088] In the present invention, welding is preferably performed by induction heating or resistance heating, but induction welding by induction heating is particularly preferred from the viewpoint of efficiency and ease of control. Induction heating is performed by passing current through an induction coil to generate a magnetic field and generate an induced current in the fiber-reinforced thermoplastic resin substrate. The induction coil can be selected as desired depending on the size and shape of the laminate.

[0089] It is also preferable to apply pressure to the laminate while inductively heating it. Methods for applying pressure include pressing an induction coil against the laminate, applying pressure while using a roller to move behind the induction coil, and placing the laminate in a vacuum bag to apply a vacuum and apply pressure.

[0090] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the descriptions of these examples. Physical properties in each example and comparative example were evaluated according to the following methods.

[0091] [Thickness of fiber-reinforced thermoplastic resin substrate] The thickness of the thermoplastic resin substrate used to prepare the laminate was measured at three points in the width direction, and the average value of the three points was taken as the thickness [mm] of the fiber-reinforced thermoplastic resin substrate.

[0092] [Thickness of the resin layer on the surface of the laminate] The sample laminate was embedded in epoxy resin ("Epoquick" (registered trademark) manufactured by Buhler) and cured at room temperature for 24 hours. Then, a cross section approximately perpendicular to the orientation direction of the reinforcing fibers in the laminate was polished, and the polished surface was photographed at a magnification of 1000 times using an ultra-deep color 3D shape measuring microscope VHX-9500 (controller unit) / VHZ-100R (measurement unit) (manufactured by Keyence Corporation). The distance from the reinforcing fibers in the surface layer to the surface was measured at 10 points, and the average value was taken as the thickness [μm] of the resin layer. At this time, the 10 measured points were selected so as to be at least 50 μm apart from each other in the plane direction.

[0093] [Fiber Volume Content] After measuring the mass W0 of the fiber-reinforced thermoplastic resin substrate obtained in each Example and Comparative Example, the fiber-reinforced thermoplastic resin substrate was heated in air at 550 ° C. for 240 minutes to burn off the resin component, and the mass W1 of the remaining reinforcing fibers was measured. The fiber volume content (Vf) [%] in the fiber-reinforced thermoplastic resin substrate was calculated using the following formula.

[0094]

[0095] ρf: density of reinforcing fiber (g / cm ３ ) ρr: density of thermoplastic resin (g / cm ３ ).

[0096] [Heating Rate] The heating rate of the laminates obtained in each Example and Comparative Example was evaluated as follows. An induced current was applied to a 300 mm x 300 mm laminate using an inverter (EASYHEAT8310LI) manufactured by Aronix, with a current of 350 A and a coil-to-sample distance of 2 mm. The initial temperatures were measured on both surfaces of the laminate, and the temperature reached by the surface temperature of the laminate after 5 seconds was measured. The heating rate [°C / sec] was calculated by dividing the difference between the initial temperature and the temperature after 5 seconds by the time. A heating rate of 35°C / sec or higher on at least one surface was evaluated as good, and any other results were evaluated as bad.

[0097] [Difference in temperature rise rate between front and back] When the temperature rise rate of the surface of the laminate closer to the coil (i.e., the fiber reinforced thermoplastic resin substrate L(k) side) was the same as or smaller than the temperature rise rate of the surface farther from the coil, it was rated as good, and when it was larger, it was rated as bad.

[0098] [Electrical Conductivity] The electrical conductivity of the laminates obtained in each of the Examples and Comparative Examples was evaluated as follows.

[0099] An 8 mm x 8 mm test piece (W1 x W2) was prepared from the laminate. A cross section of the laminate approximately perpendicular to the orientation direction of the reinforcing fibers was polished, and electrodes were formed on the front and back surfaces of the laminate, which was then connected to a DC voltage / current monitor (Advantest R6246, ADC Corporation). One of the voltage terminals was connected to a probe (Micromanipulator System MMS-77 Probe, Shimadzu Corporation), and a constant current (1 mA / mm) was applied in the thickness direction of the laminate. ２ While applying a current (V / m), the probe is scanned across the side of the laminate from the top edge to the bottom edge. The resistance of the test piece is measured based on the distance traveled during scanning and the voltage drop. The probe is perpendicular to the thickness direction of the laminate (the lamination direction of the fiber-reinforced thermoplastic resin substrate). These measurements are performed on the polished cross section at two locations in the thickness direction of each fiber-reinforced thermoplastic resin substrate and at 10 locations in the length direction of the fiber-reinforced thermoplastic resin substrate, and the average value is calculated. The resistivity of each substrate is calculated from the difference between the upper and lower ends of the fiber-reinforced thermoplastic resin substrate (both surfaces of the fiber-reinforced thermoplastic resin substrate), and the resistivity of multiple substrates is calculated from the difference between the upper and lower ends of the multiple substrates across the substrate. The resistivity (unit: Ω-m) is calculated by dividing the calculated potential gradient (unit: V / m) by a constant current, and the electrical conductivity is calculated by taking the reciprocal.

[0100] [Surface oxygen concentration of carbon fiber] The surface oxygen concentration (O / C) of carbon fiber was measured by X-ray photoelectron spectroscopy according to the following procedure: First, carbon fiber was cut into 20 mm pieces and spread out on a copper sample support. １、２ The sample chamber was filled with 1 × 10 －８Torr, and the photoelectron escape angle was set to 45°. Ｓ The binding energy value of the main peak of C1 was adjusted to 285 eV. Ｓ The peak area was determined by drawing a linear baseline in the binding energy range of 275 to 290 eV. The O1s peak area was determined by drawing a linear baseline in the binding energy range of 525 to 540 eV. The X-ray photoelectron spectroscopy instrument used was an ESCA-1600 manufactured by ULVAC-PHI, Inc.

[0101] (Example 1) [Raw Materials] Carbon fiber bundles: Toray Industries, Inc. ("Torayca" (registered trademark)) T700S-12K Thermoplastic resin: Toray Industries, Inc. ("Amilan" (registered trademark) Nylon 6) A fiber-reinforced thermoplastic resin substrate was obtained by continuously feeding unidirectionally aligned carbon fiber bundles and impregnating them with a thermoplastic resin. In addition, in order to use a portion of the obtained fiber-reinforced thermoplastic resin substrate as a slit substrate, the substrate was passed through a rotary blade roller to make a slit. In this way, fiber-reinforced thermoplastic resin substrates having various electrical conductivities as shown in Table 1 were obtained.

[0102] The obtained fiber-reinforced thermoplastic resin substrates were laminated to form the laminate configuration shown in Table 1, and pressed under a pressure of 1.5 MPa. The obtained laminate was used for the evaluations. The evaluation results are shown in Table 1.

[0103] (Comparative Examples 1 to 3) A laminate was prepared in the same manner as in Example 1 except that the fiber reinforced thermoplastic resin substrates were laminated so as to have the lamination configuration shown in Table 1, and heating and electrical conductivity were evaluated.

[0104]

[0105] As is clear from Table 1, in Example 1, the temperature rise rate was good on both the surface closer to the coil (hereinafter referred to as the "front surface") and the surface farther from the coil (hereinafter referred to as the "back surface"), and the temperature rise rate on the back surface was faster than on the front surface, resulting in a good result of the temperature rise being faster on the back surface farther from the coil. In contrast, in Comparative Example 1, the temperature rise rate on both the front and back surfaces was insufficient, and the temperature rise rate on the back surface was slower than on the front surface, resulting in the surface closer to the coil rising more quickly than the back surface. In Comparative Example 2, the temperature rise rate was good on both the front and back surfaces, but the temperature rise rate on the back surface was slower than on the front surface, resulting in the surface closer to the coil rising more quickly than the back surface. In Comparative Example 3, the temperature rise rate on both the front and back surfaces was insufficient.

[0106] (Examples 2 to 5) Unidirectionally aligned carbon fiber bundles were subjected to liquid-phase electrolytic oxidation treatment using an alkaline electrolyte and an acidic electrolyte to obtain two types of carbon fiber bundles having the surface oxygen concentrations shown in Table 2. These were each continuously fed out and impregnated with a thermoplastic resin to obtain fiber-reinforced thermoplastic resin substrates (without slits). The thermoplastic resin used was polyphenylene sulfide ("TORELINA" (registered trademark) manufactured by Toray Industries, Inc.).

[0107] The obtained fiber-reinforced thermoplastic resin substrates were stacked to form the laminate configuration shown in Table 2 (i.e., the fiber-reinforced thermoplastic resin substrate made of carbon fiber treated with an alkaline electrolyte was stacked on the side closer to the coil, and the fiber-reinforced thermoplastic resin substrate made of carbon fiber treated with an acidic electrolyte was placed farther from the coil), and pressed under a pressure of 1.5 MPa. Heating and electrical conductivity were evaluated using the obtained laminate. The evaluation results are shown in Table 2.

[0108] Comparative Examples 4 to 6 Laminates were prepared in the same manner as in Example 2, except that the electrolyte solution for the liquid-phase electrolytic oxidation treatment applied to the carbon fiber and the laminate structure of the substrate in the laminate were changed to those shown in Table 3, and heating and electrical conductivity were evaluated.

[0109]

[0110]

[0111] As is clear from Table 2, Examples 2-5 showed a high and favorable temperature rise rate on the back surface, and the temperature rise rate on the back surface was faster than that on the front surface closer to the coil, resulting in favorable results. In Example 3, good results were obtained even when C(min) was not in the outermost layer. In Examples 4 and 5, although the C(1) / C(k) value was less than 1.5, good results were obtained by satisfying the C(max) / C(min) requirement. In particular, Example 4 achieved even better results by also satisfying the C(A) / C(B) requirement. In contrast, as shown in Table 3, Comparative Example 4 showed good temperature rise rates on both the front and back surfaces, but the surface closer to the coil rose faster than the back surface. In Comparative Examples 5 and 6, the temperature rise rate on the back surface, which was far from the coil, was the same as that on the surface closer to the coil, but the temperature rise rates on both the front and back surfaces were not sufficient.

[0112] The laminate of the present invention can be molded into a desired shape by any molding method such as autoclave molding, press molding, or film molding.

[0113] Taking advantage of their excellent properties, the laminates and welded articles of the present invention can be used in a variety of applications, such as aircraft parts, automobile parts, electrical and electronic parts, building materials, various containers, daily necessities, household goods, and sanitary products. The laminates and welded articles of the present invention are particularly preferably used for applications requiring stable mechanical properties, such as aircraft engine peripheral parts, exterior aircraft parts, vehicle frames as automobile body parts, automobile engine peripheral parts, automobile underhood parts, automobile gear parts, automobile interior parts, automobile exterior parts, intake and exhaust system parts, engine cooling water system parts, automobile electrical parts, and electrical and electronic parts.

[0114] Specifically, the laminate and welded article of the present invention can be used for aircraft engine peripheral parts such as fan blades, aircraft-related parts such as landing gear pods, winglets, spoilers, edges, rudders, elevators, failings, and ribs, automobile body parts such as various seats, front bodies, underbodies, various pillars, various members, various frames, various beams, various supports, various rails, and various hinges, automobile engine peripheral parts such as engine covers, air intake pipes, timing belt covers, intake manifolds, filler caps, throttle bodies, and cooling fans, automobile underhood parts such as cooling fans, radiator tank tops and bases, cylinder head covers, oil pans, brake piping, fuel piping tubes, and exhaust system parts, automobile gear parts such as gears, actuators, bearing retainers, bearing cages, chain guides, and chain tensioners, shift lever brackets, steering lock brackets, key cylinders, door inner handles, door handle cowls, interior mirror brackets, air conditioner switches, instrument panels, and the like. Automotive interior parts such as front and rear fenders, fuel lids, door panels, door mirror stays, tailgate panels, license garnishes, roof rails, engine mount brackets, rear garnishes, rear spoilers, trunk lids, rocker moldings, moldings, lamp housings, front grilles, mudguards, side bumpers, and other automotive exterior parts; intake and exhaust system parts such as air intake manifolds, intercooler inlets, turbochargers, exhaust pipe covers, inner bushings, engine mounts, engine head covers, resonators, and throttle bodies; engine coolant system parts such as chain covers, thermostat housings, outlet pipes, radiator tanks, alternators, and delivery pipes; automotive electrical parts such as connectors, wire harness connectors, motor parts, lamp sockets, sensors, on-board switches, and combination switches; and electrical and electronic parts such as generators, electric motors, transformers, current transformers, voltage regulators,Rectifiers, resistors, inverters, relays, power contacts, switches, circuit breakers, switches, knife switches, multi-pole rods, motor cases, television housings, notebook computer housings and internal parts, CRT display housings and internal parts, printer housings and internal parts, mobile phone, mobile PC, handheld mobile and other mobile device housings and internal parts, IC and LED housings, capacitor base plates, fuse holders, various gears, various cases, electrical parts such as cabinets, connectors, SMT compatible connectors, card connectors, jacks, coils, coil bobbins They are preferably used in electronic components such as sensors, LED lamps, sockets, resistors, relays, relay cases, reflectors, small switches, power supply components, coil bobbins, capacitors, variable capacitor cases, optical pickup chassis, oscillators, various terminal boards, transformers, plugs, printed circuit boards, tuners, speakers, microphones, headphones, small motors, magnetic head bases, power modules, Si power modules and SiC power modules, semiconductors, liquid crystal displays, FDD carriages, FDD chassis, motor brush holders, transformer members, parabolic antennas, and computer-related components.

[0115] REFERENCE SIGNS LIST 1 fiber-reinforced thermoplastic resin substrate 5 scanning direction 6 probe 10 laminate

Claims

1. A laminate in which a plurality of fiber-reinforced thermoplastic resin substrates are laminated, wherein the fiber-reinforced thermoplastic resin substrate is formed by impregnating parallel, electrically conductive reinforcing fibers with a thermoplastic resin, and the plurality of fiber-reinforced thermoplastic resin substrates are such that the orientation direction of the fiber-reinforced thermoplastic resin substrate L (1) constituting one surface layer and the orientation direction of the fiber-reinforced thermoplastic resin substrate L (2) in the second layer from the one surface layer adjacent to the fiber-reinforced thermoplastic resin substrate L (1) are different from each other, and the orientation direction of the fiber-reinforced thermoplastic resin substrate L (2) and the orientation direction of the fiber-reinforced thermoplastic resin substrate L (3) in the third layer from the one surface layer are different from each other, and further, when the total number of the fiber-reinforced thermoplastic resin substrates is k (where k is a natural number of 3 or more), the electrical conductivity C (1) in the thickness direction of the fiber-reinforced thermoplastic resin substrate L (1) constituting one surface layer and the electrical conductivity C (k) in the thickness direction of the fiber-reinforced thermoplastic resin substrate L (k) constituting the other surface layer are related by the following formula (1).

2. A laminate in which a plurality of fiber-reinforced thermoplastic resin substrates are laminated, wherein the fiber-reinforced thermoplastic resin substrate is formed by impregnating electrically conductive reinforcing fibers aligned in parallel with a thermoplastic resin, and the plurality of fiber-reinforced thermoplastic resin substrates have a fiber-reinforced thermoplastic resin substrate L(1) constituting one surface layer and a fiber-reinforced thermoplastic resin substrate L(2) in the second layer from the surface layer adjacent to the fiber-reinforced thermoplastic resin substrate L(1) in a direction different from each other, and the orientation direction of the fiber-reinforced thermoplastic resin substrate L(2) in the third layer from the surface layer is mutually different. Furthermore, when the total number of the fiber reinforced thermoplastic resin substrates is k (where k is a natural number of 3 or more), and the maximum value of the thickness direction electrical conductivity C(n) (where n is a natural number such that 1≦n≦k) of each fiber reinforced thermoplastic resin substrate is C(max) and the minimum value is C(min), C(max) exists from the fiber reinforced thermoplastic resin substrate L(1) to the fiber reinforced thermoplastic resin substrate L([k / 2]), and C(min) exists from the fiber reinforced thermoplastic resin substrate L([k / 2] + 1) to the fiber reinforced thermoplastic resin substrate L(k), and C(max) and C(min) have the relationship of formula (2).

3. The thickness direction electrical conductivity C (A) of the fiber-reinforced thermoplastic resin substrate layer A consisting of the fiber-reinforced thermoplastic resin substrate L (1) constituting one of the surface layers and the fiber-reinforced thermoplastic resin substrate L (2) constituting the second layer from the one surface layer, and the fiber-reinforced thermoplastic resin substrate L (k) constituting the other surface layer and the fiber-reinforced thermoplastic resin substrate L (k-1) constituting the second layer from the other surface layer. The laminate described in claim 1 or 2, wherein the electrical conductivity C (B) in the thickness direction is related by formula (3).

4. A laminate described in any one of claims 1 to 3, wherein the regression line of the electrical conductivity of the plurality of fiber-reinforced thermoplastic resin substrates has a negative slope from the fiber-reinforced thermoplastic resin substrate L(1) to the fiber-reinforced thermoplastic resin substrate L(k).

5. A laminate according to any one of claims 1 to 4, wherein the thickness of the fiber-reinforced thermoplastic resin substrate is 0.05 mm to 0.5 mm.

6. The laminate according to any one of claims 1 to 5, which has a resin layer having a thickness of 1 to 50 µm on at least one surface of the laminate.

7. A welded body in which a plurality of laminates according to any one of claims 1 to 6 are stacked and welded together, or a welded body in which a laminate according to any one of claims 1 to 6 is stacked and welded together with another material, in which the fiber-reinforced thermoplastic resin substrate L(1) forms a weld interface in the laminate.

8. The welded body according to claim 7, wherein said welding is performed by induction heating.

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