Sandwich structure body, and integrally-molded body using same

Abstract

In order to provide an integrally-molded body that allows for thinning while achieving both the securing of installation space for an internal component and an outward design capable of coping with the demand for a flat exterior, a surface layer composed of a fiber-reinforced resin member comprising continuous reinforcing fibers and a resin is provided on both surfaces of a core layer selected from the group consisting of a film, a foam, and a porous substrate, and k (k is a natural number of 3 or more) stepped portions in which a non-design surface and a design surface are parallel and the distance between the surfaces varies are provided, and the absolute value |Ht(n)-Ht(n-1)| and |Ht(n)-Ht(n +1)| of the difference between the inter-surface distance Ht(n) [mm] of the n-th stepped portion (1≤n≤k) and the inter-surface distance Ht(n-1) [mm], Ht(n+1) [mm] of the stepped portions on both sides of the n-th stepped portions is set within the range of 0.05-5.0 [mm], thereby forming a sandwich structure body.

Description

Sandwich structure and integrally molded body using the same

[0001] The present invention relates to a sandwich structure suitable for applications requiring light weight, high strength, high rigidity and thin wall thickness, and is used as components or housings for personal computers, office automation equipment, mobile phones, etc., and to an integrally molded article using the same.

[0002] Currently, as electrical and electronic devices such as personal computers, office automation equipment, audiovisual equipment, mobile phones, telephones, facsimiles, home appliances, toys, etc. become more portable, there is a demand for them to be smaller and lighter. To achieve this, miniaturization of the components inside the housing and thinning of the housing can be achieved.

[0003] Patent Document 1 discloses an integrated molded body (C) comprising a laminate (A) having a design surface on one side thereof and a resin member (B) made of discontinuous reinforcing fibers and a thermoplastic resin bonded to the outer peripheral side of the laminate (A). The laminate (A) has a surface layer and a core layer, and has a sandwich structure in which the core layer is sandwiched between the surface layers. The surface layer includes a fiber-reinforced resin member made of continuous reinforcing fibers and a resin, and the core layer is any one selected from the group consisting of a film, a foam, and a porous substrate. Furthermore, a convex portion protruding toward the design surface is formed in a portion of the laminate (A), and the convex portion has a flat portion (E) at its maximum height. The distance between an extension line extending from the flat portion (E) in the in-plane direction of the flat portion (E) and an intersection point (F) where the extension line is moved perpendicular to the flat portion (E) and intersects with the resin member (B) is 0.05 to 4.0 mm. It is disclosed that this configuration not only provides high strength, high rigidity, light weight, and thin wall thickness, but also makes it easier to ensure space for installing components inside the housing of a personal computer or the like, and results in an integrated molded body with excellent design in terms of appearance.

[0004] International Publication No. 2023 / 276848

[0005] However, although the integrally molded body described in Patent Document 1 contributes to ensuring installation space for internal components, the laminate (A) has a characteristic of having a convex portion that protrudes convexly toward the design surface, making it difficult to apply to requirements for a flat external design, and there is room for improvement in terms of improving the external design. In other words, in order to achieve the further thinning of recent housings, it is essential to provide a sandwich structure that combines ensuring installation space for internal components with an external design that can meet the requirements for a flat external appearance.

[0006] Therefore, an object of the present invention is to provide an integrated molded body that can achieve high strength, high rigidity, light weight, and thin wall thickness while ensuring both installation space for internal components and a flat exterior design.

[0007] In order to solve the above problems, the present invention employs any of the following configurations: [1] A sandwich structure having surface layers provided on both sides of a core layer, wherein the surface layers include a member made of a fiber-reinforced resin member made of continuous reinforcing fibers and a resin, and the surface layers provided on both sides are parallel to each other at least in part, the core layer is any one selected from the group consisting of a film, a foam, and a porous substrate, one of the surface layers is a flat design surface and the other surface layer is a non-design surface having an uneven surface, at least the outer periphery of the sandwich structure is provided with a thinnest part where the inter-face distance between the non-design surface and the design surface is the shortest, and in a cross section cut in the longitudinal direction of the sandwich structure, k (k is a natural number of 3 or more) step portions are provided where the non-design surface and the design surface are parallel and have different inter-face distances, a sandwich structure according to claim 1, wherein the absolute values ​​of the differences |Ht(n) - Ht(n-1)| and |Ht(n) - Ht(n+1)| between the face-to-face distance Ht(n) [mm] of the nth step portion (1≦n≦k) and the face-to-face distances Ht(n-1) [mm] and Ht(n+1) [mm] of the step portions or thinnest portions adjacent to the nth step portion are in the range of 0.05 to 5.0 [mm], respectively. [2] The sandwich structure according to claim 1, wherein, on the cross section, a boundary surface connecting the nth (1≦n≦k) step portion present in the sandwich structure and the step portion or thinnest portion adjacent to the nth step portion is a flat slope, and an angle formed between an extension line of the thicker step portion and the boundary surface is 1 to 30°. [3] The sandwich structure according to [1] or [2], wherein the core layer is a porous substrate containing discontinuous reinforcing fibers and a thermoplastic resin. [4] The sandwich structure according to any one of [1] to [3], wherein the surface layer is a fiber-reinforced member made of unidirectional prepreg. [5] The sandwich structure according to any one of [1] to [4], wherein the fiber-reinforced resin member constituting the surface layer contains a thermosetting resin, the core layer contains a thermoplastic resin, and the glass transition temperature Tgs of the thermosetting resin is 30°C or more lower than the heat distortion temperature Tfc of the thermoplastic resin.[6] An integrally molded body in which the sandwich structure described in [1] to [5] is bonded to a resin member, and further has a thermoplastic resin layer in at least a part of the thinnest wall portion, and the resin member is bonded via the thermoplastic resin layer.

[0008] According to the present invention, it is possible to obtain a lightweight, thin-walled, high-strength, and high-rigidity integrally molded body that can secure installation space for internal components while also achieving a flat exterior design, and is suitable for use in the housings of electronic devices such as personal computers.

[0009] 1 is a schematic cross-sectional view of a conventional sandwich structure having substantially no steps (concaves and recesses) (k=1); 2 is a partial schematic cross-sectional view of a sandwich structure using a porous layer as a core layer; 3 is a schematic diagram of a matrix resin and reinforcing fibers having a three-dimensional network structure in a porous layer; 4 is a partial schematic cross-sectional view of a sandwich structure having a high-density resin-rich layer at the center of a porous layer (core layer); 5 is a schematic cross-sectional view of a sandwich structure having steps (concaves and recesses) formed therein, showing one embodiment of the present invention, in which (a) shows an embodiment in which the concaves and convexes are repeated at regular intervals, and (b) shows an embodiment in which the steps are distributed in a convex shape overall; 6 is a schematic cross-sectional view of a sandwich structure, in which (a) is a partial schematic cross-sectional view showing an embodiment in which the boundary surface connecting the thinnest portion and the thick portion adjacent to the thinnest portion is a flat slope; and 7 is a diagram showing an embodiment in which the boundary surface connecting the nth step portion and the step portion adjacent to the nth step portion and the thinnest portion provided on the outer periphery of the sandwich structure is a flat slope. FIG. 1 is a partial schematic cross-sectional view showing an enlarged view of a joint portion of an integrally molded body after a resin member is injected into a sandwich structure provided with a thermoplastic resin layer. FIG. 2 is a schematic diagram of recycled fibers used in the resin member. FIG. 3 is a partial schematic cross-sectional view showing an enlarged view of a joint portion of an integrally molded body after a resin member and a frame member are injected into a sandwich structure. FIG. 4 is a schematic diagram of a cavity shape of a mold used in Examples. FIG. 5 is a schematic cross-sectional view of a sandwich structure obtained in Examples, showing yet another embodiment of the present invention, in which steps (concavities and recesses) are formed asymmetrically with respect to the center in the longitudinal direction.

[0010] Hereinafter, embodiments will be described with reference to the drawings. Note that the present invention is not limited to the drawings or examples. In this specification, the notation "a to b" in the description of a range of values ​​means a to b, unless otherwise specified.

[0011] The sandwich structure according to the present invention is a sandwich structure 100 having surface layers 110 on both sides of a core layer 120, as shown in the schematic cross-sectional views of Figures 5(a) and 5(b) and 12. The surface layers 110 include a fiber-reinforced resin member made of continuous reinforcing fibers and resin, and the surface layers 110 on both sides of the core layer 120 are at least partially parallel to each other. The core layer 120 is any one selected from the group consisting of a film, a foam, and a porous substrate. One surface layer 110 is a flat design surface 110a, and the other surface layer 110 is a non-design surface 110b having an uneven surface. The sandwich structure 100 has a thinnest-walled portion 150 on at least its outer periphery, where the inter-surface distance between the non-design surface 110b and the design surface 110a is the shortest. In a cross section cut longitudinally through the sandwich structure 100 (preferably at regular intervals along the non-design surface 110b), there are multiple, specifically k (where k is a natural number greater than or equal to 3), step portions in which the non-design surface (top surface) and the design surface are parallel and have different inter-surface distances. The absolute values ​​of the differences between the inter-surface distance Ht(n) [mm] of the nth step portion (1≦n≦k) counting from the thinnest wall portion 150 and the inter-surface distances Ht(n−1) [mm] and Ht(n+1) [mm] of the step portions or thinnest wall portions adjacent to the nth step portion, |Ht(n)−Ht(n−1)| and |Ht(n)−Ht(n+1)|, respectively, are in the range of 0.05 to 5.0 [mm]. The positions of the step portions are determined from the perspective of the layout of the internal components. Therefore, examples include a configuration in which the holes are arranged symmetrically with respect to the center of the longitudinal cross section of the sandwich structure 100 as shown in Figure 5, and a configuration in which the holes are arranged asymmetrically with respect to the center of the longitudinal cross section of the sandwich structure 100 as shown in Figure 12.

[0012] In this specification, the "nth step portion" does not include the thinnest portion 150 provided on the outer periphery of the sandwich structure 100. Furthermore, the "nth" refers to the portions on the cut surface where the non-design surface and the design surface are parallel to each other but are spaced apart from each other, counting sequentially from one of the thinnest portions 150 provided on the outer periphery. Furthermore, "every constant width" does not only refer to a case where each step portion is provided with the same width, but also includes a case where, for example, a wide step portion and a narrow step portion are repeated, that is, a case where a certain periodicity is observed.

[0013] From the viewpoints of thinness and mechanical properties, the fiber-reinforced resin member included in the surface layer 110 of the sandwich structure 100 is preferably composed of unidirectional continuous reinforcing fibers and resin. From the viewpoints of the mechanical properties of the sandwich structure, it is preferable that such a fiber-reinforced resin member be formed in two or more layers, and that the orientation direction of the fibers in adjacent layers be different. From the viewpoint of isotropy, the deviation angle between the orientation directions of the fibers in adjacent layers is preferably 45°, 60°, or 90°, and from the viewpoints of thinness and light weight, 90° is preferred.

[0014] Examples of continuous reinforcing fibers that can be used to form the surface layer 110 include metal fibers such as aluminum fibers, brass fibers, and stainless steel fibers, inorganic fibers such as polyacrylonitrile (PAN), rayon, lignin, and pitch-based carbon fibers and graphite fibers, glass fibers, silicon carbide fibers, silicon nitride fibers, alumina fibers, silicon carbide fibers, and boron fibers, and organic fibers such as aramid fibers, polyparaphenylene benzobisoxazole (PBO) fibers, polyphenylene sulfide fibers, polyester fibers, acrylic fibers, nylon fibers, and polyethylene fibers. These reinforcing fibers may be used alone or in combination of two or more.

[0015] Among these, carbon fibers are preferred from the viewpoints of specific strength, specific rigidity, and light weight, and carbon fibers (including graphite fibers) such as polyacrylonitrile (PAN)-based carbon fibers, rayon-based carbon fibers, lignin-based carbon fibers, and pitch-based carbon fibers, which are excellent in specific strength and specific rigidity, are preferably used. In the present invention, polyacrylonitrile (PAN)-based carbon fibers are preferred from the viewpoints of cost and processability.

[0016] When carbon fibers are used as the continuous reinforcing fibers constituting the sandwich structure 100, the tensile modulus is preferably in the range of 200 to 1000 GPa from the viewpoint of the rigidity of the sandwich structure 100, and more preferably in the range of 400 to 900 GPa from the viewpoint of the handleability of the prepreg. If the tensile modulus of the carbon fiber is less than 200 GPa, the rigidity of the sandwich structure may be poor, while if it is greater than 1000 GPa, the crystallinity of the carbon fiber must be increased, making it difficult to manufacture the carbon fiber. It is preferable that the tensile modulus of the carbon fiber is within the above range in terms of further improving the rigidity of the sandwich structure and improving the manufacturability of the carbon fiber. The tensile modulus of the carbon fiber can be measured by the strand tensile test described in JIS R7301-1986.

[0017] When carbon fibers are used as the continuous reinforcing fibers that form the surface layer of the sandwich structure 100, the density is 1.6 g / cm in the case of polyacrylonitrile (PAN)-based carbon fibers. ３ 2.0g / cm or more ３ From the viewpoint of improving rigidity, 1.8 g / cm ３ 2.0g / cm or more ３ or less, and in the case of pitch-based carbon fibers, 2.0 g / cm ３ 2.5g / cm or more ３ From the viewpoint of cost, 2.0 g / cm ３ 2.3g / cm or more ３ It is preferable that:

[0018] These fibers may be surface-treated, such as by coating with a metal, by using a coupling agent, by using a sizing agent, or by applying an additive.

[0019] The resin (i.e., matrix resin) used in the surface layer 110 may be either a thermoplastic resin or a thermosetting resin. There are no particular limitations on the thermoplastic resin, and any of the thermoplastic resins exemplified below may be used. For example, polyester resins such as polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, polytrimethylene terephthalate (PTT) resin, polyethylene naphthalate (PEN resin), and liquid crystal polyester resin; polyolefin resins such as polyethylene (PE resin) and polypropylene (PP resin); polyarylene sulfide resins such as polyoxymethylene (POM) resin, polyamide (PA) resin, and polyphenylene sulfide (PPS) resin; fluorine-containing resins such as polyketone (PK) resin, polyether ketone (PEK) resin, polyether ether ketone (PEEK) resin, polyether ketone ketone (PEKK) resin, polyether nitrile (PEN) resin, and polytetrafluoroethylene resin; In addition to crystalline resins such as styrene-based resins, liquid crystal polymers (LCPs), and styrene-based resins, amorphous resins such as polycarbonate (PC) resins, polymethyl methacrylate (PMMA) resins, polyvinyl chloride (PVC) resins, polyphenylene ether (PPE) resins, polyimide (PI) resins, polyamideimide (PAI) resins, polyetherimide (PEI) resins, polysulfone (PSU) resins, polyethersulfone resins, and polyarylate (PAR) resins, as well as thermoplastic resins selected from phenol-based resins, phenoxy resins, and thermoplastic elastomers such as polystyrene-based resins, polyurethane-based resins, polybutadiene-based resins, polyisoprene-based resins, and acrylonitrile-based resins, as well as copolymers and modified products thereof.

[0020] Among these, polyolefin resins are preferred from the viewpoint of the light weight of the resulting molded product, polyamide resins are preferred from the viewpoint of strength, amorphous resins such as polycarbonate resins, styrene-based resins, and modified polyphenylene ether-based resins are preferred from the viewpoint of surface appearance, polyarylene sulfide resins are preferred from the viewpoint of heat resistance, and polyether ether ketone resins are preferably used from the viewpoint of continuous use temperature.

[0021] The exemplified thermoplastic resins may contain impact resistance improvers such as elastomers or rubber components, other fillers, and additives, provided that the object of the present invention is not impaired. Examples of these include inorganic fillers, flame retardants, conductivity imparting agents, crystal nucleating agents, ultraviolet absorbers, antioxidants, vibration dampers, antibacterial agents, insect repellents, deodorizing agents, color inhibitors, heat stabilizers, release agents, antistatic agents, plasticizers, lubricants, colorants, pigments, dyes, foaming agents, foam control agents, and coupling agents.

[0022] When the resin constituting the surface layer 110 is a thermosetting resin, preferred examples include unsaturated polyester resin, vinyl ester resin, epoxy resin, phenol (resol type) resin, urea-melamine resin, polyimide resin, maleimide resin, and benzoxazine resin. These resins may also be blends of two or more. Among these, epoxy resins are particularly preferred from the viewpoint of the mechanical properties and heat resistance of the molded body. When using an epoxy resin, it is preferred that the resin composition contain the epoxy resin as the main component in order to achieve its excellent mechanical properties. Specifically, the resin composition preferably contains 60% by weight or more of the epoxy resin.

[0023] From the viewpoint of ease of handling, the surface layer 110 is preferably made of prepreg, which is a base material in which continuous reinforcing fibers are pre-impregnated with resin. Furthermore, one surface layer 110 is preferably made by laminating two or more sheets (two layers) of prepreg.

[0024] The prepregs constituting each surface layer 110 can be freely set and laminated according to the desired rigidity, thickness, strength, etc. of the sandwich structure 100. From the viewpoint of the thickness of the sandwich structure 100, the thickness of each prepreg is preferably 0.05 to 1.00 mm. More preferably, from the viewpoint of the degree of freedom in lamination design, the thickness is preferably 0.05 to 0.20 mm.

[0025] From the viewpoint of the rigidity of the sandwich structure, it is preferable to use unidirectional (UD) prepregs for the surface layer 110 of the sandwich structure 100. Even more preferably, each surface layer is quasi-isotropic. On the other hand, from the viewpoint of the appearance of the sandwich structure 100, a fiber woven fabric substrate can also be used for the surface layer 110. A fiber woven fabric substrate is a substrate formed by using continuous reinforcing fiber bundles, each consisting of 1,000 continuous reinforcing fibers, as warp and weft yarns, and crossing these two sets of yarns at substantially right angles using a loom, and then impregnating the fabric with resin. A bundle of 1,000 continuous reinforcing fibers is generally called a 1K bundle, a bundle of 3,000 fibers is called a 3K bundle, and a bundle of 12,000 fibers is called a 12K bundle.

[0026] The fiber woven fabric is preferably at least one fabric selected from plain weave, twill weave, satin weave, and satin weave. Since fiber woven fabrics have distinctive fiber patterns, by using a fiber woven fabric substrate that highlights the distinctive fiber pattern as the outermost layer (design surface side) of the sandwich structure, an integrated molded body can be produced that exhibits a novel surface pattern. The continuous reinforcing fiber bundles are preferably 1K to 24K, and more preferably 1K to 6K from the viewpoint of the stability of the fiber pattern during processing.

[0027] When a fiber woven fabric substrate is used for the surface layer 110 of the sandwich structure 100, the core layer 120 acts as a cushion, making it possible to reduce the size of resin-deficient spots called "pits" formed at the intersections of the warp and weft threads. ２ Preferably less than 0.2 mm ２ is less than.

[0028] Importantly, the core layer 120 of the sandwich structure 100 is one selected from a film, a foam, and a porous substrate.

[0029] When a film is used as the core layer, the above-mentioned thermoplastic resins that can be used for the surface layer can be used.

[0030] Furthermore, suitable foam materials for the core layer 120 include polyurethane resin, phenolic resin, melamine resin, acrylic resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polystyrene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyetherimide resin, and polymethacrylimide resin. Specifically, to ensure lightweight properties, it is preferable to use a resin with a lower apparent density than the surface layer. Polyurethane resin, acrylic resin, polyethylene resin, polypropylene resin, polyetherimide resin, and polymethacrylimide resin are particularly preferred. The exemplified resins may contain impact resistance improvers such as elastomers or rubber components, as well as other fillers and additives, provided they do not impair the objectives of the present invention. Examples of such additives include inorganic fillers, flame retardants, conductivity imparting agents, crystal nucleating agents, ultraviolet absorbers, antioxidants, vibration dampers, antibacterial agents, insect repellents, deodorizers, color inhibitors, heat stabilizers, mold release agents, antistatic agents, plasticizers, lubricants, colorants, pigments, dyes, foaming agents, foam control agents, and coupling agents. In addition, the foam preferably has voids from the viewpoint of reducing the weight of the core.

[0031] 2, the core layer 120 may be a porous layer 122, which may be formed from a porous substrate made of discontinuous reinforcing fibers and a thermoplastic resin. The discontinuous reinforcing fibers constituting the porous layer 122 may be the same as the continuous reinforcing fibers used in the surface layer 110, but cut to a desired length.

[0032] Here, continuous reinforcing fibers and discontinuous reinforcing fibers are defined. Continuous reinforcing fibers are fibers that are arranged substantially continuously across the entire length or width of a sandwich structure, such as the reinforcing fibers contained in the surface layers of a sandwich structure. Discontinuous reinforcing fibers are fibers that are intermittently separated. Generally, fibers used in unidirectional fiber-reinforced resins formed from a substrate in which resin is impregnated with reinforcing fibers aligned in one direction, or fiber-reinforced resins formed from a fiber woven fabric substrate in which resin is impregnated with a fiber woven fabric, fall under the category of continuous reinforcing fibers. Reinforcing fibers contained in SMC (sheet molding compound) substrates used in press molding and pellet materials used in injection molding fall under the category of discontinuous reinforcing fibers.

[0033] The thermoplastic resin used for the porous layer 122 may be the same as the thermoplastic resins that can be used for films and foams.

[0034] The thermoplastic resin may also be present as a matrix resin with a three-dimensional network structure, as shown in FIG. 3 . The thermoplastic resin covers the closed surfaces formed by the discontinuous reinforcing fibers 125 in a three-dimensional network structure composed of the discontinuous reinforcing fibers 125 in a planar manner and forms multiple pores 126. In this way, the formation of the pores 126 makes the thermoplastic resin less likely to break in the stretching direction when it stretches. Furthermore, because the thermoplastic resin can bond the discontinuous reinforcing fibers 125 together, it can bond them more firmly than in a state where the thermoplastic resin is broken (a state in which the thermoplastic resin covers the intersections of the intersecting discontinuous reinforcing fibers in a block rather than in a film-like manner). Furthermore, the formation of multiple pores 126 in the thermoplastic resin allows it to stretch longer, and the porosity of the porous layer 122 can be increased, which is expected to further reduce the weight. This structure increases the rigidity of the sandwich structure 100.

[0035] 4, in a sandwich structure 100 using a porous layer as a core layer, it is also preferable to provide a high-density resin-rich layer 130 in the center of the core layer 120. This increases the shear strength of the sandwich structure 100. Furthermore, by arranging low-density porous layers 122 on both sides of the resin-rich layer 130, it is possible to achieve both strength and weight reduction.

[0036] The thickness of the resin-rich layer 130 is preferably 1 to 60% of the thickness of the core layer 120. By setting the thickness within this range, it is possible to obtain a stronger sandwich structure 100. Furthermore, from the viewpoint of adhesion between the surface layer 110 and the core layer 120, the thickness is preferably 1 to 30% of the thickness of the core layer 120, and more preferably 3 to 20% of the thickness of the core layer 120.

[0037] Of the three types of core layers mentioned above (any one selected from the group consisting of a film, a foam, and a porous substrate), a porous substrate is more preferable from the viewpoint of the rigidity of the sandwich structure and the appearance of the stepped portion.

[0038] In the present invention, the porous layer 122 is preferably formed by expanding a porous layer precursor containing discontinuous reinforcing fibers and a thermoplastic resin by 1.1 to 7.0 times in the thickness direction. From the viewpoint of achieving both moldability and light weight, the expansion is preferably 1.5 to 2.0 times, and more preferably 2.0 to 3.5 times.

[0039] Furthermore, the specific gravity of the sandwich structure 100 is preferably 0.5 to 1.4 from the viewpoint of weight reduction, and more preferably 0.5 to 1.0.

[0040] It is important that the surface layers provided on both sides of the sandwich structure 100 are at least partially parallel to each other. The surface layers may have curved portions, but it is important that the surface layers provided on both sides are at least partially parallel to each other so that the inter-surface distance described below can be measured.

[0041] It is also important that one surface of the sandwich structure 100 is a flat design surface and the other surface is a non-design surface with an uneven surface. By combining a flat design surface with an uneven non-design surface, it is possible to secure a larger space for installing internal components while maintaining a good appearance on the design surface side. Here, "the surface layer is a flat design surface" means that when the area of ​​the sandwich structure 100 projected in the thickness direction from the design surface side is 100%, the area of ​​the flat region is at least 70% or more.

[0042] Furthermore, it is important that the sandwich structure 100 has a thinnest portion on at least the periphery where the inter-face distance between the non-design surface and the design surface is the shortest, and that in a cross section cut in the longitudinal direction of the sandwich structure (preferably at a constant width on the non-design surface side), the non-design surface and the design surface are parallel, and there are k (k is a natural number of 3 or more) step portions where the inter-face distance between the non-design surface and the design surface is different. Here, having k step portions where the inter-face distance between the non-design surface and the design surface is different means that there are k step portions (k is a natural number of 3 or more) excluding the thinnest portion provided on the periphery of the sandwich structure. The inter-face distance may be different between adjacent step portions, and there may be multiple step portions where the inter-face distance between the non-design surface and the design surface is the same. Furthermore, the top surface (surface layer) of each step portion on the non-design surface side is a plane parallel to the design surface from the viewpoint of ensuring space for inserting internal components.

[0043] Furthermore, in a cross section cut in the longitudinal direction of the sandwich structure, the absolute values ​​of the difference between the inter-surface distance Ht(n) [mm] of the nth step portion (1≦n≦k) excluding the thinnest portion on the periphery of the sandwich structure and the inter-surface distance Ht(n-1) [mm], Ht(n+1) [mm] of the step portions or thinnest portions on both sides of the nth step portion, |Ht(n)-Ht(n-1)| and |Ht(n)-Ht(n+1)| are in the range of 0.05 to 5.0 [mm]. If |Ht(n)-Ht(n-1)| and |Ht(n)-Ht(n+1)| are less than 0.05 [mm], it is not possible to secure sufficient space for installing internal components. On the other hand, if it is greater than 5.0 [mm], the amount of molding will increase, resulting in poor shape-forming ability. In addition, the sandwich structure will become thick, and the effect of the thin wall of the present invention will be weakened. Furthermore, if the absolute value of the difference in inter-surface distance is large, when an external force acts on the sandwich structure, the area in question becomes a stress concentration area, raising the risk of breakage. Therefore, this value is preferably in the range of 0.05 to 5.0 mm. From the viewpoint of further increasing the strength and rigidity of the sandwich structure, the difference is preferably 0.1 to 3.0 mm, and more preferably 0.1 to 1.0 mm.

[0044] 5(a) and 5(b), it is preferable that the absolute values ​​of the differences in inter-surface distances |Ht(n) - Ht(n-1)| and |Ht(n) - Ht(n+1)| are not uniform. In other words, by using a sandwich structure in which there are multiple differences in height on the non-design surface side, it is possible to install multiple internal components (i.e., it becomes easy to install multiple types of internal components with different shapes), thereby increasing the degree of design freedom.

[0045] To obtain a sandwich structure such as that shown in Figures 5(a) and 5(b), it is preferable to make cuts, for example at regular intervals, in the fiber-reinforced resin member constituting the surface layer on the non-design surface side before molding. This allows the fiber-reinforced resin member constituting the surface layer to be divided, and by molding using a mold with a different inter-face distance corresponding to the divided area, the core layer can be crushed to form the desired inter-face distance. Alternatively, after molding at a thickness with the largest inter-face distance, the surface layer can be divided by making cuts, for example at regular intervals, in the surface layer on the non-design surface side. In this case, too, by crushing the core layer using a mold with a different inter-face distance corresponding to the divided area, the desired inter-face distance can be formed.

[0046] Furthermore, as shown in Figure 6(a), it is preferable that the boundary surface 152 connecting the thinnest portion 150 of the sandwich structure and the thick portion 160 adjacent to the thinnest portion, or as shown in Figure 6(b), between the nth (1≦n≦k) step portion existing in the sandwich structure 100 and the step portion adjacent to the nth step portion or the thinnest portion, is a flat slope.

[0047] As shown in Figure 6(a), the angle θ (°) between the extension of each top surface on the non-design surface (i.e., the step portion on the thicker side) and the boundary surface is preferably in the range of 5 to 60°, and more preferably 15 to 60°. By setting the angle to 5° or more, the width of the boundary surface can be narrowed, ensuring a sufficient area for arranging internal components. On the other hand, by setting the angle to 60° or less, stress concentration near the boundary surface and further reduction in strength can be prevented when the sandwich structure is subjected to external force.

[0048] From the viewpoint of achieving good mechanical properties and precisely forming the uneven shape of the non-design surface, the sandwich structure 100 preferably has a thermosetting resin for the surface layer 110 and a thermoplastic resin for the core layer 120, and the glass transition temperature Tgs of the thermosetting resin for the surface layer 110 is at least 30°C lower than the heat distortion temperature Tfc of the thermoplastic resin for the core layer 120. Here, the heat distortion temperature Tfc of the thermoplastic resin constituting the core layer 120 is the melting point if the thermoplastic resin is a crystalline resin, or the glass transition temperature + 50°C if the thermoplastic resin is an amorphous resin. The melting point and glass transition temperature can be values ​​obtained by differential scanning calorimetry. This configuration is preferable because it prevents the fibers from bending in the fiber-reinforced resin member of the surface layer 110 and allows for the formation of a precise uneven shape while maintaining linear orientation. As a result, it is possible to impart a desired uneven shape to the non-design surface while maintaining mechanical properties.

[0049] The glass transition temperature Tgs of the thermosetting resin constituting the surface layer 110 is preferably 80°C or higher from the viewpoint of the heat resistance of the molded product, and the heat distortion temperature Tfc of the thermoplastic resin constituting the core layer 120 is preferably 250°C or lower, more preferably 180°C or lower, from the viewpoint of the energy required during molding.

[0050] Furthermore, when joining the sandwich structure of the present invention with a separately prepared resin member to obtain an integrated molded body, it is preferable to provide a thermoplastic resin layer on at least a portion of the thinnest portion of the sandwich structure on its periphery, and then join the separately prepared resin member through the thermoplastic resin layer to obtain the integrated molded body. That is, as shown in Figure 7, for example, when one surface of the sandwich structure 100 is a design surface 110a and the other surface is a non-design surface 110b, it is preferable to provide a thermoplastic resin layer 300 on the outer surface of the non-design surface 110b, and then inject resin into the periphery of the sandwich structure 100 to form a resin member 200, which is then bonded to the thermoplastic resin layer 300. In this case, from the standpoint of lightweightness and ensuring space for installing internal components, it is preferable that the resin member 200 be joined to the sandwich structure 100 only at the thinnest portion 150 on its periphery.

[0051] Here, the type of resin constituting the thermoplastic resin layer 300 is not limited as long as it is a thermoplastic resin that can be used for the above-described surface layer 110. Among them, from the viewpoint of adhesiveness and moldability, resins such as polyester resins such as polycarbonate resins, styrene-based resins, and modified polyphenylene ether-based resins are preferred.

[0052] From the viewpoint of the bonding strength between the fiber-reinforced resin and the thermoplastic resin layer, the thermoplastic resin layer 300 is preferably formed simultaneously when the sandwich structure is manufactured, and used as part of the non-design surface of the sandwich structure. Specifically, a method can be exemplified in which a substrate for forming the thermoplastic resin layer is further laminated on the outermost layer on the non-design surface side of a laminate obtained by laminating a prepreg forming the surface layer of the sandwich structure and a substrate for forming the core layer, and then molding the laminate. Examples of the substrate for forming the thermoplastic resin layer include a film-like substrate and a nonwoven fabric-like substrate.

[0053] Furthermore, in the integrally molded body of the present invention, it is preferable that the resin member 200 is bonded to the entire outer periphery of the sandwich structure 100. By forming a bonded portion between the sandwich structure 100 and the resin member 200 over the entire outer periphery of the sandwich structure 100, it is possible to achieve high bonding strength and thinning of the entire integrally molded body 1000.

[0054] The resin constituting the resin member 200 is not limited to a specific type as long as it is a thermoplastic resin that can be used for the aforementioned surface layer 110. In particular, from the viewpoints of adhesion to the thermoplastic resin layer 300 and formability, it is preferable to use the same type of thermoplastic resin as the thermoplastic resin layer 300, and specifically, resins such as polycarbonate resin, styrene-based resin, and modified polyphenylene ether-based resin are preferred.

[0055] Furthermore, although the resin member 200 contains a thermoplastic resin, when the non-design surface 110b of the sandwich structure 100 has a thermoplastic resin layer 300, a joint structure can be formed in which the thermoplastic resin of the resin member 200 melts and bonds with the thermoplastic resin of the thermoplastic resin layer 300. This makes it possible to achieve higher joint strength as the integrated molded body 1000. The melt-bonded joint structure refers to a joint structure in which the members are melted by heat and then cooled to be solidified.

[0056] Furthermore, from the viewpoint of reducing warpage of the integrally molded body 1000, it is preferable that the resin member 200 contains reinforcing fibers. From the viewpoint of the strength of the resin member, the reinforcing fibers used in the resin member 200 are preferably carbon fibers and glass fibers. Glass fibers are more preferable, and the use of glass fibers can impart the resin member with the function of a radio wave transmitting member. The reinforcing fibers are preferably discontinuous reinforcing fibers, and preferably have a weight average fiber length of 0.3 to 3 mm.

[0057] As a method for measuring the fiber length of the discontinuous reinforcing fibers, for example, there is a method in which the discontinuous reinforcing fibers are directly extracted from the integrally molded body 1000 and measured by microscopic observation. When resin is attached to the discontinuous reinforcing fibers, the resin is dissolved using a solvent that dissolves only the resin attached to the discontinuous reinforcing fibers, and the remaining discontinuous reinforcing fibers are filtered and measured by microscopic observation (dissolution method). When there is no solvent that dissolves the resin, there is a method in which only the resin is burned off in a temperature range in which the discontinuous reinforcing fibers do not oxidize and lose weight, and the discontinuous reinforcing fibers are separated and measured by microscopic observation (burn-off method). 400 discontinuous reinforcing fibers are randomly selected, and their lengths are measured to the nearest 1 μm using an optical microscope, and the following formula can be used to calculate the weight average fiber length = Σ(Ni × Li 2) / Σ(Ni × Li), Li: fiber length (mm), Ni: number of discontinuous reinforcing fibers with fiber length Li. The discontinuous reinforcing fibers used in the resin member 200 do not need to be virgin materials, and may be fibers obtained from fiber-reinforced plastic pieces obtained by crushing fiber-reinforced plastic made of thermoplastic resin or thermosetting resin having a melting point sufficiently higher than that of the injected resin, or fibers obtained from fiber-reinforced plastic pieces that have been crushed, classified, and heat-treated for recycling. More preferably, from the viewpoint of reducing waste to be landfilled, recycled fibers obtained by crushing, classifying, and heat-treating waste fiber-reinforced plastic made of thermosetting resin are preferred.

[0058] 8, the recycled fibers may be randomly arranged in a form in which some of the recycled fibers are dispersed as single yarns and other parts are not dispersed and have bundles 210 made up of multiple single yarns. A resin different from the thermoplastic resin used in the resin member 200 may be attached to the surface of the single yarns constituting the bundles 210 in an amount of 0.1 to 30 parts by mass per 100 parts by mass of the reinforcing fibers contained in the bundles 210.

[0059] When discontinuous reinforcing fibers are included in the resin member 200, the content of the discontinuous reinforcing fibers in the resin member 200 is preferably 1 to 60% by weight. This increases the bonding strength with the sandwich structure according to the present invention and reduces warpage of the integrated molded body. If the content is less than 1% by weight, it may be difficult to ensure the strength of the sandwich structure 100. If the content is more than 60% by weight, the filling of the resin member may be partially insufficient during injection molding. From the viewpoint of moldability of the resin member, the content is preferably 5 to 55% by weight, more preferably 8 to 50% by weight, and even more preferably 12 to 45% by weight.

[0060] Furthermore, in the integrally molded body of the present invention, as shown in FIG. 9 , instead of the resin member 200, a frame member 400 and a connecting member 250 may be joined to the sandwich structure. In this case, it is preferable to separate the frame member 400 from the sandwich structure 100 and place it on its outer periphery before injecting the connecting member 250, and then injection-molding the connecting member 250 into the gap between the sandwich structure 100 and the frame member 400. This is an effective means for achieving low warpage of the integrally molded body 1000. The frame member 400 and the connecting member 250 can both be made of a thermoplastic resin that can be used for the resin member 200. Furthermore, using the same type of thermoplastic resin for the frame member 400 and the connecting member 250 is preferable because it facilitates joining.

[0061] From the viewpoint of the strength and rigidity of the integrally molded body 1000, a fiber-reinforced resin frame made of reinforcing fibers and resin is preferred as the frame member 400. The reinforcing fibers used in the resin member 200 described above can be used as the reinforcing fibers constituting the frame member 400. From the viewpoint of increasing the strength of the frame member 400, glass fiber and carbon fiber are preferred, and from the viewpoint of antenna performance, glass fiber is more preferred. On the other hand, although carbon fiber is inferior to glass fiber in terms of antenna performance, it can be used effectively for the purpose of improving strength and rigidity.

[0062] In the present invention, the total thickness of the sandwich structure 100 is preferably 0.3 mm to 2.0 mm. If it is less than 0.3 mm, the rigidity of the integrally molded body 1000 is likely to be insufficient. If it exceeds 2.0 mm, the lightness may be impaired. From the viewpoint of lightness and rigidity, the total thickness is more preferably 0.7 mm to 1.5 mm. The total thickness is a value measured at the thickest part of the sandwich structure 100.

[0063] Furthermore, in the present invention, when the core layer 120 is configured with a porous layer formed of discontinuous reinforcing fibers and a thermoplastic resin, from the viewpoint of the rigidity of the integrally molded body 1000, it is preferable that the porosity of the porous layer 122 at the joint 190 (see FIG. 7 ) between the sandwich structure 100 and the resin member 200 is different from the porosity of the porous layer 122 in the region other than the joint 190. Furthermore, it is preferable that the porosity of the porous layer 122 at the joint 190 is lower than the porosity of the porous layer 122 in the region other than the joint 190.

[0064] Furthermore, in the present invention, it is preferable that the sandwich structure and the integrally molded body have similar top view shapes (shapes when viewed from the design surface side). That is, when the desired integrally molded body 1000 has a rectangular top view shape, it is preferable that the sandwich structure 100 also has a rectangular top view shape. By making the two have similar shapes in this way, the area of ​​the resin member 200 is reduced, thereby achieving low warpage in the integrally molded body.

[0065] The present invention will now be described with reference to examples, but the present invention is not limited to these examples. Materials used are shown below.

[0066] (Material composition 1) Preparation of PAN-based carbon fiber bundle A copolymer mainly composed of polyacrylonitrile was spun, baked, and surface-treated to obtain a carbon fiber bundle with a total number of 120,000 filaments. A sizing agent was applied to the carbon fiber bundle, and the bundle was dried in heated air at a temperature of 120°C to obtain a PAN-based carbon fiber bundle. The properties of this carbon fiber bundle were as follows: Single fiber diameter: 7 μm Density: 1.8 g / cm ３ Tensile strength: 4600 MPa Tensile modulus: 220 GPa (Material composition 2) Chopped carbon fiber bundle The PAN-based carbon fiber bundle of material composition 1 was cut using a cartridge cutter to obtain chopped carbon fiber bundles with a fiber length of 6 mm.

[0067] (Material Composition 3) Preparation of Carbon Fiber Mat A dispersion liquid with a concentration of 0.1% by mass consisting of water and a surfactant (Nacalai Tesque, Inc., polyoxyethylene lauryl ether) was prepared. A carbon fiber mat was produced using this dispersion liquid and the chopped carbon fiber bundles obtained in Material Composition 2. The production apparatus was equipped with a cylindrical container with a diameter of 1000 mm having an opening cock at the bottom of the container as a dispersion tank, and a linear transport section (inclined angle 30°) connecting the dispersion tank and the papermaking tank. A papermaking tank was attached to the opening on the top surface of the dispersion tank, and chopped carbon fiber and dispersion liquid (dispersion medium) could be introduced through the opening. The papermaking tank was connected to a mesh conveyor with a papermaking surface of 500 mm at the bottom. Papermaking was performed with a carbon fiber concentration in the dispersion liquid of 0.05% by mass. The papermaking carbon fiber substrate was dried in a drying oven at 200 ° C for 30 minutes to obtain a carbon fiber mat. The obtained mat had carbon fibers isotropically dispersed in a single fiber state, and the weight per unit area was 100 g / m ２ It was.

[0068] (Material Composition 4) Preparation of Thermosetting Resin Composition 1 "Araldite (registered trademark)" MY9655 (manufactured by Huntsman Japan Co., Ltd.) 60 parts by mass, "EPON (registered trademark)" 825 (manufactured by Momentive Specialty Chemicals Co., Ltd.) 40 parts by mass, "Sumikaexcel (registered trademark)" PES5003P (manufactured by Sumitomo Chemical Co., Ltd.) 13 parts by mass, put into a kneader, heated to 180 ° C. while kneading, and kneaded at 180 ° C. for 1 hour to obtain a transparent viscous liquid. After the viscous liquid was cooled while kneading to 80 ° C., 45 parts by mass of Aradur (registered trademark)" 9664-1 (manufactured by Huntsman Japan Co., Ltd.) was added as a curing agent, and the mixture was kneaded at 80 ° C. for 30 minutes to prepare a thermosetting resin composition 1.

[0069] (Material composition 5) Preparation of thermosetting resin composition 2 20 parts by mass of "jER (registered trademark)" 828 (manufactured by Mitsubishi Chemical Corporation), 20 parts by mass of "jER (registered trademark)" 834 (manufactured by Mitsubishi Chemical Corporation), 25 parts by mass of "jER (registered trademark)" 1001 (manufactured by Mitsubishi Chemical Corporation), 35 parts by mass of "jER (registered trademark)" 154 (manufactured by Mitsubishi Chemical Corporation), and 5 parts by mass of "Vinylec (registered trademark)" K (manufactured by JNC Corporation) were placed in a kneader, heated to 150°C while kneading, and kneaded at 150°C for 1 hour to obtain a transparent viscous liquid. The viscous liquid was cooled to 60°C while being kneaded, and then 4 parts by mass of DYCY7 (manufactured by Mitsubishi Chemical Corporation) as a curing agent and 5 parts by mass of DCMU99 (manufactured by Hodogaya Chemical Co., Ltd.) as a curing accelerator were added, and the mixture was kneaded at 60°C for 30 minutes to prepare thermosetting resin composition 2.

[0070] (Material composition 6) Preparation of thermosetting resin composition 3 20 parts by mass of "jER (registered trademark)" 828 (manufactured by Mitsubishi Chemical Corporation), 20 parts by mass of "jER (registered trademark)" 834 (manufactured by Mitsubishi Chemical Corporation), 25 parts by mass of "jER (registered trademark)" 1001 (manufactured by Mitsubishi Chemical Corporation), 35 parts by mass of "jER (registered trademark)" 154 (manufactured by Mitsubishi Chemical Corporation), and 5 parts by mass of "Vinylec (registered trademark)" K (manufactured by JNC Corporation) were placed in a kneader, heated to 150°C while kneading, and kneaded at 150°C for 1 hour to obtain a transparent viscous liquid. The viscous liquid was cooled to 60°C while being kneaded, and then 4 parts by mass of DYCY7 (manufactured by Mitsubishi Chemical Corporation) as a curing agent and 5 parts by mass of Omicure 24 (manufactured by PTI Japan Co., Ltd.) as a curing accelerator were added, and the mixture was kneaded at 60°C for 30 minutes to prepare thermosetting resin composition 3.

[0071] (Material Composition 7) Preparation of Unidirectional Prepreg 1 Thermosetting resin composition 1 was applied to release paper using a knife coater to obtain a thermosetting resin film. The PAN-based carbon fiber bundles obtained in Material Composition 1 were aligned in one direction in a sheet, and two sheets of the thermosetting resin film were placed on both sides of the carbon fiber sheet. The resin was impregnated into the carbon fiber side by heating and pressurizing to produce unidirectional prepreg 1. The obtained unidirectional prepreg had a carbon fiber basis weight of 150 g / m. ２The thickness was 0.15 mm and the mass fraction of the fibers was 65 mass%.

[0072] (Material Composition 8) Preparation of Unidirectional Prepreg 2 Thermosetting resin composition 2 was applied to release paper using a knife coater to obtain a thermosetting resin film. The PAN-based carbon fiber bundles obtained in Material Composition 1 were aligned in one direction in a sheet, and two sheets of the thermosetting resin film were placed on both sides of the carbon fiber sheet. The resin was impregnated into the carbon fiber side by heating and pressurizing to produce unidirectional prepreg 2. The obtained unidirectional prepreg had a carbon fiber basis weight of 150 g / m. ２ The thickness was 0.15 mm and the mass fraction of the fibers was 65 mass%.

[0073] (Material Composition 9) Preparation of Unidirectional Prepreg 3 Thermosetting resin composition 3 was applied to release paper using a knife coater to obtain a thermosetting resin film. The PAN-based carbon fiber bundles obtained in Material Composition 1 were aligned in one direction in a sheet, and two sheets of the thermosetting resin film were placed on both sides of the carbon fiber sheet. The resin was impregnated into the carbon fiber side by heating and pressurizing to produce unidirectional prepreg 3. The obtained unidirectional prepreg had a carbon fiber basis weight of 150 g / m. ２ The thickness was 0.15 mm and the mass fraction of the fibers was 65 mass%.

[0074] (Material Composition 10) Preparation of Thermoplastic Resin Film 80% by mass of unmodified polypropylene resin (Prime Polymer Co., Ltd., "Prime Polypro (registered trademark)" J105G) and 20% by mass of acid-modified polypropylene resin (Mitsui Chemicals, Inc., "Admer (registered trademark)" QE510) were prepared and dry-blended. This dry-blend product was charged into the hopper of a twin-screw extruder, melted in the extruder, and then extruded from a T-die. Thereafter, the mixture was cooled and solidified by taking it up with a chill roll at 60°C to obtain a thermoplastic resin film. The basis weight of the obtained thermoplastic resin film was 100 g / m ２ Furthermore, when a sample was taken from the thermoplastic resin film and subjected to differential scanning calorimetry, the melting point was found to be 160°C.

[0075] (Material Composition 11) Resin Foam 1 A closed-cell polymethacrylimide foam material (manufactured by Polypla-Evonik Co., Ltd., "ROHACEL (registered trademark)" 110IG-F) was sliced ​​in the thickness direction to obtain a resin foam 1 having a thickness of 1.0 mm.

[0076] (Material Composition 12) Resin Foam 2 A polyolefin foam sheet (manufactured by Inoac Corporation, "FOLEC (registered trademark)" GS072) was sliced ​​in the thickness direction to obtain a resin foam 2 having a thickness of 1.0 mm.

[0077] (Material Composition 13) Preparation of Porous Substrate Precursor A laminate was produced by arranging the carbon fiber mat obtained with Material Composition 3 and the thermoplastic resin film obtained with Material Composition 10 in the order of [thermoplastic resin film / carbon fiber mat / thermoplastic resin film]. Next, a porous substrate precursor was obtained by going through the following steps (I) to (IV). (I) The laminate was placed in a press molding die cavity preheated to 180°C, and the die was closed. (II) Next, a pressure of 3 MPa was applied and maintained for 5 minutes. (III) While maintaining the pressure, the cavity temperature was cooled to 50°C. (IV) The die was opened, and the porous substrate precursor was removed.

[0078] Example 1 Two sheets of unidirectional prepreg 1-0° were prepared by cutting the unidirectional prepreg 1 obtained with material composition 7 to a size of 300 mm x 200 mm so that the longitudinal direction was the fiber orientation direction, and two sheets of unidirectional prepreg 1-90° were prepared by cutting the unidirectional prepreg 1 obtained with material composition 7 to a size of 300 mm x 200 mm so that the transverse direction was the fiber orientation direction. Next, the porous substrate precursor obtained with material composition 13 was cut to a size of 300 mm x 200 mm. These were laminated in the order of [unidirectional prepreg 1-0° / unidirectional prepreg 1-90° / porous substrate precursor / unidirectional prepreg 1-90° / unidirectional prepreg 1-0°] to prepare a molded precursor. Next, the molded precursor was sandwiched between release films and placed in a heated press mold with a platen temperature of 180 ° C., and the upper mold was closed. A pressure of 3 MPa was applied, and the molded precursor was heated and pressurized for 30 minutes. The mold was then opened to obtain a sandwich structure precursor. Next, the obtained sandwich structure precursor was placed in a region with a mold gap of 3.0 mm preheated to a platen temperature of 180 ° C., and the porous substrate precursor in the sandwich structure precursor was expanded in the thickness direction to form a core layer with voids. After another 4 minutes, the mold was opened and quickly placed on the platen surface of a cooling press mold having a cavity shape shown in FIG. 10 with a platen surface temperature of 40 ° C., and cold pressed at a pressure of 3 MPa. After 5 minutes, the molded product was removed from the cooling press mold to obtain a sandwich structure 1 with a smooth design surface. The longitudinal cross section of the sandwich structure 1 had a shape as shown in FIG. 11, and had a step portion where the non-design surface and the design surface were parallel and had different inter-surface distances. The sandwich structure had a face-to-face distance of 0.9 mm at the thinnest portion of the periphery, a face-to-face distance of 1.4 mm at the first step portion, a face-to-face distance of 1.0 mm at the second step portion, a face-to-face distance of 1.3 mm at the third step portion, a face-to-face distance of 1.0 mm at the fourth step portion, and a face-to-face distance of 1.4 mm at the fifth step portion. The steps had flat sloped boundaries between them, and the angles between the boundary surfaces and the extensions of the thicker step portions were each 10°. The fiber-reinforced resin portion of the surface was scraped off to sample the resin. The glass transition temperature of the resin was measured by differential scanning calorimetry, which was 175°C, higher than the melting point of the thermoplastic resin film (160°C).

[0079] Example 2 A molded precursor was prepared in the same manner as in Example 1, except that the unidirectional prepreg 1 obtained with material composition 7 was replaced with the unidirectional prepreg 2 obtained with material composition 8. Next, the molded precursor was sandwiched between release films and placed in a heated press mold with a platen temperature of 160°C. The upper mold was then closed, and the molded precursor was heated and pressurized for 6 minutes at a pressure of 3 MPa. The mold was then opened to obtain a sandwich structure precursor. After this, a sandwich structure 2 was obtained in the same manner as in Example 1. The design surface of the obtained sandwich structure 2 was smooth. The longitudinal cross section of the sandwich structure 2 had a shape as shown in FIG. 11, and had a step portion where the non-design surface and the design surface were parallel and had a different inter-surface distance. The sandwich structure had a face-to-face distance of 0.9 mm at the thinnest portion of the periphery, a face-to-face distance of 1.4 mm at the first step portion, a face-to-face distance of 1.0 mm at the second step portion, a face-to-face distance of 1.3 mm at the third step portion, a face-to-face distance of 1.0 mm at the fourth step portion, and a face-to-face distance of 1.4 mm at the fifth step portion. The steps had flat sloped boundaries between them, and the angles between the boundary surfaces and the extensions of the thicker step portions were each 13°. Furthermore, the fiber-reinforced resin portion of the surface was scraped off to sample the resin. The glass transition temperature of the resin was measured by differential scanning calorimetry, which was 140°C, 20°C lower than the melting point of the thermoplastic resin film (160°C).

[0080] Example 3 A sandwich structure 3 was obtained in the same manner as in Example 2, except that the unidirectional prepreg 2 obtained with material composition 8 was replaced with the unidirectional prepreg 3 obtained with material composition 9. The design surface of the obtained sandwich structure 3 was smooth. The longitudinal cross section of the sandwich structure 3 had a shape as shown in FIG. 11 , with a stepped portion in which the non-design surface and the design surface were parallel and had different inter-surface distances. The sandwich structure had a face-to-face distance of 0.9 mm at the thinnest portion on the periphery, a face-to-face distance of 1.4 mm at the first step portion, a face-to-face distance of 1.0 mm at the second step portion, a face-to-face distance of 1.3 mm at the third step portion, a face-to-face distance of 1.0 mm at the fourth step portion, and a face-to-face distance of 1.4 mm at the fifth step portion. A flat sloped boundary surface was present between the stepped portions, and the angle between the boundary surface and the extension line of the thicker step portion was 20°. Furthermore, the surface fiber-reinforced resin portion was scraped off to collect the resin, and the glass transition temperature of the resin was measured by differential scanning calorimetry. It was 110°C, 50°C lower than the melting point of the thermoplastic resin film, 160°C.

[0081] Example 4 Two sheets of unidirectional prepreg 2-0° were prepared by cutting the unidirectional prepreg 2 obtained with material composition 8 to a size of 300 mm x 200 mm with the longitudinal direction aligned with the fiber orientation direction, and two sheets of unidirectional prepreg 2-90° were prepared by cutting the unidirectional prepreg 2 obtained with material composition 8 to a size of 300 mm x 200 mm with the transverse direction aligned with the fiber orientation direction. Next, resin foam 1 obtained with material composition 11 was cut to a size of 300 mm x 200 mm. These were laminated in the order of [unidirectional prepreg 2-0° / unidirectional prepreg 2-90° / resin foam 1 / unidirectional prepreg 2-90° / unidirectional prepreg 2-0°] to prepare a molded precursor. Next, the molded precursor was sandwiched between release films and placed in a mold having the cavity shape shown in FIG. 10 with the platen surface temperature set to 160°C. The mold was then closed, and the molded precursor was heated and pressurized at a pressure of 3 MPa for 6 minutes. The mold was then opened to obtain sandwich structure 4. The design surface of the obtained sandwich structure 4 had a finely uneven shape. The longitudinal cross section of sandwich structure 4 had a shape as shown in FIG. 11, with a stepped portion where the non-design surface and the design surface were parallel but had different inter-surface distances. The sandwich structure had a face-to-face distance of 0.9 mm at the thinnest portion on the periphery, a face-to-face distance of 1.4 mm at the first step portion, a face-to-face distance of 1.0 mm at the second step portion, a face-to-face distance of 1.3 mm at the third step portion, a face-to-face distance of 1.0 mm at the fourth step portion, and a face-to-face distance of 1.4 mm at the fifth step portion. A flat sloped boundary surface was present between the step portions, and the angle between the boundary surface and the extension line of the thicker step portion was 20°, but some smearing was observed on the surface of the non-design surface at some of the boundary surfaces. Furthermore, the surface fiber-reinforced resin portion was scraped off to collect the resin, and the glass transition temperature of the resin was measured using differential scanning calorimetry. The result was 140°C, which was 90°C lower than the heat distortion temperature of resin foam 1, 230°C (glass transition temperature 180°C).

[0082] Example 5 A molded precursor was prepared in the same manner as in Example 4. Next, the molded precursor was sandwiched between release films and placed in a heated press mold with a platen temperature of 160°C. A 1.5 mm spacer was placed around the periphery, the upper mold was closed, and the molded precursor was heated and pressurized for 6 minutes at a pressure of 1 MPa. The mold was then opened to obtain a sandwich structure precursor. Next, incisions were made by NC machining in the surface layer on the non-design side of the obtained sandwich structure precursor to correspond to the cavity shape shown in FIG. 10, and the surface layer was divided. This sandwich structure precursor was placed in a mold having the cavity shape shown in FIG. 10 with a platen surface temperature of 160°C, and then the mold was closed and heated and pressurized for 6 minutes at a pressure of 3 MPa. The mold was then opened to obtain a sandwich structure 5. The design surface of the obtained sandwich structure 5 had a slight uneven shape. The longitudinal cross section of sandwich structure 5 did not have an inclined portion like Examples 1 to 4, but had a stepped portion where the non-design surface and the design surface were parallel and had different inter-surface distances. The sandwich structure had a face-to-face distance of 0.4 mm at the thinnest portion of the periphery, a face-to-face distance of 1.5 mm at the first step, a face-to-face distance of 0.5 mm at the second step, a face-to-face distance of 1.0 mm at the third step, a face-to-face distance of 0.5 mm at the fourth step, and a face-to-face distance of 1.5 mm at the fifth step. Furthermore, the fiber-reinforced resin portion of the surface layer was scraped off to sample the resin. The glass transition temperature of the resin was measured by differential scanning calorimetry. It was 145 ° C., 85 ° C. lower than the heat distortion temperature of resin foam 1 (230 ° C., glass transition temperature 180 ° C.).

[0083] Comparative Example 1 The unidirectional prepreg 1 obtained with material composition 7 was cut into six pieces of unidirectional prepreg 1-0°, each 300 mm x 200 mm in size, with the longitudinal direction being the fiber orientation direction, and four pieces of unidirectional prepreg 1-90°, each 300 mm x 200 mm in size, with the transverse direction being the fiber orientation direction. These were laminated in the following order: [unidirectional prepreg 1-0° / unidirectional prepreg 1-90° / unidirectional prepreg 1-0° / unidirectional prepreg 1-90° / unidirectional prepreg 1-0° / unidirectional prepreg 1-90° / unidirectional prepreg 1-0° / unidirectional prepreg 1-90° / unidirectional prepreg 1-0° / unidirectional prepreg 1-0° / unidirectional prepreg 1-90° / unidirectional prepreg 1-0°] to prepare a molding precursor. Next, the molded precursor was sandwiched between release films and placed in a heated press mold with a platen temperature of 180 ° C. The upper mold was closed and a pressure of 3 MPa was applied to heat and pressurize the molded precursor for 30 minutes. The mold was then opened to obtain a fiber-reinforced resin flat plate with a uniform thickness. Next, the fiber-reinforced resin flat plate was cut by NC processing to match the cavity shape shown in Figure 10, thereby obtaining a fiber-reinforced resin structure. Due to the cutting process, the shape was such that there was no boundary surface between the stepped portions, but peeling between the fiber-reinforced resin layers, fiber damage, and distortion of the fiber-reinforced resin structure itself were observed.

[0084] Comparative Example 2 A molded precursor was prepared in the same manner as in Example 4, except that resin foam 1 obtained with material composition 11 was replaced with resin foam 2 obtained with material composition 12. The molded precursor was then sandwiched between release films and placed in a mold having the cavity shape shown in FIG. 10 with a platen temperature of 135°C. The mold was then closed, and the molded precursor was heated and pressurized for 30 minutes at a pressure of 3 MPa. The mold was then opened to obtain sandwich structure 6. The design surface of the obtained sandwich structure 6 had a finely textured shape. In the longitudinal cross section of sandwich structure 6, the non-design surface and the design surface were parallel, but the distance between them differed only to the extent that a slight step was visible. That is, the sandwich structure had a face-to-face distance of 0.98 mm at the thinnest part of the periphery, a face-to-face distance of 1.01 mm at the first step, a face-to-face distance of 1.00 mm at the second step, a face-to-face distance of 1.02 mm at the third step, a face-to-face distance of 1.00 mm at the fourth step, and a face-to-face distance of 1.01 mm at the fifth step. Furthermore, because the step was barely visible, the angle between the extension line of the thicker step and the boundary surface could not be defined, and smearing was observed on the surface of the non-design surface. Furthermore, the fiber-reinforced resin portion of the surface was scraped off to sample the resin, and the glass transition temperature of the resin was measured by differential scanning calorimetry. It was 130 °C, 20 °C lower than the melting point of the resin foam 2, 150 °C.

[0085] The integrally molded article having the sandwich structure of the present invention can be effectively used for automobile interiors and exteriors, electrical and electronic equipment housings, bicycles, structural materials for sporting goods, aircraft interior materials, transport boxes, etc. Among these, it can be particularly suitably used for personal computer housings (for example, notebook computer housings with a side length of 200 mm to 500 mm, or even 200 mm to 400 mm) for which there is a high demand for lighter and thinner sizes.

[0086] 100: Sandwich structure 110: Surface layer 110a: Design surface 110b: Non-design surface 120: Core layer 122: Porous layer 125: Discontinuous reinforcing fibers 126: Holes 130: Resin-rich layer 150: Thinnest part 152: Boundary surface (flat inclined surface) 160: Thick part adjacent to thinnest part 170: Step lower than thick part 160 (shorter face-to-face distance) 171: Step higher than thick part 160 (longer face-to-face distance) 200: Resin member 210: Converging part 250: Connecting member 300: Thermoplastic resin layer 400: Frame member 1000: Integral molded body 2000: Mold cavity viewed from above 2100: A-A' cross section of mold cavity 3001: First step part 3002: Second step part 3003: Third step 3004: Fourth step 3005: Fifth step

Claims

1. A sandwich structure having surface layers on both sides of a core layer, the surface layers including a member made of a fiber-reinforced resin member made of continuous reinforcing fibers and resin, the surface layers on both sides being parallel to each other at least in part, the core layer being any one selected from the group consisting of a film, a foam, and a porous substrate, one of the surface layers being a flat design surface and the other surface layer being a non-design surface having an uneven surface, at least the outer periphery of the sandwich structure being provided with a thinnest part in which the inter-face distance between the non-design surface and the design surface is the shortest, and in a cut surface cut in the longitudinal direction of the sandwich structure, k (k is a natural number of 3 or more) step portions are provided in which the non-design surface and the design surface are parallel and have different inter-face distances, A sandwich structure characterized in that the absolute values ​​of the differences |Ht(n)-Ht(n-1)| and |Ht(n)-Ht(n+1)| between the face-to-face distance Ht(n) [mm] of the nth step portion (1≦n≦k) and the face-to-face distances Ht(n-1) [mm] and Ht(n+1) [mm] of the step portions on both sides of the nth step portion or the thinnest portion are in the range of 0.05 to 5.0 [mm], respectively.

2. A sandwich structure as described in claim 1, wherein, on the cut surface, a boundary surface connecting the nth (1≦n≦k) step portion present in the sandwich structure and a step portion adjacent to the nth step portion or the thinnest portion is a flat inclined surface, and an angle between an extension line of the step portion on the thick side and the boundary surface is 5 to 60°.

3. The sandwich structure according to claim 1, wherein the core layer is a porous substrate comprising discontinuous reinforcing fibers and a thermoplastic resin.

4. The sandwich structure according to claim 1, wherein the surface layer is a fiber-reinforced member made of unidirectional prepreg.

5. A sandwich structure as described in claim 1, wherein the fiber-reinforced resin component constituting the surface layer contains a thermosetting resin, the core layer contains a thermoplastic resin, and the glass transition temperature Tgs of the thermosetting resin is 30°C or more lower than the heat distortion temperature Tfc of the thermoplastic resin.

6. An integrally molded body in which the sandwich structure according to claim 1 is bonded to a resin member, the integrally molded body further having a thermoplastic resin layer on at least a portion of the thinnest wall portion, and the resin member is bonded via the thermoplastic resin layer.

Images