Porous sandwich structure and integrally molded body using same

Abstract

A porous sandwich structure comprising: a core layer obtained by bonding three-dimensionally arranged discontinuous reinforcing fibers with a thermoplastic resin; the present invention relates to a composite material comprising a core layer, and skin layers that are arranged on both sides of the core layer and contain continuous reinforcing fibers and a matrix resin, the composite material being characterized in that in the core layer, a thermoplastic resin spread in a planar shape in a region surrounded by a plurality of discontinuous reinforcing fibers has a plurality of pores, and the porosity of the core layer is 50% by volume to 76% by volume (inclusive). And an integrated molded body using the same. Provided are a porous sandwich structure and an integrated molded body, which are lightweight, have high bonding strength with other structures, and can be made thin, by integrating a porous sandwich structure having a specific internal structure and a structure different from the porous sandwich structure, with respect to a structure that is required to be thin and has a complicated shape in recent years.

Description

Technical Field

[0001] The present invention relates to porous sandwich structures suitable for applications requiring excellent design surfaces, and integral molded bodies using the same. Background Technology

[0002] Currently, with the increasing portability of electrical and electronic equipment such as personal computers, OA equipment, AV equipment, mobile phones, telephones, fax machines, home appliances, and toys, there is a demand for further miniaturization and lightweighting. To achieve this, the components that make up the equipment, especially the housing, need to avoid significant bending and contact with internal components, which could cause damage, under external loads. Therefore, high strength, high rigidity, and thin-walled construction are required.

[0003] In addition, to meet the above requirements, it is known that a molded structure is made by integrally molding other structures on a sandwich structure consisting of a core layer containing reinforcing fibers and resin and a skin layer containing reinforcing fibers and resin, thereby achieving miniaturization and lightweight. For such a molded structure, further thinning and reliable bonding are required.

[0004] Patent Document 1 discloses an integral molded body and its manufacturing method. The integral molded body can achieve excellent design surface molding when integrating a sandwich structure and a different structure. It is lightweight, high-strength and high-rigidity, has high bonding strength with other structures, and can achieve thin walls.

[0005] Patent document 2 describes a "composite material, which is a composite material formed by extruding thermoplastic resin around a reinforcing core material, characterized in that the aforementioned reinforcing core material comprises thermoplastic resin and randomly oriented carbon fibers, and the fiber-reinforced composite sheet with a porosity of 10% to 60% is molded into an irregular cross-sectional shape." It discloses that by using a reinforcing core material with a porosity in the range of 10% to 60%, it ensures impact resistance even when the material is bent, and does not crack or break, thus exhibiting excellent formability.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2018 / 142971

[0009] Patent Document 2: Japanese Patent Application Publication No. 2000-15682 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] However, Patent Document 1 does not teach the detailed core structure of a sandwich structure with uneven wall thickness, nor does it teach the optimal shape of the core structure.

[0012] Furthermore, the molding method described in Patent Document 2 does not describe the pore structure of the core material, and it is not suitable for materials that cannot be extruded. There is also no description or teaching regarding the case of joining with other laminates or components by compression molding.

[0013] Therefore, the objective of this invention is to provide a lightweight porous sandwich structure and an integrally molded body that can achieve thin walls and complex shapes, by integrating a porous sandwich structure with a specific internal structure and a different structure, in order to meet the requirements of thin-walled and complex-shaped structures in recent years.

[0014] Methods for solving problems

[0015] [1] A porous sandwich structure comprising:

[0016] The core layer is formed by bonding three-dimensionally arranged discontinuous reinforcing fibers together using thermoplastic resin; and

[0017] The skin layer, which is disposed on both sides of the core layer, comprises continuous reinforcing fibers and matrix resin.

[0018] The characteristic feature is that, in the aforementioned core layer, the thermoplastic resin, which is planarly distributed in the region surrounded by multiple discontinuous reinforcing fibers, has multiple pores.

[0019] The porosity of the aforementioned core layer is above 50% and below 76% by volume.

[0020] [2] The porous sandwich structure as described in [1], wherein the core layer comprises 5% to 75% by weight of the aforementioned discontinuous reinforcing fibers and 25% to 95% by weight of the aforementioned thermoplastic resin, wherein the aforementioned discontinuous reinforcing fibers are configured in a manner having a three-dimensional network structure.

[0021] [3] The porous sandwich structure as described in [1] or [2], wherein, in a cross section of the core layer perpendicular to the stacking direction of the aforementioned skin layer and the aforementioned core layer, the aforementioned thermoplastic resin has arm-shaped portions that branch and spread out in three to eight directions.

[0022] [4] The porous sandwich structure as described in any one of [1] to [3], wherein, in the aforementioned core layer, the aforementioned planar thermoplastic resin is distributed in every 4 mm 2 It has more than 2 and less than 300 of the aforementioned holes.

[0023] [5] The porous sandwich structure as described in any one of [1] to [4], wherein the aforementioned thermoplastic resin is at least one selected from the group consisting of polyolefin resin, polyamide resin, polyester resin, polycarbonate resin, polystyrene resin, modified polyphenylene ether resin, polyarylene sulfide resin and polyetherketone resin.

[0024] [6] The porous sandwich structure as described in any one of [1] to [5], wherein the aforementioned thermoplastic resin has strain curing properties.

[0025] [7] The porous sandwich structure as described in any one of [1] to [6], wherein a thickness-reducing step portion is formed at the end of the porous sandwich structure.

[0026] The stepped section consists of a pressing section with the smallest thickness and a boundary section whose thickness decreases from the main body section, which has no reduction in thickness, toward the aforementioned pressing section.

[0027] The porosity of the core layer in the aforementioned boundary portion and the aforementioned pressing portion is less than the porosity of the core layer in the aforementioned main body portion.

[0028] [8] An integral molded body, which is formed by joining the aforementioned pressing portion of the porous sandwich structure described in [7] with a component comprising other molded bodies.

[0029] [9] The integral molded body as described in [8], wherein one surface of the aforementioned boundary portion is inclined relative to the surface of the aforementioned main body portion at an angle of inclination of 1° to 20°.

[0030]

[10] An integral molded body as described in [8] or [9], wherein the aforementioned component comprising other molded bodies is joined to the aforementioned pressing portion by insert injection molding or injection molding on a substrate.

[0031]

[11] The integral molded body as described in any one of [8] to

[10] , wherein the porosity of the core layer in the main body portion is 50% or more and 76% or less by volume, and the porosity of the core layer in the pressing portion is 0% or more and less than 50% by volume.

[0032] The effects of the invention

[0033] According to the present invention, by integrating a porous sandwich structure having a specific internal structure with a different structure, a lightweight porous sandwich structure with high bonding strength to other structures and capable of thin-walling is provided, as well as an integrally molded body. Attached Figure Description

[0034] [ Figure 1 This is a schematic side view illustrating one embodiment of the porous sandwich structure involved in the present invention.

[0035] [ Figure 2 [This is a schematic plan view of the core layer involved in the present invention.]

[0036] [ Figure 3 This is a perspective view showing one embodiment of the integral molded body according to the present invention.

[0037] [ Figure 4 This is a schematic side view illustrating the case where the integral molded body of the present invention has a curved surface.

[0038] [ Figure 5 To be Figure 3 An enlarged schematic side view of the area near the stepped portion of the integral molded body shown. Detailed Implementation

[0039] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the present invention is not limited by these drawings. The present invention can be implemented with appropriate modifications within its scope of purpose.

[0040] The porous sandwich structure 3 involved in this invention is a porous sandwich structure as follows, such as... Figure 1 As shown, it is configured with: a core layer 2, which consists of discontinuous reinforcing fibers configured to have a three-dimensional network structure and as shown in the figure. Figure 2 The structure shown is formed by bonding discontinuous reinforcing fibers 12 together with thermoplastic resin 10; and a skin layer 1 located on both sides of the core layer 2, which contains continuous reinforcing fibers and matrix resin. In the porous sandwich structure 3, with regard to the core layer 2, the area surrounded by discontinuous reinforcing fibers 12 constituting a three-dimensional network structure is covered in a planar manner by thermoplastic resin 10, and the planar area covered by thermoplastic resin 10 has a plurality of pores 11. In the core layer 2, the proportion (porosity) of the space in which thermoplastic resin 10 and discontinuous fibers 12 do not exist relative to the core layer 2 as a whole is more than 50% by volume and less than 76% by volume.

[0041] First, the epidermal layer 1 that constitutes the porous interlayer structure 3 will be described.

[0042] First, the continuous fibers contained in the epidermal layer 1 are defined. Continuous fibers refer to the arrangement of reinforcing fibers in the surface layer constituting the porous sandwich structure 3 in a substantially continuous manner within the total length or width of the porous sandwich structure. It should be noted that discontinuous fibers, as described later, refer to reinforcing fibers that are intermittently cut.

[0043] Generally, the fibers used in unidirectional reinforcing fiber resins, which are obtained by impregnating resin with reinforcing fibers that are aligned in one direction, are equivalent to continuous fibers, while the reinforcing fibers contained in SMC (sheet molding compound) substrates used in compression molding, granular materials used in injection molding, etc., are equivalent to discontinuous fibers.

[0044] The continuous fibers used in the epidermis 1 include metal fibers such as aluminum fiber, brass fiber, and stainless steel fiber; glass fiber; polyacrylonitrile-based, rayon-based, lignin-based, and pitch-based carbon fibers; graphite fiber; aromatic polyamide fiber; polyaromatic polyamide fiber; PBO fiber; polyphenylene sulfide fiber; polyester fiber; acrylic fiber; nylon fiber; polyethylene fiber; and other organic fibers, as well as silicon carbide fiber, silicon nitride fiber, alumina fiber, silicon carbide fiber, and boron fiber. These can be used alone or in combination of two or more.

[0045] These fiber raw materials can be surface treated. Examples of surface treatments include metal coating, coupling agent-based treatment, sizing agent-based treatment, and additive attachment treatment.

[0046] From the perspective of lightweighting, carbon fibers with excellent specific strength and specific stiffness, such as polyacrylonitrile (PAN) carbon fibers, rayon carbon fibers, lignin carbon fibers, and pitch-based carbon fibers (including graphite fibers), are preferred. Among them, polyacrylonitrile (PAN) carbon fibers with excellent processability are preferred.

[0047] Furthermore, when using carbon fiber as the reinforcing fiber in a porous sandwich structure, it is preferable to use carbon fiber with a tensile modulus of elasticity that is preferably in the range of 200 GPa to 1,000 GPa from the viewpoint of the rigidity of the porous sandwich structure, and more preferably in the range of 400 GPa to 900 GPa from the viewpoint of the workability of the prepreg blank. When the tensile modulus of elasticity of the carbon fiber is less than 200 GPa, the rigidity of the porous sandwich structure is sometimes unsatisfactory; when the tensile modulus of elasticity of the carbon fiber is greater than 1,000 GPa, it is necessary to improve the crystallinity of the carbon fiber, making it difficult to manufacture the carbon fiber. When the tensile modulus of elasticity of the carbon fiber is within the aforementioned range, it is preferable from the perspective of further improving the rigidity of the porous sandwich structure and improving the workability of the carbon fiber. It should be noted that the tensile modulus of elasticity of the carbon fiber can be determined by the wire harness tensile test described in JIS R7601-1986.

[0048] When carbon fiber is used as the reinforcing fiber for the surface layer of a porous sandwich structure, the density of polyacrylonitrile (PAN)-based carbon fiber is 1.6 g / cm³. 3 Above 2.0g / cm 3From the perspective of increased rigidity, the value is 1.8 g / cm³. 3 Above 2.0g / cm 3 The following value, for pitch-based carbon fibers, is 2.0 g / cm³. 3 Above 2.5g / cm 3 From a cost perspective, 2.0 g / cm³ is further preferred. 3 The above 2.3g / cm 3 The following is a preferred description of PAN-based carbon fibers, which exhibit excellent processability.

[0049] A fiber fabric substrate can also be used in the skin layer 1 of the porous sandwich structure 3. A fiber fabric substrate refers to a substrate in which continuous reinforcing fibers are bundled in units of 1000 strands, forming both warp and weft yarns, and are intersected at approximately right angles using a loom. Typically, a continuous reinforcing fiber bundle of 1000 strands is called 1K, 3000 strands is called 3K, and 12000 strands is called 12K.

[0050] Regarding the fiber fabric substrate, at least one fabric selected from plain weave, twill weave, satin weave, and satin pattern weave is preferred. The fiber fabric substrate has characteristics in terms of fiber pattern; therefore, by using a fiber fabric substrate with a fiber pattern that highlights this characteristic on the outermost layer (design surface side) of the porous sandwich structure, it is possible to form an integrally molded body exhibiting a novel surface pattern. Regarding the continuous reinforcing fiber bundles, 1K to 24K is preferred, and from the viewpoint of fiber pattern stability during processing, 1K to 6K is further preferred.

[0051] In addition, the resin constituting the skin layer 1 of the porous sandwich structure 3 can be any of thermoplastic resins or thermosetting resins.

[0052] As the thermosetting resin, any thermosetting resin from the following examples can be used. For example, unsaturated polyester resin, vinyl ester resin, epoxy resin, phenolic (Resol type) resin, urea-melamine resin, polyimide resin, maleimide resin, benzoxazine resin, and other thermosetting resins are preferred. Two or more of these can also be mixed. Among these, epoxy resin is particularly preferred from the viewpoint of the mechanical properties and heat resistance of the molded article. To exhibit its excellent mechanical properties, it is preferable to include epoxy resin as the main component of the resin used; specifically, it is preferable to include 60% by weight or more and less than 97% by weight relative to the resin composition.

[0053] On the other hand, when using thermoplastic resins, any thermoplastic resins listed below can also be used. Examples include polyester resins such as polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, polypropylene terephthalate (PTT) resin, polyethylene naphthalate (PEN) resin, and liquid crystal polyester resin; polyolefin resins such as polyethylene (PE) resin, polypropylene (PP) resin, and polybutene resin; polyoxymethylene (POM) resin, polyamide (PA) resin, and polyphenylene sulfide (PPS) resin; and fluorinated resins such as polyketone (PK) resin, polyetherketone (PEK) resin, polyetheretherketone (PEEK) resin, polyetherketoneketone (PEKK) resin, polyethernitrile (PEN) resin, and polytetrafluoroethylene resin. ; crystalline resins such as liquid crystal polymers (LCP); styrene-based resins, and amorphous resins such as polycarbonate (PC) resin, polymethyl methacrylate (PMMA) resin, polyvinyl chloride (PVC) resin, polyphenylene ether (PPE) resin, polyimide (PI) resin, polyamide-imide (PAI) resin, polyether-imide (PEI) resin, polysulfone (PSU) resin, polyethersulfone resin, polyaryl ester (PAR) resin, and thermoplastic elastomers such as phenolic resins, phenoxy resins, polystyrene-based resins, polyurethane-based resins, polybutadiene-based resins, polyisoprene-based resins, and acrylonitrile-based resins, as well as copolymers and modifiers thereof, are selected from the following thermoplastic resins.

[0054] From the viewpoint of lightweighting of the resulting molded article, polyolefin resin is preferred; from the viewpoint of strength, polyamide resin is preferred; from the viewpoint of surface appearance, amorphous resins such as polycarbonate resin, styrene-based resin, and modified polyphenylene ether resin are preferred; from the viewpoint of heat resistance, polyarylene sulfide resin is preferred; and from the viewpoint of continuous operating temperature, polyether ether ketone resin is preferred.

[0055] Without prejudice to the purpose of this invention, the illustrated thermoplastic resin may contain impact-enhancing agents such as elastomers or rubber components, other fillers, and additives. Examples of these include inorganic fillers, flame retardants, conductivity-improving agents, nucleating agents, ultraviolet absorbers, antioxidants, vibration damping agents, antibacterial agents, insect repellents, deodorizing agents, anti-coloring agents, heat stabilizers, mold release agents, antistatic agents, plasticizers, lubricants, colorants, pigments, dyes, foaming agents, foaming agents, or coupling agents.

[0056] Next, the core layer 2 constituting the porous sandwich structure 3 will be described.

[0057] A cross-section of a typical core layer of the porous sandwich structure 3 of the present invention is shown in the figure. Figure 2In the porous sandwich structure 3, the discontinuous reinforcing fibers 12 constituting the core layer 2 form a three-dimensional network structure, and the thermoplastic resin 10 exists as the matrix resin of the three-dimensional network structure. Regarding the thermoplastic resin 10, within the mesh of the three-dimensional network structure composed of the discontinuous reinforcing fibers 12, it unfolds planarly within the region surrounded by the contour formed by the multiple discontinuous reinforcing fibers 12 arranged in a ring, forming multiple pores 11. The contour formed by the discontinuous reinforcing fibers 12 arranged in a ring is not limited to... Figure 2 The hexagon shown can also be a polygon such as a triangle or quadrilateral. By forming such pores 11, the thermoplastic resin 10, when stretched into a planar shape, is less likely to be cut off in the stretching direction, thus maintaining the bond between the discontinuous reinforcing fibers 12. Therefore, compared to the state in which no pores 11 are formed in the thermoplastic resin 10, the discontinuous reinforcing fibers 12 can be firmly bonded. Furthermore, by having multiple pores 11 in the thermoplastic resin 10, it can be stretched to a greater extent, increasing the porosity of the core layer 2, thus allowing for further weight reduction. By adopting such a structure, the rigidity of the porous sandwich structure 3 can be improved.

[0058] There are no particular limitations on the discontinuous reinforcing fibers 12 used in the core layer 2. Examples include metal fibers such as aluminum, brass, and stainless steel; polyacrylonitrile (PAN) fibers, rayon fibers, lignin fibers, pitch-based carbon fibers, graphite fibers, glass fibers, organic fibers such as aromatic polyamide resins, polyphenylene sulfide resins, polyester resins, acrylic resins, nylon resins, and polyethylene resins; and inorganic fibers such as silicon carbide and silicon nitride.

[0059] In addition, these fibers can be surface-treated. Besides coating with metal as a conductor, surface treatments include coupling agent-based treatments, sizing agent-based treatments, bundled agent-based treatments, and additive-based treatments. These discontinuous reinforcing fibers can be used individually or in combination with two or more types. From the viewpoint of lightweighting, polyacrylonitrile (PAN)-based, pitch-based, and rayon-based carbon fibers with excellent specific strength and specific stiffness are preferred.

[0060] Furthermore, from the viewpoint of improving the economy of the obtained porous sandwich structure 3 and the integral molded body 30 described later, aramid fibers are preferred. Especially from the perspective of balancing mechanical properties and impact absorption, a combination of carbon fibers and aramid fibers is preferred. Additionally, from the viewpoint of improving the electrical conductivity of the obtained molded article, reinforcing fibers coated with metals such as nickel, copper, or ytterbium can also be used. Among these, PAN-based carbon fibers with excellent mechanical properties such as strength and elastic modulus are more preferred. It should be noted that when using polyacrylonitrile (PAN)-based carbon fibers, carbon fibers possessing the aforementioned tensile elastic modulus are preferred.

[0061] The shape of the discontinuous reinforcing fiber 12 of the present invention is not particularly limited, but from the viewpoint of layered use, sheet-like shape is preferred.

[0062] The discontinuous reinforcing fibers 12 used in the core layer 2 do not need to be virgin material; they can also be fibers obtained from fiber-reinforced plastic sheets, which are fiber-reinforced plastic sheets obtained by crushing fiber-reinforced plastics formed from thermoplastic resins or thermosetting resins, or fiber-reinforced plastic sheets obtained by crushing, grading, and heat-treating recycled materials. More preferably, from the viewpoint of reducing waste disposed of in landfills, recycled fibers obtained from waste fiber-reinforced plastics using thermosetting resins are preferred.

[0063] Furthermore, the type of thermoplastic resin that can be used in the core layer 2 constituting the porous sandwich structure 3 can be the same as the thermoplastic resin used in the aforementioned skin layer 1.

[0064] From the viewpoint of lightweighting of the resulting molded article, polyolefin resin is preferred; from the viewpoint of strength, polyamide resin is preferred; from the viewpoint of surface appearance, amorphous resins such as polycarbonate resin, styrene-based resin, and modified polyphenylene ether resin are preferred; from the viewpoint of heat resistance, polyarylene sulfide resin is preferred; and from the viewpoint of continuous operating temperature, polyether ether ketone resin is preferred.

[0065] In addition, it may contain other fillers and additives as described above.

[0066] Furthermore, the thermoplastic resin used in the core layer 2 of the porous sandwich structure 3 preferably has strain-curing properties. This improves the adhesion between the discontinuous reinforcing fibers 12 in the core layer 2, contributing to increased rigidity.

[0067] Strain-curing property refers to the property of thermoplastic resin that its viscosity increases when subjected to a certain amount of deformation in its molten state. By utilizing thermoplastic resins with strain-curing property, the viscosity of the deformed portion of the thermoplastic resin specifically increases when deformed along with the fiber-reinforced resin, thereby creating a viscosity difference between the deformed and undeformed portions. This allows for deformation of the undeformed portion with lower viscosity, enabling uniform deformation of the thermoplastic resin and thus allowing it to stretch without interruption.

[0068] When the porous sandwich structure 3 is formed by expanding the porous structure 3 through the elastic force of the discontinuous reinforcing fibers 12 (described later), the viscosity of the thinly stretched portion specifically increases, thereby enabling the thermoplastic resin to expand continuously. That is, in the porous sandwich structure 3, the thermoplastic resin 10 easily expands into a planar shape while having multiple pores 11. In addition, since the viscosity of the stretched portion specifically increases, it can expand uniformly, forming a dense pore structure.

[0069] If it is a thermoplastic resin with strain curing properties, there are no particular limitations. As an example of a thermoplastic resin with strain curing properties, thermoplastic resins with a molecular weight of 300,000 or more, thermoplastic resins with long-chain branched structures, and thermoplastic resins with quasi-crosslinked structures are suitable. Polystyrene resin is a specific example.

[0070] By heating the thermoplastic resin 10 constituting the core layer 2, it is melted or softened, thereby increasing the elasticity of the discontinuous reinforcing fibers 12. That is, the porous sandwich structure 3 can be easily expanded and compressed. When the porous sandwich structure 3 expands, the porosity of the core layer 2 increases; when it is compressed, the porosity of the core layer 2 decreases. During the expansion of the core layer 2 from a compressed state, the spacing between the discontinuous reinforcing fibers 12 in the core layer 2 increases, and the thermoplastic resin 10 covering the region formed by the three-dimensional network structure is stretched into a planar shape in a way that bonds the discontinuous reinforcing fibers 12 together, thereby achieving both lightweight and high rigidity.

[0071] Furthermore, from the perspective of lightweighting, the specific gravity of the porous sandwich structure 3 is preferably 0.5 or more and 1.4 or less.

[0072] Regarding the porosity of the core layer 2, it needs to be between 50% and 76% by volume. When the porosity is less than 50% by volume, the spacing between the discontinuous reinforcing fibers 12 is small, making it difficult to form pores 11 in the thermoplastic resin 10. Compared to the case where no pores 11 are formed, it is less likely to produce differences in the bonding strength between the discontinuous reinforcing fibers 12, so the overall rigidity of the porous sandwich structure 3 is dominated by the rigidity of the skin layer 1. In addition, from the viewpoint of lightweighting and cost, this is not preferred.

[0073] On the other hand, if the porosity of the core layer 2 is 76% or more by volume, the spacing between the discontinuous reinforcing fibers 12 increases, and the area of ​​the thermoplastic resin 10 in contact with each discontinuous reinforcing fiber decreases. Furthermore, the pores 11 of the thermoplastic resin 10, which extend into a planar structure, become larger, leading to stress concentration and a decrease in the rigidity of the porous sandwich structure 3. Therefore, to achieve both lightweight and high rigidity, the porosity of the core layer 2 needs to be 50% by volume or more and 76% by volume or less. More preferably, it should be 60% by volume or more and 76% by volume or less.

[0074] Furthermore, in this invention, it is preferred that the discontinuous reinforcing fibers 12 constituting the core layer 2 are in the range of 5% to 75% by weight, and the thermoplastic resin 10 is in the range of 25% to 95% by weight.

[0075] In the formation of the core layer 2, the ratio of discontinuous reinforcing fibers 12 to thermoplastic resin 10 is a factor in determining the porosity.

[0076] There are no particular restrictions on the method for determining the ratio of discontinuous reinforcing fiber 12 to thermoplastic resin 10. For example, it can be determined by removing the thermoplastic resin 10 contained in the core layer 2 and measuring only the weight of the remaining discontinuous reinforcing fiber 12.

[0077] Methods for removing the resin components contained in the core layer 2 include, for example, dissolution or burning.

[0078] For weight determination, electronic scales or electronic balances can be used. The size of the molded material to be measured should be 100mm × 100mm square, and the number of measurements should be n = 3. The average value can be used.

[0079] Regarding the proportions of the core layer 2, it is preferable that the discontinuous reinforcing fibers are 7% to 70% by weight and the thermoplastic resin is 30% to 93% by weight; more preferably, the discontinuous reinforcing fibers are 20% to 50% by weight and the thermoplastic resin is 50% to 80% by weight; even more preferably, the discontinuous reinforcing fibers are 25% to 40% by weight and the thermoplastic resin is 60% to 75% by weight.

[0080] If the discontinuous reinforcing fibers are less than 5% by weight and the thermoplastic resin is more than 95% by weight, it is difficult for expansion to occur using the elastic force of the discontinuous reinforcing fibers, thus making it impossible to increase the porosity and resulting in difficulties in creating regions with different porosities in the core layer 2. As a result, the bonding strength with the second component 27 described later is also reduced. On the other hand, if the discontinuous reinforcing fibers are more than 75% by weight and the thermoplastic resin is less than 25% by weight, the specific stiffness of the porous sandwich structure 3 is reduced.

[0081] Regarding the thermoplastic resin 10 constituting the porous sandwich structure 3, it is important that it extends into a planar (film-like) region surrounded by discontinuous reinforcing fibers 12 and has multiple pores 11. By forming multiple pores 11 in the planar thermoplastic resin 10, the remaining thermoplastic resin 10 forms a network shape. When viewed in a two-dimensional plane in the cross-sectional image described later, the planar region of the thermoplastic resin 10 preferably branches in a manner that extends arms in three to eight directions, i.e., in a manner that forms arm-like portions, and more preferably branches in four to five directions.

[0082] Furthermore, the pores 11 formed in the thermoplastic resin 10 of the core layer 2 constituting the porous sandwich structure 3 are preferably spaced 4 mm apart in the two-dimensional plane of the cross-sectional image described later. 2 The number of items is between 2 and 300, and more preferably between 20 and 240.

[0083] It should be noted that, regarding the cross-sectional observation method of the porous sandwich structure 3 of the present invention, the epidermal layer 1 is ground perpendicular to the stacking direction of the epidermal layer 1 and the core layer 2 (parallel to the stacking sequence) to expose the core layer 2, and then observed using an optical microscope (Keyence, VHX-6000). Regarding the observation conditions, cross-sectional images taken under conditions of 500x magnification, coaxial irradiation, and an illumination overcharge time of 30 ms to 40 ms are binarized, and then the number of pores 11 formed in the thermoplastic resin 10 is counted for evaluation. When exposing the core layer 2, it is preferable to select the surface where the epidermal layer 1 and the core layer 2 are not in an interlocking state.

[0084] For the integral molded body 30, use Figure 3 Please provide an explanation.

[0085] The aforementioned porous sandwich structure 3 has a step portion 23 at one end of a single side. If the side with less step is taken as the design side and the side with step is taken as the non-design side, the step portion 23 is composed of a boundary portion 21 and a pressing portion 22. The boundary portion 21 has a boundary that connects the main body portion 20 that forms the thickest region and the pressing portion 22 that forms the thinnest region.

[0086] The porosity of the core layer 2 in the boundary portion 21 and the pressing portion 22 is configured to be lower than that of the core layer in the main body portion 20. In addition, by forming an integrated molded body 30 by joining a second component 27 containing other molded bodies to a part of the pressing portion 22, it is possible to achieve further thinning and improve the reliability of the joint.

[0087] In this invention, the maximum thickness of the porous sandwich structure 3 is preferably 0.3 mm to 2.0 mm. If it is less than 0.3 mm, the rigidity of the integrally molded body 30 may be insufficient. Furthermore, if the maximum thickness 29 of the porous sandwich structure 3 is greater than 2.0 mm, the lightweight property may be compromised. From the viewpoint of lightweight and rigidity, a thickness of 0.7 mm to 1.5 mm is more preferable. It should be noted that the maximum thickness is the value measured at the thickest part of the porous sandwich structure 3.

[0088] Furthermore, in this invention, the second component 27 is preferably formed by joining the second component 27 over the entire circumference of the outer peripheral side surface of the porous sandwich structure 3. By forming a joining surface 28 with the second component 27 over the entire circumference of the outer peripheral side surface of the porous sandwich structure 3, high bonding strength and thin wall thickness can be achieved as an integral molded body 30.

[0089] Furthermore, in this invention, before injecting the second component 27, it is preferable to pre-form a frame around the porous sandwich structure 3, which is then enclosed by the second component 27, on the outer periphery of the porous sandwich structure 3, and then separately inject the second component 27 into the gap between the porous sandwich structure 3 and the frame. This is an effective means of achieving low warpage in the integrally molded body 30.

[0090] As a molding method, the frame made from the second component can be pre-manufactured and then injection molded as an insert, as described above, or the porous sandwich structure 3 can be directly injection molded onto the substrate. For both insert injection molding and substrate injection molding, injection molding is the preferred method.

[0091] As the second component 27, from the viewpoint of strength and rigidity of the integral molded body 30, a fiber-reinforced resin comprising reinforcing fibers and resin is preferred.

[0092] The reinforcing fibers constituting the second component 27 may be the reinforcing fibers used in the aforementioned continuous fibers. From the viewpoint of increasing the strength of the second component 27, 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 effectively used to improve strength and rigidity.

[0093] In addition, the thermoplastic resin used in the core layer 2 described above can preferably be used as the material used in the second component 27.

[0094] Furthermore, from the viewpoint of reducing warpage of the integrally molded body, the second component 27 preferably includes reinforcing fibers. As this reinforcing fiber, the same type of reinforcing fiber as that used in the aforementioned core layer 2 can be used. More preferably, the reinforcing fiber is a discontinuous fiber, and the weight-average fiber length of this discontinuous fiber is preferably 0.3 mm or more and 3 mm or less.

[0095] As a method for determining the length of discontinuous fibers, for example, there is a method where discontinuous fibers are directly removed from the integrally molded body 30 and measured by observation under a microscope. When resin adheres to the discontinuous fibers, a method (dissolution method) is used: a solvent that dissolves only the resin adhering to the discontinuous fibers is used to dissolve the resin from the discontinuous fibers, the remaining discontinuous fibers are filtered out, and the measurement is performed by observation under a microscope. Alternatively, when there is no solvent to dissolve the resin, a method (burning method) is used: only the resin is burned off within a temperature range where the discontinuous fibers do not undergo oxidation and weight loss, the discontinuous fibers are separated, and the measurement is performed by observation under a microscope. Alternatively, 400 discontinuous fibers can be randomly selected, and their lengths measured to 1 μm using an optical microscope to determine the fiber length and its proportion.

[0096] In this invention, the weight percentage of discontinuous fibers included in the second component 27 is preferably 1% by weight or more and 60% by weight or less. This improves the bonding strength with the porous sandwich structure and reduces warpage of the integrally molded body. If the percentage is less than 1% by weight, it may be difficult to ensure the strength of the molded body; if it is greater than 60% by weight, the filling of the second component 27 may become insufficient in some areas during injection molding. From the viewpoint of the moldability of the second component 27, it is preferably 5% by weight or more and 55% by weight or less, more preferably 8% by weight or more and 50% by weight or less, and even more preferably 12% by weight or more and 45% by weight or less.

[0097] In this invention, the porous sandwich structure 3 and the second component 27 are preferably joined not only on the outer peripheral side of the porous sandwich structure 3, but also on the outer peripheral edge of the surface of the porous sandwich structure 3 opposite to the designed surface 31a (the non-designed surface 31b). That is, it is preferable to form a joining surface 28 with the second component 27 on the non-designed surface 31b of the porous sandwich structure 3.

[0098] For details regarding the step portion 23 of the porous sandwich structure 3, use Figure 5 Please provide an explanation.

[0099] In the porous sandwich structure 3, the boundary portion 21 preferably has an inclined surface at an angle θ (°) relative to the in-plane direction of the porous sandwich structure 3 (the direction parallel to the surface of the main body 20). Specifically, for example, it is preferable to have a configuration in which a region is provided on the outer periphery of the porous sandwich structure 3 in the in-plane direction that is approximately horizontal to the in-plane direction of the main body 20 but has a different wall thickness, and the boundary portion 21 has an inclined boundary portion 21 with an angle θ (°) extending from the skin layer 21a of the boundary portion. As a result, the bonding area is increased, and compared with the case where other structures are only bonded to the flat side of the porous sandwich structure, the bonding area can be expanded, thereby improving the bonding strength.

[0100] Here, from the viewpoint of the formability of the porous sandwich structure 3, the angle θ (°) of the inclined surface of the step portion 23 with respect to the in-plane direction of the porous sandwich structure is preferably 1° or more and 20° or less, and more preferably 1° or more and 15° or less.

[0101] Furthermore, the porosity of the core layer 25a in the region forming the main body 20 of the integral molded body 30 is 50% to 76% by volume, more preferably 66% to 76% by volume. When the porosity in the main body 20 is less than 50% by volume, the rigidity difference between the porous sandwich structure 3 with multiple pores 11 and the sandwich structure without multiple pores 11 is small. In regions with higher porosity, the rigidity difference is larger, which is also preferable from the perspective of lightweighting. On the other hand, if the porosity in the main body 20 is greater than 76% by volume, the stretched thermoplastic resin 10 will be cut off, thereby reducing the bonding strength between the discontinuous reinforcing fiber 12 and the thermoplastic resin 10.

[0102] The porosity of the pressing core layer 25b in the region forming the thinnest wall is preferably 0% or more and less than 50% by volume, and more preferably 0% or more and less than 30% by volume.

[0103] For the arched integral molded body 30, using Figure 4 Please provide an explanation.

[0104] From the viewpoint of ensuring space for internal component insertion, the integral molded body 30 of the present invention preferably has a concave portion in a portion of the non-design surface 31b, facing the design surface 31a. In this case, it is preferable that at least a portion of the concave portion is a curved surface, and from the viewpoint of ease of molding, it is more preferable that the entire surface is curved. Viewed from above, it is preferable that at least 50% of the entire non-design surface 31b is formed with a concave portion, more preferably partially or entirely curved, and even more preferably a continuously curved shape as described above. The area of ​​the curved region is more preferably 80% or more of the exposed area of ​​the porous sandwich structure 3, more preferably 90% or more, and particularly preferably formed in the entire area. In this case, the portion other than the concave portion is preferably a flat portion.

[0105] In this invention, such as Figure 4 As shown, the height difference 33 between the extension line of the maximum height portion of the porous sandwich structure 31 extending horizontally from the surface of the design surface 31a and the extension line of the minimum height portion extending horizontally from the surface of the design surface 31a is preferably greater than 0 mm and less than 5 mm. If the height difference 33 is 0 mm (completely flat), interference with internal components may occur if the porous sandwich structure 3 has a certain or greater thickness. On the other hand, if the height difference 33 is greater than 5 mm, although it is the direction that avoids interference with internal components, the convexity becomes more obvious when viewed from the design surface 31a side, which may become unfavorable in terms of appearance.

[0106] The preferred range of the height difference 33 varies depending on the part and purpose in which the integral molded body 30 is used. When considering appearance, it is generally preferred to be 4 mm or less, more preferably 2 mm or less. From the viewpoint of ensuring the insertion space of internal components, it is sometimes preferred to be greater than 0 mm and less than 0.5 mm. From the viewpoint of ensuring the insertion space of internal components and appearance, it is sometimes more preferred to be greater than 0 mm and less than 0.1 mm, and even more preferably in the range of greater than 0 mm and less than 0.05 mm.

[0107] From the viewpoint of ensuring sufficient space for internal component insertion and providing a certain thickness for the porous sandwich structure 3, the height difference 33 is sometimes preferably 1 mm or more. Regarding the convexity of the design surface 31a, the specific proportion of the area with the convex portion in the design surface when viewed from above is the same as the preferred proportion for the concave portion in the non-design surface 31b. Similar to the concave portion of the non-design surface 31b mentioned above, it is preferable that at least a portion of the area is a curved surface. More preferably, similar to the non-design surface 31b, a certain area is a curved surface, and is a convex portion that continuously increases in height from the periphery towards its center or off-center in the in-plane direction of the porous sandwich structure 3. As one of the most suitable methods, it is possible to form a single curved convex portion in the entire area of ​​the design surface 31a.

[0108] The porous sandwich structure 3 and the integral molded body 30 of the present invention are rectangular in shape, and the present invention is suitable for the top plate of electronic device housings such as laptops. It should be noted that the rectangular shape also includes the case of a roughly rectangular shape. In addition, by being rectangular in top view, the area of ​​the second component 27 is small, thus enabling low warpage of the integral molded body.

[0109] Industrial availability

[0110] The porous sandwich structure and integral molded body of the present invention are applicable to all applications requiring lightweight, high strength, high rigidity and thin walls.

[0111] Explanation of reference numerals in the attached figures

[0112] 1, 24 Epidermis

[0113] 2.25 core layer

[0114] 3, 26, 31 Porous interlayer structures

[0115] 10 thermoplastic resin

[0116] 11 holes

[0117] 12 Discontinuous Reinforcing Fibers

[0118] 20 Main body

[0119] 20a Main body epidermis

[0120] 21 Boundary Section

[0121] 21a Boundary epidermis

[0122] 22 Pressing section

[0123] 22a Pressing part epidermis

[0124] 23rd order difference part

[0125] 25a Main body core layer

[0126] 25b Pressing Core Layer

[0127] 27, 32, Part 2

[0128] 28. Joint surface

[0129] 29 Maximum thickness

[0130] 30 One-piece molded body

[0131] 31a Design Surface

[0132] 31b Non-design surface

[0133] 33. Difference in elevation

[0134] θ angle

Claims

1. A porous sandwich structure comprising: a core layer formed by bonding three-dimensionally arranged discontinuous reinforcing fibers together with a thermoplastic resin; and a skin layer disposed on both sides of the core layer and comprising continuous reinforcing fibers and a matrix resin. Its features are, In the core layer, the thermoplastic resin is used to cover a region surrounded by multiple discontinuous reinforcing fibers forming a three-dimensional network structure in a planar manner, and the planar region covered by the thermoplastic resin has multiple pores. The porosity of the core layer is above 50% and below 76% by volume.

2. The porous sandwich structure as described in claim 1, wherein, In a cross-section of the core layer perpendicular to the stacking direction of the skin layer and the core layer, the thermoplastic resin has arm-shaped portions that branch and spread out in three to eight directions.

3. The porous sandwich structure as described in claim 1, wherein, In the core layer, the planar thermoplastic resin is distributed at 4 mm intervals. 2 It has more than 2 and less than 300 holes.

4. The porous sandwich structure as described in claim 1, wherein, The thermoplastic resin is selected from at least one of the following groups: polyolefin resin, polyamide resin, polyester resin, polycarbonate resin, polystyrene resin, modified polyphenylene ether resin, polyarylene sulfide resin, and polyetherketone resin.

5. The porous sandwich structure as described in claim 1, wherein, The thermoplastic resin has strain curing properties.

6. The porous sandwich structure as described in claim 1, wherein, A stepped section with reduced thickness is formed at the end of the porous interlayer structure. The stepped section consists of a pressing section with the smallest thickness and a boundary section whose thickness decreases from the main body section, which has no reduction in thickness, toward the pressing section. The porosity of the core layer in the boundary portion and the pressing portion is less than the porosity of the core layer in the main body portion.

7. An integral molded body formed by joining the pressing portion of the porous sandwich structure of claim 6 with a component comprising other molded bodies.

8. The integrally molded body as described in claim 7, wherein, One surface of the boundary portion is inclined relative to the surface of the main body portion at an angle of inclination of 1° to 20°.

9. The integrally molded body as described in claim 7, wherein, The component containing other molded bodies is joined to the pressing part by insert injection molding or injection molding on the substrate.

10. The integrally molded body as claimed in claim 7, wherein, The porosity of the core layer in the main body is 50% to 76% by volume, and the porosity of the core layer in the pressing part is 0% to 50% by volume.

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