Porous structures and molded members made of fiber-reinforced resin

Abstract

Provided is a porous structure, made from fibre-reinforced resin, which is lightweight and has excellent mechanical characteristics. The fibre-reinforced resin comprises a reinforced fibre substrate and a thermoplastic resin, wherein the reinforced fibre substrate includes 50-100 weight% reinforcing fibres having a fibre length of 2-10mm, the total amount of reinforcing fibres being 100 weight%, and the thermoplastic resin has a long chain branched structure.

Description

[Technical Field]

[0001] This invention relates to a fiber-reinforced resin comprising a reinforcing fiber base material and a thermoplastic resin. of This relates to porous structures and molded members. [Background technology]

[0002] In recent years, market demand for lightweight industrial products such as automobiles, aircraft, sports equipment, and electronic devices has been increasing year by year. To meet this demand, porous structures, which possess both excellent lightweight properties and superior mechanical properties, are being widely used in various industrial applications. However, porous structures with voids have the drawback of being significantly inferior in mechanical properties such as compression properties, despite their excellent lightweight properties.

[0003] Patent Document 1 describes an invention of a structure consisting of resin, reinforcing fibers, and voids. It is stated that because the reinforcing fibers are discontinuous, substantially monofilamental, and randomly dispersed, the voids formed by the elastic force of the reinforcing fibers become denser, thus achieving both excellent lightness and excellent mechanical properties.

[0004] Patent Document 2 describes an invention of a polypropylene resin extruded foam containing fibrous fillers. The fibrous fillers are oriented not only in the extrusion direction but also in the thickness direction due to the presence of foam cells, thus enabling the foam to exhibit excellent mechanical properties in the thickness direction. Furthermore, by using a polypropylene resin with excellent viscoelastic properties, dense closed-cell foam can be formed, achieving both excellent lightness and excellent mechanical properties. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2017 / 110532 [Patent Document 2] International Publication No. 2006 / 054715 [Overview of the project] [Problems that the invention aims to solve]

[0006] In the structure described in Patent Document 1, the resin stretches and breaks as the structure expands due to the elastic force of the reinforcing fibers. As a result, the reinforcing fibers are only bound together by the resin at the entanglement points. Furthermore, the areas where the resin breaks tend to swell significantly, resulting in an uneven void structure. Therefore, there was room for improvement in the mechanical properties.

[0007] The extruded foam described in Patent Document 2 had a high proportion of short fibers due to the breakage of reinforcing fibers, resulting in insufficient reinforcement. Furthermore, because it was made by foaming a kneaded fiber-reinforced resin with a foaming agent, it was difficult to create a structure in which the reinforcing fibers intersected to provide reinforcement, and the reinforcing effect of the reinforcing fibers could not be fully utilized.

[0008] The present invention has been made in view of the above problems, and its objective is to provide a porous structure made of fiber-reinforced resin that is lightweight and has excellent mechanical properties. [Means for solving the problem]

[0009] The present invention, which solves the above problems, Fiber fiber-reinforced resin Porous structure And, The fiber-reinforced resin comprises a reinforcing fiber substrate and a thermoplastic resin. The aforementioned reinforcing fiber substrate contains reinforcing fibers with a fiber length of 2 to 10 mm in an amount of 50 to 100% by weight, with the total amount of reinforcing fibers being 100% by weight, and the thermoplastic resin has a long-chain branched structure. Furthermore, the reinforcing fiber substrate has a three-dimensional network structure formed by reinforcing fibers, and the thermoplastic resin forms striated structures that bind the reinforcing fibers together in the network of the three-dimensional network structure of the reinforcing fiber substrate, and also forms voids that are surrounded by the reinforcing fibers and / or the thermoplastic resin, where neither the reinforcing fibers nor the thermoplastic resin exist. Fiber-reinforced resin Porous structure That is the case. [Effects of the Invention]

[0010] According to the present invention, a porous structure made of fiber-reinforced resin that is lightweight and has excellent mechanical properties can be obtained. [Brief explanation of the drawing]

[0011] [Figure 1]It is a schematic diagram showing the dispersion state of reinforcing fibers in a reinforcing fiber base material contained in the fiber-reinforced resin of the present invention. [Figure 2] It is a schematic diagram of a plot of the extensional viscosity and the amount of strain measured with a uniaxial extensional viscometer. [Figure 3] It is a schematic diagram showing the cross-sectional structure of the porous structure of the present invention. [Figure 4] It is a schematic diagram showing an enlarged structure formed by reinforcing fibers and a thermoplastic resin in the porous structure of the present invention. [Figure 5] It is a schematic diagram showing typical cross-sectional structures in the in-plane direction (FIG. 5(a)) and the thickness direction (FIG. 5(b)) of the porous structure of the present invention.

Mode for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in detail.

[0013] <Fiber-Reinforced Resin> The present invention is a fiber-reinforced resin containing a reinforcing fiber base material and a thermoplastic resin. The reinforcing fiber base material contains 50 to 100% by weight of reinforcing fibers having a fiber length of 2 to 10 mm, with the total amount of the reinforcing fibers constituting the reinforcing fiber base material being 100% by weight. When the proportion of the reinforcing fibers having a fiber length of 2 mm or more is 50% by weight or more, the reinforcing fibers exhibit a sufficient reinforcing effect, and the mechanical properties of the obtained fiber-reinforced resin are improved. Further, when expanding by the elastic force of the reinforcing fiber base material as described later, the reinforcing fiber base material becomes bulky, so the expansion force is improved. On the other hand, when the proportion of the reinforcing fibers exceeding 10 mm in fiber length exceeds 50% by weight, although the expansion force is improved, the proportion of the bent fibers increases in the obtained fiber-reinforced resin, resulting in a decrease in mechanical properties.

[0014] The ratio of the weight-average fiber length (Lw) to the number-average fiber length (Ln) of the reinforcing fibers (Lw / Ln) is preferably 1 to 1.4, and more preferably 1 to 1.3. A small Lw / Ln indicates small variation in fiber length. Small variation in fiber length makes it easier to uniformly form the intersecting fiber structure of the reinforcing fibers, as described later. The distribution of fiber length can be calculated by removing the resin components in the fiber-reinforced resin by methods such as burning or elution, randomly selecting 400 fibers from the remaining reinforcing fibers, measuring their length to 0.01 mm, and rounding to two decimal places. <Reinforced fiber base material> The reinforced fiber substrate preferably has a three-dimensional network structure with intersections between the reinforcing fibers and voids between the numerous reinforcing fibers. With such a structure, the thermoplastic resin can be easily expanded by the elastic force of the reinforced fiber substrate by melting or softening it by heating, thereby forming a porous structure described later. That is, as it expands, the thermoplastic resin, which is in a melted or softened state, deforms and forms a striated structure that binds the reinforcing fibers together within the three-dimensional network structure formed by the reinforcing fibers. At the same time, in areas where the deformation of the thermoplastic resin does not follow the expansion of the reinforced fiber substrate, there are regions where neither reinforcing fibers nor thermoplastic resin exist, i.e., voids, resulting in a porous structure.

[0015] Specific forms of the reinforcing fiber base material include nonwoven fabric forms, and more specifically, chopped strand mats, continuous strand mats, papermaking mats, carding mats, airlaid mats, etc. Furthermore, from the viewpoint of expanding due to the elastic force of the reinforcing fibers, it is preferable that the intersecting reinforcing fibers of the reinforcing fiber base material are sealed with resin or the like. <Reinforced Fiber> The orientation of reinforcing fibers can be expressed using the concept of a two-dimensional orientation angle, that is, the angle formed by a certain reinforcing fiber single filament (a) and a reinforcing fiber single filament (b) that intersects with it. The two-dimensional orientation angle will be explained using Figure 1. Figure 1 is a schematic diagram showing the dispersion state of reinforcing fibers when only the reinforcing fibers of a fiber-reinforced resin are observed from the surface direction. Focusing on reinforcing fiber single filament 1, reinforcing fiber single filament 1 intersects with reinforcing fiber single filaments 2-5. Here, intersection means that in the observed two-dimensional plane, the reinforcing fiber single filament (a) is observed to intersect with other reinforcing fiber single filaments (b). In actual fiber-reinforced resins, it is not necessary for reinforcing fiber 1 and reinforcing fibers 2-5 to be in contact. The two-dimensional orientation angle is defined by the acute angle 6 of the two angles formed by two intersecting reinforcing fiber single filaments. There are no particular restrictions on the method of measuring the average value of the two-dimensional orientation angle, but for example, observing the orientation of the reinforcing fibers from the surface can be exemplified. In this case, polishing the surface to expose the fibers is preferable because it makes it easier to observe the reinforcing fibers. Another example is a method of observing the orientation of the reinforcing fibers using transmitted light. In this case, slicing the material thinly is preferable because it makes it easier to observe the reinforcing fibers. Furthermore, another example is a method of taking an orientation image of the reinforcing fibers by X-ray CT transmission observation. In the case of reinforcing fibers with high X-ray transparency, it is preferable to mix tracer fibers with the reinforcing fibers or to coat the reinforcing fibers with a tracer agent because it makes it easier to observe the reinforcing fibers.

[0016] The average value of the two-dimensional orientation angle is measured using the following procedure I and II. I. Measure the acute angle between a randomly selected reinforcing fiber single filament (a) and all intersecting reinforcing fiber single filaments (b), and calculate the average value of the two-dimensional orientation angle. If there are many reinforcing fiber single filaments (b) intersecting a reinforcing fiber single filament (a), you may substitute the average value of 20 randomly selected intersecting reinforcing fiber single filaments (b) as a substitute. II. Repeat the measurement described in I above five times, focusing on a different reinforcing fiber single yarn, and take the average value in two dimensions. It is calculated as the average value of the orientation angle.

[0017] In the present invention, the average value of the two-dimensional orientation angle of the reinforcing fibers is 10 to 80 degrees, preferably 20 to 70 degrees, more preferably 30 to 60 degrees, and is preferable as it approaches the ideal angle of 45 degrees. If the average value of the two-dimensional orientation angle is less than 10 degrees or greater than 80 degrees, it means that many of the reinforcing fibers remain in bundle form. An average value of 10 to 80 degrees for the two-dimensional orientation angle of the reinforcing fibers improves the moldability of the fiber-reinforced resin into complex shapes, and furthermore, because the fibers are not oriented in a specific direction, the fiber-reinforced resin exhibits isotropic mechanical properties. In addition, as will be described later, when expanded by the elastic force of the reinforcing fibers, the reinforcing fibers become bulkier, thus exhibiting sufficient expansion force. Furthermore, in the resulting porous structure, the mesh of the three-dimensional network structure formed by the reinforcing fibers becomes denser, resulting in an excellent reinforcing effect.

[0018] The type of reinforcing fiber is not particularly limited; for example, carbon fiber, glass fiber, aramid fiber, alumina fiber, silicon carbide fiber, boron fiber, metal fiber, natural fiber, mineral fiber, etc., can be used, and one or more of these may be used in combination. Among these, carbon fibers such as polyacrylonitrile (PAN), pitch, and rayon are preferably used because they have high specific strength and specific stiffness, and are effective in reducing weight. Furthermore, glass fiber can be preferably used from the viewpoint of improving the economic efficiency of the resulting fiber-reinforced resin, and in particular, it is preferable to use carbon fiber and glass fiber in combination from the viewpoint of balancing mechanical properties and economic efficiency. Furthermore, aramid fiber can be preferably used from the viewpoint of improving the shock absorption and shapeability of the fiber-reinforced resin, and it is preferable to use carbon fiber and aramid fiber in combination from the viewpoint of balancing mechanical properties and shock absorption. In addition, from the viewpoint of improving the conductivity of the fiber-reinforced resin, it is preferable to use reinforcing fibers coated with metals such as nickel, copper, or ytterbium, or pitch-based carbon fiber.

[0019] The tensile strength of the reinforcing fibers is preferably 3000 MPa or higher, and more preferably 4000 MPa or higher. By keeping the tensile strength of the reinforcing fibers within the above range, breakage of the reinforcing fibers during the process can be suppressed. Furthermore, from the viewpoint of the mechanical properties of the resulting fiber-reinforced resin, the tensile modulus of the reinforcing fibers is preferably 100 GPa or higher, and more preferably 200 GPa or higher. There are no particular upper limits on the tensile strength and tensile modulus of the reinforcing fibers. PAN-based carbon fibers are an example of reinforcing fibers that can achieve both of these conditions.

[0020] The thermoplastic resin included in the fiber-reinforced resin of the present invention is a thermoplastic resin having a long-chain branched structure. Examples of resins having a long-chain branched structure include polypropylene resin and low-density polyethylene in which a long-chain branched structure is introduced using a metallocene catalyst, and polystyrene resin, polycarbonate resin, and polyphenylene sulfide resin in which a long-chain branched structure is introduced using a branching agent. From the viewpoint of lightweight properties, polyolefins and polystyrene are preferred, and from the viewpoint of heat resistance, polyphenylene sulfide resin is preferred. Furthermore, from the viewpoint of maintaining the structure formed during expansion, crystalline resins are preferred because they are required to cool and solidify quickly from a molten state, while amorphous resins are preferred from the viewpoint of process window.

[0021] Examples of commercially available resins with long-chain branched structures include, for polypropylene resins, "MFX6, EX6000" (Nippon Polypropylene Co., Ltd.), "HMT1" (Toyo Styrene Co., Ltd.), "FN1700A" (Idemitsu Petrochemical Co., Ltd.), and "LF3G" (DIC EP Co., Ltd.), both of which have a long-chain branched structure.

[0022] By using a thermoplastic resin having a long-chain branched structure, the entanglement of molecular chains due to the long-chain branched structure causes the thermoplastic resin to behave elastically, allowing it to be stretched without breaking. When forming a porous structure by expanding it with the elastic force of a reinforcing fiber substrate as described later, this property allows the resin to expand without breaking, making it easier to form a continuous striated structure in the porous structure without the resin breaking. As an indicator of the elasticity of a thermoplastic resin, the ratio G'(0.01) / G'(0.001) of the storage modulus G'(0.01) at a frequency of 0.001 Hz, measured at a temperature of melting point + 30°C for crystalline resins and Tg + 80°C for amorphous resins (where Tg is the glass transition temperature; the same applies hereinafter), can be used. In the present invention, it is preferable to use a thermoplastic resin with a G'(0.01) / G'(0.001) ratio of 15 or less, more preferably 12 or less, even more preferably 10 or less, and even more preferably 7 or less. The storage modulus at melt is measured in accordance with ISO 6721-10 (1999). If the G'(0.01) / G'(0.001) ratio is 15 or less, as described later, when the fiber-reinforced resin expands due to the elastic force of the reinforcing fiber substrate, the small ratio of G'(0.01) / G'(0.001) allows the thermoplastic resin to be stretched without breaking when stretched by the elastic force of the reinforcing fiber substrate acting on it.

[0023] The presence of a long-chain branched structure can be confirmed in polypropylene resin by the following method. Polypropylene with a long-chain branched structure has a branched structure as shown in the structural formula of Chemical Formula 1.

[0024] [ka]

[0025] In the structural formula, Ca, Cb, and Cc represent methylene carbons adjacent to the branched carbon, and P 1 , P 2 , P 3P indicates the residue of polypropylene. 1 , P 2 , P 3 It may also contain within itself a branched carbon (Cbr) other than the Cbr shown in this structural formula. Such a branched structure is 13 It is identified by 13C-NMR analysis. The assignment of each peak can be found in Macromolecules, Vol. 35, No. 10, 2002, pp. 3839-3842. Specifically, one methylene carbon (Ca, Cb, Cc) is observed at 43.9-44.1 ppm, one at 44.5-44.7 ppm, and one at 44.7-44.9 ppm, for a total of three methylene carbons, and a methine carbon (Cbr) is observed at 31.5-31.7 ppm. The methine carbon observed at 31.5-31.7 ppm above may be abbreviated as branched carbon (Cbr) below. A characteristic feature is that the three methylene carbons adjacent to the branched methine carbon Cbr are observed as three diastereotopically non-equivalent branches. The long-chain branched structure referred to in this invention represents polypropylene residues with 5 or more carbon atoms branched from the polypropylene backbone. Furthermore, branching with four or fewer carbon atoms can be distinguished by the difference in the peak positions of the branched carbon atoms (see Macromol. Chem. Phys. 2003, Vol. 204, p. 1738).

[0026] Furthermore, this can also be confirmed by calculating the branching index g' using the relationship between molecular weight and viscosity. The branching index g' is known as a direct indicator of long-chain branching. The branching index is expressed by the following formula.

[0027]

number

[0028] When the branching index g' is less than 1, it is determined that a long-chain branched structure exists, and the value of the branching index g' decreases as the number of long-chain branched structures increases. The branching index g' can be determined using a GPC equipped with a light scattering meter and a viscometer as detectors, and the branching index (g') is calculated from the intrinsic viscosity ([η]br) obtained by measuring the target sample and the intrinsic viscosity ([η]lin) obtained separately by measuring the linear polymer. When a long-chain branched structure is introduced into a polymer molecule, the radius of inertia becomes smaller compared to a linear polymer molecule of the same molecular weight. Since a smaller radius of inertia leads to a smaller intrinsic viscosity, the branching index g', which is the ratio of the intrinsic viscosity ([η]br) of the branched polymer to the intrinsic viscosity ([η]lin) of a linear polymer of the same molecular weight, decreases as the introduction of long-chain branched structures increases. The logarithm of [η]lin of a linear polymer is the molecular weight The relationship between logarithms and linearity can be expressed as the Mark-Houwink-Sakurada equation. Since it is publicly known, the [η]lin value can be obtained by measuring the linear polymer and extrapolating it to the low molecular weight or high molecular weight side as appropriate.

[0029] The branching index g' of a polymer generally takes values ​​in the range of 0 to 1. In the case of a polymer having only linear structures, the branching index g' is 1, and as the long-chain branched structure increases, the branching index g' approaches 0. In this application, for resins other than polypropylene resin, a branching index of 0.95 or less is considered to have a long-chain branched structure. The branching index g' is preferably 0.5 to 0.95, and more preferably 0.8 to 0.95. When the branching index is 0.95 or less, the resin is more likely to form a continuous striated structure without breaking in a porous structure. On the other hand, if the branching index is too high, it hinders the expansion of the fiber-reinforced resin substrate, so it is preferable that the branching index be 0.5 or higher.

[0030] A high melt viscosity in the low-frequency range of a thermoplastic resin is preferable because it suppresses resin aggregation, and when the resin is expanded by the elastic force of a reinforcing fiber substrate as described later to form a porous structure, it can maintain a continuous striated structure without collapsing. As an indicator, the complex viscosity η(0.001) at melting point + 30°C for crystalline resins and Tg + 80°C for amorphous resins, measured at a frequency of 0.001 Hz can be used. If multiple melting points are observed, the measurement temperature is set based on the highest melting point. In this invention, it is preferable that the complex viscosity η(0.001) is 3500 [Pa·s] or higher, and more preferably η(0.001) is 6000 [Pa·s] or higher. The complex viscosity η is measured in accordance with ISO 6721-10 (1999). By setting the complex viscosity η(0.001) within the above range, the resin becomes less likely to migrate, and aggregation can be prevented. Furthermore, the melt flow rate of the thermoplastic resin is preferably 1.0 to 40 g / 10 min, and more preferably 2.0 to 35 g / 10 min. The melt flow rate is measured according to the temperature specified for each resin in accordance with JIS K7210:2014. For resins for which no temperature is specifically specified in JIS, the measurement is performed at melting point + 50°C for crystalline resins, and at Tg + 100°C and a load of 2.16 kg for amorphous resins. If the melt flow rate of the thermoplastic resin is 1 g / 10 min or more, it becomes easier to impregnate the reinforcing fiber substrate with the thermoplastic resin during the production of the fiber-reinforced resin substrate described later. On the other hand, if the melt flow rate of the thermoplastic resin is 40 g / 10 min or less, when impregnating the reinforcing fiber substrate with the thermoplastic resin, it is possible to suppress the outflow of the thermoplastic resin from the sides of the reinforcing fiber substrate, making it easier to obtain a fiber-reinforced resin of the desired shape. In thermoplastic resins with a long-chain branched structure, the viscosity in the low-frequency region is higher than the viscosity in the high-frequency region. Therefore, it is possible to increase the viscosity in the low-frequency region while maintaining the melt flow rate within a desirable range.

[0031] Furthermore, it is preferable that the thermoplastic resin has strain-curing properties. Strain-curing properties refer to the property that the viscosity of a resin increases when a certain amount of deformation or more is applied to a molten resin. By using a strain-curing resin, when the resin deforms in conjunction with the deformation of the fiber-reinforced resin, the viscosity of the resin in the deformed part increases specifically, creating a difference in viscosity between the deformed and undeformed parts of the resin. As a result, the deformation of the undeformed part with lower viscosity progresses, and the resin can be deformed uniformly, allowing it to be stretched without cutting. In addition, because the viscosity of the resin in the stretched part increases specifically, it expands uniformly and can form a dense void structure. In this specification, "strain-curing properties" means that the degree of strain curing, as determined by uniaxial extensional viscosity measurement measured at the melting point of the thermoplastic resin + 30°C in the case of crystalline resins, and at Tg + 80°C in the case of amorphous resins, is 1.1 or higher. In uniaxial extensional viscosity measurement, first, the extensional viscosity measurement results for a strain rate of 1 / sec are plotted on a log-log graph as shown in Figure 2, with strain amount [-] on the x-axis and extensional viscosity ηE (Pa·s) on the y-axis. Here, strain amount is Hencky strain, which is derived from the following formula.

[0032]

number

[0033] On that log-log graph, the viscosity just before strain hardening occurs is approximated by a straight line, and the extensional viscosity ηE (ηEmax) at which the strain amount derived from Equation 2 (the above formula) becomes 4.0 is determined, and the approximate extensional viscosity at which the strain amount of 4.0 is approximated by a straight line from the extensional viscosity gradient just before strain hardening occurs is also determined. Let ηElin be the value of strain hardening. This ηEmax / ηElin is defined as the degree of strain hardening. If the resin breaks without stretching to a strain of 4.0, the value of the break point is set to ηE(ηEmax). If no strain hardening occurs, the degree of strain hardening is set to 1. If multiple melting points are observed, the measurement temperature is set based on the highest melting point. The degree of strain hardening of thermoplastic resin is preferably 2 or higher, more preferably 4 or higher, and even more preferably 6 or higher. On the other hand, if the strain hardening is too high, it will hinder the expansion of the fiber-reinforced resin substrate, so it is preferable that the degree of strain hardening be 20 or lower.

[0034] Furthermore, thermoplastic resins may contain fillers such as mica, talc, kaolin, hydrotalcite, sericite, bentonite, xonotlite, sepiolite, smectite, montmorillonite, warlastenite, silica, calcium carbonate, glass beads, glass flakes, glass microballoons, clay, molybdenum disulfide, titanium dioxide, zinc oxide, antimony oxide, calcium polyphosphate, graphite, barium sulfate, magnesium sulfate, zinc borate, calcium borate, aluminum borate whiskers, potassium titanate whiskers, and polymer compounds, as well as conductive agents such as metal-based, metal oxide-based, carbon black, and graphite powder, halogen-based flame retardants such as brominated resins, antimony-based flame retardants such as antimony trioxide and antimony pentoxide, phosphorus-based flame retardants such as ammonium polyphosphate, aromatic phosphates, and red phosphorus, boric acid metal salts, carboxylate metal salts, and aromatic sulfonimide metal salts, depending on the application. This includes various organic acid metal salt flame retardants, inorganic flame retardants such as zinc borate, zinc, zinc oxide, and zirconium compounds, nitrogen-based flame retardants such as cyanuric acid, isocyanuric acid, melamine, melamine cyanurate, melamine phosphate, and nitrogen-based guanidine, fluorine-based flame retardants such as PTFE, silicone-based flame retardants such as polyorganosiloxanes, metal hydroxide-based flame retardants such as aluminum hydroxide and magnesium hydroxide, and other flame retardants, cadmium oxide, zinc oxide, and 150% oxide. Flame retardant additives such as copper, cupric oxide, ferrous oxide, ferric oxide, cobalt oxide, manganese oxide, molybdenum oxide, tin oxide, and titanium oxide; pigments, dyes, lubricants, mold release agents, compatibilizers, dispersants; nucleating agents such as mica, talc, and kaolin; plasticizers such as phosphate esters; heat stabilizers, antioxidants, color inhibitors, ultraviolet absorbers, flow modifiers, foaming agents, antibacterial agents, vibration dampers, deodorants, sliding modifiers, and antistatic agents such as polyether ester amides may be added. In particular, when the application is in electrical and electronic equipment, automobiles, aircraft, etc., flame retardancy may be required, and phosphorus-based flame retardants, nitrogen-based flame retardants, and inorganic flame retardants are preferably added.In order to achieve a flame-retardant effect while maintaining a good balance with the mechanical properties of the thermoplastic resin used and the resin's fluidity during molding, it is preferable to use 1 to 20 parts by weight of the flame retardant per 100 parts by weight of the thermoplastic resin. More preferably, it is 1 to 15 parts by weight.

[0035] The ratio of reinforcing fibers to the total amount of reinforcing fibers and thermoplastic resin in the fiber-reinforced resin is preferably 3 to 60 volume%, more preferably 10 to 40 volume%, and particularly preferably 15 to 30 volume%. When the volume content of reinforcing fibers is 3 volume% or more, the reinforcing effect derived from the reinforcing fibers can be sufficiently achieved. Furthermore, in order to form a porous structure using the fiber-reinforced resin of the present invention, if the ratio of thermoplastic resin is 40 volume% or more, the thermoplastic resin can easily take on a striated structure as described later, and the mechanical properties of the porous structure can be satisfied. The volume content of resin and reinforcing fibers can be measured by heating the porous structure in a crucible at a high temperature to remove the resin component, and then measuring the weight of the remaining reinforcing fibers.

[0036] There are no particular restrictions on the shape of the fiber-reinforced resin of the present invention, but from the viewpoint of using it in a laminated form, it is preferable to be in the form of a sheet.

[0037] The fiber-reinforced resin of the present invention includes embodiments that have a porous structure as described later, but embodiments that do not have a porous structure are used as a precursor. In this case, the void ratio of the fiber-reinforced resin is preferably 20% or less, more preferably 15% or less, even more preferably 10% or less, and most preferably 5% or less. By setting the void ratio within this range, the amount of unimpregnated parts where the resin is not impregnated is reduced, and therefore, it is possible to suppress the formation of defects in the resulting porous structure where the amount of resin is small and the fibers are not sufficiently fixed by the resin. The "void ratio" is a value calculated from the true specific gravity and bulk specific gravity of the fiber-reinforced resin using the following formula.

[0038]

number

[0039] The true specific gravity is measured using a pycnometer in accordance with ISO 1183 (1987) on a sample that has been pulverized into a powder with a particle size of 150 μm or less so that no voids remain inside the fiber-reinforced resin. The bulk specific gravity is measured in accordance with ISO 845 (1988) on a sample of the fiber-reinforced resin.

[0040] Furthermore, in the precursor, it is preferable that the reinforcing fiber substrate is included in a compressed state, that is, in a state in which at least a portion of the reinforcing fibers are bent, because this increases the aforementioned elastic force.

[0041] Among the fiber-reinforced resins of the present invention, the embodiment without a porous structure, as described later, is suitably used as a precursor for the fiber-reinforced resin having a porous structure. In this case, it is desirable that the fiber-reinforced resin is expandable. In this specification, a fiber-reinforced resin is defined as having an expansion ratio of 1.5 times or more when the thermoplastic resin is melted at a temperature of melting point + 20°C or higher if the thermoplastic resin is a crystalline resin, or at Tg + 100°C if the thermoplastic resin is amorphous.

[0042]

number

[0043] The true specific gravity is measured using a pycnometer in accordance with ISO 1183 (1987) on a sample that has been pulverized into a powder with a particle size of 150 μm or less so that no voids remain inside the fiber-reinforced resin after expansion. The bulk specific gravity of the fiber-reinforced resin after expansion is measured in accordance with ISO 845 (1988) on a sample of the fiber-reinforced resin.

[0044] Furthermore, the applications of the fiber-reinforced resin of the present invention in a form that does not have a porous structure are not limited to those described herein. Because it can be stretched without cutting the resin, it has excellent processability and can therefore be suitably applied to molding processes that involve stretching the resin, such as deep drawing, blow molding, foam molding, and stretch molding.

[0045] <Porous structure> As described above, the fiber-reinforced resin of the present invention may have a porous structure. In this embodiment, the fiber-reinforced resin will be referred to as a "porous structure" in this specification. In the porous structure, the reinforcing fibers constituting the reinforcing fiber base material intersect to form a three-dimensional network structure, and the thermoplastic resin forms a striated structure that binds the reinforcing fibers together in the network of the three-dimensional network structure. Furthermore, it includes regions where neither the reinforcing fibers nor the thermoplastic resin exist, surrounded by the reinforcing fibers and / or the thermoplastic resin, and such regions will be referred to as voids in this specification.

[0046] Figure 3 shows a typical cross-section of the porous structure of the present invention. As shown in Figure 3, the reinforcing fibers 7 form a network structure within the porous structure. Although Figure 3 is a two-dimensional representation because it is a cross-section, the reinforcing fibers 7 actually form a three-dimensional network structure. The thermoplastic resin 8 exists as the matrix of this three-dimensional network structure. Figure 4 is a schematic diagram showing a part of the three-dimensional network structure composed of reinforcing fibers in three dimensions. As shown in Figure 4, the thermoplastic resin 8 forms striate structures 10 that bind the reinforcing fibers together in the network of the three-dimensional network structure composed of reinforcing fibers. The voids 9 are formed in the network of the three-dimensional network structure as regions where the thermoplastic resin 8 is not present. The porous structure is reinforced by these striate structures formed by the thermoplastic resin, improving its mechanical properties.

[0047] It is preferable that the streak-like structure of the thermoplastic resin is continuously formed in the fiber-reinforced resin with a length of 300 μm or more. The continuous formation of the streak-like structure mainly refers to a structure in which the resin is continuously present in a range of 300 μm or more in the in-plane direction and the thickness direction, respectively. Also, the confirmation of whether the resin is continuous can be performed by observing the cross-section by X-ray CT observation.

[0048] The area ratio A of the voids evaluated by the cross-sectional photograph is preferably 35% or less, and more preferably 25% or less. Also, the ratio A / B of the area ratio A of the voids to the expansion ratio B described later is preferably 8 or less, more preferably 7 or less, and even more preferably 6 or less. As described above, the ratio of the void part is small, and the thermoplastic resin spreads and exists, so that the three-dimensional network structure composed of the reinforcing fibers can be efficiently reinforced. Also, when the expansion ratio is low, the elongation amount of the thermoplastic resin is small, and the thermoplastic resin is difficult to break, so the area of the voids becomes small. On the other hand, when the expansion ratio is large, it is preferable from the viewpoint of weight reduction, and the reinforcing effect of the porous structure by the thermoplastic resin becomes large. Therefore, it is preferable that the void area is small with respect to the expansion ratio.

[0049] The voids are preferably small because large voids cause stress concentration. Therefore, the average area of the voids in the cross-section of the porous structure is preferably 6000 μm 2 or less, more preferably 5000 μm 2 or less, and even more preferably 4000 μm 2 or less. Also, it is preferable that the variation in the size of the voids is small. Specifically, the coefficient of variation of the area of the voids is preferably 100% or less, more preferably 90% or less, and even more preferably 80% or less. Here, in this specification, the average area and the coefficient of variation of the voids are values calculated from 300 voids arbitrarily selected in the porous structure.

[0050] Furthermore, in order to observe the cross-section of the porous structure of the present invention, the cross-section is cut vertically in a single pass with a sharp cutter to avoid crushing the cross-section, exposing the cross-section in the thickness direction without any change in thickness. The cross-section is then observed using a scanning electron microscope (SEM) with an acceleration voltage of 0.9 kV, and the evaluation is performed by analyzing the obtained cross-sectional photograph.

[0051] Orientation angle θ of reinforcing fibers in the thickness direction in the porous structure of the present invention f θ is preferably in the range of 0.5 to 15 degrees, and more preferably in the range of 1 to 10 degrees. f By keeping the temperature below 15 degrees, the thermoplastic resin can be made to form a striated structure without breaking. fIf the angle is less than 0.5 degrees, the reinforcing fibers in the porous structure will be oriented in a planar manner, or in other words, in two dimensions, which tends to reduce the lightweight properties. θf can be measured based on observation of the in-plane cross-section of the porous structure. Figure 5 is a schematic diagram showing typical in-plane (Figure 5(a)) and thickness direction (Figure 5(b)) cross-sections of the porous structure of the present invention. In Figure 5(a), the cross-sections of the reinforcing fibers 5a and 5b are approximated as elliptical shapes for ease of measurement. Here, the cross-section of the reinforcing fiber 5a appears to have a small elliptical aspect ratio (=elliptical major axis / elliptical minor axis), while the cross-section of the reinforcing fiber 5b appears to have a large elliptical aspect ratio. On the other hand, according to Figure 5(b), the reinforcing fiber 5a has an inclination that is nearly parallel to the thickness direction Y, while the reinforcing fiber 5b has a large inclination with respect to the thickness direction Y. In this case, for reinforcing fiber 5b, the angle θx between the planar direction X of the structure and the fiber principal axis (major axis direction in the ellipse) α is approximately equal to the orientation angle θf of reinforcing fiber 5b. On the other hand, for reinforcing fiber 5a, there is a large discrepancy between the angle θx and the orientation angle θf, and it cannot be said that angle θx reflects the orientation angle θf. Therefore, when reading the orientation angle θf from a cross section perpendicular to the planar direction of the structure, the detection accuracy of the orientation angle θf can be improved by extracting fibers whose elliptical aspect ratio of the cross section is above a certain value. As an index for the elliptical aspect ratio to be extracted, if the cross-sectional shape of a single fiber is close to a perfect circle, that is, if the fiber aspect ratio in a cross section perpendicular to the fiber direction of the reinforcing fiber is 1.1 or less, the angle between the planar direction X and the fiber principal axis α is measured for reinforcing fibers with an elliptical aspect ratio of 20 or more, and this is taken as the value of the orientation angle θf. On the other hand, if the cross-sectional shape of the reinforcing fiber is elliptical or cocoon-shaped, and the fiber aspect ratio is greater than 1.1, it is better to focus on reinforcing fibers with a larger elliptical aspect ratio and measure the orientation angle θf. If the fiber aspect ratio is 1.1 or greater but less than 1.8, select reinforcing fibers with an elliptical aspect ratio of 30 or greater; if the fiber aspect ratio is 1.8 or greater but less than 2.5, select reinforcing fibers with an elliptical aspect ratio of 40 or greater; and if the fiber aspect ratio is 2.5 or greater, select reinforcing fibers with an elliptical aspect ratio of 50 or greater, and measure the orientation angle θf.

[0052] The bulk density (ρ) of the porous structure is preferably 0.01 to 1.3, more preferably 0.1 to 0.6, and even more preferably 0.15 to 0.4, from the viewpoint of lightweight properties. The bulk density is measured by cutting out a section of the porous structure and measuring it in accordance with ISO 845 (1988).

[0053] From the viewpoint of balancing lightness and mechanical properties, the expansion ratio B is preferably 1.5 to 6 times, more preferably 1.8 to 5 times, and even more preferably 2.0 to 4.5 times. If the expansion ratio B is small, the weight reduction effect obtained by expansion is small, while if the expansion ratio is too high, the mechanical properties as a structure will be insufficient. Furthermore, if the expansion ratio is increased beyond this range, the resin will break during expansion, making it difficult to form a striated structure. Note that the "expansion ratio" is the ratio of true specific gravity to bulk specific gravity, and is calculated using the formula described above.

[0054] When using porous structures as structural members, it is preferable that the compressive modulus of the porous structure be 10 MPa or higher, and more preferably 30 MPa or higher. There is no particular upper limit on the compressive modulus of the porous structure. The compressive modulus is measured by cutting out a section of the porous structure and measuring the sample dimensions of 20 mm (length) x 20 mm (width) x 4 mm (thickness), referring to ISO 844 (2004).

[0055] Similarly, the flexural modulus (Ec) of the porous structure is preferably 2.0 GPa or higher, and more preferably 2.5 GPa or higher. The flexural modulus is measured by cutting out a section of the porous structure and measuring it in accordance with ISO 178 (1993).

[0056] Furthermore, when using porous structures as structural members, it is preferable that the bending strength be 15 MPa or higher, more preferably 25 MPa or higher, and even more preferably 30 MPa or higher. The bending strength is measured by cutting out a section of the porous structure and measuring it in accordance with ISO 178 (1993).

[0057] The maximum thickness of the porous structure is preferably 0.3 mm to 10 mm, and more preferably 0.5 mm to 6 mm. Reducing the thickness of the porous structure has the effect of reducing weight, but porous structures thinner than 0.3 mm may lack sufficient rigidity.

[0058] <Molded component> Another aspect of the present invention is a molded member that contains at least a portion of the fiber-reinforced resin of the present invention. An example of such a molded member is a molded member having a sandwich structure in which a layer made of the fiber-reinforced resin of the present invention is used as the core layer, and a continuous fiber-reinforced resin, in which continuous reinforcing fibers are impregnated with resin, is used as the skin layer. In this case, the continuous reinforcing fibers of the skin layer include cloth composed of a reinforcing fiber bundle consisting of many continuous reinforcing fibers, a reinforcing fiber bundle in which many continuous reinforcing fibers are arranged in one direction (unidirectional fiber bundle), and unidirectional cloth composed of unidirectional fiber bundles.

[0059] Such molded components include, for example, electrical and electronic equipment components such as "casings, trays, chassis, interior components, or cases for personal computers, displays, office automation equipment, mobile phones, personal digital assistants (PDAs), video cameras, optical equipment, audio equipment, air conditioners, lighting equipment, entertainment goods, toys, and other home appliances," "various members, frames, hinges, arms, axles, wheel bearings, and beams," "exterior panels or body parts such as hoods, roofs, doors, fenders, trunk lids, side panels, rear end panels, front bodies, underbodies, pillars, members, frames, beams, supports, rails, and hinges," and "bumpers and bumper beams." Examples of applications include exterior parts such as moldings, undercovers, engine covers, air deflectors, spoilers, cowl louvers, and aero parts; interior parts such as instrument panels, seat frames, door trims, pillar trims, steering wheels, and various modules; structural parts for automobiles and motorcycles such as motor parts, CNG tanks, and gasoline tanks; parts for automobiles and motorcycles such as battery trays, headlamp supports, pedal housings, protectors, lamp reflectors, lamp housings, noise shields, and spare tire covers; building materials such as sound barriers and soundproof walls; and aircraft parts such as landing gear pods, winglets, spoilers, edges, rudders, elevators, fillings, ribs, and seats. From the standpoint of mechanical properties, it is desirable to use it in automobile interiors and exteriors, electrical and electronic equipment enclosures, bicycles, structural materials for sporting goods, aircraft interior materials, transport boxes, and building materials.

[0060] <Method for manufacturing fiber-reinforced resin> The fiber-reinforced resin of the present invention, which does not have a porous structure, can be manufactured by impregnating a reinforcing fiber substrate with a film or nonwoven fabric of the aforementioned thermoplastic resin under pressure. In order to obtain sufficient elasticity for expansion, it is preferable to impregnate the reinforcing fiber substrate with the thermoplastic resin while compressing it.

[0061] The reinforced fiber substrate is manufactured, for example, by pre-dispersing discontinuous reinforced fibers in a strand-like, preferably substantially monofilamental, and more preferably monofilamental form. More specifically, the reinforced fiber mat can be produced by dry processes such as the airlaid method, which disperses the reinforced fibers with an airflow to form a sheet, or the carding method, which forms a sheet by mechanically combing the reinforced fibers, or by wet processes such as the radlite method, which stirs the reinforced fibers in water to form paper. Examples of means to bring the discontinuous reinforced fibers closer to a monofilamental form include, in dry processes, providing a fiber-opening bar, vibrating the fiber-opening bar, making the card mesh finer, and adjusting the rotation speed of the card In wet processes, examples include adjusting the stirring conditions of the discontinuous reinforced fibers, diluting the concentration of reinforced fibers in the dispersion, adjusting the viscosity of the dispersion, and suppressing vortex flow when transferring the dispersion. The reinforced fiber substrate used in the present invention is preferably manufactured by a wet process that allows for easy adjustment of the proportion of reinforced fibers. In a wet process, for example, by slowing the speed of the mesh conveyor relative to the flow velocity of the reinforcing fiber dispersion, the orientation of the fibers in the resulting reinforcing fiber substrate becomes less likely to be oriented in the direction of the conveyor flow, making it possible to obtain a bulky reinforcing fiber substrate.

[0062] The pressure used when impregnating the reinforcing fiber substrate with a thermoplastic resin film or nonwoven fabric is preferably 0.5 MPa to 30 MPa, more preferably 1 MPa to 10 MPa, and even more preferably 2 MPa to 8 MPa. A pressure of 0.5 MPa or higher allows sufficient impregnation of the thermoplastic resin into the reinforcing fiber substrate, while a pressure of 30 MPa or lower facilitates thickness adjustment. The temperature used when impregnating the thermoplastic resin film or nonwoven fabric is preferably above the melting point if the thermoplastic resin is a crystalline resin, and above the Tg if the thermoplastic resin is amorphous, more preferably above the melting point + 10°C or Tg + 80°C, and even more preferably above the melting point + 20°C or Tg + 100°C. If the temperature used when impregnating the thermoplastic resin film or nonwoven fabric is too high compared to the melting point of the thermoplastic resin, decomposition or degradation of the thermoplastic resin may occur, so it is preferable that the temperature is below the melting point of the thermoplastic resin or Tg + 150°C.

[0063] Under the above conditions, a compression molding machine and a double-belt press can be suitably used as equipment to realize a method of impregnating reinforcing fibers with a thermoplastic resin film or nonwoven fabric. The compression molding machine is a batch type, and productivity can be improved by using an intermittent press system with two or more machines in parallel for heating and cooling. The double-belt press is a continuous type, and since it can easily perform continuous processing, it has excellent productivity.

[0064] A typical method for manufacturing the aforementioned porous structure is to heat and expand the fiber-reinforced resin, but the method is not limited to this. For example, one such method is a manufacturing method in which the impregnation of a thermoplastic resin and the heating process for the expansion of the fiber-reinforced resin are carried out simultaneously. In a method that uses a precursor, a precursor can be obtained by impregnating the reinforcing fiber substrate with a thermoplastic resin and cooling it in a compressed state, and then reheating the precursor to obtain a porous structure. In contrast, in a method in which the impregnation of a thermoplastic resin and the heating process for expansion are carried out simultaneously, a porous structure can be obtained in one step by expanding the thermoplastic resin without cooling it in a compressed state after heating and impregnating the reinforcing fiber substrate, resulting in excellent productivity. The temperature when heating and expanding the fiber-reinforced resin is preferably above the melting point or Tg of the thermoplastic resin. If the temperature when heating and expanding the fiber-reinforced resin is too high compared to the melting point of the thermoplastic resin, decomposition or deterioration of the thermoplastic resin may occur, so it is preferably below the melting point of the thermoplastic resin + 150°C, and more preferably below 100°C. [Examples]

[0065] The present invention will be described in more detail below with reference to examples. <Resin to be used> The following resins were used as the resin material. Polypropylene resin 1: Manufactured by Nippon Polypropylene Co., Ltd., "Waymax" (registered trademark) MFX6, a long-chain branched polypropylene resin obtained by polymerizing propylene using a metallocene catalyst (strain curing properties: yes, branching index: 0.91). Polypropylene resin 2: Prime Polymer Co., Ltd., linear random polypropylene resin "Prime PolyPro" (registered trademark) J3021GR (strain curing: none, branching index: 1.0) Polystyrene resin 1: Manufactured by Toyo Styrene Co., Ltd., polystyrene resin "Toyo Styrol" HMT1 (strain hardening: present, branching index: 0.67).

[0066] <Methods for measuring various physical properties> (1) Measurement of extensional viscosity of thermoplastic resins The strain-curing properties of thermoplastic resins were evaluated by measuring extensional viscosity at a temperature of melting point + 30°C for crystalline resins and Tg + 80°C for amorphous resins, with a strain rate of 1 / sec. A Merten rheometer manufactured by Toyo Seiki was used as the measuring device.

[0067] (2) Storage modulus and complex viscosity of thermoplastic resins at the time of melting The storage modulus and complex viscosity at melting point of the thermoplastic resin used were measured according to ISO 6721-10 (1999). Measurements were taken with n=5 at the melting point + 30°C. A TA Instruments ARESG2 dynamic viscoelasticity analyzer was used, and a parallel plate was employed as the measurement jig.

[0068] (3) Melt flow rate (MFR) of thermoplastic resins The melt flow rate of the thermoplastic resin used was measured using the method described in the specification. The number of measurements was set to n=5, and the average value was used for evaluation. A melt indexer manufactured by Toyo Seiki Co., Ltd. was used as the measuring device.

[0069] (4) Melting point measurement of thermoplastic resins The melting point of the thermoplastic resin used was measured according to JIS K7121 (1987). The heating rate was set to 10°C / min. A differential scanning calorimeter DSC 2500 manufactured by TA Instruments was used as the measuring device.

[0070] (5) Evaluation of the structure and void area of ​​porous structures The porous structure was evaluated by cutting a cross-section in the thickness direction with a cutter, observing it with a scanning electron microscope (SEM) (acceleration voltage: 0.9kV, magnification 200x), and analyzing the resulting cross-sectional images. The area of ​​regions where neither resin nor fibers existed within the cross-sectional image was measured for n=300 samples. A Keyence VHX-D510 SEM was used.

[0071] (6) Compression modulus of porous structure The compressive modulus (MPa) of a porous structure was measured in accordance with ISO 844 (2004), except that the dimensions of the test specimen were set to 20 mm (length) x 20 mm (width) x 4 mm (thickness). The number of measurements was n=5, and the average value was used for evaluation. The Instron 5565 universal material tester manufactured by Instron Japan was used as the measuring device.

[0072] (7) Bending strength and flexural modulus of porous structures The bending strength and bending modulus of the bending test specimens were measured according to ISO 178 (1993). The number of measurements was n=5, and the average value was used for evaluation. An Instron 5565 universal material tester manufactured by Instron Japan was used as the measuring device.

[0073] <Material> [Carbon fiber substrate] A continuous bundle of carbon fibers with a total of 12,000 filaments was obtained by spinning and calcining a polymer mainly composed of polyacrylonitrile. A sizing agent was applied to this continuous bundle of carbon fibers by immersion, and it was dried in heated air at a temperature of 120°C to obtain a carbon fiber bundle. The properties of this carbon fiber bundle were as follows. Single fiber diameter: 7 μm Weight per unit length: 0.8g / m Density: 1.8g / cm 3 Tensile strength: 4.2 GPa Tensile modulus: 230 GPa Sizing agent: Polyoxyethylene oleyl ether Sizing agent application amount: 1.5% by weight per 100% by weight of carbon fiber bundle.

[0074] The carbon fiber bundles prepared as described above were cut to a fiber length of 3 mm using a cartridge cutter to obtain chopped carbon fiber bundles. A 0.1% by weight aqueous dispersion of a surfactant (Nacalai Tesque Co., Ltd., polyoxyethylene lauryl ether (trade name)) was prepared, and this dispersion and the chopped carbon fiber bundles were put into a paper machine to produce a carbon fiber substrate.

[0075] The paper machine comprises a dispersion tank, a papermaking tank, and a transport unit connecting the dispersion tank and the papermaking tank. The dispersion tank is equipped with a stirrer and can disperse the introduced dispersion liquid and chopped carbon fiber bundles. The papermaking tank has a mesh conveyor with a papermaking surface at its bottom, and a conveyor capable of transporting the paper-made carbon fiber substrate is connected to the mesh conveyor. Papermaking was performed with a fiber concentration of 0.05% by weight in the dispersion liquid. The paper-made carbon fiber substrate was dried in a drying oven at 200°C. Subsequently, a 3% by weight aqueous dispersion of a binder (manufactured by Nippon Shokubai Co., Ltd., "Polyment" (registered trademark) SK-1000) was sprayed onto the upper surface of the carbon fiber substrate being transported by the conveyor. The excess binder was suctioned off, and the substrate was dried in a drying oven at 200°C to obtain the carbon fiber substrate. The basis weight of the obtained carbon fiber substrate was 110 g / m². 2 That was the case.

[0076] [Polypropylene resin film 1] Polypropylene resin 1 (manufactured by Nippon Polypropylene Co., Ltd., "Waymax" (registered trademark) MFX6), which has a long-chain branched structure, is sandwiched between release films and pressed at 220°C for 10 minutes in a press molding machine with a spacer inserted. After removing the release film together with the resin, the resin is cooled and solidified to produce polypropylene resin film 1 with a basis weight of 165 g / m². 2 This was obtained. Furthermore, the melting point of PP film 1 was measured and found to be 156°C.

[0077] [Polypropylene resin film 2] Polypropylene resin 1 (manufactured by Nippon Polypropylene Co., Ltd., "Waymax"® MFX6), which has a long-chain branched structure, was blended with polypropylene resin 2 (manufactured by Prime Polymer Co., Ltd., "Prime Polypro"® J3021GR), both 50% by weight, and compounded in an extruder. The compounded resin was sandwiched between release films and pressurized at 220°C for 10 minutes in a press molding machine with spacers inserted. After removing the release films together, the resin was cooled and solidified to produce polypropylene resin film 2 with a basis weight of 165 g / m². 2 This was obtained. Furthermore, the melting point of PP film 2 was measured and found to be 153°C.

[0078] [Polypropylene resin film 3] Polypropylene resin 1 (manufactured by Nippon Polypropylene Co., Ltd., "Waymax"® registered trademark MFX6), which has a long-chain branched structure, was blended with polypropylene resin 2 (manufactured by Prime Polymer Co., Ltd., "Prime Polypropylene"® registered trademark J3021GR), which has a long-chain branched structure, and compounded in an extruder. The compounded resin was sandwiched between release films and pressed at 220°C for 10 minutes in a press molding machine with spacers inserted. After removing the release films together, the resin was cooled and solidified to produce polypropylene resin film 3 with a basis weight of 165 g / m². 2 This was obtained. Furthermore, the melting point of PP film 3 was measured and found to be 152°C.

[0079] [Polypropylene resin film 4] Polypropylene resin 1 (manufactured by Nippon Polypropylene Co., Ltd., "Waymax"® MFX6), which has a long-chain branched structure, was blended at a weight of 10% and polypropylene resin 2 (manufactured by Prime Polymer Co., Ltd., "Prime Polypropylene"® J3021GR) at a weight of 90% and compounded in an extruder. The compounded resin was sandwiched between release films and pressed at 220°C for 10 minutes in a press molding machine with spacers inserted. After removing the release films together, the resin was cooled and solidified to produce a polypropylene resin film 4 with a basis weight of 165 g / m². 2 This was obtained. Furthermore, the melting point of PP film 4 was measured and found to be 151°C.

[0080] [Polypropylene resin film 5] Polypropylene resin 2 (manufactured by Prime Polymer Co., Ltd., "Prime Polypro" (registered trademark) J3021GR) is sandwiched between release films, and pressurized at 220°C for 10 minutes in a press molding machine with a spacer inserted. After removing the release film together with the resin, the resin is cooled and solidified to produce a polypropylene resin film 5 with a basis weight of 165 g / m². 2 This was obtained. Furthermore, the melting point of PP film 5 was measured and found to be 150°C.

[0081] [Polystyrene resin film 1] Polystyrene resin 1 (manufactured by Toyo Styrene Co., Ltd., "Toyo Styrofoam GP" HMT1), which has a long-chain branched structure, is sandwiched between release films and pressed at 240°C for 10 minutes in a press molding machine with spacers inserted. After removing the release films together and cooling and solidifying the resin, polystyrene resin film 1 is produced with a basis weight of 193 g / m². 2 This was obtained. Furthermore, the Tg of polystyrene resin film 1 was measured and found to be 103°C.

[0082] (Example 1) A porous structure was fabricated using a carbon fiber substrate and polypropylene resin film 1. After adjusting the carbon fiber substrate and polypropylene resin film to a size of 300 mm x 300 mm, they were laminated in the following order: [polypropylene resin film 1 / carbon fiber substrate / polypropylene resin film 1 / carbon fiber substrate / polypropylene resin film 1 / carbon fiber substrate / polypropylene resin film 1]. This laminate was sandwiched between release films and pressurized in a press molding machine at 180°C and 5 MPa for 10 minutes to impregnate the carbon fiber substrate with polypropylene resin. Subsequently, a fiber-reinforced resin was produced by cooling and pressing the laminate in a different press molding machine at 40°C and 5 MPa until it cooled.

[0083] Next, the fabricated fiber-reinforced resin was sandwiched between release films and pressed in a press molding machine at 180°C and 3 MPa for 10 minutes to melt the polypropylene resin contained in the fiber-reinforced resin. Subsequently, the laminate was cooled and pressed in a different press molding machine with a spacer inserted at 40°C and 5 MPa until it cooled, thereby creating a porous structure. By inserting a spacer into the press molding machine, the fiber-reinforced resin expands due to the restorative force derived from the elastic force of the carbon fiber substrate, forming a porous structure.

[0084] The resulting porous structure exhibited excellent mechanical properties and lightweight characteristics because the polypropylene resin expanded without breaking, forming a striated structure between the fibers.

[0085] (Example 2) A porous structure was fabricated in the same manner as in Example 1, except that polypropylene resin film 1 was replaced with polypropylene resin film 2.

[0086] The resulting porous structure exhibited excellent mechanical properties and lightweight characteristics because the polypropylene resin expanded without breaking, forming a striated structure between the fibers. Furthermore, the polypropylene resin's excellent fluidity allowed for good impregnation of the carbon fiber substrate.

[0087] (Example 3) A porous structure was fabricated in the same manner as in Example 1, except that polypropylene resin film 1 was replaced with polypropylene resin film 3.

[0088] The resulting porous structure exhibited excellent mechanical properties and lightweight characteristics because the polypropylene resin expanded without breaking, forming a striated structure between the fibers. Furthermore, the polypropylene resin's excellent fluidity allowed for good impregnation of the carbon fiber substrate.

[0089] (Example 4) A porous structure was fabricated in the same manner as in Example 1, except that polypropylene resin film 1 was replaced with polypropylene resin film 4.

[0090] The resulting porous structure exhibited excellent mechanical properties and lightweight characteristics because the polypropylene resin expanded without breaking, forming a striated structure between the fibers. Furthermore, the polypropylene resin's excellent fluidity allowed for good impregnation of the carbon fiber substrate.

[0091] (Example 5) A porous structure was fabricated using a carbon fiber substrate and polystyrene resin film 1. After adjusting the carbon fiber substrate and polystyrene resin film to a size of 300 mm x 300 mm, they were laminated in the following order: [polystyrene resin film 1 / carbon fiber substrate / polystyrene resin film 1 / carbon fiber substrate / polystyrene resin film 1 / carbon fiber substrate / polystyrene resin film 1]. This laminate was sandwiched between release films and pressurized in a press molding machine at 240°C and 5 MPa for 10 minutes to impregnate the carbon fiber substrate with polystyrene resin. Subsequently, a fiber-reinforced resin was produced by cooling and pressing the laminate in a different press molding machine at 40°C and 5 MPa until it cooled.

[0092] Next, the prepared fiber-reinforced resin was sandwiched between release films and pressed in a press molding machine at 180°C and 3 MPa for 10 minutes to melt the polystyrene resin contained in the fiber-reinforced resin. Subsequently, the laminate was cooled and pressed in a different press molding machine with a spacer inserted at 40°C and 5 MPa until it cooled, thereby creating a porous structure. By inserting a spacer into the press molding machine, the fiber-reinforced resin expands due to the restorative force derived from the elastic force of the carbon fiber substrate, forming a porous structure.

[0093] The resulting porous structure exhibited excellent mechanical properties and lightweight characteristics because the polystyrene resin expanded without breaking, forming a striated structure between the fibers.

[0094] (Comparative Example 1) A porous structure was fabricated in the same manner as in Example 1, except that polypropylene resin film 1 was replaced with polypropylene resin film 5.

[0095] The resulting porous structure had poor mechanical properties, although it was lightweight, because the polypropylene resin broke during expansion, preventing the formation of striated structures between the fibers.

[0096] (Comparative Example 2) A porous structure was prepared in the same manner as in Example 1, except that the fiber length of the chopped CF used as the carbon fiber base material was set to 0.5 mm. However, the expansion force of the precursor of the porous structure was insufficient, and it did not expand to the intended expansion ratio, making it impossible to prepare a sample.

[0097] [Table 1] [Explanation of symbols]

[0098] 1. Reinforced fiber single yarn (a) 2. Reinforced fiber single yarn (b) 3. Reinforced fiber single yarn (b) 4. Reinforced fiber single yarn (b) 5. Reinforced fiber single yarn (b) 6. Two-dimensional orientation angle 7. Reinforced Fibers 8. Thermoplastic resin 9. Voids 10. Striped structure of thermoplastic resins

Claims

1. A porous structure of fiber-reinforced resin, wherein the fiber-reinforced resin comprises a reinforcing fiber base material and a thermoplastic resin, the reinforcing fiber base material contains reinforcing fibers with a fiber length of 2 to 10 mm in an amount of 50 to 100% by weight, where the total amount of reinforcing fibers is 100% by weight, the thermoplastic resin has a long-chain branched structure, the reinforcing fiber base material has a three-dimensional network structure formed by the reinforcing fibers, the thermoplastic resin forms striated structures that bind the reinforcing fibers together in the network of the three-dimensional network structure of the reinforcing fiber base material, and voids are formed as regions surrounded by the reinforcing fibers and / or the thermoplastic resin where neither the reinforcing fibers nor the thermoplastic resin exist.

2. The porous structure of a fiber-reinforced resin according to claim 1, wherein the thermoplastic resin has a complex viscosity η(0.001) at melting point + 30°C in the case of a crystalline resin, and a complex viscosity η(0.001) at a frequency of 0.001 Hz at a temperature of Tg + 80°C in the case of an amorphous resin, which is 3500 Pa·s or more.

3. The porous structure of a fiber-reinforced resin according to claim 1 or 2, wherein the thermoplastic resin is measured at a temperature of melting point + 30°C in the case of a crystalline resin, or at Tg + 80°C in the case of an amorphous resin, and the ratio of the storage modulus of molten resin G'(0.01) at a frequency of 0.01 Hz to the storage modulus of molten resin G'(0.01) at a frequency of 0.01 Hz, G'(0.01) / G'(0.001), is 15 or less.

4. A porous structure of fiber-reinforced resin according to any one of claims 1 to 3, wherein the ratio of the weight-average fiber length (Lw) to the number-average fiber length (Ln) of the reinforcing fibers, Lw / Ln, is 1 to 1.

4.

5. A porous fiber-reinforced resin structure according to any one of claims 1 to 4, comprising 3 to 60 volume percent of reinforcing fibers relative to the total amount of reinforcing fibers and thermoplastic resin.

6. The porous structure of a fiber-reinforced resin according to any one of claims 1 to 5, wherein the thermoplastic resin has a long-chain branched structure and a branching index of 0.5 or more and 0.95 or less.

7. The porous structure of a fiber-reinforced resin according to any one of claims 1 to 5, wherein the thermoplastic resin has a long-chain branched structure and the branching index is 0.8 or more and 0.95 or less.

8. A porous structure of fiber-reinforced resin according to any one of claims 1 to 7, wherein the melt flow rate of the thermoplastic resin in accordance with JIS K7210:2014 is 1.0 g / 10 min or more and 40 g / 10 min or less.

9. The porous structure of the fiber-reinforced resin according to claim 1, wherein the reinforcing fiber base material is in the form of a nonwoven fabric.

10. A porous structure of a fiber-reinforced resin according to any one of claims 1 to 9, wherein the reinforcing fiber base material is fixed in a compressed state in the thermoplastic resin, and the thermoplastic resin has the property of expanding when heated to a temperature of melting point + 20°C or higher if it is a crystalline resin, or to Tg + 100°C if it is an amorphous resin.

11. The porous structure of a fiber-reinforced resin according to any one of claims 1 to 10, wherein the thermoplastic resin is a polyolefin resin or a polystyrene resin.

12. The porous structure of fiber-reinforced resin according to claim 11, wherein the striated structure made of the thermoplastic resin is formed continuously for 300 μm or more.

13. A molded member comprising at least a portion of a porous structure of fiber-reinforced resin according to any one of claims 1 to 12.

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