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 strain-hardening properties.

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 50 to 100% by weight of reinforcing fibers with a fiber length of 2 to 10 mm, with the total amount of reinforcing fibers being 100% by weight, and the thermoplastic resin is measured at a temperature of the melting point of the thermoplastic resin + 30°C in the case of a crystalline resin, or at Tg + 80°C in the case of an amorphous resin (where Tg is the glass transition temperature; the same applies hereafter), with a strain rate of 1 / sec. The degree of strain hardening (ηEmax) / (ηElin), which is expressed by the extrinsic viscosity (ηEmax) at which the strain amount derived from Equation 1 becomes 4.0 and the approximate extrinsic viscosity (ηElin) at which the strain amount becomes 4.0, approximated by a straight line from the extrinsic viscosity gradient just before strain hardening occurs, is 1.1 or greater. 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.

Advantages of the Invention

[0010] According to the present invention, a porous structure of a fiber reinforced resin having a lightweight and excellent mechanical properties can be obtained.

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic diagram showing the dispersion state of reinforcing fibers in the 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 strain amount measured by 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.

Modes 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 10 weight% of reinforcing fibers having a fiber length of 2 to 10 mm with the total amount of the reinforcing fibers being 100 weight%. When the proportion of the reinforcing fibers having a fiber length of 2 mm or more is 50 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 and the expansion force is improved. On the other hand, when the proportion of the reinforcing fibers exceeding 10 mm in fiber length exceeds 50 weight%, although the expansion force is improved, the proportion of the bent fibers in the obtained fiber reinforced resin increases and the mechanical properties deteriorate.

[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.

[0015] <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.

[0016] With this structure, the thermoplastic resin can be easily expanded by the elastic force of the reinforcing fiber substrate by melting or softening it through heating, thereby forming a porous structure as described later. Specifically, 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 reinforcing fiber substrate, there are regions where neither reinforcing fibers nor thermoplastic resin exist, i.e., voids, resulting in a porous structure. Furthermore, as the elastic force of the reinforcing fiber substrate expands, the spaces between the reinforcing fibers open up, and the resin-only portion becomes stretched. Therefore, there are no reinforcing fibers around the stretched portion of the resin, and the effect of the resin's strain-curing properties can be fully obtained without the reinforcing fibers hindering the strain-curing of the resin.

[0017] Specific forms of reinforced fiber substrates having a three-dimensional network structure include nonwoven fabrics, 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 reinforced fiber substrate are sealed with resin or the like.

[0018] <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). Here, in an actual fiber-reinforced resin, reinforcing fiber 1 and reinforcing fibers 2-5 do not necessarily need 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] The thermoplastic resin included in the fiber-reinforced resin of the present invention is a thermoplastic resin that exhibits strain-curing properties.

[0024] Stress-curing properties refer to the property of a resin in which its viscosity increases when subjected to deformation exceeding a certain amount while in a molten state. When a strain-curing resin is used, as the resin deforms in conjunction with the deformation of a fiber-reinforced resin, the viscosity of the resin in the deformed area increases specifically, creating a difference in viscosity between the deformed and undeformed areas. This allows the deformation of the undeformed area, which has lower viscosity, to proceed more rapidly, enabling uniform deformation of the resin and allowing it to be stretched without breaking. When forming a porous structure by expanding it using the elastic force of a reinforcing fiber substrate, as described later, the viscosity of the thinly stretched portion increases specifically, allowing the resin to expand without breaking, making it easier to form a continuous striated structure in the porous structure without the resin breaking. Furthermore, because the viscosity of the resin in the stretched area increases specifically, it expands uniformly, allowing for the formation of a dense void structure. While there are no particular limitations as long as the resin has strain-curing properties, examples of strain-curing thermoplastic resins include resins with high molecular weight, resins with long-chain branched structures, resins with pseudo-crosslinked structures, and polystyrene resins. Examples of resins having a long-chain branched structure include polypropylene resins and low-density polyethylene in which a long-chain branched structure is introduced using a metallocene catalyst, and polystyrene resins, polycarbonate resins, and polyphenylene sulfide resins in which a long-chain branched structure is introduced using a branching agent. Examples of resins having a pseudo-crosslinked structure include resins that have been modified and crosslinked by peroxide or electron beam irradiation, and resins that utilize ionomers.

[0025] Examples of commercially available resins with strain-curing properties include polypropylene resins such as "MFX6, EX6000" (Nippon Polypropylene Co., Ltd.), which have a long-chain branched structure; polystyrene resins such as "HRM26" (Toyo Styrene Co., Ltd.); polycarbonate resins such as "FN1700A" (Idemitsu Petrochemical Co., Ltd.), which have a long-chain branched structure; and polyphenylene sulfide resins such as "LF3G" (DIC EP Co., Ltd.), which have a long-chain branched structure. Additionally, ionomers can be used as additives to impart strain-curing properties, and an example of a commercially available ionomer is "Hymiran 1706" (Mitsui Dow Polychemical Co., Ltd.).

[0026] Resins having long-chain branched structures and resins having pseudo-crosslinked structures are preferred from the viewpoint of moldability because they have low viscosity as strain-curable resins. Thermoplastic resins having long-chain branched structures are particularly preferred from the viewpoint of cost because they are less prone to gelation. From the viewpoint of lightweight properties, polyolefins and polystyrenes are 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 the molten state. In this specification, "strain-curable" means that the degree of strain curing determined by uniaxial extensional viscosity measurement at a temperature of the melting point of the thermoplastic resin + 30°C for crystalline resins, and Tg + 80°C for amorphous resins (where Tg is the glass transition temperature; the same applies hereinafter) is 1.1 or higher. In this specification, when multiple melting points or Tg values ​​are observed, the temperature is set based on the highest temperature melting point or Tg. 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.

[0027]

number

[0028] On the 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 reaches 4.0 is determined from Equation 1 (the above formula, the same applies hereafter). Also, the approximate extensional viscosity at which the strain amount reaches 4.0, approximated by a straight line from the extensional viscosity gradient just before strain hardening occurs, is defined as ηElin. This ηEmax / ηElin is defined as the degree of strain hardening. If the resin breaks before the strain amount reaches 4.0, the value of the break point is taken as ηE(ηEmax). Furthermore, if strain hardening does not occur, 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.

[0029] When the degree of strain hardening is 1.1 or higher, the viscosity of the thinly stretched portion increases specifically when the reinforcing fiber substrate is expanded by its elastic force to form a porous structure. This allows the resin to expand without breaking, making it easier to create a continuous, striated structure in the porous material without the resin breaking.

[0030] The strain hardening degree of the thermoplastic resin is preferably 2 or higher, more preferably 4 or higher, and even more preferably 6 or higher. A higher strain hardening degree increases the difference in viscosity between the stretched and unstretched parts of the resin, allowing the resin to be deformed uniformly and stretched without cutting. On the other hand, if the strain hardening is too high, it will hinder the expansion of the fiber-reinforced resin substrate, so a strain hardening degree of 20 or lower is preferable.

[0031] Furthermore, in the extensional viscosity curve of a thermoplastic resin, it is preferable that the extensional viscosity always increases with increasing strain. In this specification, the statement that the extensional viscosity always increases with increasing strain is characterized in that, in the interval from strain 0 to 4.0 derived from Equation 1, when the strain is divided into intervals of 0.5, the starting value ηEs and ending value ηEe of each interval are expressed as (ηEe - ηEs) / ηEs ≥ 0.05. This indicates that the extensional viscosity always increases with increasing strain, and since a viscosity difference is always generated between the stretched and unstretched parts, the resin can be deformed uniformly and stretched without cutting the resin.

[0032] Furthermore, regarding the amount of strain at which the strain-curing properties of a thermoplastic resin begin to manifest, it is preferable to start with a small amount of strain, as this tends to result in a shape in the extensional viscosity curve where the extensional viscosity always increases as the amount of strain increases. It is preferable that the amount of strain at which the strain-curing properties begin to manifest is 0.5 or more, as derived from Equation 1.

[0033] On the other hand, if strain curing starts at a small amount of strain, it hinders the expansion of the fiber-reinforced resin substrate. Therefore, from the viewpoint of the expansion of the fiber-reinforced resin substrate, it is preferable that the amount of strain at which strain curing begins to occur is large, and it is preferable that the amount of strain at which strain curing begins to occur is less than 1.5, as derived from Equation 1.

[0034] To achieve both a shape in which the extensional viscosity always increases with increasing strain and the expandability of the fiber-reinforced substrate, it is most preferable that the onset of strain hardening occurs at a strain amount of 0.5 or more and less than 1.5, as derived from Equation 1.

[0035] In the measurement of the extensional viscosity of a thermoplastic resin, a larger strain at which the thermoplastic resin breaks is preferable, and it is preferable that the strain derived from Equation 1 is 4.0 or higher.

[0036] In measuring the extensional viscosity of thermoplastic resins, if the viscosity after strain hardening is too high, it hinders the expansion of the fiber-reinforced resin substrate. Therefore, it is preferable that the viscosity after strain hardening be below a certain level. As an indicator of this, in the extensional viscosity measurement, it is preferable that the extensional viscosity at a strain of 4.0, derived from Equation 1, is 1,000,000 Pa·s or less.

[0037] A high melt viscosity in the low-frequency range is preferable because it suppresses resin aggregation, thus maintaining the resin's continuous striated structure. As an indicator, the complex viscosity E(0.001) at a frequency of 0.001 Hz, measured at the melting point + 30°C for crystalline resins and at Tg + 80°C for amorphous resins, can be used. In this invention, the complex viscosity E(0.001) is preferably 3500 [Pa·s] or higher, and more preferably 6000 [Pa·s] or higher. The complex viscosity η is measured in accordance with ISO 6721-10 (1999). By setting the complex viscosity E(0.001) within the above range, the resin becomes less likely to migrate, preventing aggregation. 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 specific temperature is 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 40 g / 10 min or higher, 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 1.0 g / 10 min or lower, it is possible to suppress the outflow of the thermoplastic resin from the sides of the reinforcing fiber substrate when impregnating the reinforcing fiber substrate with the thermoplastic resin, making it easier to obtain a fiber-reinforced resin of the desired shape.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 their 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.

[0038] 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.

[0039] 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.

[0040] 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 has not penetrated 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.

[0041] 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.

[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. The bulk specific gravity is measured in accordance with ISO 845 (1988) on a sample of the fiber-reinforced resin.

[0044] 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.

[0045] 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.

[0046]

number

[0047] 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.

[0048] 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.

[0049] <Porous structure> As described above, the fiber-reinforced resin of the present invention may have a porous structure. This embodiment of the fiber-reinforced resin will be referred to as a "porous structure" in this specification. In the porous structure of the present invention, 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.

[0050] 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.

[0051] It is preferable that the striated structure of the thermoplastic resin is continuously formed for a length of 300 μm or more within the fiber-reinforced resin. Continuous formation of the striated structure means that the resin is primarily present in a continuous range of 300 μm or more in both the in-plane direction and the thickness direction. Furthermore, the continuity of the resin can be confirmed by observing a cross-section using X-ray CT observation.

[0052] The area ratio A of voids, as evaluated by cross-sectional photographs, is preferably 35% or less, and more preferably 25% or less. Furthermore, the ratio A / B, which is the ratio of the area ratio A of 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, a small proportion of voids and the spread-out presence of the thermoplastic resin allow for efficient reinforcement of the three-dimensional network structure composed of reinforcing fibers. Also, when the expansion ratio is low, the amount of elongation of the thermoplastic resin is small, and the thermoplastic resin is less likely to break, resulting in a smaller void area. On the other hand, a larger expansion ratio is preferable from the viewpoint of weight reduction, and the reinforcing effect of the porous structure by the thermoplastic resin is greater, so it is preferable that the void area is small relative to the expansion ratio.

[0053] Since excessively large voids can cause stress concentration, smaller voids are preferable. Therefore, the average area of ​​voids in the cross-section of a porous structure should be 6000 μm². 2 Preferably, the following, 5000 μm 2 It is more preferable that the following is true: 4000 μm 2 It is even more preferable that the following conditions are met. Furthermore, it is preferable that there is little variation in the size of the voids, specifically that the coefficient of variation of the void area is preferably 100% or less, more preferably 90% or less, and even more preferably 80% or less. Here, in this specification, the average void area and the coefficient of variation are values ​​calculated from 300 voids arbitrarily selected in the porous structure.

[0054] 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.

[0055] 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, or in other words, two-dimensional, state, 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.

[0056] 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).

[0057] 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.

[0058] 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).

[0059] 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).

[0060] 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).

[0061] 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.

[0062] <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.

[0063] 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.

[0064] <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.

[0065] 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.

[0066] 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. Similarly, it is 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. Therefore, similarly, it is preferable that the temperature is below the melting point or Tg + 150°C of the thermoplastic resin.

[0067] 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.

[0068] A typical method for manufacturing the porous structure of the present invention involves heating and expanding the fiber-reinforced resin described above, 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 a 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 heating and impregnating the reinforcing fiber substrate with a thermoplastic resin and expanding it without cooling it in a compressed state, thus offering excellent productivity. The temperature at which the fiber-reinforced resin is heated and expanded is preferably the melting point of the thermoplastic resin if the thermoplastic resin is a crystalline resin, or at or above the Tg of the thermoplastic resin if the thermoplastic resin is an amorphous resin. Furthermore, if the temperature at which the fiber-reinforced resin is heated to expand is too high compared to the melting point of the thermoplastic resin, decomposition or deterioration of the thermoplastic resin may occur. Therefore, it is preferable that the temperature is 150°C or less above the melting point of the thermoplastic resin, and more preferably 100°C or less. [Examples]

[0069] The present invention will be described in more detail below with reference to examples.

[0070] <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. Polypropylene resin 2: Linear random polypropylene resin "Prime PolyPro" (registered trademark) J3021GR, manufactured by Prime Polymer Co., Ltd. Polystyrene resin 1: Manufactured by Toyo Styrene Co., Ltd., polystyrene resin "Toyo Styrofoam GP" HRM26 Nylon resin 1: Toray Industries, Inc., Nylon 6 resin "Amiran" (registered trademark) CM1001 Nylon resin 2: Toray Industries, Inc., Nylon 6 resin "Amiran" (registered trademark) CM1041-LO Ionomer 1: "Hymiran" (registered trademark) 1706, a metal crosslinked carboxyl group-containing polyethylene resin manufactured by Mitsui Dow Polychemical Co., Ltd.

[0071] <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. When multiple melting points or Tg values ​​were observed, the highest temperature melting point or Tg was used as the reference for setting the measurement temperature. A Merten rheometer manufactured by Toyo Seiki was used as the measuring device.

[0072] (2) Complex viscosity of thermoplastic resins The complex viscosity of the thermoplastic resins used was measured according to ISO 6721-10 (1999). The number of measurements was n=5. For crystalline resins, measurements were taken at the melting point + 30°C, and for amorphous resins, at Tg + 80°C. When multiple melting points or Tg values ​​were observed, the highest temperature was used as the reference for setting the measurement temperature. A TA Instruments ARESG2 dynamic viscoelasticity analyzer was used, and a parallel plate was used as the measurement jig.

[0073] (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.

[0074] (4) Melting point measurement of thermoplastic resins The melting point and Tg of the thermoplastic resin used were 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 instrument.

[0075] (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.

[0076] (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.

[0077] (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.

[0078] <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 adhesion amount: 1.5% by weight based on 100% by weight of the carbon fiber bundle.

[0079] The carbon fiber bundle produced as described above was cut into 3 mm fiber lengths using a cartridge cutter to obtain a chopped carbon fiber bundle. An aqueous dispersion containing 0.1% by weight of a surfactant (Polyoxyethylene lauryl ether (trade name), manufactured by Nacalai Tesque, Inc.) was prepared, and this dispersion and the chopped carbon fiber bundle were fed into a paper making machine to produce a carbon fiber base material.

[0080] The paper making machine includes a dispersion tank, a papermaking tank, and a transport section connecting the dispersion tank and the papermaking tank. The dispersion tank is equipped with a stirrer and can disperse the fed dispersion and the chopped carbon fiber bundle. The papermaking tank has a mesh conveyor with a papermaking surface at the bottom, and a conveyor capable of transporting the papermade carbon fiber base material is connected to the mesh conveyor. Papermaking was carried out with a fiber concentration of 0.05% by weight in the dispersion. The papermade carbon fiber base material was dried in a drying oven at 200°C. Subsequently, an aqueous dispersion containing 3% by weight of a binder (Polyment (registered trademark) SK-1000, manufactured by Nippon Shokubai Co., Ltd.) was sprayed onto the upper surface of the carbon base material transported by the conveyor as a binder. The excess binder was suctioned and dried in a drying oven at 200°C to obtain a carbon fiber base material. The basis weight of the obtained carbon fiber base material was 110 g / m 2 It was.

[0081] [Polypropylene resin film 1] Polypropylene resin 1 (Waymax (registered trademark) MFX6, manufactured by Japan Polypropylene Corporation), which is a polypropylene resin having a long-chain branched structure, was sandwiched between release films, and after being pressed at 220°C for 10 minutes using a press molding machine with spacers inserted, it was taken out together with the release films, and the resin was cooled and solidified to obtain a polypropylene resin film 1 with a basis weight of 165 g / m 2 When the melting point of the polypropylene resin film 1 was measured, it was 156°C.

[0082] [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 polypropylene resin film 2 was measured and found to be 153°C.

[0083] [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 the polypropylene resin film 3 was measured and found to be 152°C.

[0084] [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. 2This was obtained. Furthermore, the melting point of the polypropylene resin film 4 was measured and found to be 151°C.

[0085] [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 the polypropylene resin film 5 was measured and found to be 150°C.

[0086] [Polystyrene resin film 1] Polystyrene resin 1 (manufactured by Toyo Styrene Co., Ltd., "Toyo Styrofoam GP" HRM26) is sandwiched between release films, and pressurized at 240°C for 10 minutes in a press molding machine with spacers inserted. After removing the release films together, the resin is cooled and solidified to produce polypropylene resin film 1 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 105°C.

[0087] [Nylon resin film 1] A nylon resin, Nylon Resin 1 (manufactured by Toray Industries, Inc., "Amiran" (registered trademark) CM1001), at a weight of 60% and Ionomer 1 (manufactured by Mitsui Dow Polychemical Co., Ltd., "Hymiran" (registered trademark) 1706), a metal crosslinked carboxyl group-containing polyethylene resin, were blended and compounded in an extruder. The compounded resin was sandwiched between release films and pressurized at 240°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 Nylon Resin Film 1 with a basis weight of 193 g / m². 2 This was obtained. Furthermore, when the melting point of nylon resin film 1 was measured, two melting points were observed: 88°C and 222°C. [Nylon resin film 2] A nylon resin, Nylon Resin 2 (manufactured by Toray Industries, Inc., "Amiran" (registered trademark) CM1041-LO), at a weight of 60% and Ionomer 1 (manufactured by Mitsui Dow Polychemical Co., Ltd., "Hymiran" (registered trademark) 1706), a metal crosslinked carboxyl group-containing polyethylene resin, were blended and compounded in an extruder. The compounded resin was sandwiched between release films and pressurized at 240°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 Nylon Resin Film 1 with a basis weight of 193 g / m². 2 This was obtained. Furthermore, when the melting point of nylon resin film 1 was measured, two melting points were observed: 89°C and 220°C. [Nylon resin film 3] A nylon resin, Nylon Resin 1 (manufactured by Toray Industries, Inc., "Amiran" (registered trademark) CM1001), is sandwiched between release films and pressed at 240°C for 10 minutes in a press molding machine with a spacer inserted. After removing the release film and allowing the resin to cool and solidify, a nylon resin film 2 is produced with a basis weight of 207 g / m². 2 This was obtained. Furthermore, the melting point of nylon resin film 2 was measured and found to be 221°C.

[0088] (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.

[0089] 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.

[0090] The resulting porous structure exhibited excellent mechanical properties and lightweight characteristics because the polypropylene resin exhibited strain-curing properties, expanding without breaking, forming a striated structure of polypropylene resin between the fibers, and densifying the void structure.

[0091] (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.

[0092] The resulting porous structure exhibited excellent mechanical properties and lightweight characteristics because the polypropylene resin exhibited strain-curing properties, expanding without breaking, forming a striated structure between the fibers and densifying the void structure. Furthermore, the polypropylene resin also exhibited excellent fluidity, resulting in good impregnation of the carbon fiber substrate.

[0093] (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.

[0094] The resulting porous structure exhibited excellent mechanical properties and lightweight characteristics because the polypropylene resin exhibited strain-curing properties, expanding without breaking, forming a striated structure between the fibers and densifying the void structure. Furthermore, the polypropylene resin also exhibited excellent fluidity, resulting in good impregnation of the carbon fiber substrate.

[0095] (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.

[0096] The resulting porous structure exhibited excellent mechanical properties and lightweight characteristics because the polypropylene resin exhibited strain-curing properties, expanding without breaking, forming a striated structure between the fibers and densifying the void structure. Furthermore, the polypropylene resin also exhibited excellent fluidity, resulting in good impregnation of the carbon fiber substrate.

[0097] (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 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.

[0098] 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.

[0099] The resulting porous structure exhibited excellent mechanical properties and lightweight characteristics because the polystyrene resin exhibited strain-curing properties, expanding without breaking, forming a striated structure of polystyrene resin between the fibers and densifying the void structure.

[0100] (Example 6) A porous structure was fabricated using a carbon fiber substrate and nylon resin film 1. After adjusting the carbon fiber substrate and nylon resin film to a size of 300 mm x 300 mm, they were laminated in the following order: [nylon resin film 1 / carbon fiber substrate / nylon resin film 1 / carbon fiber substrate / nylon resin film 1 / carbon fiber substrate / nylon 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 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.

[0101] Next, the fabricated fiber-reinforced resin was sandwiched between release films and pressurized in a press molding machine at 240°C and 3 MPa for 10 minutes to melt the nylon 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 base material, forming a porous structure.

[0102] Although the resulting porous structure did not form a striated resin structure between the fibers because the nylon resin broke during expansion, it exhibited strain-hardening properties, resulting in a densified void structure and excellent mechanical properties and lightweight characteristics.

[0103] (Example 7) A porous structure was fabricated in the same manner as in Example 6, except that nylon resin film 1 was replaced with nylon resin film 2. Although the resulting porous structure did not form a striated resin structure between the fibers, it exhibited strain-hardening properties, resulting in a densified void structure and excellent mechanical properties and lightweight characteristics.

[0104] (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.

[0105] 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.

[0106] (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.

[0107] (Comparative Example 3) A porous structure was fabricated in the same manner as in Example 6, except that nylon resin film 1 was replaced with nylon resin film 3.

[0108] The resulting porous structure had poor mechanical properties, although it was lightweight, because the nylon resin broke during expansion, preventing the formation of striated resin structures between the fibers.

[0109] [Table 1] [Explanation of Symbols]

[0110] 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.Void 10. Striped structure of thermoplastic resins

Claims

1. A porous structure of fiber-reinforced resin, wherein the fiber-reinforced resin comprises a reinforcing fiber substrate and a thermoplastic resin, the reinforcing fiber substrate contains 50 to 100% by weight of reinforcing fibers with a fiber length of 2 to 10 mm, where 100% by weight is the total amount of reinforcing fibers, and the thermoplastic resin is a crystalline resin, and in a uniaxial extensional viscosity measurement measured at a strain rate of 1 / sec at a temperature of the melting point of the thermoplastic resin + 30°C, or Tg + 80°C in the case of an amorphous resin (where Tg is the glass transition temperature; the same applies hereinafter), Equation 1 [Mathematics 1] A porous fiber-reinforced resin structure in which the degree of strain hardening (ηEmax) / (ηElin), which is expressed by the extensional viscosity (ηEmax) at which the amount of strain derived from becomes 4.0 and the approximate extensional viscosity (ηElin) at which the amount of strain becomes 4.0, approximated by a straight line from the extensional viscosity gradient immediately before strain hardening occurs, is 1.1 or greater, the reinforced fiber substrate has a three-dimensional network structure formed by the reinforced fibers, and the thermoplastic resin forms striated structures that bind the reinforced fibers together in the network of the three-dimensional network structure of the reinforced fiber substrate, and voids are formed as regions surrounded by the reinforced fibers and / or the thermoplastic resin, where neither the reinforced fibers nor the thermoplastic resin exist.

2. A porous fiber-reinforced resin structure according to claim 1, comprising 3 to 60 volume percent of reinforcing fibers relative to the total of reinforcing fibers and thermoplastic resin, 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.

3. The porous structure of fiber-reinforced resin according to claim 1 or 2, wherein the strain hardening degree (ηEmax) / (ηElin) is 2 or more and 20 or less.

4. The porous structure of a fiber-reinforced resin according to any one of claims 1 to 3, wherein the thermoplastic resin is a crystalline resin, and in a uniaxial extensional viscosity measurement performed at a temperature of the melting point of the thermoplastic resin + 30°C in the case of an amorphous resin, and at a strain rate of 1 / sec, the starting value ηEs and the ending value ηEe of each interval, when the strain amount is divided into intervals of 0.5 in the range from 0 to 4.0 derived from Equation 1, are expressed as (ηEe - ηEs) / ηEs ≥ 0.

05.

5. The porous structure of a fiber-reinforced resin according to any one of claims 1 to 4, wherein the thermoplastic resin has strain-curing properties in a uniaxial extensional viscosity measurement, which is measured at a temperature of the melting point of the thermoplastic resin + 30°C in the case of a crystalline resin, or at Tg + 80°C in the case of an amorphous resin, with a strain rate of 1 / sec, and the onset of strain-curing is 0.5 or more in terms of the amount of strain derived from Equation 1.

6. A porous structure of fiber-reinforced resin according to any one of claims 1 to 4, wherein the onset of strain hardening is less than 1.5 in terms of the amount of strain derived from Equation 1.

7. The porous structure of fiber-reinforced resin according to claim 6, wherein the onset of strain hardening is at a strain amount of 0.5 or more and less than 1.5 derived from Equation 1.

8. The porous structure of a fiber-reinforced resin according to any one of claims 1 to 7, wherein the thermoplastic resin has strain-curing properties in uniaxial extensional viscosity measurement, which is measured at a temperature of the melting point of the thermoplastic resin + 30°C in the case of a crystalline resin, and at a strain rate of 1 / sec at a temperature of Tg + 80°C in the case of an amorphous resin, and the amount of strain derived from equation 1 at which the fracture point in the extensional viscosity measurement of the resin is 4.0 or more.

9. The porous structure of a fiber-reinforced resin according to any one of claims 1 to 8, wherein the thermoplastic resin has strain-curing properties in a uniaxial extensional viscosity measurement, which is measured at a temperature of the melting point of the thermoplastic resin + 30°C in the case of a crystalline resin, and at a strain rate of 1 / sec at a temperature of Tg + 80°C, and the extensional viscosity at a strain amount of 4.0 derived from Equation 1 is 1,000,000 Pa·s or less in the extensional viscosity measurement of the resin.

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. A porous structure of fiber-reinforced resin according to any one of claims 1 to 10, which is in the form of a sheet.

12. The porous structure of fiber-reinforced resin according to claim 1, 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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