Method for manufacturing fiber-reinforced plastic molded body, and fiber-reinforced plastic molded body

Abstract

A novel method for producing a fiber-reinforced plastic molded article, and a novel fiber-reinforced plastic molded article are provided. [Solution] A method for producing a fiber-reinforced plastic molded article includes press-molding a nonwoven fabric containing a fiber reinforcement and a thermoplastic resin to obtain a molded article with a porosity of 1.0 to 29.0%. This manufacturing method produces a fiber-reinforced plastic molded article containing a thermoplastic resin and a plurality of fiber reinforcements oriented in a predetermined direction, and in which the molded article is divided into eight equal test pieces in the width direction perpendicular to the predetermined direction, and the coefficient of variation (CV) of the bending fracture load measured for each of the test pieces is 6.0% or less.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a fiber-reinforced plastic molded article, and to a fiber-reinforced plastic molded article. [Background technology]

[0002] In recent years, efforts have been made to replace metal with plastic and reduce the weight of parts used in automobiles, aircraft, etc., with the aim of reducing carbon dioxide emissions, extending driving range through electrification, etc. Such metal-substitute plastics are usually used as fiber-reinforced plastic molded bodies made by compounding reinforcing materials such as carbon fiber (CF) and glass fiber (GF) with resin.

[0003] Automobiles, in particular, use many plastic components for both the interior and exterior of their vehicles. Due to productivity and cost considerations, components molded by injection molding of thermoplastic resins are often used. However, injection-molded components currently lack sufficient strength and rigidity to be used as metal replacements. Furthermore, as a metal-substitute plastic for automotive components, sheet molding compounds (SMCs) made from thermosetting resins are used for automobile exterior panels. Molded products made by impregnating carbon fiber (CF) or glass fiber (GF) with epoxy resins and curing them in an autoclave or without an autoclave are used in Formula 1 cars, luxury car bodies, and some sports cars. Furthermore, in recent years, hydrogen tanks for hydrogen-powered vehicles have been converted to plastic, contributing to weight reduction. However, thermosetting resins cannot be reused once they harden during molding, posing a problem of poor sustainability.

[0004] Therefore, in recent years, a technology has been used to injection mold pellets (long fiber reinforced pellets; LFTP or LFT) in which long fibers made from GF or CF are dispersed in a thermoplastic resin, resulting in a replacement for metal in automobile back doors, etc. However, even when LFTP is used, the material is subjected to shear by the screw during injection molding, and the current situation is that the performance of reinforcing materials such as GF and CF cannot be fully demonstrated.

[0005] Conventionally, a technique for producing fiber-reinforced plastic molded articles without using an injection molding machine has been proposed, in which the molded articles are produced by press-molding a wet-laid nonwoven fabric or a dry-laid nonwoven fabric (stampable sheet) made by blending a reinforcing material with a thermoplastic resin (see, for example, Patent Document 1). This technique does not involve a step in which the reinforcing material is subjected to shear, as occurs in injection molding, and the fiber length is maintained almost unchanged. As a result, compared to production using injection molding, a material with higher strength and rigidity can be obtained, which has the advantage of enabling the molded article to be thinner and thus further lighter in weight. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-074197 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a novel method for producing a fiber-reinforced plastic molded article, and a novel fiber-reinforced plastic molded article. [Means for solving the problem]

[0008] A method for producing a fiber-reinforced plastic molded body according to one embodiment of the present invention is characterized in that it includes press-molding a nonwoven fabric containing a fiber reinforcement material and a thermoplastic resin to obtain a molded body having a porosity of 1.0 to 29.0%.

[0009] In addition, a fiber-reinforced plastic molded body according to another embodiment of the present invention contains a thermoplastic resin and a plurality of fiber reinforcements oriented in a predetermined direction, and is characterized in that the coefficient of variation (CV) of the bending fracture load measured for each of the test pieces obtained by dividing the molded body into eight equal parts in the width direction perpendicular to the predetermined direction is 6.0% or less. [Brief explanation of the drawings]

[0010] [Figure 1] Fig. 1 is a schematic diagram illustrating the configuration of an apparatus used in the press-molding step and the state after press-molding. Fig. 1(a) is a schematic diagram illustrating the configuration of an apparatus used in the press-molding step. Fig. 1(b) is a schematic diagram illustrating the state after a molded body 20 has been produced by press-molding a nonwoven fabric 10 in a conventional manufacturing method. Fig. 1(c) is a schematic diagram illustrating the state after a molded body 20 has been produced by press-molding a nonwoven fabric 10 in a manufacturing method according to one embodiment of the present invention. [Figure 2] Fig. 2 is a graph showing stress-strain curves (SS curves) corresponding to eight test specimens when measuring the bending fracture load of the fiber-reinforced plastic molded articles produced in the comparative examples and examples described later in the Examples section. (a) to (d) in Fig. 2 show the results of Comparative Example 1 and Examples 1 to 3, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the above-mentioned embodiments of the present invention will be described with reference to the drawings as necessary. However, the technical scope of the present invention should be defined based on the claims and is not limited to the following embodiments. Note that the dimensional ratios in the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios. In this specification, the range "X to Y" means "X or more and Y or less." Furthermore, unless otherwise specified, operations and measurements of physical properties, etc. are performed at room temperature (20 to 25°C) and a relative humidity of 40 to 50% RH.

[0012] <<Method for manufacturing fiber-reinforced plastic molded body>> In one aspect, the present invention provides a method for producing a fiber-reinforced plastic molded article, which comprises press-molding a nonwoven fabric containing a fiber reinforcement material and a thermoplastic resin to obtain a molded article having a porosity of 1.0 to 29.0%. In this specification, the "fiber-reinforced plastic molded article" may also be simply referred to as "molded article."

[0013] Conventionally, from the viewpoint of obtaining a molded body with higher strength and rigidity, it has been considered preferable to apply a high pressing pressure to the nonwoven fabric when press-molding a nonwoven fabric to obtain a molded body, thereby ensuring that the resulting molded body contains substantially no voids. Contrary to the conventional wisdom in this technical field, the present inventors attempted to control the conditions used to press-molde a nonwoven fabric to obtain a molded body, thereby incorporating a predetermined amount of voids into the resulting molded body. Surprisingly, they found that the rigidity of the molded body improves depending on the void content, ultimately contributing to further weight reduction. The mechanism behind this surprising effect is not fully understood, and it is believed that a combination of various factors is involved. However, one possible reason is that milder pressing conditions during press-molding suppress the cutting and fragmentation of the fiber reinforcement present in the nonwoven fabric, particularly near the surface, which contributes to the improved rigidity. Note that this mechanism is merely speculative, and its correctness does not affect the technical scope of the present invention.

[0014] [Press molding] FIG. 1 is a schematic diagram illustrating the configuration of an apparatus used in the press-molding process and the state after press-molding. FIG. 1(a) is a schematic diagram illustrating the configuration of an apparatus used in the press-molding process. As shown in FIG. 1(a), in the press-molding process, the upper die of a pair of press dies (upper die 110 and lower die 120) is tightened downward to pressure-mold the nonwoven fabric 10. Note that in the press-molding process, both of the pair of press dies 110, 120 may be tightened in the direction of the arrows, or one of the pair of press dies 110, 120 (e.g., lower die 120) may be fixed and the other press die (e.g., upper die 110) may be tightened to apply press pressure.

[0015] The press mold used in the press molding step may be made of, for example, steel, stainless steel, or aluminum. In the press molding step, the press mold is positioned so as to be parallel to each surface of the nonwoven fabric.

[0016] Here, in a fiber-reinforced plastic molded product obtained by press-molding a nonwoven fabric containing a fiber reinforcement material and a thermoplastic resin, generally, to obtain a molded product of a target thickness (referred to as "design thickness"), the amount of nonwoven fabric (fiber-reinforced molded product sheet) required for that thickness is set in a mold and press-molded to obtain the molded product. For example, if the molded product is 30 cm square and 2 mm thick and has a specific gravity of 1.20, 30 x 30 x 0.2 x 1.2 = 216 g of nonwoven fabric (fiber-reinforced molded product sheet) is set in a mold and press-molded to obtain a 2 mm molded product. Alternatively, if the volume of the molded product to be obtained is predetermined, for example, 500 cm 3 Assuming that a material with a specific gravity of 1.20 is used for the molded body, a 2 mm molded body can be obtained by placing 500 x 1.2 = 600 g of nonwoven fabric (fiber-reinforced molded body sheet) in a mold and press-molding it.

[0017] 1(b) is a schematic diagram illustrating a state in which a nonwoven fabric 10 is press-molded to produce a molded body 20 in a conventional manufacturing method. In the conventional manufacturing method, when the nonwoven fabric 10 is press-molded to obtain the molded body 20, the pressing conditions are set so that the thickness t of the obtained molded body 20 is approximately the same as the design thickness T of the molded body 20. As a result, the obtained molded body 20 does not substantially contain voids.

[0018] In contrast, the method for producing a fiber-reinforced plastic molded article according to this embodiment is characterized in that a molded article having a porosity of 1.0 to 29.0% is obtained by press-molding a nonwoven fabric. Fig. 1(c) is a schematic diagram illustrating a state in which a molded article 20 is produced by press-molding a nonwoven fabric 10 in a production method according to one embodiment of the present invention. In this embodiment, when press-molding the nonwoven fabric 10 to obtain the molded article 20, the pressing conditions are set so that the thickness t of the obtained molded article 20 is somewhat larger than the design thickness T of the molded article 20. As a result, the obtained molded article 20 contains a predetermined amount of voids 22.

[0019] As described above, it has been found that the inclusion of a predetermined amount of voids in the produced molded body improves the rigidity of the molded body depending on the void content, ultimately contributing to further weight reduction. From the viewpoint of further demonstrating this effect, the porosity value of the obtained molded body is preferably 2.5 to 25.0%, more preferably 3.0 to 23.0%, and even more preferably 3.3 to 22.5%. This porosity value may be, for example, 4.0% or more, 5.0% or more, 6.0% or more, 7.0% or more, 8.0% or more, 9.0% or more, 10.0% or more, 11.0% or more, or 12.0% or more. Furthermore, this porosity value may be, for example, 22.0% or less, 21.0% or less, 20.0% or less, 19.0% or less, 18.0% or less, 17.0% or less, 16.0% or less, 15.0% or less, or 14.0% or less.

[0020] The pressure during the press molding process and the temperature of the nonwoven fabric used in the press molding process are not particularly limited as long as they are controlled so that the resulting molded body contains the predetermined amount of voids described above. These conditions can be set appropriately taking into account the viscosity of the resin when melted. As an example, the pressure during the press molding process is preferably 1 MPa or more, more preferably 2 MPa or more, even more preferably 3 MPa or more, and particularly preferably 5 MPa or more. Furthermore, the pressure during the press molding process is preferably 50 MPa or less, more preferably 40 MPa or less, even more preferably 30 MPa or less, and particularly preferably 28 MPa or less.

[0021] The temperature of the nonwoven fabric is preferably equal to or higher than the softening temperature of the thermoplastic resin contained in the nonwoven fabric, and more preferably equal to or higher than the softening temperature of the thermoplastic resin + 20°C. For example, when polypropylene is used as the thermoplastic resin, the temperature of the nonwoven fabric subjected to the press molding process is preferably equal to or higher than 150°C, more preferably equal to or higher than 165°C, even more preferably equal to or higher than 180°C, and particularly preferably equal to or higher than 190°C. The temperature of the nonwoven fabric subjected to the press molding process is preferably equal to or lower than 230°C, more preferably equal to or lower than 220°C, and particularly preferably equal to or lower than 210°C. The softening temperature of the thermoplastic resin can be measured using a microscope, DSC, or the like. Typically, the softening temperature of a crystalline resin is the melting point, and the softening temperature of an amorphous resin is the glass transition temperature.

[0022] The press molding process may be a so-called heat-and-cool process. In the heat-and-cool process, first, a nonwoven fabric is placed in a mold at a temperature of about 40 to 100°C, and then heated to the above-mentioned temperature. Next, the nonwoven fabric is pressed to a predetermined thickness to obtain a molded body, and then the mold is cooled. The molding cycle time in the heat-and-cool process is preferably within 20 minutes, more preferably within 19 minutes. A cold press process may also be performed to shorten the molding time in the heat-and-cool process. The cold press process includes a preheating step and a press molding step. In the preheating step, the nonwoven fabric is heated to above the melting point of the thermoplastic resin using near-infrared rays or a heatable press machine to melt the resin, and then the resin is quenched in the press step (mold temperature of about 40 to 130°C) and press molded. This method has the advantage that the preheating (melting step) and the press molding (cooling) can be separated, and the time required for one cycle can be reduced to 5 minutes or less.

[0023] After the press molding in the press molding step, it is preferable to further provide a step of cooling the fiber-reinforced plastic molded body molded from the nonwoven fabric. In this case, it is preferable that the fiber-reinforced plastic molded body is cooled to at least the softening temperature of the thermoplastic resin −50° C. or less, and then removed from the press mold.

[0024] <Nonwoven fabric> The nonwoven fabric used in the press molding process contains a fiber reinforcement material and a thermoplastic resin and is also referred to in this technical field as a "stampable sheet." Among these, a nonwoven fabric containing carbon fiber and thermoplastic resin fiber is preferred, and a wet-laid nonwoven fabric containing carbon fiber and thermoplastic resin fiber is more preferred. However, the effects of the present invention can be similarly achieved even when a dry-laid nonwoven fabric is used. Here, the wet-laid papermaking method involves dispersing chopped strands of thermoplastic resin fiber and fiber reinforcement material in a solvent, followed by removing the solvent to form a web. Meanwhile, the dry-laid papermaking method involves mixing fiber reinforcement material and thermoplastic fiber in a gas atmosphere and then capturing the mixture on a net to obtain a mat; this method is also referred to as airlaid. The resulting dry-laid nonwoven fabric is often needle-punched to produce a nonwoven fabric for press molding.

[0025] (thermoplastic resin) Examples of thermoplastic resins include polyester, polyethylene, polypropylene, polycarbonate (PC), polyamide (PA6, PA66, PA9T), ABS, polyether ether ketone (PEEK), polyamide imide (PAI), polyphenylene sulfide (PPS), polyether imide (PEI), polyether ketone ketone (PEKK), and polystyrene (PS).

[0026] In this specification, thermoplastic resins are also referred to as "matrix resins" because they form bonds at the intersections of the matrix or fiber components during press molding. Nonwoven fabrics using such thermoplastic resins do not require autoclave treatment and require shorter heating and pressure molding times during processing, compared to sheets using thermosetting resins, which can contribute to improved productivity.

[0027] The thermoplastic resin contained in the nonwoven fabric is preferably in a fibrous form. A fibrous thermoplastic resin maintains its fibrous form before press molding. Therefore, the sheet itself is flexible and drapes well before forming a fiber-reinforced plastic molded body. Therefore, the nonwoven fabric can be stored and transported in a rolled form, which has the advantage of being easy to handle.

[0028] When the thermoplastic resin is in the form of fibers, the number-average fiber length of the thermoplastic resin fibers is preferably 3 mm or more, more preferably 4 mm or more, and even more preferably 5 mm or more. The number-average fiber length of the thermoplastic resin fibers is preferably 30 mm or less, more preferably 20 mm or less, and even more preferably 15 mm or less. By setting the number-average fiber length of the thermoplastic resin fibers within the above range, it is possible to prevent the thermoplastic resin fibers from falling off during the production of nonwoven fabric. Furthermore, by setting the number-average fiber length of the thermoplastic resin fibers within the above range, it is possible to produce a fiber-reinforced plastic molded product with excellent strength.

[0029] When the thermoplastic resin is in the form of fibers, the average fiber diameter of the thermoplastic resin fibers is preferably 3 μm or more and 50 μm or less. By setting the average fiber diameter of the thermoplastic resin fibers within the above range, the strength of the fiber-reinforced plastic molded product can be increased.

[0030] The content of the thermoplastic resin in the nonwoven fabric is preferably 46% by volume or more, more preferably 52% by volume or more, and even more preferably 57% by volume or more, based on the total volume of the nonwoven fabric. Furthermore, the content of the thermoplastic resin in the nonwoven fabric is preferably 95% by volume or less, more preferably 85% by volume or less, and even more preferably 76% by volume or less, based on the total mass of the nonwoven fabric. Here, the content (volume %) refers to the volume fraction (percentage) of the thermoplastic resin in the total volume of the nonwoven fabric, calculated from the true specific gravity of the nonwoven fabric. For example, if the specific gravity of polypropylene (PP) is 0.9 and the specific gravity of carbon fiber (CF) is 1.80, and the mass ratio of these in the nonwoven fabric is 50:50, the volume of PP is calculated as 50 / 0.9 = 55.6. Similarly, the volume of CF is calculated as 50 / 1.8 = 27.8. Therefore, the PP content in this total is calculated to be 55.6 × 100 / (55.6 + 27.8) = 66.7 volume %, and similarly the CF content is calculated to be 33.3 volume % (the preferred range (volume %) of the carbon fiber content in the nonwoven fabric will be described later).

[0031] (fiber reinforcement) The specific form of the fiber reinforcement is not particularly limited, and conventionally known knowledge in the technical field of fiber-reinforced plastic molded articles can be referred to as appropriate. Among these, the fiber reinforcement preferably contains one or more inorganic fibers selected from the group consisting of carbon fiber (CF) and glass fiber (GF), and more preferably contains carbon fiber (CF). These fiber reinforcements may be used alone or in combination of two or more. Of course, fiber reinforcements other than those mentioned above may also be used, and for example, organic fibers with excellent heat resistance, such as aramid fiber and PBO (polyparaphenylenebenzoxazole) fiber, may also be used. Among these, the fiber reinforcement preferably contains carbon fiber, and more preferably consists of carbon fiber alone.

[0032] Examples of carbon fibers that can be used include polyacrylonitrile (PAN)-based, petroleum / coal pitch-based, rayon-based, and lignin-based carbon fibers. These carbon fibers may be used alone or in combination of two or more types. Among these carbon fibers, polyacrylonitrile (PAN)-based carbon fibers are preferred from the viewpoints of industrial-scale productivity and mechanical properties. Furthermore, from the viewpoint of particularly long fiber length, recycled carbon fibers (rCF) obtained by recycling carbon fibers used in fiber-reinforced plastic molded articles used in aircraft components and the like are also preferred.

[0033] The number average fiber length of the carbon fibers is preferably 3 mm or more, more preferably 4 mm or more, and even more preferably 5 mm or more. Furthermore, the number average fiber length of the carbon fibers is preferably 50 mm or less, more preferably 40 mm or less, and even more preferably 30 mm or less. That is, the number average fiber length of the carbon fibers is preferably 3 to 50 mm, and more preferably 5 to 30 mm. By setting the number average fiber length of the carbon fibers within the above range, it is possible to prevent the carbon fibers from falling off during the production of a nonwoven fabric. Furthermore, by setting the number average fiber length of the carbon fibers within the above range, it is possible to mold a fiber-reinforced plastic molded article having excellent strength.

[0034] The average fiber diameter of the carbon fibers is preferably 3 μm or more and 20 μm or less. By setting the average fiber diameter of the carbon fibers within the above range, the strength of the fiber-reinforced plastic molded article can be increased.

[0035] The single fiber strength of the carbon fiber is preferably 4150 MPa or more, and more preferably 4700 MPa or more. The single fiber strength refers to the tensile strength of the monofilament. The single fiber strength can be measured in accordance with JIS R7601:2000 "Testing method for tensile properties of carbon fiber single fiber."

[0036] The content of the fiber reinforcement in the nonwoven fabric is preferably 5% by volume or more, more preferably 15% by volume or more, and even more preferably 24% by volume or more, based on the total mass of the nonwoven fabric. Furthermore, the content of the fiber reinforcement in the nonwoven fabric is preferably 54% by volume or less, more preferably 48% by volume or less, and even more preferably 43% by volume or less, based on the total mass of the nonwoven fabric. That is, the content of the fiber reinforcement in the nonwoven fabric is preferably 5 to 54% by volume, based on the total mass of the nonwoven fabric. By setting the content of the fiber reinforcement within the above range, a fiber reinforced plastic molded article with excellent moldability is more easily obtained. Furthermore, by setting the content of the fiber reinforcement within the above range, a fiber reinforced plastic molded article with excellent strength can be molded.

[0037] The total content of the thermoplastic resin and the fiber reinforcement in the nonwoven fabric is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 98% by mass or more, based on the total mass of the nonwoven fabric.

[0038] The nonwoven fabric subjected to the press molding step may be a pre-press sheet (prepreg sheet). Here, the pre-press sheet is a sheet obtained by heating and press-molding an unpressurized nonwoven fabric containing a fiber reinforcement material and a thermoplastic resin at low pressure. In this specification, the pre-press sheet (prepreg sheet) refers to a sheet obtained by heating and press-molding a molded body sheet one or more times to the extent that there is (remains) room for molding.

[0039] (optional ingredient) The nonwoven fabric to be subjected to the press molding step may contain optional components in addition to the fiber reinforcement and the thermoplastic resin, such as a binder component.

[0040] Examples of binder components include polyester resins commonly used in the manufacture of nonwoven fabrics, such as polyethylene terephthalate and modified polyethylene terephthalate, and binder fibers with a core-sheath structure that combine these, acrylic resin, styrene-(meth)acrylate copolymer resin, urethane resin, epoxy resin, PVA resin, various starches, cellulose derivatives, sodium polyacrylate, polyacrylamide, polyvinylpyrrolidone, acrylamide-acrylate-methacrylate copolymer, alkali salt of styrene-maleic anhydride copolymer, alkali salt of isobutylene-maleic anhydride copolymer, polyvinyl acetate resin, styrene-butadiene copolymer, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, styrene-butadiene-(meth)acrylate copolymer, etc.

[0041] The content of the binder component is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, based on the total mass of the nonwoven fabric. By setting the content of the binder component within the above range, the strength of the nonwoven fabric can be increased and the handleability can be improved.

[0042] As optional components, for example, coupling agents, antioxidants, light stabilizers, flame retardants, and colorants such as carbon black may be used.

[0043] <Fiber-reinforced plastic molding> According to the manufacturing method of one aspect of the present invention described above, a fiber-reinforced plastic molded body is produced. The inventors' studies have revealed that molded bodies produced in this manner have smaller variations in physical properties between the center and edges of the molded body compared to molded bodies produced by conventional manufacturing methods. That is, according to another aspect of the present invention, a novel fiber-reinforced plastic molded body is provided, which contains a thermoplastic resin and a plurality of fiber reinforcing materials oriented in a predetermined direction, and in which the coefficient of variation (CV) of the bending fracture load measured for each of test pieces obtained by dividing the molded body into eight equal parts in the width direction perpendicular to the predetermined direction is 6.0% or less. This fiber-reinforced plastic molded body can be produced by the manufacturing method of one aspect of the present invention described above. However, the fiber-reinforced plastic molded body of this aspect is not limited to those produced by the manufacturing method of one aspect of the present invention.

[0044] Here, if the coefficient of variation (CV) of the bending fracture load of a fiber-reinforced plastic molded article exceeds 6.0%, it can be said that there is a large variation in strength depending on the region of the molded article. Molded articles with such strength variations are difficult to apply to applications requiring high strength, such as automotive components. In contrast, molded articles with a small coefficient of variation as described above are fully suitable for applications requiring high strength, such as automotive components. Here, the value of the coefficient of variation (CV) of the bending fracture load described above is preferably 5.0% or less, more preferably 4.0% or less, even more preferably 3.5% or less, particularly preferably 3.0% or less, and most preferably 2.8% or less. While there is no particular lower limit for the coefficient of variation, it is usually 0.5% or more. The value of the coefficient of variation is calculated using the method described in the Examples section below (the same applies to the various physical properties below).

[0045] Specific gravity of the compact [g / cm 3

[0043] is preferably as small as possible from the viewpoint of weight reduction, provided that physical properties such as strength and rigidity are the same. As an example, the specific gravity of the molded article is preferably less than 1.20, more preferably 1.16 or less, even more preferably 1.00 or less, and particularly preferably 0.95 or less. There is no particular restriction on the lower limit of the specific gravity, but it is usually 0.85 or more.

[0046] The bending breaking load [N] of a molded article is an index of strength against bending stress, and may vary depending on the size of the molded article at the time of measurement and the types and composition of the constituent components, but is preferably 165.0 or more, more preferably 168.0 or more, even more preferably 175.0 or more, particularly preferably 180.0 or more, and most preferably 200.0 or more. There is no particular upper limit to the bending breaking load, but it is usually 300.0 or less.

[0047] The flexural modulus [GPa] of the molded article is an index of the ability to return to the original shape under bending stress, and is preferably 22.0 or more, more preferably 25.0 or more, even more preferably 28.0 or more, and particularly preferably 30.0 or more. There is no particular upper limit to the flexural modulus, but it is usually 50.0 or less.

[0048] The rigidity [N / mm] of a molded body is an index of resistance to deformation due to external forces, and may vary depending on the size of the molded body at the time of measurement and the type and composition of the constituent components, but is preferably 25.0 or more, more preferably 28.0 or more, even more preferably 30.0 or more, particularly preferably 35.0 or more, and most preferably 40.0 or more. There is no particular upper limit to the rigidity, but it is usually 60.0 or less.

[0049] The Charpy impact energy [J] (notched) of a molded product is an index of brittleness and toughness, and although it may vary depending on the size of the molded product at the time of measurement and the types and composition of its constituent components, it is preferably 0.350 or more, more preferably 0.390 or more, and even more preferably 0.440 or more. There is no particular upper limit for the Charpy impact energy, but it is usually 0.600 or less.

[0050] The weight reduction ratio of the compact relative to iron is an index showing the usefulness of the compact as a substitute for iron, with a smaller value indicating a greater contribution to weight reduction. This weight reduction ratio is preferably 30.0 or less, more preferably 29.0 or less, even more preferably 28.0 or less, even more preferably 27.0 or less, particularly preferably 26.0 or less, and most preferably 25.0 or less. There is no particular limit on the lower limit of the weight reduction ratio, but it is usually 20.0 or more.

[0051] Examples of uses of the fiber reinforced plastic molded article according to this embodiment include "casings for office automation equipment, mobile phones, smartphones, personal digital assistants, tablet PCs, digital video cameras and other portable electronic devices, air conditioners and other home appliances, and reinforcing materials such as ribs attached to the casings; diaphragms for speakers in home and car audio and electronic musical instruments; sports and leisure goods such as golf clubs, fishing rods and running shoes; aircraft materials; civil engineering and building materials such as "pillars, panels and reinforcing materials"; exterior panels or body parts such as various frames, various wheel bearings, various beams, doors, trunk lids, side panels, upper back panels, front bodies, underbodies, various pillars, various frames, various beams and various supports, and reinforcing materials for such exterior panels or body parts" and "instruments." Suitable for use in automobile and motorcycle parts such as "interior parts such as panels and seat frames," "fuel system, exhaust system, or intake system parts such as gasoline tanks, various pipes, and various valves," "engine coolant joints, air conditioner thermostat bases, headlamp supports, pedal housings," "aircraft parts such as winglets and spoilers," "railroad vehicle parts such as seat components for railroad cars, outer panels, reinforcing materials attached to outer panels, ceiling panels, air conditioner vents," and "reinforcing materials for molded bodies made of resin (thermosetting resin, thermoplastic resin), reinforcing materials for molded bodies made of resin and reinforcing fiber, reinforcing materials for plant-derived sheets (kraft paper, cardboard, grease-resistant paper, insulating paper, conductive paper, release paper, impregnated paper, glassine paper, cellulose nanofiber sheets, etc.)."

[0052] The following items are also included within the scope of the present invention: Item 1: A method for producing a fiber-reinforced plastic molded body, comprising press-molding a nonwoven fabric containing a fiber reinforcement material and a thermoplastic resin to obtain a molded body having a porosity of 1.0 to 29.0%; Item 2: The method for producing a fiber-reinforced plastic molded article according to Item 1, wherein the porosity is 2.5 to 25.0%; Item 3: The method for producing a fiber-reinforced plastic molded article according to Item 2, wherein the porosity is 3.0 to 23.0%; Item 4: The method for producing a fiber-reinforced plastic molded article according to any one of Items 1 to 3, wherein the fiber reinforcement material includes carbon fiber (CF); Item 5: The method for producing a fiber-reinforced plastic molded article according to Item 4, wherein the carbon fiber contains recycled carbon fiber (rCF); Item 6: The method for producing a fiber-reinforced plastic molded article according to Item 4 or 5, wherein the carbon fibers have a number average fiber length of 3 to 50 mm; Item 7: The method for producing a fiber-reinforced plastic molded article according to any one of Items 1 to 6, wherein the nonwoven fabric is a wet-laid nonwoven fabric containing carbon fibers and thermoplastic resin fibers; Item 8: The method for producing a fiber-reinforced plastic molded article according to any one of Items 1 to 7, wherein the content of the fiber reinforcement in the nonwoven fabric is 5 to 54 volume % relative to the total volume of the nonwoven fabric; Item 9: A fiber-reinforced plastic molding containing a thermoplastic resin and a plurality of fiber reinforcements oriented in a predetermined direction, a fiber-reinforced plastic molded body, in which the coefficient of variation (CV) of bending fracture load measured for each of test pieces obtained by dividing the molded body into eight equal parts in the width direction perpendicular to the predetermined direction is 6.0% or less; Item 10: The fiber-reinforced plastic molded article according to Item 9, having a porosity of 1.0 to 29.0%; Item 11: The fiber-reinforced plastic molded article according to Item 10, having a porosity of 2.5 to 25.0%; Item 12: The fiber-reinforced plastic molded article according to Item 11, wherein the porosity is 3.0 to 23.0%; Item 13: The fiber-reinforced plastic molded body according to any one of Items 9 to 12, wherein the fiber reinforcement material includes carbon fiber (CF); Item 14: The fiber-reinforced plastic molded product according to Item 13, wherein the carbon fiber comprises recycled carbon fiber (rCF); Item 15: The fiber-reinforced plastic molded product according to Item 13 or 14, wherein the carbon fibers have a number average fiber length of 3 to 50 mm; Item 16: Specific gravity is 1.20 [g / cm 3 Item 16. The fiber-reinforced plastic molded article according to any one of Items 9 to 15, wherein the fiber-reinforced plastic molded article has a viscosity of less than 1000 ppm; Item 17: The fiber-reinforced plastic molded article according to any one of Items 9 to 16, having a bending fracture load of 165.0 [N] or more measured at standard dimensions in accordance with JIS K7074:1988 three-point bending test (method A); Item 18: The fiber-reinforced plastic molded article according to any one of Items 9 to 17, having a flexural modulus of 22.0 [GPa] or more measured at standard dimensions in accordance with JIS K7074:1988 three-point bending test (method A); Item 19: The fiber-reinforced plastic molded product according to any one of Items 9 to 18, having a rigidity of 25.0 [N / mm] or more measured at standard dimensions in accordance with JIS K7074:1988 three-point bending test (method A); Item 20: The fiber-reinforced plastic molding according to any one of Items 9 to 19, having a Charpy impact energy (notched) of 0.350 [J] or more, measured in accordance with JIS K7111-1 / leA:2012 using a test specimen having dimensions of length 80 mm, width 10 mm, and thickness 2 mm; Item 21: The fiber-reinforced plastic molded article according to any one of Items 9 to 20, having a weight reduction ratio relative to iron of 30.0 or less. [Example]

[0053] The present invention will be explained in more detail below using examples and comparative examples, but it should be understood that the present invention is not limited to the following examples.

[0054] <<Production of fiber-reinforced plastic molded body>> [Comparative Example 1] (Production of sheets for fiber reinforced plastic moldings (CF nonwoven fabric)) Recycled carbon fiber (rCF) with a number-average fiber length of 12 mm was added to water to give a slurry concentration of 0.5%. After initial dispersion by stirring using a pulper for 30 seconds, the mixture was diluted with water to a slurry concentration of 0.15% (carbon fiber slurry).

[0055] On the other hand, polypropylene fibers containing polypropylene, maleic acid-modified polypropylene, and a resin stabilizer were prepared. The polypropylene fibers were added to the carbon fiber slurry so that the blending ratio of carbon fiber to polypropylene fiber was 1:1 (mass ratio) (raw material slurry). Then, the raw material slurry was continuously fed to an inclined wire paper machine, and a paper sheet having a width of 1200 mm and a basis weight of 100 g / m was produced. 2 The CF nonwoven fabric was produced by papermaking, and both ends in the width direction were cut to obtain CF nonwoven fabrics with a width of 1,000 mm. The CF nonwoven fabrics obtained in this manner have fiber orientation. Therefore, the longitudinal direction (fiber flow) of the nonwoven fabric roll was defined as the MD direction, and the direction perpendicular to the MD direction (width direction) was defined as the TD direction. This nonwoven fabric was then cut into MD nonwoven fabrics (cut to a size of 300 mm in the MD direction and 210 mm in the TD direction) and TD nonwoven fabrics (cut to a size of 300 mm in the TD direction and 210 mm in the MD direction).

[0056] (press molding process) A 210 x 300 mm flat mold was prepared for press molding. A heat and cool press molding machine was used as the molding method. The design thickness of the molded body was 2 mm, and since the true specific gravity of the components of the molded body was 1.20, 151 g of a fiber-reinforced plastic molded body sheet (CF nonwoven fabric) was placed in the mold. Specifically, the MD-direction nonwoven fabric and TD-direction nonwoven fabric cut out above were alternately stacked to cancel out the orientation direction, and a total of 24 sheets of nonwoven fabric were stacked.

[0057] Specifically, the CF nonwoven fabric obtained above was first placed in a mold heated to 40°C. Next, the upper mold of the press molding machine was lowered to a position where it would not completely press down on the CF nonwoven fabric. The mold was heated to 210°C while applying a 0.8 ton spring load attached to the mold, a load that would not damage the nonwoven fabric. Once the temperature reached 210°C, this temperature was maintained for 3 minutes to melt the CF nonwoven fabric. Subsequently, while maintaining the temperature at 210°C, a press pressure of 28 MPa was applied for 2 minutes. The mold was then cooled to 40°C while still maintaining the same pressure, and the mold was opened when the temperature reached 40°C, yielding a fiber-reinforced plastic molded article of this comparative example. The molding cycle time was the time from placing the CF nonwoven fabric in the mold at 40°C to heating, pressurizing, cooling, and removing the molded article. The molding cycle time values ​​are shown in Table 1 below.

[0058] [Example 1] A fiber-reinforced plastic molded article of this example was obtained using the same method as in Comparative Example 1 described above, except that the pressing pressure was changed from 28 MPa to 10 MPa.

[0059] [Example 2] A fiber-reinforced plastic molded article of this example was obtained using the same method as in Comparative Example 1 described above, except that the pressing temperature was changed from 210°C to 190°C.

[0060] [Example 3] A fiber-reinforced plastic molded article of this example was obtained using the same method as in Example 2 described above, except that the pressing pressure was changed from 28 MPa to 5 MPa.

[0061] <Evaluation of the physical properties of fiber-reinforced plastic moldings> For the evaluation of physical properties, a bending test piece was prepared by cutting out the fiber reinforced plastic molded body using a contour machine.

[0062] First, one end of the molded body in the width direction (210 mm) was cut by 10 mm using a contour machine. Next, since the width of the bending test piece was 100 mm, the molded body was cut in a width of 100 mm from the position where the 10 mm was removed above, and cut into a size of 100 mm x 300 mm. Further, it was cut in 15 mm increments in the longitudinal direction (300 mm) to obtain 20 samples each measuring 15 mm x 100 mm. The first and last two samples were removed, and the odd-numbered samples were collected to obtain n = 8 bending test pieces.

[0063] Furthermore, since the width of the Charpy impact test specimen was 80 mm, the molded body was cut at a width of 80 mm from the position where the 100 mm was cut out above, and cut into pieces measuring 80 mm x 300 mm. Furthermore, two 15 mm pieces were cut into each end in the longitudinal direction (300 mm), and the remaining pieces were cut into 10 mm pieces, resulting in 24 10 mm samples, sampled in the following order: (1) Charpy notched, (2) unnotched, and (3) other, yielding n = 8 test specimens for each. The other specimens were used in a separate test. Unless otherwise specified, the following physical property evaluations were carried out for each of the eight test pieces, and the arithmetic mean values ​​of the measured values ​​for each test piece were calculated.

[0064] (Measurement of thickness of molded body) The thickness of the molded body was measured using a micrometer, and the results are shown in Table 1 below.

[0065] (Measurement of specific gravity of molded body) The specific gravity of the molded article was measured in accordance with JIS K7112:1999 (Method for measuring density and specific gravity of plastics-non-foamed plastics). The results are shown in Table 1 below.

[0066] (Calculation of porosity of molded body) The porosity [%] was calculated from the measured specific gravity of the green body obtained above and the true specific gravity of the constituent components of the green body. The results are shown in Table 1 below.

[0067] (Measurement of bending failure load, bending modulus, and stiffness) The bending fracture load [N] and bending modulus [GPa] were measured in accordance with the three-point bending test (Method A) of JIS K7074:1988 (Bending test method for carbon fiber reinforced plastics). The results are shown in Table 1 below. Table 1 also shows the calculated value of the coefficient of variation (CV) of the bending fracture load, which is calculated by dividing the standard deviation of the eight measured values ​​of the bending fracture load by the arithmetic mean value of the bending fracture load. The stress-strain curves (SS curves) corresponding to the eight test specimens when the bending fracture load was measured are shown in Figure 2 (a) to (d).

[0068] In addition, the stiffness [N / mm] was calculated from the slope of the straight line in the elastic region of the stress-strain curve (SS curve) when the bending breaking load was measured for the test piece closest to the center in the width direction.

[0069] (Charpy impact energy) In accordance with JIS K7111-1 / leA:2012 (Plastics - Determination of Charpy impact properties - Part 1: Non-instrumented impact test), the Charpy impact energy [J] was measured using test specimens measuring 80 mm in length, 10 mm in width, and 2 mm in thickness. This measurement was performed on both notched and unnotched test specimens.

[0070] (Measurement of the thickness of the compact equivalent to the stiffness of 1mm thick steel) The relationship between the flexural modulus of an elastic body, the size of the test specimen, the amount of change in bending load, and the amount of change in deflection is expressed by the following Equation 1:

[0071]

number

[0072] In Equation 1, L is the distance between supports, b is the width of the test piece, h is the thickness of the test piece, ΔF is the change in bending load, and Δs is the change in deflection.

[0073] Here, the flexural modulus of iron is known to be 206 [GPa]. Assuming the thickness of the iron is 1 mm, the rigidity of the iron (ΔF / Δs [N / mm]) can be calculated. Using this, the "rigidity of iron" value calculated above, as well as the size and flexural modulus measurements of each test piece, were substituted into Equation 1 above to calculate the thickness of the molded body equivalent to the rigidity of 1 mm thick iron. The results are shown in Table 1 below.

[0074] (Calculation of weight reduction ratio of molded body to steel) First, assuming the thickness of the iron to be 1 mm, this thickness (1 mm) was multiplied by the specific gravity of iron (7.8) to calculate the mass A per unit area. Meanwhile, the thickness of the compact measured above was multiplied by the specific gravity of the compact measured above to calculate the mass B per unit area. Mass B was then divided by mass A and multiplied by 100 to calculate the weight reduction ratio (relative to iron). The results are shown in Table 1 below. Note that this weight reduction ratio value corresponds to the mass of the compact required to replace 1 mm of iron, and the smaller this value, the more effectively the compact contributes to weight reduction.

[0075] [Table 1]

[0076] In typical press molding, if the press pressure or temperature is low during molding, the resulting molded body will be thicker than the designed thickness, resulting in the inclusion of voids (air gaps) within the molded body. This has traditionally been considered to result in quality problems, such as poor physical properties. Contrary to this conventional wisdom, the molded bodies of Examples 1 to 3, despite containing a certain amount of voids, exhibited several performance improvements over the molded body of Comparative Example 1, which contained no voids. For example, it can be seen that the rigidity and notched Charpy impact energy of the molded bodies of Examples 1 to 3 were significantly improved compared to Comparative Example 1. Furthermore, despite the improved rigidity, Examples 1 to 3 also exhibited a superior weight reduction ratio relative to steel compared to Comparative Example 1, making them highly promising metal replacement materials for various components, such as automotive parts.

[0077] Furthermore, in Comparative Example 1, as shown in Figure 2, the bending fracture load near both ends of the molded body is smaller than that in the center, and the coefficient of variation is also large, indicating that the strength varies depending on the part of the molded body. In Comparative Example 1, the thickness of the molded body is the same as the design thickness, but if such variation in strength occurs, it would be difficult to apply it to automotive components, etc. In contrast, in Examples 1 to 3, the variation in bending fracture load depending on the part of the molded body (coefficient of variation) was reduced compared to Comparative Example 1, indicating that the molded body is fully suitable for practical use.

[0078] In addition, in Examples 2 and 3, the temperature during press molding was set to 190°C, which shortened the temperature increase time and temperature decrease time during heat and cool, thereby shortening the molding cycle time.

[0079] As described above, the present invention allows for the production of fiber-reinforced plastic molded articles that exhibit high strength, high rigidity, improved quality, reduced weight, and reduced cost, depending on the molding conditions during press molding. In press molding using high-hardness fiber-reinforced materials, such as inorganic fiber-reinforced materials, the pressure during press molding is thought to cause damage due to contact between fibers. However, the manufacturing method of the present invention is believed to mitigate this damage, thereby improving strength and rigidity. Another advantage is that it does not require the use of a blowing agent or foam molding equipment, as in foam molding. In the above-described examples, as one embodiment of the present invention, a fiber-reinforced plastic molded article was produced using a wet papermaking method using an equal-weight mixture of polypropylene fiber and recycled carbon fiber as a raw material. However, given the mechanism by which the effects of the present invention are realized, the method can also be applied to the production of fiber-reinforced plastic molded articles using dry-laid nonwoven fabrics or other thermoplastic resins, and therefore has great industrial applicability. [Explanation of symbols]

[0080] 10 nonwoven fabrics, 20 Fiber-reinforced plastic moldings, 22 void, 110 upper mold, 120 Lower mold, T design thickness, t is the thickness of the compact.

Claims

1. A method for producing a fiber-reinforced plastic molded body (excluding those containing organic fibers and thermoplastic composite materials consisting of fiber bundles impregnated with polypropylene emulsion in which multiple reinforcing fibers are aligned in a predetermined direction) comprises press-molding a nonwoven fabric containing a fiber reinforcement material and a thermoplastic resin (excluding those containing reinforcing fiber bundles) to obtain a molded body having a porosity of 1.0 to 29.0%.

2. The method for producing a fiber-reinforced plastic molded body according to claim 1, wherein the porosity is 2.5 to 25.0%.

3. The method for producing a fiber-reinforced plastic molded body according to claim 2, wherein the porosity is 3.0 to 23.0%.

4. The method for producing a fiber-reinforced plastic molded article according to claim 1 or 2, wherein the fiber reinforcement material contains carbon fiber (CF).

5. The method for producing a fiber-reinforced plastic molded article according to claim 4, wherein the carbon fiber contains recycled carbon fiber (rCF).

6. The method for producing a fiber-reinforced plastic molded body according to claim 4, wherein the number average fiber length of the carbon fibers is 3 to 50 mm.

7. The method for producing a fiber-reinforced plastic molded article according to claim 1 or 2, wherein the nonwoven fabric is a nonwoven fabric containing carbon fibers and thermoplastic resin fibers.

8. The content of the fiber reinforcement in the nonwoven fabric is 5 to 54% by volume as a volume ratio of the thermoplastic resin to the total volume of the nonwoven fabric calculated from the true specific gravity of the nonwoven fabric. The method for producing a fiber-reinforced plastic molded body according to claim 1 or 2.

9. A fiber-reinforced plastic molded body containing a thermoplastic resin and a plurality of fiber reinforcements oriented in a predetermined direction, the coefficient of variation (CV) of bending fracture load measured for each of test pieces obtained by dividing the molded body into eight equal parts in the width direction perpendicular to the predetermined direction is 6.0% or less; A fiber-reinforced plastic molded body, wherein the content of the fiber reinforcing material in the fiber-reinforced plastic molded body is 48 volume % or less with respect to the total mass of the molded body.

10. A fiber-reinforced plastic molding containing a thermoplastic resin and a plurality of fiber reinforcing materials oriented in a predetermined direction, the coefficient of variation (CV) of bending fracture load measured for each of test pieces obtained by dividing the molded body into eight equal parts in the width direction perpendicular to the predetermined direction is 6.0% or less; A fiber-reinforced plastic molded body (excluding those containing a thermosetting resin) in which the content of fiber reinforcing material in the fiber-reinforced plastic molded body is 48 volume % or less relative to the total mass of the molded body.

11. The fiber-reinforced plastic molded body according to claim 9 or 10, having a porosity of 1.0 to 29.0%.

12. The fiber-reinforced plastic molded body according to claim 11, having a porosity of 2.5 to 25.0%.

13. The fiber-reinforced plastic molded body according to claim 12, wherein the porosity is 3.0 to 23.0%.

14. The fiber-reinforced plastic molding according to claim 9 or 10, wherein the fiber reinforcement material comprises carbon fiber (CF).

15. The fiber-reinforced plastic molding according to claim 14, wherein the carbon fiber comprises recycled carbon fiber (rCF).

16. The fiber-reinforced plastic molded body according to claim 14, wherein the number average fiber length of the carbon fibers is 3 to 50 mm.

17. Specific gravity is 1.20 [g / cm ３ The fiber-reinforced plastic molding according to claim 9 or 10, wherein the fiber-reinforced plastic molding has a viscosity of less than 1000 MPa.

18. The fiber-reinforced plastic molding according to claim 9 or 10, having a bending fracture load of 165.0 [N] or more measured in standard dimensions in accordance with JIS K7074:1988 three-point bending test (method A).

19. The fiber-reinforced plastic molding according to claim 9 or 10, having a flexural modulus of 22.0 GPa or more measured at standard dimensions in accordance with JIS K7074:1988 three-point bending test (method A).

20. The fiber-reinforced plastic molding according to claim 9 or 10, having a rigidity of 25.0 [N / mm] or more measured in standard dimensions in accordance with JIS K7074:1988 three-point bending test (method A).

21. Charpy impact energy (notched) measured in accordance with JIS K7111-1 / leA: 2012 with a test specimen having dimensions of 80 mm in length, 10 mm in width, and 2 mm in thickness is 0.350 [J] or more. The fiber-reinforced plastic molded body according to claim 9 or 10.

22. The fiber-reinforced plastic molded article according to claim 9 or 10, having a weight reduction ratio relative to iron of 30.0 or less.

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