Fiber-reinforced material and method for manufacturing the same

Abstract

The present invention provides a fiber-reinforced material obtained by recycling virgin material, which has sufficient impact resistance. [Solution] A fiber-reinforced material having pseudo-isotropy, comprising fragments of a thermoplastic fiber-reinforced resin composite material before disposal, wherein the thermoplastic fiber-reinforced resin composite material is a laminate, and the laminate comprises at least one layer of fiber-reinforced sheets containing a reinforcing fiber base material and a thermoplastic matrix resin, wherein in a Charpy impact test in accordance with ISO 179-1, the Charpy impact strength of the fiber-reinforced material is 75% or more of the maximum Charpy impact strength of the thermoplastic fiber-reinforced resin composite material before disposal, and the length of the fragments is greater than 15 mm and less than or equal to 100 mm.

Description

[Technical Field]

[0001] This invention relates to a fiber-reinforced material that includes fragments of a thermoplastic fiber-reinforced resin composite material before it is decommissioned. [Background technology]

[0002] Fiber-reinforced materials containing reinforcing fiber substrates and thermoplastic resins are used in a wide range of applications, including the exteriors and casings of electronic devices, automotive parts, and building materials.

[0003] On the other hand, in recent years, in order to aim for a sustainable society, there has been a demand to reduce the amount of reinforcing fibers and thermoplastic resins used, and to use recycled materials made from thermoplastic fiber-reinforced resin composite materials (virgin materials) that are no longer in use as fiber-reinforcement materials.

[0004] Patent Document 1 discloses a method for recycling carbon fiber reinforced thermoplastic resin molded products, characterized by crushing recovered carbon fiber reinforced thermoplastic resin molded products (virgin material) into pellets, and then mixing these pellets with new carbon fiber reinforced thermoplastic resin pellets for use in injection molding. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2006-218793 [Overview of the project] [Problems that the invention aims to solve]

[0006] Currently, in countries around the world, as exemplified by EPEAT in the United States, there is a demand for recycled materials to retain as much of the impact resistance of virgin materials as possible when it comes to general plastic components. And this demand is no exception in the field of fiber-reinforced materials.

[0007] Therefore, the present invention aims to provide a fiber-reinforced material obtained by recycling virgin material, which has sufficient impact resistance. [Means for solving the problem]

[0008] To solve the above problems, the present invention provides a fiber-reinforced material having pseudo-isotropy, comprising (1) a fragment of a thermoplastic fiber-reinforced resin composite material before disposal, wherein the thermoplastic fiber-reinforced resin composite material before disposal is a laminate, and the laminate comprises at least one layer of fiber-reinforced sheets containing a reinforcing fiber base material and a thermoplastic matrix resin, wherein in a Charpy impact test in accordance with ISO 179-1, the Charpy impact strength of the fiber-reinforced material is 75% or more of the maximum Charpy impact strength of the thermoplastic fiber-reinforced resin composite material before disposal, which can be determined from the measurement method described below, and the length of the fragment is greater than 15 mm and less than or equal to 100 mm. (A) The fiber direction of the reinforcing fibers contained in the fiber-reinforced sheet constituting the outermost layer of the thermoplastic fiber-reinforced resin composite material before disposal is defined as 0°, and test pieces for measuring Charpy impact strength in accordance with ISO 179-1 are cut out in three directions: 0°, 45°, and 90°. (B) Measure the Charpy impact strength of each test specimen cut in (A) according to ISO 179-1. (C) The maximum value among the measurements in (B) is taken as the maximum Charpy impact strength.

[0009] (2) The fiber-reinforced material according to (1), characterized in that the strips are formed in a rectangular shape with an aspect ratio of 1.0 or more and 4.0 or less.

[0010] (3) The fiber-reinforced material according to (1), characterized in that 20% or more of the total number of reinforcing fibers contained in the strip are 15 mm or longer.

[0011] (4) The fiber-reinforced material according to (1), characterized in that the thermoplastic fiber-reinforced resin composite material before disposal is composed of multiple fiber-reinforced sheets, the reinforcing fiber base material being a unidirectional material or a cross material.

[0012] (5) The fiber-reinforced material according to (1), characterized in that the thermoplastic fiber-reinforced resin composite material before being discarded has a configuration in which a core material that is an expandable resin is sandwiched between at least one layer of the fiber-reinforced sheet.

[0013] (6) The fiber-reinforced material according to (1), characterized in that the thermoplastic matrix resin is a phenoxy resin.

[0014] (7) A method for producing the fiber-reinforced material according to any one of (1) to (6), comprising: a processing step of processing the thermoplastic fiber-reinforced resin composite material before being discarded into a large number of the strips; a charging step of charging the strips into a mold set in a hot press such that the fiber directions of the strips are random; and a hot pressing step of performing hot pressing on the mold charged with the strips. The method for producing a fiber-reinforced material is characterized by comprising the above steps. Effects of the Invention

[0015] According to the present invention, it is possible to provide a fiber-reinforced material obtained by recycling virgin material, which has sufficient impact resistance. Brief Description of the Drawings

[0016] [Figure 1] It is a schematic flow chart for producing the fiber-reinforced material 1 according to the present invention. [Figure 2] It is a plan view of the strip 20 constituting the fiber-reinforced material 1. [Figure 3] It is a cross-sectional view of the strip 20 cut along the YZ plane. [Figure 4] It is a flow chart showing the method for producing the fiber-reinforced material 1 according to the present invention. [Figure 5] It is a cross-sectional view of a strip 20' cut along the YZ plane in a second embodiment of the present invention. [Figure 6] It is a diagram showing the cutting direction of a test piece when evaluating the presence or absence of anisotropy in an example. [Figure 7]It is a diagram illustrating the cutting direction of a test piece when evaluating impact resistance in an example. MODE FOR CARRYING OUT THE INVENTION

[0017] <First Embodiment> Hereinafter, a first embodiment of the fiber-reinforced material according to the present invention will be described.

[0018] (Schematic flow for manufacturing fiber-reinforced material 1) Figure 1 is a schematic flow for manufacturing the fiber-reinforced material 1 according to the present invention. Figure 2 is a plan view of a strip 20 constituting the fiber-reinforced material 1. In Figure 2, the X-axis indicates the longitudinal direction of the strip 20, the Y-axis indicates the width direction of the strip 20, the Z-axis indicates the thickness direction of the strip 20, and the X-axis, Y-axis, and Z-axis are orthogonal to each other. The definitions of the X-axis, Y-axis, and Z-axis are the same in the following figures.

[0019] Referring to Figure 1 and Figure 2, the fiber-reinforced material 1 according to the present invention is formed by stacking a large number of rectangular strips 20 obtained by processing a thermoplastic fiber-reinforced resin composite material 2 before being discarded (hereinafter also referred to as virgin material 2), followed by hot pressing. The virgin material 2 may be a thermoplastic fiber-reinforced resin composite material recovered from materials or defective products generated from a waste route in a molded product manufacturing process (pre-consumer recycling), or may be a thermoplastic fiber-reinforced resin composite material recovered from used molded products shipped to the market (post-consumer recycling), or may include both. For example, the virgin material 2 is a thermoplastic fiber-reinforced resin composite material recovered from one or more types of molded products selected from electronic component housings, electronic component transport cases, automobile parts, and building materials.

[0020] (Background leading to the creation of the present invention) The background of the present invention will be described below. Fiber-reinforced materials are used in a wide range of applications, including the exteriors and casings of electronic devices, automotive parts, and building materials. However, in order to reduce the amount of reinforcing fibers and thermoplastic resins used, there is a demand for the use of recycled fiber-reinforced materials (recycled materials) made from recycled thermoplastic fiber-reinforced resin composite materials (virgin materials) before they are discarded. Meanwhile, in countries around the world, as exemplified by EPEAT in the United States, there is a growing demand for recycled materials to retain as much of the impact resistance of virgin materials as possible when it comes to general plastic components. EPEAT is a certification system that demonstrates that electronic products are environmentally friendly. In the United States, more than 95% of government-procured products are required to be EPEAT compliant, making it an important certification for companies. One of EPEAT's requirements for general plastic components is that "in a Charpy impact test conducted in accordance with ISO 179-1, the Charpy impact strength of recycled materials must be at least 75% of that of virgin materials." Therefore, in order to quantitatively evaluate whether the fiber-reinforced material 1 obtained by recycling virgin material 2 has sufficient impact resistance, the inventors conceived of using a Charpy impact test in accordance with ISO 179-1, following the general requirements for plastic components described in EPEAT as described above. However, the "Charpy impact strength of virgin material" varies depending on the cutting direction of the test piece cut from the virgin material and subjected to the Charpy impact test. This is thought to be because the amount of fiber in the direction of the impact load changes depending on the cutting direction. Therefore, in order to quantitatively evaluate whether the fiber-reinforced material 1 (recycled material) obtained by recycling virgin material 2 has sufficient impact resistance, the inventors used the following indicator: "In a Charpy impact test conducted in accordance with ISO 179-1, the Charpy impact strength of the recycled material is 75% or more of the maximum value of the Charpy impact strength measured in each test piece cut in three directions: 0°, 45°, and 90°, with the reinforcing fibers contained in the outermost layer of the virgin material being set to 0°."

[0021] Here, in the manufacturing process of fiber-reinforced material 1 (recycled material), the fine fragments 20 are piled up so that the fiber-reinforced material 1 (recycled material) has pseudo-isotropy (described later). "Pseudo-isotropy" refers to a state in which the physical properties are almost the same in all directions parallel to the surface of the fiber-reinforced material 1 (recycled material). Therefore, the "Charpy impact strength of recycled material" in the above index can be the Charpy impact strength measured on test pieces cut from the recycled material in random directions.

[0022] In order to achieve the above indicators, the inventors conducted diligent studies and found that the above indicators can be achieved when the length of the virgin material fragments constituting the fiber-reinforced material according to the present invention is greater than 15 mm and less than or equal to 100 mm. If the length of the virgin material fragments is 15 mm or less, the fragments become excessively short, making it impossible to ensure sufficient impact resistance, and it is also necessary to cut and crush the virgin material into very small pieces, which increases the labor and cost of the work. On the other hand, if the length of the virgin material fragments is greater than 100 mm, the anisotropy of the resulting fiber-reinforced material tends to be large. In the rectangular fragments 20 according to this embodiment, referring to Figure 2, the above indicators can be achieved when the length A of the long side 20a is greater than 15 mm and less than or equal to 100 mm.

[0023] The length of the virgin material strips is preferably 20 mm or more and 80 mm or less, and more preferably more than 30 mm and 80 mm or less. If the length of the virgin material strips is 20 mm or more, the resulting fiber-reinforced material can have more sufficient impact resistance, and if the length of the virgin material strips is more than 30 mm, the resulting fiber-reinforced material can have even more sufficient impact resistance. Furthermore, by setting the length of the virgin material strips to 80 mm or less, the anisotropy of the resulting fiber-reinforced material can be further suppressed.

[0024] Furthermore, for the virgin material fragments, it is desirable that the proportion of reinforcing fibers with a length of 15 mm or more among the total number of reinforcing fibers contained in the fragments be 20% or more, and more preferably 30% or more. This configuration increases resistance to impact loads, thereby improving impact resistance. The proportion of reinforcing fibers with a length of 15 mm or more among the total number of reinforcing fibers contained in the fragments can be calculated using existing calculation methods, for example, mathematically calculated from the basis weight of the molding material used in the manufacture of the virgin material.

[0025] The thickness of the virgin material used in the Charpy impact test is adjusted in advance, for example, by laminating multiple layers of virgin material, so that it is the same thickness as the fiber-reinforced material 1 (recycled material) used in the Charpy impact test.

[0026] Furthermore, according to the present invention, by recycling virgin material 2, the environmental burden when disposing of thermoplastic fiber-reinforced resin composite materials, which are difficult to dispose of, can be reduced, and energy consumption when manufacturing fiber-reinforced material 1 can be significantly reduced, thereby lowering costs. In addition, the present invention contributes to the advancement of recycling technology, which in turn promotes the development of new products and can contribute to the realization of a sustainable society.

[0027] (Composition of 20 fragments) The structure of the strip 20 will be described in more detail. Figure 3 is a cross-sectional view of the strip 20 cut in the YZ plane. Referring to Figure 3, the strip 20 is formed by laminating multiple fiber-reinforced sheets 3 containing a reinforcing fiber base material and a thermoplastic matrix resin. In the first embodiment, the strip 20 is formed by laminating fiber-reinforced sheets 3a, 3b, 3c, and 3d in this order. Since the strip 20 is manufactured by cutting the virgin material 2 in the thickness direction, the laminated structure of the strip 20 is the same as the laminated structure of the virgin material 2 from which it was processed, and this is also the case in the following embodiments.

[0028] The fiber direction of the reinforcing fibers contained in the fiber-reinforced sheets (fiber-reinforced sheets 3a and 3d) that constitute the outermost layer of the strip 20 is not particularly limited. Therefore, the fiber direction of the reinforcing fibers contained in the fiber-reinforced sheets 3a and 3d is not limited to the X-axis direction, but may be, for example, the Y-axis direction or the diagonal direction. Furthermore, the fiber direction of the reinforcing fibers in one fiber-reinforced sheet (fiber-reinforced sheet 3a) and the other fiber-reinforced sheet (fiber-reinforced sheet 3d) that constitute the outermost layer of the strip 20 may be different.

[0029] The reinforcing fibers in the fiber-reinforced sheet 3a, which constitutes the outermost layer of the strip 20, can be arranged so that their fiber directions are different from those of the reinforcing fibers in the fiber-reinforced sheet 3b, which is continuously laminated with the fiber-reinforced sheet 3a in the Z-axis direction. Similarly, the reinforcing fibers in the fiber-reinforced sheet 3d, which constitutes the outermost layer of the strip 20, can be arranged so that their fiber directions are different from those of the reinforcing fibers in the fiber-reinforced sheet 3c, which is continuously laminated with the fiber-reinforced sheet 3d in the Z-axis direction. The fiber directions of the reinforcing fiber sheets 3b and 3c may be the same or different. In this embodiment, the reinforcing fibers in fiber-reinforced sheets 3a and 3d are oriented so that their fiber direction is in the X-axis direction, and the reinforcing fibers in fiber-reinforced sheets 3b and 3c are oriented so that their fiber direction is in the Y-axis direction (cross-laminated configuration).

[0030] Examples of reinforcing fibers contained in virgin material 2 (fiber-reinforced sheet 3) include carbon fibers, glass fibers, aramid fibers, boron fibers, metal fibers, inorganic fibers, and natural fibers. However, considering the difficulty of disposing of virgin material and the mechanical properties of the fiber-reinforced material obtained through reuse, it is preferable to use glass fibers or carbon fibers as reinforcing fibers, and carbon fibers are more preferable. The carbon fibers used may be continuous fiber systems or short fiber systems such as felt or nonwoven fabrics. In addition, there are PAN-based carbon fibers and pitch-based carbon fibers, and either one or both may be used.

[0031] The reinforcing fibers in all fiber-reinforced sheets 3 may be of the same type, or some of the reinforcing fibers in some fiber-reinforced sheets 3 may be of a different type from those in other fiber-reinforced sheets 3. In this embodiment, it is preferable that the reinforcing fibers in fiber-reinforced sheets 3a and 3d be PAN-based carbon fibers, and the reinforcing fibers in fiber-reinforced sheets 3b and 3c be pitch-based carbon fibers. With this configuration, the mechanical strength of the strips 20 is increased, and consequently, the mechanical strength of the fiber-reinforced material 1 may also be increased.

[0032] Examples of thermoplastic matrix resins included in virgin material 2 include, but are not limited to, nylon, polycarbonate, polyolefin, thermoplastic polyester resin, phenoxy resin, and acrylic resin. However, it is preferable that the thermoplastic matrix resin included in virgin material 2 is a thermoplastic resin whose weight-average molecular weight in the state contained in fiber-reinforced material 1 is 90% to 110% of its weight-average molecular weight in the state contained in virgin material 2. Such thermoplastic resins are preferable because they hardly cause a decrease in mechanical strength due to thermal degradation during recycling (significant decrease in molecular weight) or deterioration of moldability due to repolymerization (significant increase in molecular weight). Examples of such thermoplastic resins include phenoxy resin, and particularly preferably in-situ polymerized phenoxy resin. This is because phenoxy resin itself undergoes little thermal degradation, retains a certain degree of polymerization reactivity even in the polymer state due to being an in-situ polymerized type, and has high impact resistance because it is an amorphous thermoplastic resin. Here, "in-situ polymerization type phenoxy resin" refers to a reactive precursor composition that is initially in the state of monomer or oligomer, and which can be rapidly polymerized in situ by heat or other means to be converted into a high molecular weight phenoxy resin.

[0033] Preferably, the thermoplastic matrix resin contained in the virgin material 2 is a thermoplastic resin that can maintain a weight-average molecular weight of 85% or more of the weight-average molecular weight of the original virgin material 2 even after being recycled to the fiber-reinforced material 1 five times. Examples of such thermoplastic resins include phenoxy resins, including in-situ polymerized phenoxy resins.

[0034] Examples of virgin material 2 include cloth material made by impregnating a matrix resin into a woven fabric in which continuous reinforcing fibers are plain woven or twill woven, unidirectional reinforced fiber material (UD material) made by aligning continuous fibers in one direction and impregnating them with matrix resin, and random mat material made by assembling the aforementioned unidirectional reinforced fiber material into small pieces such as strips. However, from the viewpoint of ensuring the impact resistance of the fiber-reinforced material, it is desirable to use continuous fibers, so it is preferable to adopt cloth material or UD material as the form of virgin material 2.

[0035] The Vf (fiber volume content) of the virgin material 2 is not particularly limited, but is preferably between 40 and 65. By setting the Vf (fiber volume content) of the virgin material 2 to between 40 and 65, the balance of the volume ratio between the thermoplastic matrix resin and reinforcing fibers contained in the virgin material 2 becomes better, thus obtaining a fiber-reinforced material with more sufficient mechanical strength.

[0036] Referring to Figure 2, the aspect ratio of the strip 20 (the ratio of the length A of the long side 20a to the length B of the short side 20b) is not particularly limited, but is preferably between 1.0 and 4.0. By setting the aspect ratio of the strip 20 to 4.0 or less, the anisotropy of the resulting fiber-reinforced material can be further suppressed.

[0037] Referring to Figure 3, the thickness C of the strips 20 is not particularly limited, but is preferably 0.3 mm or more and 1.0 mm or less. By setting the thickness C of the strips 20 to 0.3 mm or more, each strip 20 has sufficient thickness, thus increasing the mechanical strength. By setting the thickness C of the strips 20 to 1.0 mm or less, the gaps that occur between the strips 20 during hot pressing can be reduced, so that gaps are less likely to occur in the fiber-reinforced material 1 after hot pressing, thus increasing the mechanical strength.

[0038] In this embodiment, the strip 20 is composed of a single layer of laminate made of fiber-reinforced sheets 3a, 3b, 3c, and 3d, but it is not limited to this, and the strip 20 may be composed of two or more layers of this laminate. Also, the number of layers of fiber-reinforced sheets 3 that make up the strip 20 is not particularly limited as long as it is two or more layers, but for example it is 10 layers or less.

[0039] (Composition of fiber-reinforced material 1) The fiber-reinforced material 1 may contain a binder resin in addition to the fragments 20 of the virgin material 2. The binder resin may be of the same type as the thermoplastic matrix resin pre-contained in the fragments 20 of the virgin material 2, or it may be of a different type. However, in order to improve the integration with the fragments 20 of the virgin material 2, it is preferable that the binder resin be of the same type as the thermoplastic matrix resin of the virgin material 2. The preferred type of binder resin is the same as that of the thermoplastic matrix resin of the virgin material 2, so the explanation is omitted. However, by not including other binder resins in the fiber-reinforced material 1, the labor and costs of the work can be reduced.

[0040] The Vf (fiber volume content) of the fiber-reinforced material 1 is not particularly limited, but is preferably 30 to 60. By setting the Vf (fiber volume content) of the fiber-reinforced material 1 to 30 to 60, the balance of the volume ratio between the thermoplastic matrix resin and reinforcing fibers contained in the virgin material 2 becomes better, and thus it is possible to obtain more sufficient mechanical strength.

[0041] Fiber-reinforced materials can be used in a variety of applications requiring impact resistance, such as electronic equipment casings.

[0042] (Method for manufacturing fiber-reinforced material 1) Here, the method for manufacturing the fiber-reinforced material 1 according to the present invention will be described with reference to Figure 4. Figure 4 is a flowchart showing the method for manufacturing the fiber-reinforced material 1 according to the present invention.

[0043] First, the virgin material 2 is processed into numerous rectangular strips 20 (S1). The processed strips 20 may have different lengths and widths, as long as their length is greater than 15 mm and less than or equal to 100 mm (in this embodiment, the length A of the long side 20a is greater than 15 mm and less than or equal to 100 mm).

[0044] Next, the numerous strips 20 produced in S1 are loaded into a mold provided in the hot press (S2). Here, the method of loading the strips 20 is not particularly limited as long as the strips 20 are loaded in such a way that the fiber direction of the strips 20 is random in order to form a pseudo-isotropic fiber-reinforced material 1. For example, as shown in Figure 1, the strips 20 can be randomly piled in the mold so that when they are made into a fiber-reinforced material 1, their fiber direction will be random, thereby creating a pseudo-isotropic fiber-reinforced material 1. Alternatively, for example, the strips 20 can be regularly arranged and stacked in the mold so that their fiber direction is random, thereby creating a pseudo-isotropic fiber-reinforced material 1. "Fiber direction of the strips" refers to the longitudinal direction (X-axis direction) if the strip 20 is rectangular, as shown in Figure 2, and refers to the direction in which the reinforcing fibers of the fiber-reinforced sheet 3a or 3d constituting the outermost layer of the strip 20 extend if the strip 20 is square. When the fiber-reinforced material 1 contains a binder resin, in S2, the fine pieces 20 and the binder resin may be mixed in advance and then loaded into the mold, or the binder resin may be loaded into the mold separately from the fine pieces 20.

[0045] The fiber-reinforced material 1 is formed by operating a hot press and hot-pressing the numerous pieces 20 loaded into the mold in S2 (S3). The thermoplastic resin, which is the matrix resin (and later mixed binder resin) contained in the pieces 20 and is contained in the fiber-reinforced material 1, generally has higher toughness the larger its weight-average molecular weight, but tends to decrease due to thermal degradation. Therefore, in order to ensure the impact resistance of the fiber-reinforced material 1 recycled from virgin material 2, it is necessary to suppress the thermal degradation of the thermoplastic resin, which is the matrix resin of the fiber-reinforced material 1. However, this requires the use of large amounts of additives such as antioxidants and heat stabilizers, which may increase costs and discourage the recycling of virgin material 2 itself. Therefore, the inventors focused on in-situ polymerizable resins that can increase in molecular weight through repolymerization reactions. However, because polymerization reactivity remains during recycling, if a large thermal history is applied during recycling, the molecular weight may become excessive, reducing fluidity and potentially worsening moldability. Furthermore, unexpected crosslinking reactions may occur, leading to brittleness and a decrease in impact resistance. In light of these findings, after diligent research, the inventors conceived the idea of ​​deliberately lowering (or shortening) the temperature, pressure, and pressurizing time in order to suppress excessive polymerization and crosslinking reactions of the thermoplastic matrix resin (and the binder resin mixed later) contained in the strips 20 during hot pressing. For this reason, the hot pressing conditions are preferably a temperature of 140°C to 220°C, a pressure of 1 MPa to 20 MPa, and a pressurizing time of 0.5 minutes to 10 minutes.

[0046] <Second Embodiment> A second embodiment of the present invention will be described below with reference to Figure 5. Figure 5 is a cross-sectional view obtained by cutting a strip 20' in the YZ plane in the second embodiment of the present invention.

[0047] The second embodiment differs from the first embodiment only in the layered structure of the strips. Components similar to those in the first embodiment are denoted by the same reference numerals as in the first embodiment.

[0048] In the second embodiment, the strip 20' is formed by laminating fiber-reinforced sheets 3a, 3b, core material 4, and fiber-reinforced sheets 3c, 3d in this order.

[0049] The core material 4 is made of a foamed resin, and can be made of foamed materials such as polyurethane, polystyrene, polypropylene, polycarbonate, or polyethylene terephthalate. By using a foamed resin as the core material 4, the fiber-reinforced material 1 can be made lighter, and the core material 4 is crushed during hot pressing under the hot pressing conditions described above, increasing the volume fraction of the fiber-reinforced sheet 3 relative to the fiber-reinforced material 1, thereby further improving impact resistance. For this reason, the density of the core material 4 is, for example, 0.4 g / cm³. 3 The following is preferable:

[0050] In this embodiment, the strip 20' is composed of a single layer of laminate consisting of fiber-reinforced sheets 3a, 3b, core material 4, and fiber-reinforced sheets 3c, 3d. However, it is not limited to this, and the strip 20' may be composed of two or more layers of this laminate. Furthermore, the fiber-reinforced sheets 3 that constitute the strip 20' are not particularly limited as long as there is one or more layers at each position sandwiching the core material 4, but for example, there are five or fewer layers each. In addition, the number of layers of core material 4 that constitute the strip 20' is not particularly limited as long as there is one or more layers, but it is preferable that there be two or fewer layers.

[0051] Referring to Figure 5, the thickness C' of the strips 20' is not particularly limited, but is preferably 1.0 mm or more and 2.0 mm or less. By setting the thickness C' of the strips 20' to 1.0 mm or more, each strip 20' has sufficient thickness, thus increasing the mechanical strength. By setting the thickness C' of the strips 20' to 2.0 mm or less, the gaps that occur between the strips 20' during hot pressing can be reduced, so that gaps are less likely to occur in the fiber-reinforced material 1 after hot pressing, thus increasing the mechanical strength. Furthermore, since foamed resin is used for the core material 4, the strips 20' in this embodiment are thicker than the strips 20 in the first embodiment.

[0052] (Examples) The present invention will be specifically described below with reference to examples.

[0053] [Example 1] In Example 1, the prepreg PPLFR1-242-110-33 (carbon fiber reinforced plastic, reinforcing fiber: PAN-based carbon fiber, thermoplastic matrix resin: in-situ polymerized phenoxy resin, fiber basis weight 110 g / m²) was used. 2 PPLFR2-801-110-35 (carbon fiber reinforced plastic, reinforcing fibers: pitch-based carbon fiber, thermoplastic matrix resin: in-situ polymerized phenoxy resin, fiber basis weight 110 g / m²), is formed by arranging the reinforcing fibers such that their fiber direction is perpendicular to that of PPLFR1-242-110-33, with the fiber direction of the reinforcing fibers being perpendicular to that of PPLFR1-242-110-33. 2 A 0.4 mm thick plate-shaped thermoplastic fiber-reinforced resin composite material (corresponding to virgin material 2 in the above embodiment) was used, in which four fiber-reinforced sheets were laminated in the order of 0-degree sheet / 90-degree sheet / 90-degree sheet / 0-degree sheet to form the laminated structure shown in Figure 3, using NS-TEPreg (with a resin weight content of 35% by weight, hereinafter referred to as "90-degree sheet"), and a virgin material (corresponding to virgin material 2 in the above embodiment) was used. The density of this virgin material was 1.63 g / cm³ 3The weight-average molecular weight of the matrix resin was 70,000. The weight-average molecular weight of the matrix resin was determined by measuring it using gel permeation chromatography (GPC) with tetrahydrofuran (THF) as the eluent and converting it using a standard polystyrene calibration curve. This virgin material was cut in the thickness direction to produce numerous rectangular flakes (corresponding to flake 20 in the above embodiment) with a longitudinal length of 20 mm and a transverse length of 10 mm. The fiber direction of the carbon fibers in the outermost layer of the flakes was the same as the longitudinal direction of the flakes, and of the total number of carbon fibers (reinforcing fibers) contained in these flakes, 45% were carbon fibers (reinforcing fibers) with a length of 15 mm or more. These fragments were piled into a mold on a hot press so that the fiber direction was random. After preheating the mold to 170°C for 9 minutes, the press was hot-pressed at a constant pressure of 15 MPa for 60 seconds at an ambient temperature of 160°C to obtain a fiber-reinforced material measuring 150 mm in length, 150 mm in width, and 4 mm in thickness (corresponding to fiber-reinforced material 1 in the above embodiment). The density of this fiber-reinforced material (recycled material) was 1.59 g / cm³. 3 The weight-average molecular weight of the matrix resin was 76,000. Therefore, the weight-average molecular weight of the matrix resin in the recycled material (hereinafter referred to as the molecular weight ratio) to that of the virgin material was 109%.

[0054] [Method for evaluating the presence or absence of anisotropy] First, to evaluate whether the fiber-reinforced material (recycled material) described above exhibited anisotropy, a bending test was conducted in accordance with JIS K7074. Specifically, for the fiber-reinforced material (recycled material) T obtained by the method described above, test piece a-1 was cut in a predetermined direction, and test piece b-1 was cut in a direction perpendicular to the predetermined direction, as shown in Figure 6. The size of the cut test pieces was 80 mm in length, 10 mm in width, and 4 mm in thickness. Then, a bending test was performed on each test piece using a universal testing machine to obtain the measured value (flexural modulus), and this measured value was substituted into the following formula (1) for calculation. As a result, if the calculated value (hereinafter referred to as the flexural modulus) was within the range of 0.9 to 1.1, it was determined that the fiber-reinforced material (recycled material) obtained by the method described above did not exhibit anisotropy (it had pseudo-isotropy), and the evaluation was set to "None". On the other hand, if the calculated value falls within the range of less than 0.9 or greater than 1.1, it is determined that the fiber-reinforced material (recycled material) obtained by the above method is anisotropic (lacks pseudo-isotropy), and the evaluation is set to "Yes". Flexural modulus = Flexural modulus of specimen a-1 / Flexural modulus of specimen b-1 …(1)

[0055] Table 1 shows the experimental conditions and evaluation results for Example 1. As shown in Table 1, in Example 1, the flexural modulus in the predetermined direction ("X direction" in Table 1) was 34.9 GPa, and the flexural modulus in the orthogonal direction ("Y direction" in Table 1) was 37.1 GPa. The flexural modulus ratio calculated by equation (1) was 0.94. Therefore, it was determined that the recycled material obtained in Example 1 did not exhibit anisotropy, and the evaluation was set to "None".

[0056] [Method for evaluating impact resistance] To evaluate impact resistance, Charpy impact tests were conducted on the aforementioned fiber-reinforced material (recycled material) and virgin material in accordance with ISO 179-1 (JIS K7111-1). Specifically, the same lamination pattern as the virgin material was repeatedly laminated multiple times (10 times in Example 1), and a virgin material S for impact resistance measurement, which would serve as the base material for the Charpy impact test, was created by vacuum forming to the same thickness as the fiber-reinforced material (recycled material) (4 mm in Example 1). Then, referring to Figure 7, a 0-degree oriented test piece A-1 was cut from the virgin material S in the same direction as the fiber direction W of the reinforcing fibers of the outermost layer (TEP-FR-PAN110-33) (0-degree direction), a 45-degree oriented test piece A-2 was cut in a direction inclined at 45 degrees from the fiber direction W, and a 90-degree oriented test piece A-3 was cut in a direction perpendicular to the fiber direction W (90-degree direction). Furthermore, as described above, the recycled material T was evaluated as having no anisotropy (possessing pseudo-isotropy). Therefore, recycled material test specimens AR were cut from recycled material T in random directions. The size of each cut specimen was 80 mm in length, 10 mm in width, and 4 mm in thickness (Type 1 specimen). A notch was then made in the longitudinal center of each specimen, and a 2 J hammer strike was applied with the striking direction being edgewise to measure the Charpy impact strength.

[0057] The ratio of the Charpy impact strength measured on recycled material specimen AR to the maximum value measured on virgin material specimens A-1 to A-3 (hereinafter referred to as the strength retention rate) was calculated. As a result, if the strength retention rate was 75% or higher, it was evaluated as having excellent impact resistance and was given a "○" rating. If the strength retention rate exceeded 100%, it was evaluated as having better impact resistance than virgin material and was given a "◎" rating. On the other hand, if the strength retention rate was less than 75%, it was evaluated as having insufficient impact resistance and was given a "×" rating.

[0058] [Example 2] In Example 2, compared to Example 1, in addition to the 0-degree sheet and 90-degree sheet used in Example 1, a foamed core material (thickness 1.0 mm, density 0.3 g / cm³) was used as the virgin material. 3The difference lies in the use of a 1.4 mm thick thermoplastic fiber-reinforced resin composite material, in which five fiber-reinforced sheets are laminated in the order of 0-degree sheet / 90-degree sheet / core material / 90-degree sheet / 0-degree sheet. The density of this virgin material is 0.71 g / cm³. 3 The weight-average molecular weight of the matrix resin was 71,000. This virgin material was cut in the thickness direction to produce numerous rectangular flakes (corresponding to flake 20' in the above embodiment) with a longitudinal length of 20 mm and a transverse length of 10 mm. The fiber direction of the carbon fibers in the outermost layer of the flakes was the same as the longitudinal direction of the flakes, and of the total number of carbon fibers (reinforcing fibers) contained in these flakes, 45% were carbon fibers (reinforcing fibers) with a length of 15 mm or more. These flakes were deposited in a mold provided in a hot press so that the fiber direction was random, and a fiber-reinforced material (corresponding to fiber-reinforced material 1 in the above embodiment) with a length of 150 mm, a width of 150 mm and a thickness of 4 mm was obtained in the same manner as in Example 1, except that the hot pressing time was 600 seconds. The density of the obtained fiber-reinforced material (recycled material) was 1.42 g / cm³. 3 The weight-average molecular weight of the matrix resin was 75,000. Therefore, the molecular weight ratio was 106%.

[0059] Similar to Example 1, the presence or absence of anisotropy in the fiber-reinforced material (recycled material) obtained in Example 2 was evaluated, and since the flexural modulus was 1.08, it was determined that there was no anisotropy, and the evaluation was set to "none" (see Table 1). Therefore, based on the impact resistance evaluation method described above, the same lamination pattern as the virgin material was repeated three times, and a 4 mm thick virgin material for impact resistance measurement was created by vacuum forming, and test pieces were cut out in the 0-degree direction, 45-degree direction, and 90-degree direction. In addition, recycled material test pieces were cut out in random directions from the recycled material obtained by the method described above, and the Charpy impact strength was measured in the same way as in Example 1, and the impact resistance was evaluated by the strength retention rate. The experimental conditions and evaluation results for Example 2 are shown in Table 1.

[0060] [Example 3] In Example 3, unlike Example 1, the 0° sheet and 90° sheet used in Example 1 were used as virgin materials, and a 0.5 mm thick thermoplastic fiber-reinforced resin composite material in which three fiber-reinforced sheets were laminated in the order of 0° sheet / 90° sheet / 0° sheet was used. The density of this virgin material is 1.58 g / cm 3 , and the weight average molecular weight of the matrix resin was 73,000. This virgin material was cut in the thickness direction to produce a large number of rectangular strips having a length of 20 mm in the longitudinal direction and 10 mm in the transverse direction. The fiber direction of the carbon fibers in the outermost layer of the strips was produced to be the same as the longitudinal direction of the strips, and among the total number of carbon fibers (reinforcing fibers) contained in the strips, carbon fibers (reinforcing fibers) having a length of 15 mm or more accounted for 59%. The strips were deposited in a mold provided in a hot press such that the fiber directions were random, and a fiber-reinforced material having a length of 150 mm, a width of 150 mm and a thickness of 4 mm (corresponding to the fiber-reinforced material 1 in the above embodiment) was obtained by the same method as in Example 1. The density of the obtained fiber-reinforced material (recycled material) is 1.53 g / cm 3 , and the weight average molecular weight of the matrix resin was 73,000. Therefore, the molecular weight ratio was 100%.

[0061] In the same manner as in Example 1, the presence or absence of anisotropy of the fiber-reinforced material (recycled material) obtained in Example 3 was evaluated. Since the flexural elastic ratio was 1.01, it was determined that there was no anisotropy, and the evaluation was rated as "Absent" (see Table 1). Then, based on the impact resistance evaluation method described above, the same lamination pattern as that of the virgin material was repeated 8 times, a virgin material for impact resistance measurement having a thickness of 4 mm was prepared by vacuum molding, 0° direction test pieces, 45° direction test pieces, and 90° direction test pieces were cut out, and recycled material test pieces were cut out in random directions from the recycled material obtained by the above method. The Charpy impact strength was measured by the same method as in Example 1, and the impact resistance was evaluated based on the strength retention rate. The experimental conditions and evaluation results of Example 3 are shown in Table 1.

[0062] [Example 4] In Example 4, the same procedures and evaluations as in Example 3 were performed, except that the strips were made into a rectangular shape of 40 mm x 10 mm. The outermost layer of carbon fibers in the strips was manufactured so that the fiber direction was the same as the longitudinal direction of the strips, and of the total number of carbon fibers (reinforcing fibers) contained in these strips, 59% were carbon fibers (reinforcing fibers) with a length of 15 mm or more. The experimental conditions and evaluation results for Example 4 are shown in Table 1.

[0063] [Comparative Example 1] In Comparative Example 1, the same procedures and evaluations as in Example 1 were performed, except that the strips were made into 10 mm x 10 mm squares. The fiber direction of the carbon fibers in the outermost layer of the strips was the same as that of one of the two pairs of opposite sides of the square strip, and of the total number of carbon fibers (reinforcing fibers) contained in this strip, 0% were carbon fibers (reinforcing fibers) with a length of 15 mm or more. The experimental conditions and evaluation results for Comparative Example 1 are shown in Table 1. In Comparative Example 1, since anisotropy was confirmed in the fiber-reinforced material (recycled material), the test piece of recycled material T used in the Charpy impact test was cut in the same direction as test piece b-1, which had low bending strength.

[0064] [Comparative Example 2] In Comparative Example 2, the same procedure and evaluation as in Example 3 were performed, except that the strips were made into 10 mm x 10 mm squares. The fiber direction of the carbon fibers in the outermost layer of the strips was the same as that of one of the two pairs of opposite sides of the square strip, and of the total number of carbon fibers (reinforcing fibers) contained in this strip, 0% were carbon fibers (reinforcing fibers) with a length of 15 mm or more. The experimental conditions and evaluation results for Comparative Example 2 are shown in Table 1. In Comparative Example 2, since anisotropy was confirmed in the fiber-reinforced material (recycled material), the test piece of recycled material T used for the Charpy impact test was cut in the same direction as test piece a-1, which had low bending strength.

[0065] Note that the "molecular weight ratio" in Table 1 refers to the weight-average molecular weight of the matrix resin in the recycled material relative to the weight-average molecular weight of the matrix resin in the virgin material. [Table 1]

[0066] As shown in Table 1, in all of the examples, the Charpy impact strength of the 0-degree oriented test specimen was the highest among the various test specimens (0-degree oriented test specimen, 45-degree oriented test specimen, and 90-degree oriented test specimen) cut from virgin material. Therefore, the strength retention rate shown in Table 1 is the ratio of the Charpy impact strength of the recycled material test specimen to the Charpy impact strength of the 0-degree oriented test specimen.

[0067] In Examples 1-4, the strength retention rates were 75%, 148%, 91%, and 99%, respectively, resulting in evaluations of "○," "◎," "○," and "○." On the other hand, in Comparative Examples 1 and 2, the strength retention rates were all below 75%, resulting in evaluations of "×." Furthermore, from Examples 3-4 and Comparative Example 2, it was confirmed that impact resistance tends to improve as the length of the flakes obtained from virgin material increases. In Example 2, the strength retention rate exceeded 100% because the core material contained in the flakes was crushed by hot pressing during the manufacturing of the recycled material, increasing the volume fraction of carbon fiber reinforced plastic (0-degree sheet and 90-degree sheet) relative to the recycled material.

[0068] (modified version) In the embodiment described above, the virgin material 2 was processed into a number of rectangular pieces 20. However, the shape of the pieces is not limited to rectangular, and may be an irregular shape obtained by coarsely crushing the virgin material 2. In this case, "length of the piece" refers to the longest distance between any two points taken on the contour line when viewing the piece from above. [Explanation of symbols]

[0069] 1. Fiber-reinforced material (recycled material) 2. Thermoplastic fiber-reinforced resin composite material (virgin material) before disposal 3. Fiber-reinforced sheets 3a, 3d: Fiber-reinforced sheets constituting the outermost layer 4. Core material 20 fragments

Claims

1. A pseudo-isotropic fiber-reinforced material comprising fragments of a thermoplastic fiber-reinforced resin composite material before its disposal, The aforementioned thermoplastic fiber-reinforced resin composite material before disposal is a laminate, and the laminate comprises at least one layer of fiber-reinforced sheets containing a reinforcing fiber substrate and a thermoplastic matrix resin. In a Charpy impact test in accordance with ISO 179-1, the Charpy impact strength of the fiber-reinforced material is 75% or more of the maximum Charpy impact strength of the thermoplastic fiber-reinforced resin composite material before disposal, as determined by the following measurement method. The length of the aforementioned strip is greater than 15 mm and less than or equal to 100 mm. A fiber-reinforced material characterized by the following features. (1) The fiber direction of the reinforcing fibers contained in the fiber-reinforced sheet that constitutes the outermost layer of the thermoplastic fiber-reinforced resin composite material before disposal is defined as 0°, and test pieces for Charpy impact strength measurement in accordance with ISO 179-1 are cut out in three directions: 0°, 45°, and 90°. (2) The Charpy impact strength of each test piece cut out in (1) is measured in accordance with ISO 179-1. (3) The maximum value among the measurements in (2) shall be defined as the maximum Charpy impact strength.

2. The aforementioned segments are formed in a rectangular shape with an aspect ratio of 1.0 to 4.

0. The fiber-reinforced material according to claim 1, characterized in that...

3. Of the total number of reinforcing fibers contained in the aforementioned fragment, 20% or more of the reinforcing fibers are 15 mm or longer. The fiber-reinforced material according to claim 1, characterized in that...

4. The aforementioned thermoplastic fiber-reinforced resin composite material before disposal is Multiple fiber-reinforced sheets, each having a unidirectional or cross-woven reinforcing fiber base material, are laminated together to form this structure. The fiber-reinforced material according to claim 1, characterized in that...

5. The aforementioned thermoplastic fiber-reinforced resin composite material before disposal is The configuration comprises a core material, which is a foamed resin, sandwiched between at least one layer of the fiber-reinforced sheet. The fiber-reinforced material according to claim 1, characterized in that...

6. The thermoplastic matrix resin is a phenoxy resin. The fiber-reinforced material according to claim 1, characterized in that...

7. A method for producing a fiber-reinforced material according to any one of claims 1 to 6, A processing step of processing the aforementioned thermoplastic fiber-reinforced resin composite material before disposal into a large number of the aforementioned small pieces, A loading step in which the fine pieces are loaded into the mold set in the hot press machine so that the fiber direction of the fine pieces is random, A hot pressing step is performed on the mold into which the aforementioned pieces are inserted, A method for producing a fiber-reinforced material, characterized by comprising the following:

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