Impact absorbing material

Abstract

Provided is an impact-absorbing member of which the shape can be designed relatively freely, which is lightweight, and which has high collision safety. This impact-absorbing member has one or more plate-shaped members, and is characterized in that: at least one of the plate-shaped members is formed by laminating a thermoplastic resin tape containing inorganic fibers; in the plate-shaped member containing the inorganic fibers, the inorganic fibers are oriented in a direction perpendicular to the thickness direction of the plate-shaped member, and have random orientations in a plane along the perpendicular direction; and the inorganic fibers account for 30-60 vol% in the plate-shaped member.

Description

[Technical Field]

[0001] The present invention relates to an impact absorbing member. [Background technology]

[0002] Conventionally, crash energy-absorbing members that absorb crash energy have been arranged to protect occupants in vehicles such as passenger cars. For example, crash energy-absorbing members such as front side members and rear side members are arranged in locations on a vehicle where a crash is expected to be applied. In a crash energy-absorbing member, crash energy is applied in the axial direction, which is a direction in which the crash energy can be efficiently absorbed, and when the magnitude of the crash energy exceeds the yield stress, the crash energy-absorbing member deforms to absorb the impact.

[0003] It is important for impact absorbing members to absorb collision energy sufficiently and efficiently, and impact absorbing members are often manufactured using metal such as steel plate.

[0004] For example, Patent Document 1 discloses an automobile collision energy absorption component that is a cylindrical member made of a metal plate such as a steel plate. The cylindrical member is made by spot-welding a hat-shaped cross-section member having a top plate portion, a vertical wall portion, and a flange portion to a flat plate-shaped member at the flange portion, and it is disclosed that when a collision object collides with the axial tip of the cylindrical member, collision energy is efficiently absorbed.

[0005] Although the shock absorbing member of Patent Document 1 can absorb collision energy, it is difficult to say that it is lightweight because it uses a metal plate such as a steel plate. In recent years, while high collision safety is required, there is also a demand for lighter impact absorbing members to improve fuel efficiency. However, when a metal plate such as a steel plate is used as in Patent Document 1, there is a limit to how much weight can be reduced.

[0006] In view of these problems with metal impact absorbing members, resin impact absorbing members have been proposed, which offer a high weight reduction effect. However, simply replacing a metal impact absorbing member with a resin impact absorbing member results in a decrease in impact absorption. On the other hand, if the impact absorbing member is made thicker to avoid a decrease in impact absorption, the weight of the impact absorbing member increases, preventing fuel economy from improving. Impact absorbing members such as those in Patent Documents 2 to 4 have been disclosed as impact absorbing members that use resin to achieve weight reduction while maintaining high collision safety.

[0007] Patent Document 2 discloses a front side member comprising a fiber-reinforced plastic energy absorption section with a cylindrical cross section made of reinforcing fibers and resin, and a support section that is connected to the fiber-reinforced plastic energy absorption section and is also formed of fiber-reinforced plastic and joined to a vehicle body part, and describes a method of producing an energy absorption member by sheet winding a continuous fiber sheet impregnated with a thermosetting resin, or by pre-shaping a woven fabric of reinforcing fibers and performing an RTM method.

[0008] Patent Document 3 discloses, as an energy absorbing member, a fiber-reinforced resin hollow cylinder composed of reinforcing fiber yarns and a resin composition impregnated into the reinforcing fiber yarns, and discloses that the hollow cylinder is formed by a filament winding method.

[0009] Patent Document 4 discloses an impact absorbing component for a vehicle having a cylindrical portion and a top surface portion formed to close one of the axial openings of the cylindrical portion, and discloses that the impact absorbing component of Patent Document 4 absorbs impact energy by compressively deforming in the axial direction due to an impact load input to the top surface portion. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 2019-206246 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-271875 [Patent Document 3] International Publication No. 2020 / 217573 [Patent Document 4] Patent Publication No. 2021-67291 Summary of the Invention [Problem to be solved by the invention]

[0011] However, since the reinforcing fibers (reinforcing fibers) in the absorbing members of Patent Documents 2 and 3 are present as continuous fibers, the molding costs are high and the moldability is poor, limiting the shapes that can be molded, making it difficult to form the impact absorbing member into a complex shape as shown in Figures 1 and 2 described below.

[0012] The shock absorbing member of Patent Document 4 has a special shape in which at least one rib for supporting the load during an impact is connected to the top surface portion on the inside of the cylindrical portion and is spaced apart from the cylindrical portion, which limits the shape of the shock absorbing member. Also, because the shock absorbing member of Patent Document 4 is designed to be molded by injection molding, it is difficult to increase the amount of energy absorbed by the shock absorbing member when the material breaks, which results in low shock absorption.

[0013] An object of the present invention is to provide a shock absorbing member that can be relatively freely designed in shape, is lightweight, and has high collision safety. [Means for solving the problem]

[0014] As a result of intensive research conducted by the present inventors to solve the above-mentioned problems, they discovered an impact absorbing member having a plate-shaped member formed by laminating thermoplastic resin tapes containing inorganic fibers, and by controlling the orientation of the inorganic fibers in the plate-shaped member to satisfy predetermined conditions, which allows for a reduction in weight while providing high collision safety, and they arrived at the present invention.

[0015] That is, the present invention comprises the following configurations. [1] An impact absorbing component having one or more plate-shaped members, at least one of which is formed by laminating thermoplastic resin tapes containing inorganic fibers, characterized in that in the plate-shaped member containing inorganic fibers, the inorganic fibers are oriented in a direction perpendicular to the thickness direction of the plate-shaped member, and are randomly oriented in the plane along the perpendicular direction, and the inorganic fibers account for 30 to 60 volume % of the plate-shaped member. [2] The impact absorbing member according to [1], wherein the inorganic fibers include at least one of glass fibers and carbon fibers. [3] The impact absorbing member according to [1] or [2], wherein the inorganic fibers have an average fiber length of 10 to 150 mm. [4] The impact absorbing member according to any one of [1] to [3], wherein the melt flow rate of the resin contained in the thermoplastic resin tape is 15 to 100 g / 10 min when measured at a temperature of 230°C and a load of 2.16 kg. [5] The impact absorbing member according to any one of [1] to [4], wherein the thermoplastic resin tape has a length of 10 mm to 100 mm, a width of 5 mm to 50 mm, and a thickness of 0.05 mm to 0.3 mm. [6] An impact absorbing member having a cylindrical portion and a bottom surface portion, wherein the cylindrical portion and the bottom surface portion are made of the plate-like member, the bottom surface portion closes one bottom surface of the cylindrical portion, and the difference between the content of the inorganic fibers in the cylindrical portion and the content of the inorganic fibers in the bottom surface portion is 5 volume % or less, as described in any of [1] to [5]. [7] The impact absorbing member according to any one of [1] to [6], wherein the inorganic fibers have an average orientation angle of 0 to 20° with respect to a plane perpendicular to the thickness direction in the bottom surface portion. [Effects of the Invention]

[0016] The present invention provides an impact absorbing member having a plate-shaped member formed by laminating thermoplastic resin tapes containing inorganic fibers, and by controlling the orientation of the inorganic fibers in the plate-shaped member to satisfy predetermined conditions, it is possible to achieve both weight reduction and high collision safety. Furthermore, the impact absorbing member of the present invention has excellent moldability and can be relatively freely shaped, so it can be used not only in impact absorbing devices for passenger cars, but also in vehicles other than passenger cars and various structures. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a perspective view of an impact absorbing member according to an embodiment of the present invention; [Figure 2] FIG. 10 is a perspective view of a modified example of the impact absorbing member according to the embodiment of the present invention. [Figure 3] FIG. 10 is a perspective view of a further modified example of the impact absorbing member according to the embodiment of the present invention. [Figure 4] FIG. 2 is a bottom view of the impact absorbing member of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below.

[0019] The impact absorbing member of the present invention has one or more plate-shaped members. In this specification, the term "plate-shaped member" includes not only planar members but also curved plate members such as corrugated plates, cylinders, semi-cylinders, and hemispheres, folded members such as zigzags, and may be any of these shapes or a combination of these shapes.

[0020] <Plate-shaped components> In the present invention, at least one of the plate-like members is formed by laminating thermoplastic resin tapes containing inorganic fibers, and in the plate-like member containing inorganic fibers, the inorganic fibers are oriented in a direction perpendicular to the thickness direction of the plate-like member and are randomly oriented in the plane along the perpendicular direction. Note that, hereinafter, a plate-like member "formed by laminating thermoplastic resin tapes containing inorganic fibers, and in the plate-like member containing inorganic fibers, the inorganic fibers are oriented in a direction perpendicular to the thickness direction of the plate-like member and are randomly oriented in the plane along the perpendicular direction" is referred to as a "predetermined plate-like member."

[0021] In the specified plate-shaped member, the inorganic fibers are oriented in a direction perpendicular to the thickness direction, thereby exhibiting excellent collision safety. Below, we will explain why the impact absorbing member of the present invention having the specified plate-shaped member has excellent impact absorption (impact safety). Before that, we will explain the fracture state when a metal impact absorbing member is used and the problems that arise when an impact absorbing member is molded using a thermoplastic resin by a conventional method.

[0022] In the case of metal impact absorbing components, the destruction mode is one in which the entire component breaks, and the impact energy cannot be absorbed stably. For this reason, metal impact absorbing components are designed so that when impact energy is applied, they buckle locally while the overall collapse progresses in a bellows-like pattern.

[0023] When a shock-absorbing component is molded using a thermoplastic resin containing inorganic fibers and designed to have the same failure mode as a metal shock-absorbing component, the low elongation of the thermoplastic resin results in brittle failure rather than the ductile failure seen in metal shock-absorbing components. When brittle failure occurs, the impact load applied to the shock-absorbing component fluctuates significantly during the fracture of the shock-absorbing component, making it impossible to stably absorb the impact energy and potentially causing the shock-absorbing component to become unable to withstand the impact load during the fracture process.

[0024] Furthermore, if brittle fracture occurs, the resin will shatter at the time of fracture, which could cause secondary disasters due to flying fragments.

[0025] The impact-absorbing member of the present invention has a predetermined plate-shaped member, in which inorganic fibers are oriented perpendicular to the thickness direction. When a predetermined plate-shaped member in which inorganic fibers are oriented perpendicular to the thickness direction is used, the plate-shaped member exhibits excellent impact absorption properties due to fracture behavior in which the plate-shaped member splits perpendicularly while continuing in the direction of the inorganic fiber orientation. The reason for this fracture behavior is believed to be that the predetermined plate-shaped member resembles a laminate of multiple thermoplastic resin layers containing inorganic fibers, and when impact energy is applied to the predetermined plate-shaped member, fracture progresses with delamination. Furthermore, the impact load applied to the plate-shaped member when delamination occurs is more stable than the impact load applied to the plate-shaped member when buckling occurs, thereby further improving energy absorption efficiency (shock absorption). Furthermore, when the impact-absorbing member of the present invention is used, fracture occurs with delamination, so the resin does not shatter upon fracture, significantly reducing the amount of flying debris.

[0026] In a given plate-like member, the direction of the inorganic fibers does not have to be strictly perpendicular to the "direction perpendicular to the thickness direction of the plate-like member." For example, in a shock-absorbing member having a bottom surface that is a plate-like member, the average orientation angle of the inorganic fibers with respect to the plane perpendicular to the thickness direction is preferably 0 to 20°, and in a shock-absorbing member having a tubular portion that is a plate-like member, the average orientation angle of the inorganic fibers with respect to the plane perpendicular to the thickness direction at the axial center of the tubular portion is preferably 0 to 35°. A method for measuring the average orientation angle will be described later. In the following, the "axial direction" refers to the direction in which the shock-absorbing member is compressively deformed by an impact load.

[0027] In addition, in a given plate-like member, the inorganic fibers are randomly oriented in the plane perpendicular to the thickness direction of the plate-like member. "Random orientation in the plane" means pseudo-isotropy, and the in-plane orientation parameter (cos 2 θy / cos2 θx) is preferably greater than 0.67 and less than 1.5, and more preferably 0.75 or more and 1.33 or less. When the in-plane orientation parameter is 1, it means that the carbon fibers are oriented completely randomly in the in-plane direction, and when the in-plane orientation parameter is out of the above range, the randomness of the fiber orientation in the in-plane direction is lost, which may result in a decrease in impact absorption. The in-plane orientation parameter is measured as follows, and the in-plane orientation parameters of the plate-like members (bottom portion and tubular portion of the impact absorbing member) used in the examples described later are all greater than 0.67 and less than 1.5. The in-plane orientation parameter is calculated for each inorganic fiber by calculating cos 2 θx and cos 2 Calculate θy and cos 2 The average value of θy is cos 2 The value divided by the average value of θx is the in-plane orientation parameter (cos 2 θy / cos 2 θx).

[0028] <In-plane orientation parameter measurement method> Five specimens measuring approximately 15 mm x 25 mm were cut from the plate-shaped material, and three-dimensional X-ray CT measurements were performed on each specimen. Cartesian coordinates were determined so that the X and Y axes were in the in-plane direction of the plate-shaped material, and the Z axis was in the thickness direction. The specimens were cut with a length in the X-axis direction of 15 mm and a length in the Y-axis direction of 25 mm. Using a Yamato Scientific three-dimensional X-ray CT scanner (TDM1000-IS), data were collected by rotating the scanner 360 degrees at intervals of 0.5 degrees or less under the following conditions: acceleration voltage 40-60 kV, tube current 10-40 μA, and integration time 0.5-1 s. Reconstruction was performed under conditions such that the pixel size was 50 μm or less. Only the data in the 15 mm x 15 mm x thickness region of the plate-shaped material was extracted from the reconstructed data, and the in-plane orientation parameters were calculated using the anisotropy measurement function of the Tri3D BON software from Ratoc Systems Engineering.

[0029] <Thermoplastic resin tape> The length of the thermoplastic resin tape is preferably 10 to 100 mm, more preferably 20 to 50 mm. If the length is less than 10 mm, it may be difficult to cause the above-mentioned delamination, and if it exceeds 100 mm, the flowability during molding may be poor.

[0030] The width of the thermoplastic resin tape is preferably 5 to 50 mm, more preferably 10 to 40 mm. If the width is outside the above range, production efficiency may decrease.

[0031] The thickness of the thermoplastic resin tape is preferably 0.05 to 0.3 mm, and more preferably 0.07 to 0.2 mm. If the thickness is less than 0.05 mm, production efficiency may be reduced, and if it exceeds 0.3 mm, the impregnation of the thermoplastic resin into the inorganic fibers may be insufficient.

[0032] <Thermoplastic resin> The thermoplastic resin is not particularly limited, and examples thereof include polyamide-based resins such as nylon 6, nylon 11, nylon 66, and nylon 46; polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate; polyolefin-based resins such as polyethylene and polypropylene; polyether ketone resins; polyphenylene sulfide resins; polyetherimide resins; and polycarbonate resins. The thermoplastic resin may be a modified product of any of the above-listed resins. The thermoplastic resin may be a single type or a combination of two or more types.

[0033] The modified thermoplastic resin may be, for example, an acid-modified one. The acid-modified thermoplastic resin has an acid-modified group introduced therein. The type of acid-modified group is not particularly limited, and the acid-modified group may be one type or two or more types. However, a carboxylic acid anhydride residue (-CO-O-OC-) or a carboxylic acid residue (-COOH) is preferred. The acid-modified group may be introduced by any compound. Examples of the carboxylic acid anhydride include unsaturated carboxylic acid anhydrides such as maleic anhydride and itaconic anhydride. Examples of the carboxylic acid include unsaturated polycarboxylic acids such as maleic acid, itaconic acid, and fumaric acid; saturated polycarboxylic acids such as succinic acid, glutaric acid, and adipic acid; and unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid. Among these, unsaturated carboxylic acid anhydrides are preferred. Unsaturated carboxylic acids or unsaturated carboxylic acid anhydrides can be used as radical polymerizable monomers to modify thermoplastic resins. Polycarboxylic acids can be used as polycondensation monomers to modify thermoplastic resins. In this specification, the term "thermoplastic resin" also encompasses modified thermoplastic resins such as acid-modified thermoplastic resins.

[0034] The thermoplastic resin used in the present invention preferably contains at least one of polyamide resin, polyolefin resin, and acid-modified polyolefin resin from the viewpoints of ease of handling and cost, and is preferably an acid-modified polyolefin resin from the viewpoint of improving the strength of the thermoplastic resin molded body by improving the interfacial adhesion with inorganic fibers. Furthermore, the thermoplastic resin used in the present invention may contain additives such as a crystal nucleating agent, a heat deterioration inhibitor, an oxidation deterioration inhibitor, and an ultraviolet absorber, as needed, for the purpose of improving physical properties, moldability, and durability. The content of these additives can vary depending on the purpose, but the total content of the additives is preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less, based on 100% by mass of the thermoplastic resin.

[0035] The thermoplastic resin used in the present invention preferably has a melt flow rate of 15 to 100 g / 10 min, more preferably 30 to 80 g / 10 min, and even more preferably 40 to 60 g / 10 min, when measured at 230°C under a load of 2.16 kg. If the melt flow rate is less than 15 g / 10 min, the inorganic fibers may not be sufficiently impregnated with the thermoplastic resin, resulting in reduced impact absorption. On the other hand, if the melt flow rate is greater than 100 g / 10 min, the molecular weight of the thermoplastic resin may be low, resulting in reduced toughness and reduced impact absorption. In this specification, the melt flow rate of a resin is sometimes referred to as "MFR." MFR is measured in accordance with ISO 1133-1, but when using commercially available products, the value listed in a catalog may be used. The preferred range of MFR of the resin contained in the thermoplastic resin tape used in the present invention is the same as the preferred range of MFR of the thermoplastic resin used in the present invention.

[0036] <Inorganic fibers> The inorganic fibers used in the present invention may be any inorganic fibers that are solid at the processing temperature of the thermoplastic resin used, and preferably include at least one of glass fiber and carbon fiber, and more preferably include glass fiber. The inorganic fibers are preferably fully opened, and by fully opening the inorganic fibers, the impregnation of the thermoplastic resin into the inorganic fibers can be improved, resulting in improved impact absorption. Furthermore, it is preferable to use inorganic fibers in which single fibers are bundled together, and the total cross-sectional area of ​​the bundled inorganic fibers is 0.2 to 1.5 mm. 2 It is preferable that the thickness is 0.4 to 1.0 mm. 2 It is more preferable that:

[0037] The inorganic fibers are preferably short fibers, and specifically, the average fiber length of the inorganic fibers is preferably 5 to 200 mm, more preferably 10 to 150 mm, even more preferably 20 to 100 mm, and particularly preferably 30 to 50 mm.

[0038] The average fiber diameter of the inorganic fibers is preferably 3 to 30 μm, and more preferably 5 to 20 μm. If the average fiber diameter is less than 3 μm, the impact absorption properties may decrease. If the average fiber diameter is more than 30 μm, the number of inorganic fibers in the impact absorbing member may decrease, and the impact absorption properties may decrease.

[0039] The average fiber length and average fiber diameter of the inorganic fibers can be determined by arithmetically averaging values ​​measured in accordance with JIS R 3420 using a scanning electron microscope (SEM).

[0040] (glass fiber) The glass fiber is not particularly limited, and examples thereof include known glass fibers such as E-glass, S-glass, and C-glass, with E-glass being preferred. Only one type of glass fiber may be used, or two or more types may be used.

[0041] (carbon fiber) The carbon fiber is not particularly limited, and examples thereof include polyacrylonitrile (PAN)-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, cellulose-based carbon fiber, vapor-grown carbon fiber, and graphitized fibers thereof. The carbon fiber preferably includes PAN-based carbon fiber. PAN-based carbon fiber is carbon fiber made from polyacrylonitrile fiber. Pitch-based carbon fiber is carbon fiber made from petroleum tar or petroleum pitch. Cellulose-based carbon fiber is carbon fiber made from viscose rayon, cellulose acetate, or the like. Vapor-grown carbon fiber is carbon fiber made from hydrocarbons or the like. Only one type of carbon fiber may be used, or two or more types may be used.

[0042] <Inorganic fiber content> The inorganic fiber content in a given plate-shaped member is 30 to 60 volume %, preferably 35 to 55 volume %, and more preferably 40 to 50 volume %. If it is less than 30 volume %, the inorganic fibers will not provide the reinforcing effect of the plate-shaped member, and the stability of the impact absorbing member against collisions will be reduced, resulting in unstable fracture behavior of the impact absorbing member and reduced impact absorption. On the other hand, if it exceeds 60 volume %, production efficiency will decrease and the inorganic fibers will not be sufficiently impregnated with the thermoplastic resin, resulting in unstable fracture behavior of the impact absorbing member and reduced impact absorption.

[0043] <Shock absorbing material> The impact absorbing member of the present invention preferably has a tubular portion made of a predetermined plate-like member. By aligning the axial direction of the tubular portion with the direction of impact, impact can be absorbed efficiently, and since the tubular portion is similar to a state in which multiple thermoplastic resin layers containing inorganic fibers are laminated, when impact energy is applied to the predetermined plate-like member, delamination occurs and destruction progresses, thereby further improving collision safety.

[0044] Furthermore, it is preferable that the impact absorbing member has a bottom portion that closes one bottom surface of the cylindrical portion in addition to the cylindrical portion made of a predetermined plate-like member, because closing the bottom surface of the cylindrical portion with the bottom portion can efficiently disperse impact over the entire circumferential direction of the cylindrical portion. In the impact absorbing member of the present invention, the bottom portion is preferably a plate-like member, more preferably the bottom portion is a predetermined plate-like member, and even more preferably the cylindrical portion and the bottom portion are made of a predetermined plate-like member.

[0045] The shape of the shock absorbing member will be described below with reference to FIG. 1. FIG. 1 is a perspective view of a shock absorbing member according to an embodiment of the present invention. The rectangular shock absorbing member 11 has four rectangular tubular portions 13 extending vertically from the outer periphery of one surface of a bottom portion 12 of a plate-like member that is rectangular in shape when viewed in the thickness direction. The shock absorbing member 11 is partitioned by the bottom portion 12 and the tubular portions 13, thereby forming four rectangular internal spaces 14 in a lattice pattern inside the shock absorbing member 11. In other words, the external shape of the shock absorbing member 11 is such that plate-like members are erected in the vertical direction from the four sides that are the outer periphery of the bottom portion 12. Note that the bottom portion 12 and the tubular portions 13 form the internal space 14, but the plate-like members of the tubular portions 13 located inside the shock absorbing member 11 are commonly used to form the two internal spaces 14. In addition, the axial bottom surfaces of all four internal spaces 14 are blocked by bottom surface portions 12, and the side surfaces of all four internal spaces 14 are formed by cylindrical portions 13, but the top surfaces of all four internal spaces 14 are not blocked.

[0046] The bottom surface portion 12 is not particularly limited, and examples thereof include a plate-shaped, mesh-shaped, and lattice-shaped member. Among these, a plate-shaped member is preferable, but as long as it covers one bottom surface of the tubular portion 13, the bottom surface portion 12 does not need to be completely flat and may have partial irregularities. The thickness of the bottom surface portion is not particularly limited, and is preferably 1 to 8 mm, and more preferably 2 to 6 mm. The thickness of the bottom surface portion 12 refers to the thickness of the thinnest part of the bottom surface portion, and the thickness of the thickest part of the bottom surface portion 12 is preferably no more than twice the thickness of the bottom surface portion. The shape of the bottom surface portion 12 as viewed in the thickness direction (axial direction of the shock-absorbing member 11) is not particularly limited, and examples thereof include a circle, an ellipse, and a polygon, but it may also be a part of these shapes or a combination of these shapes. From the viewpoint of increasing the moment of inertia of area of ​​the energy absorption region and absorbing energy efficiently, the shape of the bottom surface portion 12 as viewed in the thickness direction is preferably a circle, an ellipse in which the ratio of the minor axis to the major axis is 0.5 to less than 1, an equilateral triangle, a triangle in which the ratio of the shortest side to the longest side is 0.5 to less than 1, a square, a rectangle in which the ratio of the shortest side to the longest side is 0.5 to less than 1, a regular hexagon, or a hexagon in which the ratio of the shortest side to the longest side is 0.5 to less than 1. Furthermore, the bottom surface portion 12 may have through holes for ventilation, bolt fastening, wiring, etc. In this case, the holes may be formed in a mold using a shear or the like simultaneously with molding the impact absorbing member, or may be formed as a post-processing step using a drill, punching, cutting, or the like.

[0047] The cylindrical portion 13 is provided so as to extend from the bottom surface portion 12 in a direction perpendicular to the bottom surface of the bottom surface portion 12 (in the thickness direction of the bottom surface portion), and the cylindrical portion 13 is preferably a plate-like member. When the cylindrical portion 13 is a plate-like member, collision energy is applied along the axial direction of the plate-like member, and when the magnitude of the collision energy exceeds the limit value of the plate-like member, the plate-like member deforms to absorb the impact, thereby efficiently absorbing the impact energy. Furthermore, from the viewpoint of efficiently absorbing collision energy, it is preferable that the heights of all the cylindrical portions 13 are the same.

[0048] Furthermore, from the viewpoint of efficiently absorbing collision energy, the cylindrical portion 13 is preferably in a shape in which a plate-shaped member is erected in the vertical direction of the bottom portion 12 from at least a part of the outer periphery of the bottom portion 12, and more preferably in a shape in which a cylindrical member is erected in the vertical direction of the bottom portion 12 from the entire outer periphery of the bottom portion 12, but in order to adjust the amount of collision energy absorbed, the cylindrical portion 13 may also be in a shape in which a plate-shaped member is erected in the vertical direction of the bottom portion 12 from a position inside the outer periphery of the bottom portion 12.

[0049] The height of the cylindrical portion 13 is not particularly limited, but when the shape of the bottom portion 12 as viewed in the thickness direction is a circle, ellipse, equilateral triangle, square, rectangle, regular hexagon, or hexagon, the height is preferably 0.5 to 3 times, more preferably 0.6 to 2 times, and even more preferably 0.65 to 1.5 times the shortest side or minor diameter of the bottom portion 12. If the height of the cylindrical portion 13 is less than 0.5 times the shortest side or minor diameter of the bottom portion 12, when impact energy is applied to the cylindrical portion 13 and it attempts to break or deform, there is insufficient space for the break or deformation, which may result in unstable breaking behavior of the shock-absorbing member 11 and reduced shock absorption. On the other hand, if the height is more than 3 times the shortest side or minor diameter of the bottom portion 12, there is a high possibility of buckling when an impact load is applied, and the molding cost may increase due to the need to set a high molding pressure during molding.

[0050] The cylindrical portion 13 is preferably provided in a direction perpendicular to the bottom surface of the bottom portion 12, but does not have to be strictly perpendicular as long as shock absorption is ensured. In this case, the angle between the bottom portion 12 and the cylindrical portion 13 is preferably 30 to 120°, and more preferably 40 to 90°. Note that the cylindrical portion 13 may be provided with an angle to ensure the draft angle of the mold, as long as it does not impair the intent of the present invention.

[0051] There are no particular limitations on the thickness of the cylindrical portion 13, and it may be the same as or different from the thickness of the bottom portion 12, but it is preferably 1 to 8 mm, more preferably 2 to 6 mm.

[0052] In the impact absorbing member of the present invention, it is preferable that the cylindrical portion 13 forms two or more closed cross-sectional structures when viewed from the axial direction of the cylindrical portion 13 (thickness direction of the bottom surface portion 12). The closed cross-sectional structure is not particularly limited, but from the viewpoint of efficiently absorbing collision energy, it is preferable that it has a shape that is line-symmetric or point-symmetric, and examples thereof include a circle, an ellipse, a polygon, or a combination of these shapes, but a triangle, a rectangle, a square, or a hexagon is preferable because it allows the internal spaces 14 to be arranged in a shape without gaps.

[0053] The difference between the inorganic fiber content in the cylindrical portion and the inorganic fiber content in the bottom portion is preferably 5% by volume or less, more preferably 3% by volume or less, even more preferably 2% by volume or less, and particularly preferably 1.5% by volume or less. If the difference exceeds 5% by volume, the impact energy (stress) may be concentrated in an unexpected location, potentially reducing impact absorption. Furthermore, when using commercially available stampable sheets such as GMT (Glass Mat Reinforced Thermoplastics), the tip of the cylindrical portion may be in a resin-rich state with a lower inorganic fiber content than the other portions. This can lead to the impact absorbing material shattering into pieces as the damage progresses, or the increased elongation of the impact absorbing material can cause buckling-like deformation, similar to the damage behavior of metal impact absorbing materials, resulting in the impact absorbing material breaking. In a shock absorbing member having multiple internal spaces, the "difference between the inorganic fiber content in the cylindrical portion and the inorganic fiber content in the bottom portion" refers to the greater absolute value of the difference between the inorganic fiber content at the tip of the axial direction of the outermost cylindrical portion and the inorganic fiber content at the tip of the axial direction of each cylindrical portion other than the outermost cylindrical portion. For the bottom portion, the inorganic fiber content is measured at the location farthest from the point where it is joined to the cylindrical portion (for example, the diagonally shaded area (measurement location 41) in Figure 4 for the shock absorbing member in Figure 1).

[0054] 2 is a perspective view of a modified example of a shock-absorbing member according to an embodiment of the present invention. Shock-absorbing member 21 has a rectangular parallelepiped shape. A bottom surface 22 of a plate-like member has a rectangular shape when viewed in the thickness direction. A hexagonal prism-shaped cylindrical portion 23 is provided vertically from one surface of the bottom surface 22 to form a honeycomb structure. By being partitioned by bottom surface 22 and cylindrical portion 23, four hexagonal prism-shaped internal spaces 24 are provided inside shock-absorbing member 21 to form a honeycomb structure. However, near the outer periphery of shock-absorbing member 21 in the axial direction, there are also portions shaped like partial hexagonal prisms, such as internal space 25. Furthermore, shock-absorbing member 21 has an external shape in which plate-shaped members are provided vertically from the four sides of the outer periphery of bottom surface 22. Note that the internal spaces 24 and 25 are formed by the cylindrical portion 23, and the plate-like member of the cylindrical portion 23 located inside the impact absorbing member 21 is used in common to form the two internal spaces 24, to form the internal space 24 and the internal space 25, or to form the two internal spaces 25. The bottom surfaces of the internal spaces 24 and 25 in the axial direction are closed by the bottom surface portion 22, and the side surfaces are all formed by the cylindrical portion 23, but the top surfaces are not closed.

[0055] 3 is a perspective view of another modified example of the impact absorbing member according to the embodiment of the present invention. Impact absorbing member 31 is a plate-shaped member having a rectangular shape when viewed in the thickness direction. Four cylindrical tubular portions 33 are provided at the center of bottom portion 32 of the impact absorbing member 31 so as to extend vertically from one surface of bottom portion 32. Bottom portion 32 and tubular portions 33 are formed so as to minimize gaps (internal spaces 35 described below) between tubular portions 33, and internal space 35 is formed so as to be surrounded by three adjacent internal spaces 34. The axial bottom surfaces of internal spaces 34 and 35 are closed by bottom portion 32, and all side surfaces are formed by tubular portions 33, but the top surfaces are not closed.

[0056] <Method of manufacturing impact absorbing member> The method for manufacturing an impact-absorbing component of the present invention is not particularly limited, as long as the orientation direction of the inorganic fibers in a predetermined plate-shaped component contained in the impact-absorbing component satisfies the above-mentioned requirements and the inorganic fiber content in the predetermined plate-shaped component falls within a certain range. However, for example, a preferred method involves manufacturing a relatively thin thermoplastic resin sheet using opened inorganic fiber roving and a thermoplastic resin, cutting the thermoplastic resin sheet to obtain a thermoplastic resin tape, then using the cut thermoplastic resin tape to produce a relatively thick thermoplastic resin sheet, and finally molding the thick thermoplastic resin sheet into a mold to obtain an impact-absorbing component of the desired shape. Note that, hereinafter, the term "containing inorganic fibers" will be omitted and the term "thermoplastic resin tape" will be simply used. The relatively thin thermoplastic resin sheet will sometimes be referred to as a "thin thermoplastic resin sheet," and the relatively thick thermoplastic resin sheet will sometimes be referred to as a "thick thermoplastic resin sheet." Details of each step of the manufacturing method are described below.

[0057] An inorganic fiber roving is opened, and the opened inorganic fiber roving is introduced into a tank (hereinafter referred to as a resin impregnation tank) containing a heated and melted thermoplastic resin, and the inorganic fiber roving is continuously impregnated with the thermoplastic resin. After the opened inorganic fiber roving is impregnated with the resin, it is crushed with a shaping roller and cooled and solidified, thereby producing a thin thermoplastic resin sheet. The thin thermoplastic resin sheet is then cut with a cutter such as a fan cutter to produce a thin thermoplastic resin sheet.

[0058] In the opening step, it is preferable to align the inorganic fibers and then fully open them before use. It is desirable to carry out this step with almost no twist, and roller and air opening steps are usually used, but are not limited to these. In order to continuously and efficiently impregnate the thermoplastic resin, it is preferable to apply a pressure of 0.1 MPa to the resin (passing it through a resin impregnation tank with a pressure of 0.1 MPa or more). If the pressure is less than 0.1 MPa, it is difficult to achieve sufficient impregnation. A higher pressure in the resin impregnation tank is preferable because it improves impregnation, more preferably 0.3 MPa or more, and even more preferably 0.5 MPa or more. A higher pressure in the resin impregnation tank is preferable because it improves impregnation, but it also increases equipment costs, so a pressure of 2 MPa or less is preferred.

[0059] The inorganic fibers that have passed through the resin impregnation tank tend to bundle due to the take-up tension, and in this state the thermoplastic resin does not fully impregnate the fine parts of the inorganic fibers. Therefore, by crushing the fibers with a shaping roller and cooling and solidifying them to produce a thermoplastic resin tape, it is possible to improve the resin impregnation and handling properties.

[0060] A thick thermoplastic resin sheet can be obtained by randomly scattering and laminating the thermoplastic resin tapes obtained as described above, compressing them using a compression molding machine equipped with a mold whose temperature has been adjusted to a temperature above the melting point of the thermoplastic resin, cooling the mold, and then opening the mold.

[0061] Because the thick thermoplastic resin sheet is produced by randomly scattering and laminating thermoplastic resin tapes, the inorganic fibers are oriented in a direction perpendicular to the thickness direction of the thick thermoplastic resin sheet, and the inorganic fibers are oriented in the planar direction of the thick thermoplastic resin sheet, with random orientation in the direction perpendicular to the planar direction. When such a thick thermoplastic resin sheet is press-molded as described below, a plate-shaped member can be produced in which the inorganic fibers are oriented in a direction perpendicular to the thickness direction of the plate-shaped member, and the inorganic fibers are randomly oriented in the plane along the perpendicular direction. When an impact-absorbing member having such a plate-shaped member is used, fracture progresses with delamination when impact energy is applied, thereby improving collision safety.

[0062] When molding a thick thermoplastic resin sheet, the mold temperature is preferably equal to or lower than the solidification temperature of the thermoplastic resin, and is preferably between the solidification temperature −60° C. and the solidification temperature −10° C. A higher mold temperature improves the moldability of the thick thermoplastic resin sheet, but a lower mold temperature is better in order to prevent warping of the thick thermoplastic resin sheet.

[0063] Furthermore, when molding a thick thermoplastic resin sheet, the press pressure is preferably 0.1 MPa or more, and more preferably 1 MPa or more. If it is less than 0.1 MPa, sufficient pressure will not be applied to the thermoplastic resin tape, which may result in the formation of bubbles or poor surface quality. When molding a thick thermoplastic resin sheet, a higher press pressure is preferable because it will result in higher sheet quality, but since this increases equipment costs, it is preferable that the press pressure be 10 MPa or less. The press holding time is preferably 0.5 to 20 minutes, and more preferably 1 to 10 minutes.

[0064] Press molding is preferred as a molding method for producing the impact-absorbing member of the present invention using a thermoplastic resin sheet. Examples of press molding include heat and cool molding and stamping molding, but stamping molding is preferred in terms of cycle time and molding costs. Stamping molding refers to molding performed by heating and melting a thermoplastic resin sheet to a temperature above the melting point of the thermoplastic resin used using infrared heating or high-frequency heating, feeding it into a mold adjusted to a temperature below the melting point, and demolding it after cooling. The molding conditions during stamping, such as mold temperature, press pressure, and press holding time, can be set appropriately depending on the thermoplastic resin used, but are preferably performed under the following conditions.

[0065] When performing stamping molding, the mold temperature is preferably equal to or lower than the solidification temperature of the thermoplastic resin, and is preferably from the solidification temperature −60° C. to the solidification temperature −10° C. A higher mold temperature improves moldability, but a lower mold temperature is better in order to prevent warping of the molded body.

[0066] Furthermore, when performing stamping molding, the press pressure is preferably 1 MPa or more, and more preferably 10 MPa or more. If it is less than 1 MPa, sufficient pressure will not be applied to the thermoplastic resin sheet, which may result in molding defects due to insufficient flow or the formation of bubbles inside the molded product. A higher press pressure during stamping molding is preferable because it will result in higher quality molded products, but this increases equipment costs, so it is preferably 50 MPa or less. The press holding time is preferably 1 to 10 minutes, and more preferably 1 to 5 minutes.

[0067] In the above-mentioned manufacturing method, since a thermoplastic resin tape is obtained by cutting a thermoplastic resin sheet, the thin thermoplastic resin sheet preferably has a thickness equivalent to that of the thermoplastic resin tape. The thickness of the thick thermoplastic resin sheet is preferably 0.35 to 1.2 mm, and more preferably 0.5 to 1.0 mm. If the thickness is less than 0.35 mm, production efficiency may be reduced, and if it exceeds 1.2 mm, it is not preferable from the standpoint of cost.

[0068] This application claims the benefit of priority based on Japanese Patent Application No. 2021-169137 filed on October 14, 2021, and Japanese Patent Application No. 2021-171100 filed on October 19, 2021. The entire contents of the specifications of Japanese Patent Application No. 2021-169137 filed on October 14, 2021, and Japanese Patent Application No. 2021-171100 filed on October 19, 2021 are incorporated herein by reference. [Example]

[0069] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The evaluation methods used in each example and comparative example are as follows.

[0070] <Volume content of inorganic fibers> Samples were cut out from the bottom, the axial tip of the outermost cylindrical part, and the axial tip of the other cylindrical parts, and the volume content of inorganic fibers in each part was calculated using the weight content of inorganic fibers measured by the direct ashing method in accordance with JIS K7250-1 according to the following formula. The units of fiber density and resin density are g / cm. 3 Let's say.

[0071]

number

[0072] In addition, for the bottom portion, the inorganic fiber content was measured near the center of the bottom portion in the internal space, and near the center of the bottom portion in the internal space refers to the shaded area (measurement area 41) in Figure 4 for the impact absorbing member in Figure 1, and the same applies to Figures 2 and 3. Furthermore, the axial tip of the tubular portion refers to the tip on the side where collision energy is first applied (the tip on the opposite side from the bottom portion). The tubular portion located at the outermost periphery refers to the tubular portion other than the part commonly used to form the two internal spaces (the part used to form only one internal space).

[0073] <Drop weight impact test> A drop weight impact test was conducted on the manufactured shock absorbing component using a large-scale, high-speed impact compression testing machine (IM10T-30, manufactured by IMATEK). The drop weight impact test was conducted by freely dropping a 121.2 kg cone from a position 2.5 m above the shock absorbing component, applying an impact compressive load in the axial direction of the shock absorbing component. The impact load was measured using a load cell attached to the cone. The measured impact load and displacement were used to draw a load-displacement curve and integrate it to calculate the absorbed energy of the shock absorbing component during the drop weight impact test. The specific absorbed energy was calculated by dividing the calculated absorbed energy by the weight of the part destroyed by the drop weight impact test.

[0074] <Average orientation angle> The average orientation angle of the inorganic fibers relative to a plane perpendicular to the thickness direction in the bottom surface of the impact absorbing member of Fig. 1 was measured. Specifically, the orientation angle of each inorganic fiber near the center of the bottom surface in the internal space 14 (the shaded area (measurement area 41) in Fig. 4) was measured, and the average orientation angle was calculated.

[0075] Example 1 Inorganic glass fiber roving (Nitto Boseki Co., Ltd., RS 110 QL-483, E-glass, fineness: 1150 tex, number of fibers (f): 2000, average fiber diameter: 17 μm) was opened using a 2 cm diameter roller. Next, a tank was prepared and filled with maleic acid-modified polypropylene resin (MFR: 45 g / 10 min at 230 °C and a load of 2.16 kg) consisting of a blend of Prime Polymer J137M (MFR: 30 g / 10 min at 230 °C and a load of 2.16 kg) and Asahi Techno Kogyo Co., Ltd. PP-04M (MFR: 88 g / 10 min at 230 °C and a load of 2.16 kg). The resin temperature in the tank was raised to 240 °C, and a pressure of 0.6 MPa was applied to the resin. The opened glass fiber roving was then passed through the tank, allowing the glass fibers to be continuously impregnated with the resin. The resin-impregnated glass fibers were then crushed with a shaping roller and cooled to solidify, producing a thermoplastic resin sheet. Finally, the thermoplastic resin sheet was cut to produce a thermoplastic resin tape A having a width of 30 mm, a length of 35 mm, and a thickness of 0.1 mm and containing 48% by volume of inorganic fibers.

[0076] Next, thermoplastic resin tape A was randomly laminated in a metal heat-resistant release container and pressed at 0.2 MPa for 5 minutes in a mold heated to 240°C. After sufficient air was removed from the sheet, it was pressed at 2 MPa for 2 minutes in a mold set at 100°C to produce a 6 mm thick stamping sheet. The stamping sheet was cut to the same volume as the mold and heated to 220°C using a far-infrared heater. It was then placed in a mold set at 130°C and stamped at 25 MPa for a 2-minute dwell time to produce an impact-absorbing component with the shape shown in Figure 1. The impact-absorbing component in Figure 1 had a base measuring 80 mm long, 100 mm wide, and 4 mm thick. The cylindrical portion was 52 mm high, and the tip of the cylindrical portion was 2.2 mm thick. The height of the cylindrical portion was 0.65 times the shortest side of the base. The inorganic fiber content in the bottom surface of the impact absorbing member of Example 1 was 47.5% by volume, the inorganic fiber content in the cylindrical portion located at the outermost periphery was 47.9% by volume, and the inorganic fiber content in the cylindrical portions other than the outermost periphery was 48.4% by volume. The impact absorbing member of Example 1 had a specific absorption energy of 36.6 kJ / kg and an average orientation angle of 3.7°.

[0077] Example 2 A stamping sheet was prepared in the same manner as in Example 1. The prepared stamping sheet was cut out and heated to 220°C using a far-infrared heater. The stamping sheet was then placed in a mold set at 130°C and stamped to obtain an impact-absorbing member having the shape shown in FIG. 2. The impact-absorbing member in FIG. 2 had a bottom surface measuring 60 mm in length, 60 mm in width, and 4 mm in thickness, a tubular portion measuring 52 mm in height, and a tip portion of the tubular portion having a thickness of 2.2 mm. The height of the tubular portion was 0.87 times the shortest side of the bottom surface. The impact-absorbing member in Example 2 had an inorganic fiber content of 47.8% by volume in the bottom surface, a tubular portion located at the outermost periphery of the impact, a tubular portion having a inorganic fiber content of 48.2% by volume, and a tubular portion other than the outermost periphery of the impact. The specific absorption energy of the impact-absorbing member in Example 2 was 40.5 kJ / kg.

[0078] Example 3 A thermoplastic resin tape B having an inorganic fiber content of 50%, a width of 15 mm, a length of 35 mm and a thickness of 0.1 mm was produced in the same manner as in Example 1, except that a carbon fiber roving (T-700 manufactured by Toray Industries, Inc., polyacrylonitrile, fineness: 800 Tex, 12000 f, average fiber diameter: 7 μm) was used instead of the glass fiber roving described in Example 1, and a maleic acid-modified polypropylene (G2H manufactured by Toyobo Co., Ltd., MFR: 50 g / 10 min at a temperature of 230°C and a load of 2.16 kg) was used instead of the acid-modified polypropylene resin used in Example 1.

[0079] An impact absorbing member having the shape shown in Figure 1 was obtained in the same manner as in Example 1, except that thermoplastic resin tape B was used instead of thermoplastic resin tape A. The inorganic fiber content in the bottom portion of the impact absorbing member in Example 3 was 49.4 volume %, the inorganic fiber content in the cylindrical portion located at the outermost periphery was 50.3 volume %, and the inorganic fiber content in the cylindrical portions other than the outermost periphery was 50.1 volume %. The specific absorption energy of the impact absorbing member in Example 3 was 49.5 kJ / kg.

[0080] Example 4 An impact absorbing member having the shape shown in Figure 2 was obtained in the same manner as in Example 2, except that thermoplastic resin tape B was used instead of thermoplastic resin tape A. The inorganic fiber content in the bottom portion of the impact absorbing member in Example 4 was 50.3 volume %, the inorganic fiber content in the cylindrical portion located at the outermost periphery was 49.8 volume %, and the inorganic fiber content in the cylindrical portions other than the outermost periphery was 49.9 volume %. The specific absorption energy of the impact absorbing member in Example 4 was 54.2 kJ / kg.

[0081] (Comparative Example 1) An impact absorbing member having the shape shown in FIG. 1 was obtained in the same manner as in Example 1, except that a stamping molding sheet containing polypropylene and glass fibers (P4038GMT manufactured by Mitsubishi Chemical Advanced Materials Corporation, fiber length: 100 mm, inorganic fiber content: 20 vol%, thickness: 3.8 mm) was used. The inorganic fiber content in the bottom surface of the impact absorbing member in Comparative Example 1 was 24.8 vol%, the inorganic fiber content in the cylindrical portion located at the outermost periphery was 17.8 vol%, and the inorganic fiber content in the cylindrical portions other than the outermost periphery was 16.2 vol%. The specific absorption energy of the impact absorbing member in Comparative Example 1 was 21.5 kJ / kg. Furthermore, the behavior at the time of failure in the drop weight impact test differed from Examples 1 to 4, with the failure progressing as the cone broke into pieces starting from the vicinity of the point of contact.

[0082] (Comparative Example 2) An impact absorbing member having the shape shown in FIG. 2 was obtained in the same manner as in Example 1, except that a stamping molding sheet was prepared in the same manner as in Comparative Example 1. The inorganic fiber content in the bottom surface of the impact absorbing member of Comparative Example 2 was 24.2 vol%, the inorganic fiber content in the cylindrical portion located at the outermost periphery was 16.8 vol%, and the inorganic fiber content in the cylindrical portions other than the outermost periphery was 18.5 vol%. The specific absorption energy of the impact absorbing member of Comparative Example 2 was 25.2 kJ / kg. Furthermore, the behavior at the time of fracture in the drop weight impact test was the same as in Comparative Example 1, with the fracture progressing as the cone broke into pieces from the vicinity of the point of contact. [Industrial Applicability]

[0083] The impact absorbing member of the present invention achieves both weight reduction and high collision safety and has excellent formability, so it can be used in impact absorbing devices for passenger cars and is expected to make a significant contribution to industry in terms of vehicle weight reduction and energy conservation. Furthermore, the impact absorbing member of the present invention can be used not only in impact absorbing devices for passenger cars, but also in vehicles other than passenger cars and various structures. [Explanation of symbols]

[0084] 11, 21, 31 Impact absorbing member 12, 22, 32 Bottom part 13, 23, 33 Cylindrical part 14, 24, 25, 34, 35 Internal space 41 Measurement site

Claims

1. An impact absorbing member having one or more plate-shaped members, At least one of the plate-like members is formed by laminating thermoplastic resin tapes containing inorganic fibers, the thermoplastic resin tape is obtained by cutting a thermoplastic resin sheet in which the inorganic fibers are oriented in the length direction, In the plate-like member containing the inorganic fibers, the inorganic fibers are oriented in a direction perpendicular to the thickness direction of the plate-like member, and are randomly oriented in the plane along the perpendicular direction, and the inorganic fibers account for 30 to 60 volume % of the plate-like member.

2. The impact absorbing member according to claim 1 , wherein the inorganic fibers include at least one of glass fibers and carbon fibers.

3. 3. The impact absorbing member according to claim 1, wherein the inorganic fibers have an average fiber length of 10 to 150 mm.

4. 3. The impact absorbing member according to claim 1, wherein the melt flow rate of the resin contained in the thermoplastic resin tape is 15 to 100 g / 10 min when measured at a temperature of 230° C. under a load of 2.16 kg.

5. 3. The impact absorbing member according to claim 1, wherein the thermoplastic resin tape has a length of 10 mm to 100 mm, a width of 5 mm to 50 mm, and a thickness of 0.05 mm to 0.3 mm.

6. An impact absorbing member having a cylindrical portion and a bottom portion, the cylindrical portion and the bottom surface portion are formed by the plate-like member, the bottom surface portion closes one bottom surface of the cylindrical portion, 3. The impact absorbing member according to claim 1, wherein the difference between the content of the inorganic fibers in the tubular portion and the content of the inorganic fibers in the bottom portion is 5% by volume or less.

7. 7. The impact absorbing member according to claim 6, wherein the inorganic fibers have an average orientation angle of 0 to 20° with respect to a plane perpendicular to the thickness direction in the bottom surface portion.

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