JP7823658B2 - Impact absorbing material - Google Patents

Description

The present invention relates to an impact absorbing member.

Conventionally, crash energy-absorbing components are installed in vehicles such as passenger cars to protect occupants. For example, crash energy-absorbing components such as front side members and rear side members are installed in locations on a vehicle where an impact is expected to be applied. In a crash energy-absorbing component, crash energy is applied in the axial direction, which is the direction in which the crash energy can be efficiently absorbed. When the magnitude of the crash energy exceeds the yield stress, the crash energy-absorbing component deforms to absorb the impact.

It is important for impact absorbing components to absorb collision energy sufficiently and efficiently, and impact absorbing components are often manufactured using metals such as steel plates.

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

The shock absorbing member in Patent Document 1 can absorb collision energy, but because it uses metal plates such as steel plates, it cannot be said to be lightweight. While high collision safety has been required in recent years, there has also been a demand for lighter impact absorbing members to improve fuel economy. However, when metal plates such as steel plates are used, as in Patent Document 1, there are limits to how much weight can be reduced.

In light of these problems with metal impact absorbing members, resin impact absorbing members have been proposed, which offer a significant 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 improvements. 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 also providing high collision safety.

Patent document 2 discloses a front side member consisting of a fiber-reinforced plastic energy absorption section with a cylindrical cross section made of reinforcing fibers and resin, and a support section connected to the fiber-reinforced plastic energy absorption section and formed of fiber-reinforced plastic to be joined to a vehicle body part. It also 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 process.

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 that the hollow cylinder is formed by a filament winding method.

Patent document 4 discloses a vehicle impact absorbing component having a cylindrical portion and a top surface portion formed to close one of the axial openings of the cylindrical portion. It is disclosed 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.

Japanese Patent Application Laid-Open No. 2019-206246 Japanese Patent Application Laid-Open No. 2005-271875 International Publication No. 2020/217573 Japanese Patent Application Laid-Open No. 2021-67291

However, because the reinforcing fibers (reinforcing fibers) in the absorption members of Patent Documents 2 and 3 are present as continuous fibers, molding costs are high and moldability is poor, limiting the shapes that can be molded. This makes it difficult to create impact absorbing members with complex shapes like those shown in Figures 1 and 2 below.

The shock-absorbing member in 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 and spaced apart from the cylindrical portion on the inside of the cylindrical portion, which limits the shape of the shock-absorbing member. Furthermore, because the shock-absorbing member in Patent Document 4 is designed for injection molding, it is difficult to increase the amount of energy absorbed by the shock-absorbing member when the material breaks, resulting in low shock absorption.

The object of the present invention is to provide an impact absorbing member that can be shaped relatively freely, is lightweight, and has high collision safety.

As a result of extensive research into solving the above-mentioned problems, the inventors discovered an impact absorbing component 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 specified conditions, which allows for lightweight impact absorbing components while providing high collision safety, leading to the present invention.

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 a thermoplastic resin tape containing inorganic fibers, wherein 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. [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.

The impact-absorbing component has a plate-shaped member formed by laminating thermoplastic resin tapes containing inorganic fibers. By controlling the orientation of the inorganic fibers in the plate-shaped member to meet specific conditions, it is possible to achieve both lightweight and high collision safety. Furthermore, the impact-absorbing component of the present invention has excellent moldability and can be shaped relatively freely. Therefore, it can be used not only in impact-absorbing devices for passenger cars, but also in vehicles other than passenger cars and various other structures.

1 is a perspective view of an impact absorbing member according to an embodiment of the present invention; FIG. 10 is a perspective view of a modified example of the impact absorbing member according to the embodiment of the present invention. FIG. 10 is a perspective view of a further modified example of the impact absorbing member according to the embodiment of the present invention. FIG. 2 is a bottom view of the impact absorbing member of FIG. 1 .

The present invention is described in detail below.

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

<Plate-shaped member>
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" will be referred to as a "predetermined plate-like member."

In the specified plate-shaped member, the inorganic fibers are oriented perpendicular to the thickness direction, providing excellent collision safety. Below, we will explain why the impact-absorbing member of the present invention, which has the specified plate-shaped member, has excellent impact absorption (impact safety). Before that, we will first explain the damage that occurs when a metal impact-absorbing member is used, and the problems that arise when an impact-absorbing member is molded using a thermoplastic resin using conventional methods.

In the case of metal impact absorbing components, the failure mode is one in which the entire component breaks, making it impossible for the component to stably absorb impact energy. For this reason, metal impact absorbing components are designed so that when impact energy is applied, they buckle locally while the overall component collapses in a bellows-like pattern.

When a shock-absorbing component is molded using a thermoplastic resin containing inorganic fibers and designed to fail in the same manner 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 on the shock-absorbing component fluctuates significantly during its failure, which not only prevents stable absorption of collision energy, but also poses the risk of the shock-absorbing component being unable to withstand the impact load during failure.

In addition, if brittle fracture occurs, the resin will shatter, which could cause secondary disasters due to flying fragments.

The impact-absorbing member of the present invention has a specified plate-shaped member, in which inorganic fibers are oriented perpendicular to the thickness direction. When a specified plate-shaped member in which inorganic fibers are oriented perpendicular to the thickness direction is used, the plate-shaped member exhibits superior impact absorption properties due to fracture behavior in which the plate-shaped member splits perpendicularly while remaining connected to the inorganic fiber orientation. The reason for this fracture behavior is believed to be that the specified plate-shaped member resembles a laminate of multiple thermoplastic resin layers containing inorganic fibers, and when impact energy is applied to the specified 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, preventing the resin from shattering upon fracture, significantly reducing the amount of flying debris.

In a given plate-shaped member, the inorganic fibers do not have to be strictly perpendicular to the "direction perpendicular to the thickness direction of the plate-shaped member." For example, in an impact absorbing member having a bottom surface that is a plate-shaped member, the average orientation angle of the inorganic fibers relative to the plane perpendicular to the thickness direction is preferably 0 to 20°, and in an impact absorbing member having a tubular portion that is a plate-shaped member, the average orientation angle of the inorganic fibers relative to the plane perpendicular to the thickness direction at the axial center of the tubular portion is preferably 0 to 35°. The method for measuring the average orientation angle will be described later. In the following, "axial direction" refers to the direction in which the impact absorbing member is compressed and deformed by an impact load.

Furthermore, 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 in-plane orientation" refers to pseudo-isotropy, and the in-plane orientation parameter (cos ² θy/cos ² θx) of the inorganic fibers in the direction perpendicular to the thickness direction of the plate-like member is preferably greater than 0.67 and less than 1.5, more preferably 0.75 or greater and 1.33 or less. When the in-plane orientation parameter is 1, the carbon fibers are completely randomly oriented in the in-plane direction. If the in-plane orientation parameter is outside the above range, the randomness of the fiber orientation in the in-plane direction is impaired, which may result in reduced impact absorption. The in-plane orientation parameter is measured as follows. The plate-like members (bottom and tubular portions of the impact-absorbing member) used in the examples described below all have in-plane orientation parameters greater than 0.67 and less than 1.5. The in-plane orientation parameter (cos ² θy/cos ² θx) is determined by calculating cos 2 θx and cos ² θy for each inorganic fiber and dividing the average value of cos ² θy by the average value of cos ^{2 θx} .

<Method for measuring in-plane orientation parameters>
Five test pieces measuring approximately 15 mm x 25 mm were cut from the plate-like member, and three-dimensional X-ray CT measurements were performed on each test piece. Cartesian coordinates were determined so that the X and Y axes were in the in-plane direction of the plate-like member, and the Z axis was in the thickness direction. The test pieces were cut out 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 measurement X-ray CT device (TDM1000-IS), data was collected by rotating 360 degrees at intervals of 0.5 degrees or less under the conditions of an acceleration voltage of 40-60 kV, a tube current of 10-40 μA, and an accumulation time of 0.5-1 second. Reconstruction was performed under conditions such that the size of one pixel was 50 μm or less. From the obtained reconstruction data, only data in the 15 mm x 15 mm x plate-like member thickness region was extracted, and the in-plane orientation parameters were calculated using the anisotropy measurement function of the software "Tri3D BON" manufactured by Ratoc Systems Engineering.

<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.

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

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.

<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. Modified products of the above-listed resins may also be used as the thermoplastic resin. The thermoplastic resin may be one type or two or more types.

The modified thermoplastic resin may be, for example, an acid-modified thermoplastic resin. An acid-modified thermoplastic resin has an acid-modified group introduced into it. The type of acid-modified group is not particularly limited, and the acid-modified group may be a single 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 carboxylic acid anhydrides include unsaturated carboxylic acid anhydrides such as maleic anhydride and itaconic anhydride. Examples of carboxylic acids 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. Of 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. Note that, in this specification, "thermoplastic resin" also includes modified thermoplastic resins, such as acid-modified thermoplastic resins.

From the standpoints of ease of handling and cost, the thermoplastic resin used in the present invention preferably contains at least one of polyamide resin, polyolefin resin, and acid-modified polyolefin resin. Acid-modified polyolefin resin is preferred from the standpoint of improving interfacial adhesion with inorganic fibers, thereby improving the strength of the thermoplastic resin molded body. Furthermore, the thermoplastic resin used in the present invention may optionally contain additives such as nucleating agents, heat degradation inhibitors, oxidation degradation inhibitors, and ultraviolet absorbers to improve physical properties, moldability, and durability. The content of these additives may vary depending on the purpose, but the total content of 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.

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 lower 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 higher 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; however, when using commercially available products, the value listed in the 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.

<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, with glass fiber being preferred. 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, inorganic fibers formed by bundling single fibers into a single bundle are preferably used, and the total cross-sectional area of the bundled inorganic fibers is preferably 0.2 to 1.5 ^mm² , more preferably 0.4 to 1.0 ^mm² .

The inorganic fibers are preferably short fibers. 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.

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, impact absorption may be reduced. If the average fiber diameter is more than 30 μm, the number of inorganic fibers in the impact absorbing component will be reduced, which may result in reduced impact absorption.

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

(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.

(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 a carbon fiber made from polyacrylonitrile fiber. Pitch-based carbon fiber is a carbon fiber made from petroleum tar or petroleum pitch. Cellulose-based carbon fiber is a carbon fiber made from viscose rayon, cellulose acetate, or the like. Vapor-grown carbon fiber is a 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.

<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 reinforcing effect of the inorganic fibers on the plate-shaped member cannot be obtained, and the stability of the impact absorbing member against collisions is 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 impregnation of the inorganic fibers with the thermoplastic resin will be insufficient, resulting in unstable fracture behavior of the impact absorbing member and reduced impact absorption.

<Impact 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.

It is also preferable for the impact absorbing member to have a cylindrical portion made of a specified plate-like member, as well as a bottom portion that closes one of the bottom surfaces of the cylindrical portion, because closing the bottom surface of the cylindrical portion with the bottom portion allows for efficient dispersion of impact around the entire circumference of the cylindrical portion. In the impact absorbing member of the present invention, the bottom portion is preferably a plate-like member, more preferably a specified plate-like member, and even more preferably the cylindrical portion and the bottom portion are made of a specified plate-like member.

The shape of the impact absorbing member will be described below with reference to FIG. 1. FIG. 1 is a perspective view of an impact absorbing member according to an embodiment of the present invention. The impact absorbing member 11 has a rectangular parallelepiped shape. Four rectangular parallelepiped tubular portions 13 extend vertically from the outer periphery of one side of the bottom portion 12 of the impact absorbing member, which has a rectangular shape when viewed in the thickness direction. The impact absorbing member 11 is divided by the bottom portion 12 and the tubular portions 13, forming four rectangular parallelepiped internal spaces 14 in a lattice pattern within the impact absorbing member 11. In other words, the external shape of the impact absorbing member 11 is such that plate-like members are erected perpendicular to the four sides of 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 impact 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.

The bottom surface portion 12 is not particularly limited, and examples include plate-shaped, mesh-shaped, and lattice-shaped members. While a plate-shaped member is preferred, the bottom surface portion 12 does not need to be completely flat as long as it covers one bottom surface of the tubular portion 13; it 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 impact absorbing member 11) is not particularly limited, and examples include a circle, ellipse, polygon, and the like, but it may also be a part of any 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 efficiently absorbing energy, 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.

The cylindrical portion 13 extends from the bottom portion 12 in a direction perpendicular to the bottom surface of the bottom portion 12 (in the thickness direction of the bottom portion), and is preferably a plate-shaped member. When the cylindrical portion 13 is a plate-shaped member, collision energy is applied along the axial direction of the plate-shaped member, and when the magnitude of the collision energy exceeds the limit value of the plate-shaped member, the plate-shaped member deforms to absorb the impact, thereby efficiently absorbing the impact energy. Furthermore, from the perspective of efficiently absorbing collision energy, it is preferable that all of the cylindrical portions 13 have the same height.

In addition, from the viewpoint of efficiently absorbing collision energy, the cylindrical portion 13 is preferably shaped such that a plate-shaped member is erected in the vertical direction of the bottom portion 12 from at least a portion of the outer periphery of the bottom portion 12, and more preferably such that a cylindrical member is erected in the vertical direction of the bottom portion 12 from the entire outer periphery of the bottom portion 12. However, in order to adjust the amount of collision energy absorbed, the cylindrical portion 13 may also be shaped such that 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.

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, it 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, there may be insufficient space for destruction or deformation when impact energy is applied to the cylindrical portion 13, resulting in unstable destruction behavior of the impact absorbing member 11 and reduced impact 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 may be an increased possibility of buckling when an impact load is applied, or the molding pressure may need to be set high, resulting in increased molding costs.

The cylindrical portion 13 is preferably arranged perpendicular to the bottom surface of the bottom portion 12, but does not need 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 degrees, and more preferably 40 to 90 degrees. The cylindrical portion 13 may also be angled to ensure a draft angle for the mold, as long as this does not impair the intent of the present invention.

There are no particular restrictions on the thickness of the tubular portion 13, and it may be the same as or different from the thickness of the bottom portion 12, but a thickness of 1 to 8 mm is preferred, and 2 to 6 mm is more preferred.

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 portion 12). The closed cross-sectional structure is not particularly limited, but from the perspective of efficiently absorbing collision energy, it is preferable that it has a shape that is line-symmetric or point-symmetric. Examples include circles, ellipses, polygons, and combinations of these shapes. However, triangles, rectangles, squares, and hexagons are preferred because they allow the internal spaces 14 to be lined up without gaps.

The difference between the inorganic fiber content in the tubular 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, collision 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 difference exceeds 5% by volume and the tip of the tubular portion becomes resin-rich, with a lower inorganic fiber content than 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 observed when using 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 a location farthest from the location 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 of Figure 1).

Figure 2 is a perspective view of a modified example of an impact absorbing member according to an embodiment of the present invention. The impact absorbing member 21 has a rectangular parallelepiped shape. A hexagonal prism-shaped cylindrical portion 23 is provided vertically from one side of the bottom surface portion 22 of the plate-shaped member, which is rectangular in shape when viewed in the thickness direction, to form a honeycomb structure. By being separated by the bottom surface portion 22 and the cylindrical portion 23, four hexagonal prism-shaped internal spaces 24 are provided inside the impact absorbing member 21 to form a honeycomb structure. However, near the outer periphery of the impact absorbing member 21 in the axial direction, there are also portions shaped like partial hexagonal prisms, such as internal space 25. The external shape of the impact absorbing member 21 is such that plate-shaped members are erected vertically from the four sides of the outer periphery of the bottom surface portion 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.

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

<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.

The inorganic fiber roving is opened and introduced into a tank (hereinafter referred to as the resin impregnation tank) containing heated and molten 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 to produce 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.

The opening process is preferably carried out by aligning the inorganic fibers and then fully opening them before use. It is desirable to carry out this process with minimal twist, and roller and air opening processes are typically used, but are not limited to these. 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 will be difficult to achieve sufficient impregnation. A higher pressure in the resin impregnation tank improves impregnation, and is therefore preferred; more preferably 0.3 MPa or more, and even more preferably 0.5 MPa or more. A higher pressure in the resin impregnation tank improves impregnation, and is preferred; however, equipment costs also increase, so a pressure of 2 MPa or less is preferred.

After passing through the resin impregnation tank, inorganic fibers tend to bundle together due to the pulling tension, and in this state the thermoplastic resin does not fully impregnate the fine details of the inorganic fibers. Therefore, by crushing the fibers with a shaping roller, cooling and solidifying them to produce a thermoplastic resin tape, it is possible to improve resin impregnation and handleability.

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 above the melting point of the thermoplastic resin, cooling the mold, and then opening the mold.

The thick thermoplastic resin sheet is made by randomly scattering and laminating thermoplastic resin tapes. This means that the inorganic fibers are oriented perpendicular to the thickness of the thick thermoplastic resin sheet, and are also 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 component can be formed in which the inorganic fibers are oriented perpendicular to the thickness of the plate-shaped component and are randomly oriented in the plane along the perpendicular direction. When an impact-absorbing component containing such a plate-shaped component is used, delamination occurs as the component fractures when impact energy is applied, improving collision safety.

When molding a thick thermoplastic resin sheet, the mold temperature is preferably below the solidification temperature of the thermoplastic resin, and is preferably between solidification temperature -60°C and solidification temperature -10°C. A higher mold temperature improves the formability of the thick thermoplastic resin sheet, but a lower mold temperature is better to prevent warping of the thick thermoplastic resin sheet.

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 as it will result in higher sheet quality, but this increases equipment costs, so a pressure of 10 MPa or less is preferable. The press hold time is preferably 0.5 to 20 minutes, and more preferably 1 to 10 minutes.

Press molding is preferred as a molding method for producing the impact-absorbing component 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 in which a thermoplastic resin sheet is heated to a temperature above the melting point of the thermoplastic resin used using infrared heating or high-frequency heating, melted, fed into a mold adjusted to a temperature below the melting point, and then demolded after cooling. The molding conditions during stamping, such as mold temperature, press pressure, and press hold time, can be set appropriately depending on the thermoplastic resin used, but the following conditions are preferred.

When performing stamping molding, the mold temperature should preferably be below the solidification temperature of the thermoplastic resin, preferably between solidification temperature -60°C and solidification temperature -10°C. A higher mold temperature improves moldability, but a lower mold temperature is better to prevent warping of the molded product.

When performing stamping molding, the press pressure is preferably 1 MPa or more, and more preferably 10 MPa or more. If the pressure 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 air bubbles inside the molded product. A higher press pressure during stamping molding is preferable as it will result in higher quality molded products, but this increases equipment costs, so a pressure of 50 MPa or less is preferable. The press holding time is preferably 1 to 10 minutes, and more preferably 1 to 5 minutes.

In the above manufacturing method, thermoplastic resin tape is obtained by cutting a thermoplastic resin sheet, so it is preferable that the thin thermoplastic resin sheet has the same thickness as 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. A thickness of less than 0.35 mm may result in poor production efficiency, and a thickness of more than 1.2 mm is undesirable from a cost perspective.

This application claims the benefit of priority from 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.

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

<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 a cylindrical part other than the outermost cylindrical part, and the volume content of inorganic fiber in each part was calculated using the weight content of inorganic fiber measured by the direct ashing method in accordance with JIS K7250-1 according to the following formula. The fiber density and resin density are expressed in g/ ^cm3 .

For the bottom portion, the inorganic fiber content was measured near the center of the bottom portion in the internal space. 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 is similar for Figures 2 and 3. The axial tip of the tubular portion refers to the tip on the side where impact energy is first applied (the tip opposite the bottom portion). The tubular portion located at the outermost periphery refers to the tubular portion other than the portion commonly used to form the two internal spaces (the portion used to form only one internal space).

<Drop weight impact test>
A drop weight impact test was conducted on the prepared impact absorbing member using a large-scale, high-speed impact compression testing machine (IM10T-30, manufactured by IMATEK Corporation). The drop weight impact test was performed by freely dropping a cone weighing 121.2 kg from a position 2.5 m higher than the impact absorbing member, thereby applying an impact compression load in the axial direction of the impact absorbing member. The impact load was measured using a load cell attached to the cone side. The absorbed energy of the impact absorbing member during the drop weight impact test was calculated by drawing and integrating a load-displacement curve using the measured impact load and displacement. The specific absorbed energy was calculated by dividing the calculated absorbed energy by the weight of the portion destroyed by the drop weight impact test.

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

Example 1
Inorganic glass fiber roving (manufactured by 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 filled with maleic acid-modified polypropylene resin (temperature 230 ° C., load 2.16 kg MFR: 45 g / 10 min) consisting of a blend of Prime Polymer J137M (temperature 230 ° C., load 2.16 kg MFR: 30 g / 10 min) and Asahi Techno Kogyo Co., Ltd. PP-04M (temperature 230 ° C., load 2.16 kg MFR: 88 g / 10 min) was prepared, the temperature of the resin in the tank was set to 240 ° C., and a pressure of 0.6 MPa was applied to the resin. Subsequently, the opened glass fiber roving was passed through the tank, and the glass fibers were 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.

Thermoplastic resin tape A was then 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 resulting stamping sheet was cut to the same volume as the mold. The stamping sheet was heated to 220°C using a far-infrared heater and then placed in a mold set at 130°C. Stamping was performed at 25 MPa with a dwell time of 2 minutes to produce an impact-absorbing member with the shape shown in Figure 1. The impact-absorbing member in Figure 1 had a base measuring 80 mm long, 100 mm wide, and 4 mm thick. The cylindrical portion was 52 mm high, with a tip thickness of 2.2 mm. 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°.

Example 2
A stamping sheet was prepared in the same manner as in Example 1. The prepared stamping sheet was cut out, heated to 220 ° C. with a far-infrared heater, and then placed in a mold set at 130 ° C. for stamping, thereby obtaining an impact absorbing member having the shape shown in FIG. 2. The impact absorbing member in FIG. 2 had a bottom portion measuring 60 mm in length, 60 mm in width, and 4 mm in thickness, a tubular portion having a height of 52 mm, and a thickness of 2.2 mm at the tip of the tubular portion. The height of the tubular portion was 0.87 times the shortest side of the bottom portion. The inorganic fiber content in the bottom portion of the impact absorbing member in Example 2 was 47.8 vol%, the inorganic fiber content in the tubular portion located at the outermost periphery was 48.2 vol%, and the inorganic fiber content in the tubular portions other than the outermost periphery was 47.5 vol%. The specific absorption energy of the impact absorbing member in Example 2 was 40.5 kJ/kg.

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

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 surface of the impact absorbing member in Example 3 was 49.4 vol%, the inorganic fiber content in the cylindrical portion located at the outermost periphery was 50.3 vol%, and the inorganic fiber content in cylindrical portions other than the outermost periphery was 50.1 vol%. The specific absorption energy of the impact absorbing member in Example 3 was 49.5 kJ/kg.

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.

(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 was prepared using Mitsubishi Chemical Advanced Materials P4038GMT (GMT, fiber length: 100 mm, inorganic fiber content: 20 vol%, thickness: 3.8 mm) containing polypropylene and glass fibers. 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 portion 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 cone shattering into pieces as the failure progressed from the vicinity of the point of contact.

(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 portion of the impact absorbing member in 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 in Comparative Example 2 was 25.2 kJ/kg. Furthermore, the behavior at the time of failure in the drop weight impact test was the same as in Comparative Example 1, with the cone shattering into pieces starting from the vicinity of the point of contact.

The impact absorbing member of the present invention achieves both lightweight and high collision safety, and has excellent formability, making it suitable for use in impact absorbing devices for passenger cars. It is expected to make a significant contribution to industry in terms of reducing vehicle weight and saving energy. 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.

11, 21, 31 Impact absorbing member 12, 22, 32 Bottom surface portion 13, 23, 33 Cylindrical portion 14, 24, 25, 34, 35 Internal space 41 Measurement portion

Claims (7)

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. The impact absorbing member according to claim 1, wherein the inorganic fibers include at least one of glass fibers and carbon fibers. The impact absorbing component according to claim 1 or 2, wherein the inorganic fibers have an average fiber length of 10 to 150 mm. The impact absorbing component according to claim 1 or 2, 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. The impact absorbing component according to claim 1 or 2, 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. 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. 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.