JP2010201990A - Impact absorbing material for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an impact absorbing material for vehicles which improves an impact load absorbing effect more than before and is not broken. <P>SOLUTION: The impact absorbing material formed by foam-molding of foaming resin beads has an interface break ratio of 90% or more at the time when an impact load is applied. An absorbing material body 1 of the impact absorbing material is formed with a mold 5 structured by fitting a fixed mold 3 and a movable mold 4 together, by setting a one-sided heating step to 20 seconds or shorter, a reversal one-sided heating step to 10 seconds or shorter, and a water cooling step to 15 seconds or shorter. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vehicle shock absorber that protects a lower limb of an occupant of a vehicle.

At the foot of the vehicle occupant, a vehicle shock absorber formed of foamed resin is provided in order to protect the lower limbs of the vehicle occupant against a collision or the like when the vehicle is suddenly braked (see Patent Document 1). ). As shown in the sectional view of FIG. 11 (a), when a concave portion (10) is formed on the lower surface of the absorbent body (1) and an impact load N is applied from above the absorbent body (1), FIG. As shown in (b), the entire absorbent body (1) is compressed and deformed so that the recess (10) expands. In this way, the impact load N is absorbed, and the lower limbs of the occupant are protected from the impact load N.
There is also a prior art that discloses an absorbent body (1) that becomes a plurality of pieces when subjected to an impact load (see Patent Document 2).

JP 2007-246042 A JP 2007-98962 A

12 (a), 12 (b), and 12 (c) are enlarged views of a portion where the impact load N is applied to the absorbent body (1). Since the absorbent body (1) is made of foamed resin, the foamed resin beads (2) are arranged side by side. Adjacent foamed resin beads (2) are strongly bonded to each other and have high peel strength.
As shown in FIG. 12 (a), when an occupant's heel (75) is placed on the upper surface of the absorbent body (1) and an impact load N is applied, a plurality of foamed resins in which the impact load N due to the heel (75) is arranged side by side. Add on beads (2). At this time, the foamed resin beads (2a) that are adjacent to the foamed resin beads (2) to which the impact load N is applied but are not directly subjected to the impact load N are caused by the foamed resin beads (2) that have received the impact load N. Receives downward shear force. In this case, since the reaction force n resisting the shearing is generated during the shearing, the absorbent body (1) absorbs only the Nn impact load obtained by subtracting the reaction force n from the impact load N. That is, the impact load absorbing effect of the absorbent body (1) was not sufficient.
Patent Document 2 discloses a content that becomes a plurality of fragments when the absorbent body (1) is subjected to an impact load, but this does not cause a reaction force due to shearing, but the absorbent body (1). Will be crushed, and then the effect of absorbing the impact load will be lost.
An object of the present invention is to provide an impact absorbing material for a vehicle that improves the impact load absorbing effect than before and that does not crush.

When the foamed resin beads constituting the foamed molded body are subjected to an impact, the foamed resin beads themselves are not crushed, but the foamed resin beads are separated from each other by breaking the interface where the foamed resin beads are joined. Interfacial fracture was caused.
And the impact-absorbing material formed by foam-molding foamed resin beads has an interface fracture rate of 90% or more when pulled.

  In the present invention, the interface fracture rate when an impact load is applied is as high as 90% or more, and the peel strength between adjacent foamed resin beads is set weak. The higher the interface fracture rate, the greater the energy absorption at impact. When a load is applied to the surface of the absorbent main body, the foamed resin bead (2) to which the load is applied peels from the foamed resin bead (2) that is not subjected to an impact load. That is, even if an impact load is applied, the foamed resin beads (2) themselves do not shear, so that no reaction force due to shearing occurs. As a result, the impact load absorbing effect of the vehicle shock absorber can be improved as compared with the conventional case. Even if the absorbent body (1) is subjected to an impact load, the adjacent foamed resin beads are first peeled off and the absorbent body (1) is not crushed, so that the function of absorbing the impact load remains.

(a), (b) is a figure which shows the state at the time of applying the impact load N to the upper surface of an absorber main body. It is sectional drawing of a metal mold | die. It is a perspective view of a test piece. (a), (b) is explanatory explanatory drawing which shows the state of the foamed resin bead in a torn surface. It is a table | surface which shows the result of an interface fracture rate, and energy absorption efficiency. It is a perspective view which shows an impact test. It is sectional drawing which fractured | ruptured the test piece after a scissors indenter fall in the vertical surface containing the AA line of FIG. It is a graph which shows the relationship between an impact load and a displacement. It is explanatory drawing for showing how to obtain | require energy absorption efficiency. It is a graph which shows the relationship between an interface fracture | rupture rate and energy absorption efficiency. (a), (b) is sectional drawing of the conventional absorber main body. (a), (b), (c) is the enlarged view of the part to which the impact load N was added to the absorber main body.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The cross-sectional shape of the absorbent body (1) is the same as that shown in FIG.
1 (a) and 1 (b) are diagrams showing a state when an occupant's heel (75) is placed on the upper surface of the absorbent body (1) of this example and an impact load N is applied. The upper surface of the main body (1) is enlarged. In this example, the peel strength of the adjacent foam resin beads (2) is set weak, and as shown in FIG. 1 (a), when an impact load is applied to the surface of the absorbent body (1), As shown in FIG. 1B, the foamed resin beads (2) to which the impact load N is applied are peeled from the foamed resin beads (2a) not subjected to the adjacent impact load N. Thereby, no shear force is generated between the foamed resin beads (2) and (2a), and the impact absorbing effect is enhanced.
This foamed resin bead (2) is easy to peel off from the adjacent foamed resin bead (2a). As described later, the molding condition of the mold (5) can be changed from the conventional absorbent body. Formed by.

As is well known, as shown in FIG. 2, a foamed resin molded product is molded by a mold (5) having a fixed mold (3) and a movable mold (4). Fill the gap (50) between the molds (3) and (4) with pre-foamed foamed resin beads, inject heat steam into the mold (5), and foam the foamed resin beads (2) to form. Form an article.
In order to set the peel strength of the adjacent foam resin beads (2) to be weak, the molding conditions during molding, specifically, the time for heating or cooling the foam resin beads (2) in the mold (5), The length was set shorter than before, and the adjacent foamed resin beads (2) were lightly adhered. Before explaining the molding conditions, the fixed mold (3) and the movable mold (4) will be briefly described.

The fixed mold (3) shown in FIG. 2 has a first steam valve (30) for taking in the heating steam and a first drain valve (31) for releasing the heating steam, and the movable mold (4) has the heating steam. And a second drain valve (41) for releasing heated steam. The stationary mold (3) and the movable mold (4) are provided with ventilation plates (32) and (42) at locations facing the gap (50), respectively, and the heating steam passes through the ventilation plates (32) and (42). Fine through holes (not shown) are opened.
At the time of molding, after mold clamping, pre-expanded resin beads are filled into the gap (50), both steam valves (30) (40) and both drain valves (31) (41) are opened, and the mold (5) is heated. Flow steam. This is called mold heating.
Next, the first steam valve (30) and the second drain valve (41) are opened, the second steam valve (40) and the first drain valve (31) are closed, and the movable mold ( 4) Heat the steam to the side. This is called one-side heating.
Next, the second steam valve (40) and the first drain valve (31) are opened, the first steam valve (30) and the second drain valve (41) are closed, and the fixed mold (from the movable mold (4) side) 3) Heat the steam to the side. This is called reverse one-side heating.
Next, both steam valves (30) and (40) are opened, both drain valves (31) and (41) are closed, and the heating steam is allowed to flow through the mold (5). This is called double-sided heating.
Next, both steam valves (30) and (40) and both drain valves (31) and (41) are opened, cooling water is poured, and the mold (5) is rapidly cooled. This is a water cooling step, and then the mold (5) is evacuated and slowly cooled. This is the cooling process. Thereafter, both molds (3) and (4) are opened, and the molded product is taken out.

(i)と(ii)が本例に係わる吸収材本体に似せた試験片(６)であり、(iii)が従来の吸収材本体に似せた試験片(６)である。即ち、(i)と(ii)が一方加熱、逆一方加熱又は水冷の各工程の何れかの時間を従来品である(iii)よりも短くして、隣り合う発泡樹脂ビーズ(２)(２)の剥離強度を弱めた。 The applicant formed a test piece (6) resembling three types of absorbent body in the above-described process. This is defined as (i), (ii), and (iii), and the time of each step, which is the molding condition of each test piece (6), is shown in Table 1 below (unit: seconds).

(i) and (ii) are test pieces (6) resembling the absorbent body according to this example, and (iii) is a test piece (6) resembling a conventional absorbent body. That is, in (i) and (ii), the time of either one heating, reverse one heating or water cooling is made shorter than that of the conventional product (iii), and the adjacent expanded resin beads (2) (2) ) Was weakened.

Here, the applicant uses the concept of the interfacial fracture rate as an index indicating the impact absorption effect of the test piece (6). In this example, the interfacial fracture means that the foamed resin beads (2) to which the load N is applied are easily separated from the adjacent foamed resin beads (2) without shearing the beads themselves. In order to measure the interfacial fracture rate, as shown in FIG. 3, the test piece (6) formed with a width H of 40 mm, a depth W of 15 mm, and a height T of 100 mm was pulled at a pulling speed of 500 mm / min to break. The fracture surface was visually observed.
If the peel strength of the foamed resin beads (2) is weak, the foamed resin beads (2) will not be sheared, so the foamed resin beads (2) will remain granular as shown in FIG. Absent. In contrast, when the peel strength of the foamed resin beads (2) is strong, the foamed resin beads (2) in which the shear marks (20) remain are exposed as shown in FIG. 4 (b). Of the total number of the foamed resin beads (2) exposed on the fracture surface, the ratio of the foamed resin beads (2) having no shear mark (20) is referred to as the interfacial fracture rate (unit:%).

  The results of the interface fracture rate are shown in the table of FIG. In the table of FIG. 5, the molded product magnification refers to the ratio of heating and expanding the pre-foamed foamed resin beads, and the number of fractured surface foamed particles is the number of foamed resin beads exposed on the fractured surface (2) The number of interfacial fracture particles refers to the number of foamed resin beads (2) having no shear mark (20). From the graph of FIG. 5, (i) and (ii), which are test pieces (6) resembling the absorbent body according to this example, have a much larger interface fracture rate than the conventional product (iii), and impact It can be seen that the absorption effect is high.

Next, in order to further confirm the impact absorbing effect of the test piece (6), the applicant conducted an impact test in accordance with JIS Z0235: 2002 “Dynamic compression test method for packaging cushioning material”. As shown in FIG. 6, this causes a saddle indenter (7) having a weight of about 8.4 kg to resemble a passenger's heel to fall from a height H1 of about 1 m. After the drop indenter (7) is dropped, the upper surface of the test piece (6) is recessed, that is, displaced, as shown in the cross-sectional view of FIG.
An accelerometer was attached to the scissors indenter (7), and the relationship between the impact load (unit: N) applied to the test piece (6) and the displacement (unit: mm) as the amount of depression was examined. The result is shown in the graph of FIG. It can be seen from the graph of FIG. 8 that the test piece (6) resembling the conventional product has the smallest amount of displacement, that is, the amount of depression (t in FIG. 7) for the same load, and the impact absorbing effect is weak. Can be guessed.

Next, the applicant determined the energy absorption efficiency (unit:%) from the graph of FIG. Here, the energy absorption efficiency refers to the ratio of the energy absorbed by the test piece (6) out of the energy due to the applied impact load. Specifically, the total energy (unit: joule) due to the applied impact load is indicated by the area of the hatched region X + Y in FIG. 9 obtained by multiplying the displacement amount by the load.
On the other hand, since the energy absorbed by the test piece (6) is indicated by the area of the hatched region X in FIG. 9, the energy absorption efficiency is indicated by X / (X + Y). This energy absorption efficiency is shown in the right column of the table of FIG. The table in FIG. 5 shows the energy absorption efficiency when the displacement is 10 mm and the displacement 20 mm. In either case, the test piece (6) of (i) and (ii) is the same as the test piece of (iii). It can be seen that the energy absorption efficiency is higher than (6).
FIG. 10 shows the results of the impact test using the test piece (6) of (i), (ii), and (iii) above, the interface fracture rate (unit:%) and the energy absorption efficiency (unit:%) when the displacement is 20 mm. %). It can be seen that the energy absorption efficiency increases as the interface fracture rate increases.

As shown in FIG. 7, as a result of the impact test performed on the test piece (6), the adjacent foamed resin beads are peeled off, and the test piece (6) is recessed, but is not crushed. Therefore, the effect of absorbing the impact load remains after the depression. For example, when the absorbent body (1) is placed at the foot of a vehicle occupant and the brake is applied suddenly while the vehicle is running, the upper surface of the absorbent body (1) is stepped on and dented. After that, even if the brake is applied again, the effect of absorbing the impact load of the absorbent body (1) remains.
In the test pieces (6) of (i) and (ii) this time, the porosity, that is, the ratio of the gap between the foamed resin beads (2) and (2) to the total capacity of the test piece (6) is 10 to 25. %Met. By setting the porosity to this ratio, it is considered that when the absorbent material is provided in the vehicle, it has a sound absorbing effect.

The above description of the embodiments is for explaining the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope thereof. In addition, the configuration of each part of the present invention is not limited to the above embodiment, and various modifications can be made within the technical scope described in the claims.
The shock absorbing material of the present invention can be used for shock absorption from the side by being arranged on the side of the door in addition to the object installed on the floor of the vehicle.
The foamed resin forming the beads (2) includes polystyrene resin, polyolefin resin (eg, polypropylene resin, polyethylene resin), polyester resin (eg, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate), Examples thereof include polycarbonate resin and polylactic acid resin. Among these, it is preferable to use a composite resin of polystyrene and polyethylene.

(1) Absorber body
(2) Foamed resin beads
(3) Fixed type
(4) Movable type
(5) Mold
(6) Test piece

Claims (2)

An impact absorbing material formed by foam molding foamed resin beads, wherein the interface breaking rate when pulled is 90% or more. The impact absorbing material according to claim 1, wherein a porosity, which is a ratio of a gap between the foamed resin beads to a total capacity of the test piece, is 10 to 25%.

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