JP2005083399A - Shock absorbing member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shock absorbing member having excellent shock absorbing performance. <P>SOLUTION: This shock absorbing member 1 made of foaming thermoplastic resin is provided with a basic part 2 like a flat plate and a slit-like rib structure 3 protruding on at least one face 22 of the basic part 2. The slit-like rib structure 2 is composed of combination of a plurality of ribs 32, 34 having different height of two steps or more. When height h1 of the first rib 32 is 100, height h2 of the second rib 34 is 40 or more and less than 80. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to an impact absorbing member that absorbs a part of energy when an impact load is applied to mitigate the impact, and more particularly, an impact made of foamed thermoplastic resin suitable for applications such as automobile bumpers and doors. The present invention relates to an absorbent member.

  For example, in the case of an automobile, in order to protect the occupant from the impact in the event of an impact, the body can be easily deformed structurally, with bumpers and ceilings to minimize the impact damage to the cabin. In general, an impact absorbing member is provided inside the door, and the impact absorbing member absorbs as much impact as possible at the time of collision.

  Conventionally, as the above-described impact absorbing member, thermosetting urethane foam has been often used. However, thermosetting urethane foam is difficult to recycle and is not only expensive, but also has problems with stability over time of water resistance and heat resistance, and it is difficult to maintain the initial impact absorption performance. Met.

  Therefore, in recent years, foamed thermoplastic resins such as foamed polystyrene and foamed polypropylene, which are easy to recycle and are widely used as cushioning materials for packaging, are often used as impact absorbing members for the above purposes. .

  However, such foamed thermoplastic resins also have the following problems in terms of impact absorption performance. That is, in an impact absorbing member formed of a foamed thermoplastic resin such as expanded polystyrene or expanded polypropylene, the impact load once received means a compressive strain (the ratio of compressive deformation to the original thickness of the impact absorbing material, When the amount of strain (%) in this explanation is greater than 50%, the stress (compressive stress) generated inside increases rapidly, and thereafter the performance as an impact absorbing member is significantly reduced.

  Therefore, when an impact absorbing member made of foamed thermoplastic resin is used for an application such as an automobile bumper, it must be designed within the allowable stress range for compressive strain (amount of strain). There is a problem that the amount is not enough.

  In addition, it is necessary to increase the thickness of the shock absorbing member in order to respond to various impact loads and develop the required shock absorbing performance within the required stress range, such as bumpers, ceilings, doors, etc. There is a problem that the size of each part of the substrate must be increased.

Generally, an impact absorbing member used in an automobile has a limited amount of crushing of the impact absorbing member due to the installation space, and is about 30 to 100 mm. On the other hand, since the impact absorbing member is intended to protect the occupant at the time of collision, the stress applied to the person must be kept within several tens N / cm ² .

  The work of the shock absorbing member (that is, the shock absorbing energy) is expressed by the integrated value of the crushing amount of the shock absorbing member due to the collision and the stress value at that time, so it is larger within the allowable stress value range. It is necessary to secure a crushing allowance.

  The present inventors have previously found that a foam molded article made of a foamed resin and having a specific rib structure exhibits high impact absorption performance (Patent Document 1). This foam molded product is effective as a shock absorber designed with a relatively short crushing allowance, but is not suitable for a shock absorbing member that must secure a larger crushing allowance to absorb a larger impact energy. It was a simple structure.

Further, the inventors of the present invention are made of a foamed resin, and a main rib formed on one surface of the base, and the main rib and the thickness (base) formed on the same surface of the base crossing the main rib. It has been found that a structure combining sub-ribs having different heights from the surface is excellent in impact absorption performance (Patent Document 2).
However, there is a further demand for an impact absorbing material having excellent impact absorbing performance.

Japanese Patent Application No. 2002-157782 Japanese Patent Application No. 2002-261084

  The present invention has been made in view of the above problems, and the stress when an impact load is applied is not more than a predetermined value and is higher by changing between predetermined dynamic compressive strains. An object of the present invention is to provide a shock absorbing member that can secure shock absorbing energy, and is particularly suitable for use in automobiles.

  In order to achieve the above object, the present inventors have intensively studied, and formed of a foamed thermoplastic resin, formed on at least one surface side of the base, and projecting in a direction in which an impact load acts, a height ( According to the shock absorbing member having a slit-like rib structure having a plurality of ribs (partitions) having different distances from the base surface), the heights of the partition walls forming the slits are not uniform and are different. When an impact is applied, the present inventors have found that even when a high rib is folded laterally, the low rib has a function of maintaining stress. As a result, it has been found that the stress value lowering phenomenon due to rib breakage, which can occur in a simple slit-like rib structure composed of ribs of uniform height, can be prevented, and a constant stress value can be exhibited. The present invention has been completed.

  A first aspect of the present invention is an impact absorbing member made of a foamed thermoplastic resin, comprising a flat plate-like base portion and a slit-like rib structure protruding on at least one surface of the base portion. Provided is an impact absorbing member whose structure is a combination of a plurality of ribs having two or more different heights.

  A second aspect of the present invention provides a composite shock absorbing member comprising a combination of the above shock absorbing members.

  According to the present invention, it is possible to obtain an impact absorbing member that is excellent in impact absorbing performance.

Hereinafter, the impact absorbing member of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a partial cross-sectional view of an impact absorbing member according to an embodiment of the present invention.
The shock absorbing member 1 includes a base 2 and a slit-like rib structure 3.
The base 2 has a flat plate shape and has a first surface 22 and a second surface 24 that face each other.
The slit-like rib structure 3 protrudes substantially perpendicularly on the first surface 22 of the base 2 and has a first rib 32 having a first height h1 and a second rib 34 having a second height h2. Consists of.
The arrow indicates the direction of action of the impact load.

The first ribs 32 are formed at equal intervals on the first surface 22 of the base 2, and the second ribs 34 are formed at regular intervals between the first ribs 32. In this embodiment, it is formed between the first ribs 32 as shown in the figure (see FIG. 3), and the interval w1 between the first ribs 32 is the first rib 32 and the second rib. It is approximately twice the interval w2 of 34.
The height h1 of the first rib is not more than the maximum allowable height of the slit-like rib structure 3, and is preferably the maximum allowable height. When the height h1 of the first rib is 100, the height of the second rib h2 is preferably 40-80, and more preferably 60-80.
Here, the “maximum allowable height” is the maximum rib height at which the slit-like rib structure can be formed with respect to the total thickness of the shock absorber, which is determined from the relationship of the installation space. When used for an automobile or the like, it is usually about 30 to 100 mm.

  If the difference between the height h1 and the height h2 is too small, the stress becomes high. On the other hand, if the difference is too large, it may not be possible to prevent a decrease in stress due to rib breakage.

  When the total thickness t3 of the shock absorbing member 1 is 100, the height h1 of the first rib is preferably 50 to 90, more preferably 70 to 90. Similarly, the thickness t4 of the base 2 is preferably 10 to 90, and more preferably 10 to 30. If the height h1 of the first rib is too small with respect to the total thickness t3 of the shock absorbing member 1, sufficient absorbed energy may not be obtained.

  The widths of the first and second ribs 32 and 34 are the same regardless of the height of the ribs, from the width t1 of the lower bottom (base side) to the width t2 of the upper bottom (tip side).

  This shock absorbing member 1 is used by being arranged so that the slit-like rib structure 3 faces the arrow method in which an impact acts. Even if the impact load is applied from the arrow method and the first rib 32 is folded sideways, the second rib 34 can maintain the stress. Therefore, the shock absorbing member 1 can absorb a shock with a constant stress value.

In the above embodiment, the overall shape of the shock absorbing member 1 and the shape and / or number of the base 2 and the ribs 32 and 24 can be appropriately determined according to the purpose of use. The following modifications are possible without departing from the effects of the present invention.
(1) In the above embodiment, the widths of the first and second ribs 32, 24 are the same along the height, but as shown in FIG. The widths t1 and t2 may be tapered from the base side toward the tip side (ie, t1> t2). At this time, the inclination angle α from the perpendicular to the base 2 to the ribs 32 and 34 is preferably 0 ° <α ≦ 7 °. When the inclination angle α is larger than 7 °, the stress increase with respect to the compressive strain gradually increases, which is not preferable.
In this manner, the ribs can be prevented from being folded laterally by being tapered.
In this case, only some of the ribs may be tapered.

(2) In the above embodiment, every other second rib 34 is present between the first ribs 32. However, even if the second ribs 34 are present at a larger interval. Alternatively, it may be present between all the first ribs 32. Preferably, the number of second ribs 34 is about 2 to 8 of the number of first ribs 32.
Moreover, in said embodiment, although w1 and w2 differ, they may be the same. That is, you may arrange | position the 1st and 2nd ribs 32 and 34 at equal intervals.

(3) In the above embodiment, the ribs 32 and 34 have two different heights h1 and h2. However, the ribs 32 and 34 may have three or more different heights. In that case, similarly, when the height of the second (secondary) highest rib is 100, the height of the second (secondary) higher rib is preferably 40 to 80, and 60 to 80 It is more preferable that Thus, it is preferable that the height of the rib having a certain height and the next highest rib sequentially reach the above ratio.
Further, the arrangement of the ribs having different heights of three or more stages may be replaced with the second rib 34 in the above-described embodiment. The widths of the ribs having three or more different heights may be the same or tapered.

(4) In the above embodiment, the base 2 is planar, but may be curved. There may also be unevenness.
(5) In the above embodiment, the slit-like rib structure 3 is formed only on the first surface 22 of the base 2, but may be formed on the second surface 24.
(6) In the above embodiment, the tips of the ribs 32 and 34 are flat, but they may be semicircular or triangular.
The widths of the ribs 32 and 24 are the same, but may be different. The intervals w1 and w2 between the ribs 32 and 24 are the same between the ribs, but may be different. Each rib 32, 24 may extend with the same length on the base 2 or may extend with a different length. Moreover, each rib 32 and 24 may have a notch partway.

  Further, two or more of the shock absorbing members 1 described above can be combined and used as a composite shock absorbing member. For example, the two impact absorbing members 1 can be used by aligning the second surfaces 24 of the base portion 2 in the same direction as the direction of the impact load. Moreover, you may arrange. In this way, by superposing a plurality of the impact absorbing members 1 of the present invention, it is possible to exert a greater impact absorbing performance with respect to a larger impact load as compared with a single impact absorbing member.

Next, the constituent material of the impact absorbing member of the present invention will be described.
The impact absorbing member of the present invention is a foamed resin molded article obtained by filling foamed thermoplastic resin particles obtained by primary foaming of foamable thermoplastic resin particles into a mold and heating with a heating medium such as steam. It is.

  The foamed thermoplastic resin, which is the material of the impact absorbing member of the present invention, is obtained by first foaming thermoplastic resin particles having foamability into foamed thermoplastic resin particles, filling the mold with a desired shape, and heating. It is obtained by doing. The foamed thermoplastic resin is not particularly limited as long as it has foamability and thermoplasticity. Specifically, for example, maleimide monomers such as polystyrene, styrene and acrylonitrile, methacrylonitrile, α-methylstyrene, maleic anhydride, phenylmaleimide, cyclohexylmaleimide, and acrylic acids such as acrylic acid and acrylate esters. Monomers, styrene copolymers copolymerized with methacrylic monomers such as methacrylic acid and methacrylic acid esters, homopolymers of methacrylic monomers, methacrylic monomers and acrylic acids Examples thereof include copolymers by a combination of two or more monomers, and olefin resins such as polyethylene and polypropylene.

  Of the above-mentioned foamed thermoplastic resins, styrene copolymers are preferable from the viewpoint of production cost, recyclability, foam moldability, etc. Among them, acrylonitrile / styrene copolymers having excellent heat resistance and oil resistance are particularly preferable. . In addition, “HIBEADS GR” (trade name) manufactured by Hitachi Chemical Co., Ltd. can be suitably used as a commercially available resin of foamable acrylonitrile / styrene copolymer. Of course, other resins may be used as long as they have the above-described physical properties and can be used as, for example, an impact absorbing member for automobiles. The impact absorbing member of the present invention produced from a foamed styrenic polymer can be suitably used for automobile bumpers, ceilings, and doors.

  In order to perform primary foaming (also referred to as pre-foaming), the foamable thermoplastic resin particles are heated with a heating medium such as steam using a foaming agent generally used in the production of foamable styrene resins and the like. Examples of the foaming agent that can be used include readily volatile organic compounds that are gases or liquids at normal temperature and pressure and do not dissolve the thermoplastic resin. Specific examples of such an organic compound include aliphatic hydrocarbons such as butane, propane, and pentane, and cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane. Further, when foaming, an organic solvent such as ethylbenzene, toluene, styrene, xylene or the like, which can dissolve or swell the thermoplastic resin, epoxidized soybean oil, vegetable oil or the like can be added as a plasticizer.

  The density of the primary foamed thermoplastic resin particles is usually preferably in the range of 0.033 to 0.2 g / mL (foaming factor: 5 to 30 times), although it depends on the type of resin. More preferably, it is in the range of 0.05 to 0.1 g / mL (foaming factor: 10 to 20 times).

  The foamed thermoplastic resin constituting the impact absorbing member of the present invention must generate an appropriate compressive stress according to the use of the impact absorbing member when an impact load is applied. If this compressive stress is too large, the repulsive force when the impact load is applied becomes too large to absorb the impact sufficiently. On the other hand, if it is too small, it will not be able to withstand the impact load and will be easily destroyed, making it impossible to obtain the desired impact absorption performance.

  For example, when the impact absorbing member of the present invention is applied to an automobile, the 50% compressive stress measured according to the method defined in JIS-Z0235 is preferably in the range of 0.01 to 2.5 MPa. The range is more preferably in the range of 0.05 to 2.0 MPa, and still more preferably in the range of 0.1 to 1.5 MPa. If the 50% compressive stress is less than 0.01 MPa, the compressive stress is too small to obtain sufficient impact absorbing performance. On the other hand, when the pressure is larger than 2.5 MPa, the compressive stress is too large, the repulsive force against the impact load is increased, and it is difficult to absorb the impact and the impact absorption performance is deteriorated.

  The density of the foamed thermoplastic resin constituting the impact absorbing member of the present invention is preferably 0.03 g / mL to 0.2 g / mL, more preferably 0.05 g / mL to 0.1 g / mL. preferable. When the density of the resin is less than 0.033 g / mL, it is difficult to obtain physical properties that achieve the required stress. When the resin density exceeds 0.2 g / mL, not only the stress value increases, but also the weight of the impact absorbing member. Reduction becomes difficult.

The static compressive stress when the strain rate of the foamed thermoplastic resin constituting the shock absorbing member of the present invention is 25% is preferably 35 N / cm ^{2 to} 350 N / cm ² ,
And more preferably ^{50N / cm 2 ~150N / cm 2} .

  In order to make a static compressive stress into the said range, it adjusts so that the density of the foaming thermoplastic resin which comprises an impact absorber may be 0.03-0.2 gm / mL, for example.

  The impact-absorbing member of the present invention is a foamed resin molded product in which the first foamed foamed thermoplastic resin particles are filled in a mold having a desired shape and heated with a heating medium such as steam. It is.

  The impact absorbing member of the present invention is composed of the above-mentioned foamed thermoplastic resin, and has a slit-like rib structure as described above, so that higher impact absorbing energy can be secured, and particularly for automotive applications such as bumpers and ceilings. Suitable for doors, side bumps.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited by these.

Example 1
(1) Primary foaming of expandable thermoplastic resin particles Expandable acrylonitrile / styrene copolymer resin particles (manufactured by Hitachi Chemical Co., Ltd .: HIBEADS GR) are used as a batch type foaming machine for polystyrene foam (manufactured by Hitachi Chemical Technoplant Co., Ltd.). : HBP-500LW), and first foamed to a bulk density of 0.057 g / mL (foaming factor: 17.5 times), and then stored in a silo with good ventilation for 18 hours until molding.

(2) Manufacture (molding) of impact absorbing members
A mold having a shape having a slit-like rib structure shown in Table 1 and FIG. 3 was set in a polystyrene foam molding machine (manufactured by Hitachi Chemical Co., Ltd .: Moldex 10VS) and clamped. 3A is a plan view of the shock absorbing member, and FIG. 3B is a cross-sectional view thereof. The resin particles primarily foamed in the above (1) are filled in a mold, heated with 0.08 MPa gauge water vapor for 25 seconds, cooled together with the mold and vacuum cooled, and then the molded product is taken out from the mold. . At this time, the density of the foamed thermoplastic resin constituting the molded product was 0.057 g / mL, and the static compressive stress at a strain rate of 25% was 57 N / cm ² . The static compressive stress at a strain rate of 25% was measured according to JISZ0235.

(3) Impact absorbing performance evaluation of impact absorbing member The foamed resin molded product obtained in (2) above was used as a test body having a length of 140 mm, a width of 140 mm, and a thickness of 46 mm, and an impact load test was performed. In the impact load test, a mass variable weight having a plane wider than the specimen is dropped at a specified speed perpendicularly onto the surface of the specimen having the slit-like rib structure, and the acceleration (G value) generated in the weight and the test are tested. The amount of change in body thickness (compression strain) was measured, and the impact absorbing performance of the impact absorbing member was evaluated. The weight was 4.5 kg and the drop height was 2.5 m.

Example 2
Except that the mold was replaced, an impact absorbing member having the shape shown in Table 1 below was produced in the same manner as in Example 1, and the impact absorbing performance was evaluated in the same manner as in Example 1.

Comparative Example 1
Except for replacing the mold, a shock absorbing member having a slit-like rib structure composed of ribs having a uniform height as shown in Table 1 and FIG. Similarly, the impact absorption performance was evaluated. 4A is a plan view of the impact absorbing member of Comparative Example 1, and FIG. 4B is a cross-sectional view thereof.

  FIG. 5 shows the impact absorbing performance of the impact absorbing members manufactured in Examples 1 and 2 and Comparative Example 1 as a graph showing compressive strain (%) with respect to dynamic compressive stress.

  From the graph of FIG. 5, it can be seen that the change in dynamic compressive stress with respect to the amount of compressive strain is small.

  The present invention can be used as an impact absorbing member. Since it has excellent shock absorbing performance, it is particularly suitable for use in automobiles, for example, bumpers, ceilings, doors, and side impact pads.

It is a fragmentary sectional view of the impact-absorbing member of one Embodiment of this invention. It is a fragmentary sectional view of the shock absorption member of other embodiments of the present invention. FIG. 3A is a plan view of the impact absorbing member manufactured in Example 1, and FIG. 3B is a cross-sectional view thereof. 4A is a plan view of the impact absorbing member manufactured in Comparative Example 1, and FIG. 4B is a cross-sectional view thereof. It is a graph which shows the relationship of the compressive strain (%) with respect to the dynamic compressive stress (N / cm < ² >) in the impact-absorbing member manufactured in Example 1, 2 and Comparative Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shock absorption member 2 Base 22 First surface of base 24 Second surface of base 3 Slit-like rib structure 32 First rib 34 Second rib t1 Width of bottom bottom portion of rib t2 Width of top bottom portion of rib t3 Total member thickness t4 Base thickness h1 First rib height h2 Second rib height W1 First rib spacing W2 First rib to second rib spacing α Rib angle of inclination

Claims (9)

An impact absorbing member made of foamed thermoplastic resin,
A flat base, and
A slit-like rib structure protruding on at least one surface of the base,
An impact absorbing member comprising a combination of a plurality of ribs in which the slit-like rib structure has two or more different heights. When the height of the rib having the maximum height is 100, the height of the second highest rib is 40 to 80,
The shock absorbing member according to claim 1, wherein the height of the second highest rib is 100 when the height of the second highest rib is 100 when the height is different in three or more stages. .   The shock absorbing member according to claim 2, wherein a height of the rib having the maximum height is a maximum allowable height of the slit-like rib structure.   The maximum height of the slit-like rib structure is 50 to 90, and the thickness of the base is 10 to 90 when the total thickness of the shock absorbing member is 100. 4. Shock absorbing member.   The impact absorbing member according to any one of claims 1 to 4, wherein the width of each rib constituting the slit-like rib structure is the same from the base side to the tip side.   The width of each rib constituting the slit-like rib structure decreases in a tapered manner from the base side toward the tip side, and the inclination angle α from the perpendicular to the base portion to the rib is 0 ° <α ≦ 7 The impact-absorbing member according to any one of claims 1 to 4, which is within a range of °. The density of the foamed thermoplastic resin constituting the impact absorbing member is 0.033 g / mL to 0.2 g / mL, and the static compressive stress when the strain rate is 25% is 35 N / cm ^{2 to} 350 N / cm. The impact absorbing member according to claim 1, which is ² .   The impact-absorbing member according to any one of claims 1 to 7, wherein the foamed thermoplastic resin is a foamed styrene copolymer.   A composite impact absorbing member comprising a combination of a plurality of impact absorbing members according to claim 1.

Images