JP2009292919A - Energy absorbing component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an energy absorbing component composed of a foamed thermoplastic resin, absorbing much energy by keeping a definite load while suppressing the maximum generation load and suitable for a bumper core, a side impact absorbing material, etc. <P>SOLUTION: The energy absorbing component composed of a foamed thermoplastic resin is characterized in that the part broken by compressing the energy absorbing component has a laminar form essentially perpendicular to the compression direction and the part adjacent to the breaking part is successively broken to proceed the compression. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an energy absorbing member made of a thermoplastic resin foam.

  Energy absorbing members are used in various applications such as automobile bumper cores and side projections, and weight reduction is required from the viewpoint of improving fuel consumption and reducing costs.

  When the energy absorbing member receives an impact, the energy absorbing member itself absorbs the impact energy by partial destruction or deformation, so that the protected object does not receive the impact directly, but a load is still generated by the impact. If this load is too large, the object to be protected is destroyed and the function is lost. Therefore, an energy absorbing member that suppresses the maximum load generated as much as possible is desirable.

  On the other hand, the energy absorption amount is an integration of the impact load and the deformation amount of the energy absorbing member, and a larger impact load can absorb more energy. From these two conflicting events, the most important performance required for the energy absorbing member is to absorb more energy by maintaining a constant load while suppressing the maximum load generated.

  As an energy absorbing member exhibiting such performance, a rigid polyurethane foam and a honeycomb-like structure, which are materials that sequentially buckle when compressed, are known. When a material that sequentially buckles continues to be compressed, the same buckling occurs successively after the surface buckling perpendicular to the compression direction starts, so a substantially constant load is applied after the buckling starts. Persists.

  Patent Document 1 discloses a shock absorber having a honeycomb structure. When compressing a shock absorber made of a honeycomb structure, a constant compressive stress is exhibited up to a large compressive strain by sequentially buckling, but since a large stress peak is generated when the material buckles in the initial stage of compression, the object to be protected A large impact force is applied to an object, and it is difficult to say that the characteristics are sufficient as an energy absorbing member.

  Patent Document 2 discloses a rigid polyurethane foam that does not have a yield point in a stress-compression strain curve, has a constant stress in a compression rate range of 10 to 65%, and sequentially undergoes cell destruction when compressed. However, rigid polyurethane foam is not suitable as a core material for automobile bumpers exposed to the outside air because of its high cost and large volume increase due to moisture absorption. In addition, the rigid polyurethane foam is inferior to the thermoplastic resin foam in terms of weight reduction because the foam density for obtaining the same compressive stress is larger than that of a general thermoplastic resin foam. It is also difficult to recycle.

  In Patent Document 3, a plurality of thermoplastic extruded strand foams are combined to obtain a foam having a higher compressive strength in one direction than the other, and an impact is applied in the direction in which the compressive strength is higher. To absorb shocks. This foam is shown to have a higher compressive strength at 25% strain than a foam of the same material and density. However, this document only discloses a foam made of polyolefin. Polyolefins have a large temperature dependency of their mechanical properties, and have a drawback that they cannot exhibit sufficient shock absorbing performance when the temperature becomes high in an automobile having a relatively high temperature.

As described above, the energy absorbing member that is buckled and deformed sequentially during compression in the prior art has a problem in a large stress peak in the initial stage of compression, difficulty in recycling, light weight, and dimensional change when absorbed. There is a need for a good energy absorbing member made of a thermoplastic resin foam that is lightweight, recyclable, and has little dimensional change when absorbed.
JP 60-49144 A JP-A-5-331364 JP-T-2002-511917

  The object of the present invention is made of a thermoplastic resin foam and has the ability to absorb more energy by maintaining a constant load while suppressing the maximum load generated, such as a bumper core, a side bumper, etc. It is providing the energy absorption member suitable for.

  A first aspect of the present invention is an energy absorbing member made of a thermoplastic resin foam, and when the energy absorbing member is compressed, the broken portion forms a layer shape substantially perpendicular to the compression direction, The present invention relates to an energy absorbing member that is compressed by sequentially destroying a portion adjacent to the portion.

As a preferred embodiment,
(1) It is characterized by comprising a thermoplastic resin having a bending fracture strain of 0.1% to 2.5%,
(2) The thermoplastic resin is a polystyrene resin.
(3) The thermoplastic resin is a monomer composed of an aromatic vinyl, an unsaturated dicarboxylic acid anhydride, and an N-alkyl-substituted maleimide, and the monomer is an aromatic vinyl or vinyl cyanide. A thermoplastic resin composition obtained by mixing a copolymer of
The present invention relates to the energy absorbing member described above.

  The 2nd of this invention is related with the bumper core for motor vehicles which consists of an energy absorption member of the said description, and the 3rd of this invention is related with the side protrusion material for motor vehicles which consists of the said energy absorption member.

  The energy absorbing member of the present invention has a performance of absorbing more energy by maintaining a constant load while suppressing the maximum load generated. Moreover, since it consists of a thermoplastic resin foam, the volume increase by moisture absorption is small, and there exists an effect that it can recycle and is lightweight.

  The energy absorbing member of the present invention is made of a thermoplastic resin foam, and when compressed, the part to be destroyed forms a layer substantially perpendicular to the compression direction, and the parts adjacent to the part are sequentially destroyed. It will be compressed by going.

  In order to confirm such compression deformation behavior, compression is performed at a constant speed using a compression tester and the behavior is observed. Specifically, the energy absorbing member is cut or molded into a three-dimensional shape formed by translating a plane figure in a direction perpendicular to the surface, such as a cylinder or a rectangular parallelepiped, to obtain a test piece. Place this test piece between panels (hereinafter also referred to as compression plates), draw about 10 straight lines in the direction perpendicular to the compression direction on the side of the test piece at regular intervals, and increase the compression strain to 80% or more. Compress until you see the straight line and see which part is compressed.

  When the energy absorbing member of the present invention is compressed by this method, at the initial stage of compression, usually at a compression strain of 3% to 20%, a portion where the linear interval is clearly narrower than the portion before compression appears. It is clearly distinguished from the part. The part where the distance between the straight lines is narrow is a part where the energy absorber is destroyed, and this part forms a layer perpendicular to the compression direction. This broken layered portion often occurs at the end of the test piece that is in contact with the compression plate, but may also occur at the center of the rectangular parallelepiped.

  As the area is further compressed, the area adjacent to the layered destroyed area is sequentially destroyed, increasing the number of parts where the straight line interval becomes narrower, and the destroyed area is still destroyed. It is clearly distinguished from a portion where the interval between the straight lines is almost the same as that in the initial compression, and forms a layer perpendicular to the compression direction.

  When the compression is further continued and the compression strain reaches approximately 60% to 90%, the broken portion extends over the entire test piece, that is, the portion where the interval between the straight lines is clearly narrower than the interval before compression extends over the entire test piece.

  In order to show such behavior when compressed, various factors such as resin type / characteristics, expansion ratio, cell structure, etc. are assumed. It is done.

As one aspect, the energy absorbing member of the present invention preferably has anisotropy in the cell shape. The anisotropy of the cell shape means that the cell has a shape that is long in a specific direction. Specifically, by measuring the cell size of 3 mutually orthogonal directions, and the maximum principal dimension D ₁ of the largest cell diameter, the cell diameter of the intermediate and the intermediate main dimension D _2, the minimum principal dimension of the smallest cell diameter D ₃ . Of the three directions, the direction with the largest cell diameter is called direction 1, the direction with the middle cell diameter is called direction 2, and the direction with the smallest cell diameter is called direction 3.

And cell anisotropy factors R ₁ and R ₂ are respectively set to R ₁ = D ₁ / D _2.
And R ₂ = D ₁ / D ₃
, It is preferable that the value of R ₂ is greater than 1.25. In the case of such an anisotropic thermoplastic resin foam, if the direction (direction 1) in which the cell diameter is large is the compression direction, the energy absorbing member is sequentially destroyed according to the present invention.

  In the case of a foam having anisotropy, the average cell diameter D is preferably 100 μm or more and 1000 μm or less.

  As a method for obtaining a foam having anisotropy, for example, a thermoplastic resin is melt-kneaded in an extruder, and a foaming agent is further injected and kneaded, and then extruded into the atmosphere from a slit die to obtain a foam. There is an extrusion foaming method.

  Since the foam expands in the thickness direction when it is extruded, a foam having a cell-shaped anisotropy factor larger than 1.25 can be obtained. In order to significantly increase the cell anisotropy factor, it is preferable to increase the thickness expansion rate when the molten resin is foamed into the atmosphere during extrusion foaming. As a method of increasing the thickness enlargement ratio, there is a method of reducing the speed of the forming roll in order to increase the forming resistance at the time of forming.

  Also, a bead foam molding method in which foamable resin particles impregnated with a foaming agent are prepared, the foamable resin particles are heated to be prefoamed to produce prefoamed particles, and the prefoamed particles are foamed in-mold. In the above, the pre-expanded particles are filled in a mold, heated to melt the pre-expanded particles and expand to form a foam without any gaps between the particles, and then move one mold, By further expanding the foam in that direction, it is possible to obtain a molded body in which the cell shape is elongated in the moving direction.

  Another preferred embodiment of the energy absorbing member of the present invention is a thermoplastic resin foam having a large average cell diameter D.

The average cell diameter D mentioned here is defined by the following equation from the maximum main dimension D ₁ , the intermediate main dimension D ₂ , and the minimum main dimension D ₃ described above.
D = (D ₁ × D ₂ × D ₃ ) ^1/3
In this embodiment, the average cell diameter D is preferably 350 μm or more and 3000 μm or less, and more preferably 400 μm or more and 2500 μm or less.

  When the average cell diameter is in the above range, there is a tendency to exhibit a behavior during compression like the energy absorbing member of the present invention.

  As a method for producing a thermoplastic resin foam having a large average cell diameter, for example, foamable resin particles impregnated with a foaming agent are prepared, and the foamable resin particles are heated to be prefoamed to produce prefoamed particles. In the method of foam-molding the pre-expanded particles, a volatile foaming agent and a resin are put in a pressure vessel without using water as a dispersion medium when impregnating the foaming agent. Pre-expanded particles having a large average cell diameter D are prepared by heating and pre-expanding the expandable resin particles prepared by maintaining high pressure so as to be in a liquid state and impregnating the foaming agent by heating and stirring. Can do. Furthermore, a thermoplastic resin foam can be obtained by molding the pre-expanded particles in a mold.

  In addition, in pre-expansion molding of beads, pre-foamed particles are prepared by extruding a strand-like foam using a round bar-shaped die and then cutting it into a fixed shape to obtain a large average cell diameter D. There is a method of producing particles and molding pre-expanded particles in a mold.

  In addition, in a extrusion molding method in which a thermoplastic resin is melt-kneaded in an extruder, a foaming agent is further injected and kneaded, and extruded from the die into the atmosphere to obtain a foamed molded product, extrusion is performed using a round bar-shaped die. Accordingly, there is a tendency that the energy absorbing member of the present invention having an average cell diameter D of 350 μm or more and 3000 μm or less can be obtained.

  In the present invention, the thermoplastic resin constituting the thermoplastic resin foam preferably has a bending fracture strain of 0.1% to 2.5%, more preferably 0.1% to 1.5. is there.

  When bending deformation is applied to a thermoplastic resin foam made of a thermoplastic resin having a bending fracture strain of 0.1% or more and 2.5% or less, the portion that is destroyed while the deformation is small is substantially in the compression direction. Tends to occur in a layered pattern perpendicular to When compressive deformation is applied to such a foam, a layered broken part perpendicular to the compression direction is generated, and the broken part is sequentially generated as the compressive strain is increased. It is thought that there is a tendency to persist and exhibit good energy absorption properties.

The bending fracture strain is measured according to JIS K 7171. A foam base resin was molded into a strip-shaped test piece having a thickness of 6 mm, a width of 15 mm, and a length of 120 mm, and left for 24 hours in a thermostatic chamber at 23 ° C. ± 1 ° C. to obtain a test piece for a bending test. A three-point bending test was performed using a tensile compression tester. The distance between fulcrums was 90 mm, and the test speed (indenter descending speed) was 2 mm / min. The breaking strain ε _b [%] is given by the following equation from the deflection s _b [mm] at break, the thickness h [mm] of the test piece, and the distance L [mm] between fulcrums.
ε _b = (6 × h × s _b × 100) / (L ² )
Specific examples of the thermoplastic resin having such characteristics include polystyrene resins, polyethylene naphthalate resins, polycarbonate resins, polyether ether ketone resins, phenylene ether resins, and the above resins and styrene resins. Of the mixture. Further, a copolymer of the monomer constituting the resin with maleic anhydride, N-alkyl substituted maleimide, etc., a copolymer of aromatic vinyl with maleic anhydride, N-alkyl substituted maleimide, etc., aromatic vinyl -Vinyl cyanide copolymer and resin compositions comprising these resins. Among them, a thermoplastic resin composition obtained by mixing a copolymer of aromatic vinyl, unsaturated dicarboxylic acid anhydride and N-alkyl-substituted maleimide and an aromatic vinyl-vinyl cyanide copolymer, or a polystyrene resin. preferable.

  The thermoplastic resin foam of the present invention has a load ratio (S60%) of a stress at 60% strain (hereinafter referred to as S60%) and a load at 10% strain (hereinafter referred to as S10%) based on a compression test. ) / (S10%) is preferably 0.70 or more and 1.30 or less. In order to absorb the energy while suppressing the generated maximum load as much as possible, 0.75 or more and 1.20 or less are more preferable.

  The compression test is performed according to ASTM D1621. The sample is compressed at a constant speed, and calculation is performed by (stress) = (compression load) / (sample cross-sectional area) and strain = (compression deformation amount) / (initial sample thickness).

  In the present invention, additives such as a nucleating agent, a stabilizer, a lubricant, a flame retardant, an antistatic agent, a plasticizer, a water absorbing agent, and a radiation inhibitor are blended in the thermoplastic resin composition as necessary. May be.

  As a foaming agent for obtaining the thermoplastic resin foam of the present invention, one or a mixture of two or more selected from the group consisting of a physical foaming agent and a chemical foaming agent can be used.

  Specific examples of the physical foaming agent include hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, neopentane, and cyclopentane; 1,1-difluoroethane, 1,2-difluoroethane 1,1,1-trifluoroethane, 1,1,2-trifluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane, 1,1,1 , 2,2-pentafluoroethane, difluoromethane, trifluoromethane and other fluorinated hydrocarbons; carbon dioxide, nitrogen, water, argon, helium and other inorganic gases; dimethyl ether, diethyl ether, methyl ethyl ether, isopropyl ether, n- And ethers such as butyl ether and diisoamyl ether. These can be used alone or in admixture of two or more.

  Specific examples of the chemical foaming agent include, for example, N, N′-dinitrosopentamethylenetetramine, p, p′-oxybis-benzenesulfonylhydrazide, hydrazodicarbonamide, sodium carbonate, azodicarbonamide, terephthalazide, 5 -Phenyltetrazole, p-toluenesulfonyl semicarbazide and the like. These can be used alone or in admixture of two or more.

The density of the thermoplastic resin foam constituting the energy absorbing member of the present invention is preferably 11 kg / m ³ or more and 110 kg / m ³ or less from the viewpoint of obtaining good energy absorption characteristics, and 15 kg / m ^The density is more preferably ³ or more and 100 kg / cm ³ or less, and the density can be adjusted in accordance with a desired impact load within this range.

  The thermoplastic resin foam used for the energy absorbing member of the present invention preferably has heat resistance. The heat resistance referred to in the present invention means that the volume change rate when exposed to a hot air circulating dryer maintained at 80 ° C. for 168 hours is 3% or less.

  Since the energy absorbing member of the present invention has excellent shock absorbing performance, it is suitably used for side impact pads of automobiles, core materials for bumpers, and the like.

  Hereinafter, although the energy absorption member of this invention is demonstrated in detail by a specific Example, this invention is not limited only to this Example.

(Test method)
(Observation of compression deformation behavior)
A 25 mm-thick rectangular parallelepiped shape or a cylindrical shape is cut out from the foam as a test piece, lines perpendicular to the thickness direction are drawn at intervals of 3 mm on the side of the foam, and a constant speed of 2.5 mm / min in the thickness direction is drawn. A test was performed to compress the compression strain to 88% at a speed, and the compression deformation behavior was observed.

(Average cell diameter)
Draw a line in the vertical / horizontal direction of the foam cross-section, count the number of cells crossing each line, and divide the length of the line by the number of cells to calculate the width per cell in the vertical and horizontal directions. To do. The cell diameter in each direction is calculated according to the following formula.

Cell diameter = 1.5 × width per cell On the photograph of one cross section orthogonal to the first cross section, a line perpendicular to both of the two directions where the cell diameter was calculated is drawn, and the cell diameter Is calculated in the same way. The cell diameters in the three directions perpendicular to each other in the foam are determined in this order as the largest main dimension D ₁ , the intermediate main dimension D ₂ , and the minimum main dimension D ₃ . The average cell diameter D was calculated according to the following formula.

D = (D ₁ × D ₂ × D ₃ ) ^1/3
(Anisotropy factor)
The cell-shaped anisotropy factor R _{1 is represented} by the following formula: R ₁ = D ₁ / D ₂
Calculated by the anisotropic factor _{R 2} of the cell shape _R 2 _{= D} 1 / D ₃
Calculated by

(Compression characteristics)
Measurement was performed according to ASTM D1621, and a stress strain curve was calculated. The stress was calculated by (compression load) / (sample cross-sectional area), and the compressive strain was calculated by (compression deformation amount) / (initial sample thickness).

(Example 1)
Copolymer A is a copolymer of 49% by weight of styrene, 50% of N-phenylmaleimide and 1% by weight of maleic anhydride, manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: DENKA IP MS-NA, copolymer As B, AS-XGS made by Denki Kagaku Kogyo Co., Ltd., which is a copolymer of 25% by weight of acrylonitrile and 75% by weight of styrene, is used, and 60% by weight / 40% by weight of copolymer A / copolymer B is used. The thermoplastic resin composition was mixed at a ratio of The bending fracture strain of the thermoplastic resin plastic was 0.49%. This thermoplastic resin composition was supplied at a rate of 50 kg / hour to a two-stage connected extruder in which a first-stage extruder having a diameter of 65 mm and a second-stage extruder having a diameter of 90 mm were connected in series. After the thermoplastic resin composition supplied to the 65 mm diameter extruder is melted and kneaded at about 260 ° C., the foaming agent is added to 100 parts by weight of the thermoplastic resin composition near the tip of the first stage extruder. As a result, 2.5 parts by weight of dimethyl ether and 3.5 parts by weight of n-butane were press-fitted into the molten thermoplastic resin composition. Thereafter, the resin is cooled so as to have a resin temperature of 180 ° C. with an extruder having a diameter of 90 mm connected thereto, and is extruded into the atmosphere from a rectangular slit die provided at the tip of the extruder having a diameter of 90 mm. A plate-like foam having m ³ was obtained. The cell structure of the foam obtained by a microscope is observed to calculate the maximum main dimension D ₁ , the intermediate main dimension D ₂ , and the minimum main dimension D ₃ of the cell diameter, and the average cell diameter is calculated from D ₁ , D ₂ , and D _3. D and cell anisotropy factors R ₁ and R ₂ are calculated and shown in Table 1. The direction 1 giving the maximum principal dimension was the thickness direction of the plate-like foam. A rectangular parallelepiped shape having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm is cut out from the foam to obtain a test piece, lines perpendicular to the thickness direction are drawn on the side of the foam at intervals of 3 mm, and a constant speed of 2.5 mm / A test of compressing to a compressive strain of 88% at a speed of minutes was performed, and the compression deformation behavior was observed. Up to 4% of the compressive strain, the whole was uniformly compressed, then began to break from the upper bottom surface, and was sequentially broken from the top. During the compression, it was possible to clearly distinguish the destroyed part where the interval between the straight lines was clearly narrowed and the undestructed part where the interval between the lines was almost the same as before the compression. The destroyed part was layered almost perpendicular to the compression direction. The compressive force was almost constant during sequential failure. When the compression strain reached 83%, it seemed that almost the whole was destroyed, and the compression force suddenly increased from here. Table 1 shows the stress ratio calculated from the stress strain curve of the compression test = (S60%) / (S10%). A photograph of the process of compression deformation behavior is shown in FIG.

(Example 2)
Copolymer A is a copolymer of 49% by weight of styrene, 50% by weight of N-phenylmaleimide and 1% by weight of maleic anhydride, manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: DENKA IP MS-NA, As the blend B, AS-XGS made by Denki Kagaku Kogyo Co., Ltd., which is a copolymer of acrylonitrile 25% by weight and styrene 75% by weight, was used, and the copolymer A / copolymer B was 30% by weight / 70% by weight. % Was mixed to obtain a thermoplastic resin composition. The bending fracture strain of the thermoplastic resin plastic was 0.74%. The first stage extruder having a diameter of 65 mm and the second stage extruder having a diameter of 90 mm were supplied to a two-stage connected extruder connected in series at a rate of 50 kg / hour. After the resin composition supplied to the extruder having a diameter of 60 mm is heated to about 240 ° C. and melt-kneaded, the foam composition is used as a foaming agent with respect to 100 parts by weight of the thermoplastic resin composition near the tip of the first-stage extruder. 2.5 parts by weight of dimethyl ether and 3.5 parts by weight of n-butane were pressed into the molten thermoplastic resin composition. Thereafter, the resin is cooled so as to have a resin temperature of 140 ° C. with an extruder having a diameter of 90 mm connected thereto, and extruded from the die lip of a rectangular slit die provided at the tip of the extruder having a diameter of 90 mm, to a density of 28. A plate-like foam of 8 kg / m ³ was obtained. Table 1 shows cell diameters D ₁ , D ₂ , D ₃ , average cell diameter D, and cell anisotropy ratios R ₁ , R ₂ by observing the cell structure of the foam obtained by a microscope. The direction 1 with the largest cell diameter was the thickness direction of the plate-like foam. A rectangular parallelepiped having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm cut out from the foam was used as a test piece, a compression test was performed in the same manner as in Example 1, and the compression deformation behavior was observed. At this time, the foam exhibited a behavior of breaking sequentially from the center, and during the compression, the broken portion and the unbroken portion could be clearly distinguished. The destroyed part was layered almost perpendicular to the compression direction. The load ratio calculated from the stress strain curve = (S60%) / (S10%) is shown in Table 1.

(Example 3)
The same thermoplastic resin composition as in Example 2 was supplied at a rate of 12 kg / hour to a two-stage connected extruder in which a first-stage extruder having a diameter of 40 mm and a second-stage extruder having a diameter of 50 mm were connected in series. After the resin composition supplied to the 40 mm diameter extruder is melted and kneaded at about 250 ° C., dimethyl ether as a blowing agent is used in the vicinity of the tip of the first-stage extruder as a blowing agent with respect to 100 parts by weight of the thermoplastic resin. 0 part by weight and 2.0 parts by weight of n-butane were press-fitted into the molten thermoplastic resin composition. Thereafter, the resin is cooled so that the resin temperature becomes 180 ° C. with an extruder having a diameter of 50 mm connected thereto, and is extruded into the atmosphere from a round bar die provided at the tip of the extruder having a diameter of 50 mm. to obtain a rod-shaped foam is m ^3. The cell structure of the foam obtained by a microscope is observed to calculate the maximum main dimension D ₁ , the intermediate main dimension D ₂ , and the minimum main dimension D ₃ of the cell diameter, and the average cell diameter is calculated from D ₁ , D ₂ , and D _3. D and cell anisotropy factors R ₁ and R ₂ are calculated and shown in Table 1. Both R ₁ and R ₂ were 1.18 or less, and there was substantially no anisotropy. A cylindrical shape having a diameter of 25 mm and a height of 25 mm was used as a test piece, and a compression test was performed in the same manner as in Example 1 to observe the compression deformation behavior. At this time, the foam shows the behavior of breaking sequentially from the bottom surface.During compression, the broken part where the distance between the straight lines is clearly narrowed and the part where the straight line is not broken are almost the same as before compression. A clear distinction could be made. The destroyed part was layered almost perpendicular to the compression direction. Table 1 shows the stress ratio calculated from the stress strain curve of the compression test = (S60%) / (S10%).

(Example 4)
Example 1 except that the same thermoplastic resin composition as in Example 2 was changed to a heat kneading temperature of 40 ° C. at a diameter of 40 mm, a cooling temperature of 200 ° C. at a diameter of 50 mm, and 4.0 parts by weight of dimethyl ether as a foaming agent. A rod-like foam having a density of 95.8 kg / m ³ was obtained under the same conditions as above. The cell structure of the foam obtained by a microscope is observed to calculate the maximum main dimension D ₁ , the intermediate main dimension D ₂ , and the minimum main dimension D ₃ of the cell diameter, and the average cell diameter is calculated from D ₁ , D ₂ , and D _3. D and cell anisotropy factors R ₁ and R ₂ are calculated and shown in Table 1. Both R ₁ and R ₂ were 1.18 or less, and there was substantially no anisotropy. A compression test was performed in the same manner as in Example 1 using a cylindrical shape having a diameter of 25 mm and a height of 25 mm as a test piece, and the compression deformation behavior was observed. At this time, the foam showed a behavior of breaking sequentially from the upper bottom surface, and during the compression, it was possible to clearly distinguish the broken portion and the non-broken portion. The destroyed part was layered almost perpendicular to the compression direction. The stress ratio calculated from the stress strain curve = (S60%) / (S10%) is shown in Table 1.

(Example 5)
PS Japan polystyrene resin with a bending fracture strain of 0.92% Product name: G9401 to a two-stage connected extruder in which a first-stage extruder with a diameter of 65 mm and a second-stage extruder with a diameter of 90 mm are connected in series It was fed at a rate of 50 kg / hour. After the thermoplastic resin composition supplied to the extruder having a diameter of 60 mm is heated to about 200 ° C. and melt-kneaded, the foaming agent is added to 100 parts by weight of the thermoplastic resin composition near the tip of the first-stage extruder. As a result, 4.0 parts by weight of dimethyl ether and 3.0 parts by weight of i-butane were pressed into the melted thermoplastic resin composition. Thereafter, the resin is cooled so as to have a resin temperature of 130 ° C. with an extruder having a diameter of 90 mm connected thereto, and extruded from the die lip of a rectangular slit die provided at the tip of the extruder having a diameter of 90 mm to a density of 32. A plate-like foam of 1 kg / m ³ was obtained. Table 1 shows cell diameters D ₁ , D ₂ , D ₃ , average cell diameter D, and cell anisotropy ratios R ₁ , R ₂ by observing the cell structure of the foam obtained by a microscope. The direction 1 with the largest cell diameter was the thickness direction of the plate-like foam. A rectangular parallelepiped having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm cut out from the foam was used as a test piece, a compression test was performed in the same manner as in Example 1, and the compression deformation behavior was observed. At this time, the foam showed a behavior of breaking sequentially from the center, and during the compression, it was possible to clearly distinguish the broken portion and the non-broken portion. The destroyed part was layered almost perpendicular to the compression direction. The load ratio calculated from the stress strain curve = (S60%) / (S10%) is shown in Table 1.

(Comparative Example 1)
100 parts by weight of a thermoplastic resin plastic obtained by the same method as in Example 1 was supplied to a single screw extruder and melt kneaded to obtain resin particles having a weight of 0.8 mg per grain. A 6 L autoclave equipped with a stirrer was charged with 100 parts by weight of the obtained thermoplastic resin particles, 100 parts by weight of water, 0.2 parts by weight of calcium phosphate, and 0.006 parts by weight of α-olefin sulfonate. Next, 10 parts by weight of normal butane is added, the temperature is raised to 125 ° C. with stirring, the temperature is maintained for 9.5 hours, and the foaming agent is impregnated into the thermoplastic resin particles to obtain expandable thermoplastic resin particles. It was.

The mixture was heated with 190 ° C. steam generated by an overheated steam generator for 2 minutes and 40 seconds to obtain pre-expanded particles having a bulk magnification of 25 times. The obtained pre-expanded particles were filled in a mold having a length of 450 mm × width of 350 mm × thickness of 40 mm, and heated and fused with saturated steam of 0.38 MPa for 10 seconds, and cooled to a density of 45 kg / cm. ³ foam molded articles were obtained. When the cell structure of the foam obtained by a microscope was observed, it was a composite cell structure in which a large cell of about 30 to 100 μm and a small cell of about 2 to 10 μm were mixed. There was substantially no anisotropy. A rectangular parallelepiped having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm cut out from the foam is used as a test piece, lines perpendicular to the thickness direction are drawn at intervals of 3 mm on the side of the foam, and a compression test is performed in the same manner as in Example 1. The compression deformation behavior was observed. Up to a compression strain of 5%, the whole was uniformly compressed, and then a straight line-distorted portion, which seems to be derived from fracture, was randomly generated in the foam, and the upper, lower and central portions were compressed almost simultaneously. During this time, the compressive force gradually increased, and the slope of the increase in compressive force became steep after the strain exceeded 60%. The compression deformation behavior which can be said to be the whole compression was clearly different from that in the case of being broken into layers as in Example 1. The load ratio calculated from the stress strain curve = (S60%) / (S10%) is shown in Table 1. A photograph of the process of compression deformation behavior is shown in FIG.

(Comparative Example 2)
The same thermoplastic resin as in Example 3 was heated and kneaded at a diameter of 40 mm at 250 ° C., the cooling temperature at a diameter of 50 mm was 160 ° C., and 100 parts by weight of the thermoplastic resin composition was dimethyl ether 4.0 as a foaming agent. A rod-like foam having a density of 33.8 kg / m ³ was obtained under the same conditions as in Example 3 except that the amount was 3.5 parts by weight and n-butane. Table 1 shows the cell diameters D ₁ , D ₂ , D ₃ , the average cell diameter D, and the cell anisotropy ratios R ₁ , R ₂ calculated by observing the cell structure of the foam obtained by a microscope. There was substantially no anisotropy. A cylindrical shape having a diameter of 25 mm and a height of 25 mm was used as a test piece, a compression test was performed in the same manner as in Example 1, and the compression deformation behavior was observed. It was compressed almost uniformly throughout. Table 1 shows the calculated load ratio = (S60%) / (S10%).

(Comparative Example 3)
The same thermoplastic resin composition as in Example 5 was supplied at a rate of 50 kg / hour to a two-stage connected extruder in which a first-stage extruder having a diameter of 65 mm and a second-stage extruder having a diameter of 90 mm were connected in series. The thermoplastic resin composition supplied to the extruder having a diameter of 60 mm is heated to about 200 ° C. and melt-kneaded, and then foamed with respect to 100 parts by weight of the thermoplastic resin composition in the vicinity of the tip of the first-stage extruder. As an agent, 2.5 parts by weight of dimethyl ether and 4.5 parts by weight of i-butane were press-fitted into the molten thermoplastic resin composition. Thereafter, the resin is cooled so that the resin temperature becomes 130 ° C. with an extruder having a diameter of 90 mm connected thereto, and extruded into the atmosphere from a die lip of a rectangular slit die provided at the tip of the extruder having a diameter of 90 mm. A plate-like foam of 4 kg / m ³ was obtained. Table 1 shows cell diameters D ₁ , D ₂ , D ₃ , average cell diameter D, and cell anisotropy ratios R ₁ , R ₂ by observing the cell structure of the foam obtained by a microscope. There was substantially no anisotropy. A rectangular parallelepiped having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm cut out from the foam was used as a test piece, and a compression test similar to that of Example 1 was performed to observe the compression deformation behavior. At this time, the foam was almost uniformly compressed throughout. The load ratio calculated from the stress strain curve = (S60%) / (S10%) is shown in Table 1.

  As shown in Table 1, in the energy absorbing member of the present invention, the value of the stress ratio (S60%) / (S10%) at the time of compression is in the range of 0.75 to 1.20 and exhibits good energy absorption characteristics. .

It is the figure which showed the process of the compressive deformation behavior of the foam of Example 1. From the upper left, the compression state is 0%, 10%, 20%, from the middle left, the compression strain is 30%, 40%, 50%, and from the lower left, the state of the foam is 60%, 70%, 80%. Is shown. It is the figure which showed the process of the compression deformation behavior of the foam of the comparative example 1. From the upper left, the compression state is 0%, 10%, 20%, from the middle left, the compression strain is 30%, 40%, 50%, and from the lower left, the state of the foam is 60%, 70%, 80%. Is shown.

Claims (6)

  An energy absorbing member made of a thermoplastic resin foam, wherein when the energy absorbing member is compressed, the broken portion forms a layer substantially perpendicular to the compression direction, and the portions adjacent to the portion are sequentially An energy absorbing member characterized by being compressed by being destroyed.   2. The energy absorbing member according to claim 1, wherein the energy absorbing member is made of a thermoplastic resin having a bending fracture strain of 0.1% to 2.5%.   The energy absorbing member according to claim 1, wherein the thermoplastic resin is a polystyrene resin.   The thermoplastic resin is a copolymer composed of aromatic vinyl, unsaturated dicarboxylic acid anhydride and N-alkyl-substituted maleimide as a monomer, and a copolymer composed of aromatic vinyl and vinyl cyanide as a monomer. The energy absorbing member according to any one of claims 1 to 3, which is a thermoplastic resin composition obtained by mixing a coalescence.   The bumper core for motor vehicles consisting of the energy absorption member as described in any one of Claims 1-4.   The side protrusion material for motor vehicles which consists of an energy absorption member as described in any one of Claims 1-4.