JP3838752B2 - Shock absorbing member for automobile and manufacturing method thereof - Google Patents

Description

【００２４】
【発明の効果】
本発明によれば、特定の閉断面二層構造を採用することにより、衝撃緩衝効果が高く、耐座屈性にすぐれ、軽量化も維持される自動車用衝撃緩衝部材が得られる。また、射出成形手段のみによって成形できるとともに、外殻部の形成で実質賦形が完了し、内部の発泡構造層の冷却を特に待つことなく離型が可能であり成形サイクルの点でもすぐれている。さらに、部材全体が同一の材料で形成されるのでリサイクル性にもすぐれたものである。
【００２５】
【図面の簡単な説明】
【図１】本発明の自動車用衝撃緩衝部材の概略正面図
【図２】本発明の自動車用衝撃緩衝部材の概略平面図
【図３】本発明の自動車用衝撃緩衝部材の概略切断図（図１のＡ−Ａ断面）
【図４】本発明の自動車用衝撃緩衝部材の他の例の概略切断図（図１のＡ−Ａ断面）
【図５】本発明の製造方法を説明するための、成形前の金型の断面図
【図６】本発明の製造方法を説明するための、成形後の金型の断面図
【図７】比較例の自動車用衝撃緩衝部材の概略切断図
【符号の説明】
１：自動車用衝撃緩衝部材
２：自動車本体への取り付け部
３：取り付け用ボルト穴
４：外殻非発泡構造部
５：発泡構造部
６：高密度発泡部
７：固定型
８：移動型
９：スライトコア
１０：金型キャビティ
１１：スプルー
１２：前面用本体部材
１３：裏面用部材
１４：溶着部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automobile impact cushioning member and a method for manufacturing the same. More particularly, the present invention relates to an automobile impact cushioning member having excellent impact cushioning characteristics and buckling resistance and improved productivity, and a method for manufacturing the same.
[0002]
[Prior art]
Conventionally, metal shock-absorbing members such as bumpers and bumper beams have been frequently used. Metal shock-absorbing members have no drawbacks in strength, but are susceptible to corrosion, and are disadvantageous in that they are heavy and cannot respond to recent demands for resource saving. For this reason, those made of synthetic resin have been adopted from the viewpoints of weight reduction, resource saving, recyclability, and the like. These shock-absorbing members for automobiles made of synthetic resin are generally effective to have a shape with a closed cross-sectional structure, but since the rigidity is lower than that of metal, optimization of shape, thickness distribution, etc. is required. It is.
[0003]
As a manufacturing method of an impact buffer member for an automobile having a closed cross-sectional structure, there is a method in which a front main body member and a rear surface member are separately formed by integral molding or injection molding by blow molding and bonded by secondary processing. Since the automobile shock-absorbing member obtained by any of the methods has a closed cross-section hollow structure, when an impact is applied, such as during a car collision, the buckling deformation and the strength may not be sufficient. Increasing the wall thickness to ensure strength increases the product weight and reduces the merit of using the resin.
[0004]
In addition, it is conceivable to form the closed cross-section structure with a foam, but even if weight reduction can be achieved, the strength and the like are insufficient and there is no practicality. It is also possible to integrate the foam by inserting it inside, but it is a combination of two kinds of materials, secondary processing is required, such as strength, impact buffering, buckling resistance, Practical use is difficult in terms of productivity.
[0005]
[Problems to be solved by the invention]
Under such circumstances, the present invention utilizes the excellent moldability of the thermoplastic resin and adopts a special molding method, thereby maintaining strength while maintaining weight reduction while being integrally molded by injection molding. An object of the present invention is to provide an automobile impact cushioning member excellent in rigidity, impact cushioning and buckling resistance and an efficient manufacturing method thereof.
[0006]
[Means for Solving the Problems]
The present inventor has conducted various studies on the application to an impact buffer member for automobiles with regard to excellent productivity of injection molding and weight reduction by foam molding. As a result, a shock-absorbing member for automobiles having a composite structure composed of a non-foamed, high-density outer shell and a low-density inner foamed structure portion is obtained by using a slide core in the molding die and combining with a foamable resin. I found out. The present invention has been completed based on such findings.
[0007]
That is, (1) A shock-absorbing member for an automobile, which is a monolithic structure forming body made of a thermoplastic resin, and the inside excluding the outer shell portion has a foam structure.
(2) internal foamed structure portion, automotive shock absorbing member according to the above (1) to a built-in rib structure continuous in the direction before and after the vehicle a higher density than the inner foam structure portion.
(3) The automobile shock absorbing member according to (1) or (2), wherein the shock absorbing member has 1 to 4 rib structures in the longitudinal direction.
(4) After the foaming thermoplastic resin is injected and filled into the cavity formed from the projecting slide core that can be advanced and retracted into the mold cavity, the slide core is then retracted to foam the inside. A method of manufacturing an impact buffer member for an automobile.
(5) The automobile impact cushioning member according to (4), wherein after filling and injecting a foamable thermoplastic resin, the slide core is retracted while injecting gas and then the pressure is removed to foam the inside. Production method.
(6) The method for producing an impact buffering member for an automobile according to (4) or (5) above, wherein a mold cavity having 1 to 4 slide cores in the longitudinal direction is used.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
First, there is no restriction | limiting in particular as a thermoplastic resin which comprises the impact buffer member for motor vehicles of this invention, The thermoplastic resin which can be injection-molded is used. Examples of these resins include polypropylene, ethylene-propylene random copolymer or block copolymer, crystalline polyolefin such as high and medium density polyethylene, polyamide, polyester, polycarbonate, and ABS resin. These resins can be used alone or in combination of two or more. Among these, crystalline polyolefins such as polypropylene, propylene-ethylene block copolymer, and high density polyethylene are preferable.
[0009]
Thermoplastic resins include known low-crystalline ethylene-α-olefin copolymers (EPR, EBR, EPDM, etc.), styrene-butadiene rubber, for the purpose of improving impact resistance, rigidity, and heat resistance. Impact strength improving compounding agent such as styrene-butadiene-styrene block copolymer rubber, styrene-ethylene-butylene-styrene block copolymer, strength, rigidity, heat resistance improving compounding agent, unsaturated such as talc, mica, glass fiber, etc. Carboxylic acid modified polyolefin resin etc. can also be mix | blended as needed. These blending amounts are usually 50 parts by weight or less with respect to 100 parts by weight of the thermoplastic resin. Furthermore, crystallization accelerators, antioxidants (phosphorus, phenol, sulfur, etc.), neutralizers, lubricants, dispersants, peroxides, heat stabilizers, UV absorbers, light stabilizers, antistatic agents Additives such as flame retardants, flame retardant aids, plasticizers, epoxy compounds, metal deactivators, pigments and dyes can be added as appropriate.
[0010]
In producing the automobile impact buffer member of the present invention, it is necessary to add a foaming agent to impart foamability to the thermoplastic resin. As the foaming agent, one that decomposes by heat to generate gas is used, and examples thereof include oxalic acid derivatives, azo compounds, hydrazine derivatives, semicarbazides, azide compounds, nitroso compounds, triazoles, urea, and related compounds. Specific examples include azodicarbonamide (ADCA), benzenesulfohydrazide, N, N-dinitropentamethylenetetramine, terephthalazide and the like.
[0011]
The shock-absorbing member for automobiles of the present invention is an integral structure molded body made of a thermoplastic resin, and the inside excluding the outer shell portion has a foamed structure. In other words, it is not a uniform foam structure, as in the case of a molded product obtained by molding with a foamable resin by a general injection molding method. The structure consists of a substantially two-layer structure. An example of the shock absorbing member for automobile according to the present invention will be described with reference to the drawings.
[0012]
FIG. 1 is a front view of an impact buffer member for an automobile, and FIG. 2 is a plan view. In the figure, 1 is an impact buffer member for an automobile, 2 is an attachment portion to the vehicle body, and 3 is a bolt hole for attachment. FIG. 3 is a cross-sectional view taken along the line AA of the automobile shock absorbing member of FIG. 1. FIG. 4 is a sectional view taken along the line AA of another example. In the figure, 4 indicates an outer shell structure part which is a non-foamed part, and 5 indicates a foamed structure part. The impact buffering member for automobiles of the present invention is usually composed of a long curved part and attachment parts to the automobile body provided at both ends as shown in FIGS. Further, as a whole, it has a characteristic in that it has a closed cross-section integrated structure and a multi-layer structure of a non-foamed structure portion and a foamed structure portion of the outer shell. FIG. 3 shows a case where the foamed structure portion is substantially uniform throughout, and FIG. 4 shows a case where the foamed structure portion is divided into three in the longitudinal direction across a relatively high density partition wall. The partition wall, that is, the rib structure, is formed in the front-rear direction with respect to the vehicle body of the automobile shock-absorbing member, and is usually formed continuously along the longitudinal direction. The partition walls are usually 1 to 4 and preferably 2 to 3 from the viewpoints of deformation, buckling resistance, moldability and the like. Here, it is preferable that the cross-sectional shape of the shock-absorbing member for automobiles is a trapezoid in which the outer shell having a cross-section perpendicular to the longitudinal direction forms a substantially rectangular shape or a taper from the automobile body side toward the front surface side. The angle α of the tapered portion is preferably set in the range of 1 to 20 degrees, more preferably in the range of 1 to 10 degrees. If this range is exceeded, the moldability and buckling resistance will decrease. As described above, when the shape has a certain angle, the thickness of the upper and lower portions of the outer shell on the vehicle body attachment side is increased, and the buckling resistance is further improved.
[0013]
The density of the internal foam structure does not necessarily have to be uniform, and the boundary with the non-foamed portion need not be clearly distinguished, and the density may be continuously changed. In addition, it is preferable that the partition wall is substantially formed of a non-foamed resin, but the effect of the present invention is achieved if the density is higher than other foamed portions. Furthermore, the attachment means and position to the automobile body are also arbitrary, and not only in the case of both sides of the member in the case of FIG. 2, but also a portion consisting only of a non-foamed portion may be formed at the center of both ends.
[0014]
Here, the thickness of the outer shell and the partition may be appropriately determined in consideration of the overall design weight of the member, required characteristics, the density of the foamed portion and the non-foamed portion, and the like. In addition, the thickness of the outer shell, the area of the cross section, etc., can be constant in the longitudinal direction of the member, but are determined appropriately according to factors such as the type, weight, width of the vehicle, necessary load resistance, and buckling resistance. can do.
[0015]
By adopting the closed cross-section structure as described above, it has superior shock mitigation characteristics, deformation resistance, and buckling resistance compared to the same weight automotive impact cushioning member that does not have a foam structure inside. It will be.
Next, the manufacturing method of the impact buffer member for automobiles of the present invention will be described.
In the manufacturing method of the present invention, a foamable thermoplastic resin is injected and filled into a cavity formed from a projecting slide core that can advance and retreat into a mold cavity, and then the slide core is retracted to foam the inside. It is characterized by that. That is, unlike general foam injection molding, when the molten resin is injected and filled, the volume of the resin is smaller than the cavity volume of the final molded product, that is, the volume corresponding to the injection resin (no foaming) is prevented from causing foaming of the resin. Fill completely. A non-foamed outer shell portion is formed by cooling with a mold, and this formation is completed. When the inside of the outer shell portion can be foamed in a molten state, the slide core is retracted to foam the molten resin. In this case, if necessary, when the slide core is retracted, a high-pressure gas such as nitrogen is introduced to fill the space generated by the slide core retreat, and cooling of the outer shell is performed in this state. Next, a method of filling the space by degassing and foaming the resin can be adopted. Therefore, in this case, the formation of the outer shell and the suppression of foaming will continue even after the slite core is retracted.
[0016]
Next, the concept of the production method of the present invention will be described with reference to the drawings. FIG. 5 is a cross-sectional view of the mold showing the state of the mold when the slide core is moved forward and the resin is injected, and FIG. 6 is a state of the mold when the slide core is completely retracted. 5 and 6, reference numeral 7 denotes a fixed type that forms the front side of the automobile shock absorbing member, and 8 denotes a movable type that forms the back side. Reference numeral 9 denotes a slide core mold projecting from the movable mold toward the fixed mold so as to be able to advance and retreat, and a molding cavity 10 is formed by these.
[0017]
In the manufacturing method of the shock absorbing member for automobiles, first, the fixed mold and the movable mold are clamped, and then the slide core 9 is protruded into the cavity so that the volume corresponding to the weight of the shock absorbing member for automobiles is filled. Thus, the cavity volume is reduced. At this time, if necessary, by introducing a high pressure gas of 0.5 to 2 Mpa into the cavity 10, foaming of the foamable resin to be injected next can be prevented and the surface appearance can be improved. The foamable molten resin is injected from the sprue 11 into the cavity so that the resin does not foam, and is filled and filled in the cavity. When the molten resin is completely filled in the cavity, the resin is cooled and the portion that contacts the mold is cured without foaming, and an outer shell made of non-foamed resin is formed by this curing. Next, when the inside is still in a molten state, the slide core 9 is moved backward to make the cavity volume the volume of the final molded product. At this time, it is preferable to introduce a high-pressure gas into the top of the slide core in order to temporarily secure a cavity enlarged portion formed by the retraction of the slide core 9 as a space. The introduced gas is discharged after the slide core has been retracted. The molten resin is foamed by the decompression due to the expansion of the cavity or the decompression due to the discharge of the gas, and then cooled and hardened to form the foamed layer portion inside.
[0018]
As shown in FIG. 4, the automobile impact cushioning member formed by such a method has a non-foamed structural layer 4 formed in the outer shell portion and a foamed structural portion 5 formed therein. Note that the internal foam structure portion includes a portion 6 that forms a relatively high density rib structure as shown in FIG. The formation of this relatively high density rib structure part is that the molten resin in contact with the slide core is not as much as the outer shell part, but is cooled relatively faster than other parts inside, and the slide core is retracted and depressurized. It is thought that this is caused by the coupling of the wall surfaces separated by the slide core. In addition, the non-foamed structure layer of the outer shell and the foamed structure layer in the inner part do not necessarily have a clear boundary in terms of density, and may change with a certain width. In the present manufacturing method, the case of FIG. 4 in which the rib structure is formed inside has been described. However, the automobile shock absorbing member shown in FIG. 3 has a single slide core and can be manufactured more easily. The thickness of the non-foamed outer shell can be adjusted by controlling the cooling conditions of the mold and the retreat timing of the slide core. Moreover, when using a some slide core, a cooling means can also be provided in slite core itself.
[0019]
As described above in detail, the impact buffering member for automobiles of the present invention has an impact cushioning member for automobiles that is formed only by the outer shell portion by forming the non-foamed structural layer of the outer shell and the foamed structural layer of the inner body integrally. Exhibits superior properties than the members. In addition, by adopting a two-stage molding means, such an automobile impact cushioning member clearly forms a non-foamed structural layer when the slide core advances, and forms an internal foamed structural layer when the slide core moves backward, It can be integrally formed with a single molding machine and can be manufactured with high productivity without the need for secondary processing such as heat welding.
[0020]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
Example 1
Using an injection molding machine [Mitsubishi Heavy Industries, Ltd .; 850 MGW (clamping force 850 tons)], an impact buffer member for automobiles having a shape shown in FIGS. 1, 2, and 4 [length: 1200 mm, width: 125 mm, Height: 100 mm, taper (α): 2 degrees] was molded. As the resin, polypropylene (manufactured by Idemitsu Petrochemical Co., Ltd .; IDEMITSU PP J-466HP, MI = 3 g / 10 min (230 ° C., 2.16 kg load)) and 2 blowing agents (manufactured by Eiwa Kasei Kogyo Co., Ltd .; Polyslen EE206) are used. What added weight% was used. The resin was melted and 100% injection-filled so as not to foam into the cavity whose outer shell had a thickness of 5.8 mm in a state where the slide core divided into three parts was advanced. Next, the slide core was retracted to a position corresponding to the shape of the final molded product while introducing 2 MPa of nitrogen gas into the top of the slide core. Then, after cooling, the mold was opened and the automobile shock absorbing member was taken out.
[0021]
As shown in FIG. 4, the obtained impact buffering member for automobiles was formed of a non-foamed structure layer portion and a foamed structure layer portion (×: high density portion, points: highly foamed portion) in the shaded portion. The impact buffer member for automobiles was subjected to a pendulum collision test (vehicle weight: 1.1 ton, collision condition: 5 miles) to evaluate the maximum deformation, generated load, and buckling state. The evaluation results are shown in Table 1.
[0022]
Comparative Examples 1-2
As shown in FIG. 7, the front body member and the back surface member of the automobile shock absorbing member were separately molded by injection molding. Then, the final shock absorbing member for automobiles was obtained by heat welding the two members. In Comparative Example 1, the product weight is the same as in Example 1, and Comparative Example 2 shows the case where the weight is increased. The results of evaluation according to the examples are shown in Table 1. From these evaluations, it is clear that the shock absorbing member for automobiles of the present invention has excellent shock absorbing characteristics with a small maximum deformation amount in consideration of the product weight in spite of a small manufacturing process.
[0023]
[Table 1]

[0024]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the impact-buffering member for motor vehicles by which a specific impact cross-section two-layer structure is employ | adopted has a high impact buffering effect, is excellent in buckling resistance, and a weight reduction is also obtained. In addition to being able to be molded only by injection molding means, substantial shaping is completed by forming the outer shell, and it is possible to release without particularly waiting for the cooling of the internal foam structure layer, which is also excellent in terms of molding cycle. . Furthermore, since the entire member is made of the same material, it is excellent in recyclability.
[0025]
[Brief description of the drawings]
FIG. 1 is a schematic front view of an impact buffer member for an automobile according to the present invention. FIG. 2 is a schematic plan view of an impact buffer member for an automobile according to the present invention. 1 AA cross section)
FIG. 4 is a schematic sectional view of another example of the shock absorbing member for automobile according to the present invention (cross section AA in FIG. 1).
FIG. 5 is a sectional view of a mold before molding for explaining the manufacturing method of the present invention. FIG. 6 is a sectional view of a mold after molding for explaining the manufacturing method of the present invention. Schematic cutaway view of impact buffer member for automobile of comparative example 【Explanation of symbols】
DESCRIPTION OF SYMBOLS 1 : Impact buffer member for motor vehicles 2: Attachment part to motor vehicle body 3: Bolt hole 4 for attachment: Non-foaming structure part 5: Foam structure part 6: High density foam part 7: Fixed type 8: Moving type 9: Slite core 10: mold cavity 11: sprue 12: front body member 13: back member 14: welded portion

Claims (6)

A shock-absorbing member for automobiles, wherein the shock-absorbing member is a monolithic structure molded body made of a thermoplastic resin, and the inside excluding the outer shell portion has a foamed structure. Internal foam structure portion, automotive shock absorbing member according to claim 1 wherein a built-in rib structure continuous with the front-rear direction of the vehicle body to a higher density than the inner foam structure portion. The shock-absorbing member for automobile according to claim 1 or 2, having 1 to 4 rib structures in the longitudinal direction. For automobiles characterized in that a foamable thermoplastic resin is injected and filled into a cavity formed from a projecting slide core that can be advanced and retracted into a mold cavity, and then the slide core is retracted to foam the inside. A method of manufacturing the shock absorbing member. 5. The method for producing an impact buffering member for an automobile according to claim 4, wherein the foaming thermoplastic resin is injected and filled, and then the slide core is retracted and then depressurized while gas is being injected to foam the inside. The method for producing an impact buffer member for an automobile according to claim 4 or 5, wherein a mold cavity having 1 to 4 slide cores in the longitudinal direction is used.

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