JPH0517327Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Application Field] The present invention relates to a core material for an automobile bumper. In recent years, efforts have been made to reduce the weight of automobiles in order to improve the efficiency of energy consumption, and together with the development of the material industry, various plastics are being used for automobile parts. The present invention aims to provide a core material for an automobile bumper, which is made of a foam molded product of a propylene polymer having different densities and has excellent energy absorption efficiency. [Prior Art and Problems] Many proposals have been made to date to use plastic foam as a core material for automobile bumpers. For example, JP-A No. 57-1999-1, which is made from a foamed molded product of poly(styrene-ethylene) copolymer,
No. 40136, Utility Model Publication No. 163254/1983, Japanese Patent Application Publication No. 60-189660 using polypropylene foam molded material,
Utility Model Application No. 60-70165 and Utility Model Application No. 62-60457, which are made from resin foams with different densities of these resins.
No. 62-29964, No. 62-29965
There is also an introduction to urethane bumpers in Automotive Technology, Vol. 35, No. 8 (1981), p. 971. However, none of these materials yet has sufficient properties as a core material for automobile bumpers. The performance required of the core material of a bumper is to have high compressive stress and energy absorption capacity and energy absorption efficiency at the time of impact, and also to quickly recover from deformation after the impact force is removed and return to its pre-impact state as much as possible. and lightweight. As a method of investigating such required performance, a correlation diagram between compressive stress and compressive strain as shown in Fig. 4 is obtained, and the compressive stress A such as 50% compression of the foam is 1 kg/cm ²
Above, energy absorption efficiency (area of OBC surrounded by curve OB, straight line OC and BC ÷ square)
Make sure that the OABC area) is large (more than 50%). The area of OBC is called the energy absorption amount. Generally, when the bumper core material is a single-material foam, the higher the density of the foam (lower the expansion ratio), the higher the compressive stress and the higher the amount of energy absorbed. Therefore, it is preferable to use a foam with a high density as the core material, but this increases the weight of the core material itself and increases the load generated during a collision (large compressive stress). The transmitted impact load increases. Therefore, it is necessary to increase the strength of the structural material of the car body, which in turn increases the thickness of the car body material, so from the perspective of reducing the weight of the car, there is a limit to increasing the density of the foam core material. There is. As a means to solve this problem, the 62nd Utility Model
-29964 is an automobile bumper core material made of polyolefin resin foam, which has a density of
Density 0.1~ inside the foam layer of 0.015~0.1g/ ^cm3
An automobile, characterized in that a synthetic resin molded body of 1.5 g/cm ³ is embedded, and the ratio of the weight of the foam layer to the weight of the synthetic resin molded body is 50/1 to 1/1. We are proposing a bumper core material for However, since the outer side of this bumper core material is all foam with a low density (0.015 to 0.1 g/cm ³ ), the stress of the foam is small, and the core material deforms due to the load generated during a collision. often does not recover. In addition, Utility Model Application Publication No. 62-125651 uses two or more types of urethane foam with different specific gravity, and the part that hits first in the event of a collision (the impact-receiving surface side of the core material) is made of foam with a higher specific gravity (lower expansion ratio). We are proposing a bumper core material with a Since this bumper core material generates a large load in the event of a collision, it is necessary to use thick material for the vehicle body. As a result of intensive research, the inventors of the present invention found that by combining a foam made of styrene-grafted polyethylene copolymer with a specific density range into a specific structure,
It has been discovered that a core material for automobile bumpers can be obtained that exhibits extremely high energy absorption efficiency. [Means for solving the problem] The present invention reduces the load generated during a collision, and
The purpose is to provide a bumper core material with small deformation. That is, the present invention consists of a high-density foam A with a density of 0.030 to 0.100 g/cm ³ and a low-density foam B with a density of 0.015 to 0.08 g/cm ³ , and the foam A and the foam B
The core material for an automobile bumper is a core material for an automobile bumper made by combining two types of propylene polymer foams with different densities, the difference in density of which is 0.01 g/cm ³ or more. At least one
To provide a core material for an automobile bumper having a structure in which two pieces of high-density foam A are located in the upper half and one piece is located in the lower half of the center line, and these high-density foams A are interconnected. (See Figure 1). In this case, it is also an effective improvement factor that the ratio of the effective impact pressure receiving area of the high-density foam A to the effective impact pressure receiving area at the tip of the bumper core material is 10 to 50%. The term "substantial impact pressure receiving area" as used herein refers to the actual area that receives an impact when an impact load is applied to the bumper. Although an actual impact may occur from many directions, in the present invention, the cross section of the bumper is perpendicular to the center line of the vehicle, which has the highest probability of receiving an impact. In addition, a normal bumper is not necessarily a rectangular parallelepiped, but has curved parts, tapered parts, hollow parts, etc. due to design and fit, and does not have a uniform cross section on all sides.
In the vertical cross section above, when a load is applied in the direction of the center line, it means the total area of the part where the force is directly transmitted to the vehicle body. For example, in FIG. 2, A-
The cross section of A' is the effective impact pressure receiving area, and in FIG. 3, the sum of A ₁ -A ₁ ' and A ₂ - _{A 2} ' is the effective impact pressure receiving area. Here, the energy absorption efficiency means that when a compressive load is applied to the energy absorber (bumper core material) and a stress-strain curve O to B is obtained as shown in Figure 4, the shaded area OBC is relative to the area of the rectangle OABC. The area ratio is called energy absorption efficiency, and the larger this value, the better the energy absorption as a bumper core material. The curve OB changes depending on the material of the absorber. Using relatively high-density, high-strength foam increases the area OBC, but the stress at point B (or point A) (maximum load received during a collision) also increases, which increases the load on the vehicle body. , it becomes necessary to increase the strength of the vehicle body, which is undesirable as it increases the cost. An ideal stress-strain curve, as shown in Figure 5, shows that the stress increases rapidly at the beginning of a collision, and then becomes a gentle curve from near point D, which is a certain value that is safe for the driver and the vehicle body. In other words, there is no increase in stress and only an increase in strain occurs. In this way, bumper characteristics with a large area ODBC as a whole, that is, a high energy absorption efficiency can be obtained. In the present invention, a propylene polymer foam is used and the foam is made into a composite material in order to approximate the above-mentioned ideal curve as much as possible. That is, by combining relatively high-density foam A and relatively low-density foam B, a higher Young's modulus (Young's modulus = stress /
When member A buckled near D, the Young's modulus suddenly decreased and reached B. In order to achieve the above-mentioned objectives, the selection of components and the design of their arrangement are necessary. (Material of the member) By selecting such a foam, as mentioned above, it exhibits a high Young's modulus at the initial stage of impact, buckles during the compressive load, and does not break. also requires toughness.
For this purpose, foamed polystyrene or hard urethane cannot provide such characteristics. Therefore, the members used in this invention are:
Plastic foam, particularly propylene polymer foam with excellent heat resistance, is preferred.
Moreover, the most preferable characteristics can be obtained by combining the high-density foam and the low-density foam. The propylene polymer is a propylene homopolymer, which has propylene as its main component, and ethylene, butene-1, pentene-1, hexene-1, etc.
Copolymers with one or more selected α-olefins such as 1,4-methylpentene-1, propylene/ethylene block copolymers, etc. can be used. (High-density foam A) The high-density foam A used in the present invention functions to absorb most of the load at the initial stage of impact, and has a relatively high Young's modulus. In the composite of the present invention, the density range is from 0.03 to
The density range is 0.100 g/cm ³ , preferably 0.05 to 0.08 g/cm ³ . (Low-density foam B) The low-density foam B of the present invention maintains the actual shape of the bumper core material, and is composited with the high-density foam A.
It mainly functions to absorb and buffer the load after buckling. In this invention, the density range
0.015-0.08g/ ^cm3 , preferably 0.025-0.06g/cm3
^cm3 . In the present invention, the difference in density between the high-density foam A and the low-density foam B is also important. This achieves the combination of a high Young's modulus that absorbs most of the initial impact load and a low Young's modulus that buffers a certain load or more as intended by the present invention. In this invention, the difference in density between the two is 0.01g/
The amount is preferably 0.015 g/cm ³ or more, more preferably 0.015 g/cm ³ or more. (Arrangement of members) In the present invention, the members of the high-density foam A are:
It is necessary that the bumper core material is divided into an upper half and a lower half in the height direction. That is, when a car collides with an object, it can be roughly divided into the following three cases depending on the object. a When the load is applied to the entire surface Fig. 6-a b When the load is applied to the upper part Fig. 6-b c When the load is applied to the lower part Fig. 6-c Considering these possibilities, in either case In order to accommodate this, it is preferable that the member of the high-density foam A is divided into an upper half and a lower half. (Connection of high-density foam A) In the present invention, the high-density foam A placed in two or more parts of the upper and lower halves of the horizontal line at the center of the bumper core material is They need to be connected across the horizontal line. Although the high-density foam A is adhered to or inserted into the low-density foam B, it may peel off or turn over due to the impact of a collision. In particular, the high-density foam A at the ends of the core material is likely to peel off. In addition, especially when subjected to repeated impacts, the weakness of this portion becomes an important problem. In the present invention, this problem is solved by interconnecting the high-density foams A that are arranged separately. Various methods can be used for the connection. For example, several parts of the high-density foam A may be connected with connecting rods, or they may be glued together with a stick made of the same type of foam as the high-density foam, or the high-density foam A may be fixed to a plate that covers the front surface of the bumper core material. Alternatively, as shown in FIG. 1b or FIG. 7, the high-density foam A of FIG. 1a may be formed into a U-shape. In this case, the energy absorption rate of the bumper core material is determined by the impact pressure-receiving area of the high-density foam A divided and arranged, and is not affected much by the plate arranged only on the front side. (Ratio of members used) In order to achieve the above-mentioned object, it is also important to select the ratio of the members of the high-density foam A and the members of the low-density foam B. That is, high density foam A
If the strength of the members is too high, the maximum stress will increase and this stress will be transmitted to the vehicle body, which is not desirable. Moreover, if the strength is too low, the reinforcing effect will not be improved as a matter of course. For this purpose, the proportion of the pressure-receiving area of the high-density foam member A in the entire actual impact-receiving area is 10 to 50%, preferably 20 to 40%.
%. The present invention will be explained in more detail with reference to Examples below. [Example 1] Bumper core materials 1, 2, 3, and 4 of the present invention and target core materials 5, 6, and 7 were created (length 1500 mm, width 100 mm, height 115 mm).
The basic shape of the bumper core material is as shown in FIG. 7, and the dimensions, area ratios, and densities of each part are as follows.

[Table] The plastic foam used to manufacture these core materials has an ethylene content of 2.6% by weight, a propylene content of 97.4% by weight, and a melt index of 4g/10.
The material is a propylene-ethylene copolymer (JP-A-62-26145, JP-A-63-4940).
These test core materials were tested under the following conditions: Testing machine: Instron universal testing machine Compression speed: 10 mm/min Ambient temperature: 23°C Ambient humidity: 50% RH The energy absorption efficiency and compressive stress at 50% strain calculated from the stress-strain curves obtained from the above measurements were as follows:

[Effect of idea]

The present invention is a bumper for an automobile that is constructed by dividing a member made of high-density foam A into two upper and lower parts and combining it with low-density foam B, and further connecting the high-density foam A. Since it is the core material of
It has high energy absorption efficiency and can keep the maximum load to an appropriate level in relation to the strength of the vehicle body. Furthermore, since the entire bumper is made of foamed plastic, the weight of the bumper is light, contributing to lighter automobiles and reduced energy consumption.

[Brief explanation of the drawing]

Figure 1a is a perspective view of the high-density foam;
FIG. 1B and FIG. 1C are perspective views showing an example of the bumper core material of the present invention. In the figure, A indicates high-density foam A, and B indicates low-density foam B.
FIG. 2 is a plan view of an example of a bumper core material.
In the figure, the line A-A' indicates the actual pressure-receiving surface.
FIG. 3 is a plan view of another example of the bumper core material. In the figure, A ₁ −A ₁ ′ and A ₂ −A ₂ ′ indicate substantial pressure receiving surfaces. FIG. 4 shows an example of a stress-strain curve in a bumper core material. FIG. 5 shows a preferred example of the stress-strain curve in the bumper core material. Figures 6a, b and c show how the bumper core material is loaded with load during a collision. FIG. 7 is a sectional view showing an example of the shape of the bumper core material used in the test of the present invention. In the figure, A ₁ , A ₂ and
A ₃ indicates the thickness of each part of the high-density foam A, B ₁ ,
B ₂ and B ₃ indicate the thickness of each part of the low density foam B.

Claims (1)

[Claims for Utility Model Registration] 1 Consists of a high-density foam A with a density of 0.030 to 0.100 g/cm ³ and a low-density foam B with a density of 0.015 to 0.08 g/cm ³ , and The density difference
A core material for an automobile bumper made by combining two types of propylene polymer foams with different densities of 0.01 g/cm ³ or more, in which the high-density foam A is dispersed in at least two places. , when set as a bumper core material, at least one piece is located in the upper half and one piece is located in the lower half of the center line, and these high-density foams A are interconnected. A core material for automobile bumpers with a structure of 2. The core material for an automobile bumper according to claim 1, wherein the ratio of the impact pressure receiving area of the high-density foam A to the impact pressure receiving area at the tip of the bumper core material is 10 to 50%.