U.S. patent number RE32,780 [Application Number 07/098,052] was granted by the patent office on 1988-11-08 for core material for an automobile bumper.
This patent grant is currently assigned to Japan Styrene Paper Corporation. Invention is credited to Akira Adachi, Shohei Yoshimura.
United States Patent |
RE32,780 |
Yoshimura , et al. |
November 8, 1988 |
Core material for an automobile bumper
Abstract
For use in an automobile bumper, a core material composed of a
molded article of prefoamed polyolefin resin particles. The core
material has a density of 0.05 to 0.15 g/cm.sup.3 and the relation
represented by the following expression wherein E.sub.20 is the
amount of energy absorption (kg-cm/cm.sup.3) when the core material
is compressed to 50% at 20.degree. C., and .rho. is the density
(g/cm.sup.3) of the core material.
Inventors: |
Yoshimura; Shohei (Tomioka,
JP), Adachi; Akira (Shakura, JP) |
Assignee: |
Japan Styrene Paper Corporation
(Tokyo, JP)
|
Family
ID: |
12694368 |
Appl.
No.: |
07/098,052 |
Filed: |
September 17, 1987 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
708937 |
Mar 6, 1985 |
04600636 |
Jul 15, 1986 |
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Foreign Application Priority Data
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Mar 8, 1984 [JP] |
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59-44541 |
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Current U.S.
Class: |
428/304.4;
428/71; 428/76; 521/144; 521/58 |
Current CPC
Class: |
B60R
19/03 (20130101); C08J 9/18 (20130101); C08J
9/232 (20130101); C08J 2323/02 (20130101); Y10T
428/249953 (20150401); Y10T 428/233 (20150115); Y10T
428/239 (20150115) |
Current International
Class: |
B60R
19/03 (20060101); C08J 9/00 (20060101); C08J
9/232 (20060101); C08J 9/18 (20060101); B32B
003/18 (); B32B 005/18 () |
Field of
Search: |
;428/71,76,304.4,313.5,317.9,403,407 ;521/58,144 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Van Balen; William J.
Attorney, Agent or Firm: Banner, Birch, McKie &
Beckett
Claims
What is claimed is:
1. A core material for use in automobile bumpers, said core
material being composed of a molded article of prefoamed particles
of a polyolefin resin, and having a density of 0.05 to 0.15
kg-g/cm.sup.3 and the relation represented by the following
expression
wherein E.sub.20 is the amount of energy absorption
(kg-cm/cm.sup.3) when the core material is compressed to 50% at
20.degree. C., and .rho. is the density (g/cm.sup.3) of the core
material.
wherein said particles are nearly spherical in shape, have a
particle diameter of 2 to 15 mm, a cell diameter of 0.10 to 2.00 mm
and a proportion of closed cells of at least 90% and contain air
filled within the cells.
2. The core material of claim 1 which has a density of 0.06 to 0.13
g/cm.sup.3 and the relation represented by the following expression
E.sub.20 /.rho..gtoreq.22 kg-cm/g.
3. In an automobile bumper which is composed of a core material and
a surface covering material, the improvement wherein said core
material is composed of a molded article of prefoamed particles of
a polyolefin resin, and having a density of 0.05 to 0.15 g/cm.sup.3
and the relation represented by the following expression
wherein E.sub.20 is the amount of energy absorption
(kg-cm/cm.sup.3) when the core material is compressed to 50% at
20.degree. C., and .rho. is the density (g/cm.sup.3) of the core
material,
wherein said particles are nearly spherical in shape, have a
particle diameter of 2 to 15 mm, a cell diameter of 0.10 to 2.00 mm
and a proportion of closed cells of at least 90% and contain air
filled within the cells.
4. The automobile bumper of claim 3 wherein the core material has a
density of 0.06 to 0.13 kg-g/cm.sup.3 and the relation represented
by the following expression
5. The automobile bumper of claim 3 which has a bumper height of
from 50 to 100 millimeters.
6. The automobile bumper of claim 3 wherein the polyolefin resin is
selected from the group consisting of polypropylene,
ethylene/propylene random copolymer and high-density
polyethylene.
7. The automobile bumper of claim 3 wherein the polyolefin resin is
an ethylene/propylene random copolymer.
8. The automobile bumper of claim 3 wherein the polyolefin resin is
high-density polyethylene. .Iadd.
9. The core material of claim 1, wherein the polyolefin resin is
not cross linked. .Iaddend. .Iadd.10. The core material of claim 1,
wherein the polyolefin resin is cross linked. .Iaddend. .Iadd.11.
The automobile bumper of claim 3 wherein the core material is
composed of a polyolefin resin that is not cross linked. .Iaddend.
.Iadd.12. The automobile bumper of claim 3 wherein the core
material is composed of a polyolefin resin that is cross linked.
.Iaddend. .Iadd.13. The automobile bumper of claim 7 wherein said
copolymer is not cross linked. .Iaddend. .Iadd.14. The automobile
bumper of claim 7 wherein said copolymer is cross linked. .Iaddend.
Description
This invention relates to a core material for use in an automobile
bumper.
Conventional automobile bumpers are made of a metallic material,
but as modern automobiles have been required to be light in weight
for energy saving, plastic foams such as a polyurethane foam have
been suggested as substitutes for the metallic material. Such
bumpers are usually composed of a core material of a plastic foam
and a surface material of a synthetic resin encasing the foam core
material. Polyurethane foams and polystyrene foams are two typical
examples proposed as the plastic foam core material.
The bumper core material made of a foam is an important member
which affects the performance of the automobile bumper. Generally,
the core material is required to have excellent energy absorbing
property and shock resistance. Furthermore, in view of the recent
requirement for lighter automobile weight, the core material has
also been required to be lighter.
The polyurethane foam as a conventional core material for an
automobile bumper has the defect that because of its lower energy
absorption per unit weight, it cannot be sufficiently made light in
weight, and its cost is also high. The polystyrene foam, on the
other hand, has the defect of being inferior in oil resistance and
shock resistance. Thus, the conventional core materials for
automobile bumpers have their advantages and disadvantages, and
cannot fully meet the requirements for bumper cores.
As an attempt to remove the defects of the conventional bumper
cores, Japanese Laid-Open Patent Publication No. 221,745/1983
discloses a bumper core material composed of a molded article of
foamed polypropylene resin particles having a density of 0.015 to
0.045 g/cm.sup.3 and a compressive stress at 50% compression of at
least 1 kg/cm.sup.2. This core material can give a lightweight
automobile bumper having excellent energy absorbing property.
Nowadays, bumpers are required to be rendered lighter in weight and
smaller in size for a larger passenger occupying space within the
range of a fixed automobile length; in other words, the bumper
height l (the width of the bumper in its front-rear direction) as
shown in FIG. 4 should be decreased. But in the case of a bumper
core material composed of the molded article of foamed
polypropylene resin particles, there is a limit to the extent to
which the bumper height l can be decreased without reducing the
shock resistance required of the bumper, and this core material
still leaves room for improvement.
The present invention has been accomplished in view of the above
state of the art, and has for its object the provision of a core
material for automobile bumpers which can lead to size and weight
reduction without reducing shock resistance.
According to this invention, there is provided a core material for
use in automobile bumpers, said core material being composed of a
molded article of prefoamed particles of a polyolefin resin, and
having a density of from 0.05 to 0.15 g/cm.sup.3 and the relation
represented by the following expression
wherein E.sub.20 is the amount of energy absorption
(kg-cm/cm.sup.3) when the core material is compressed to 50% at
20.degree. C., and .rho. is the density (g/cm.sup.3) of the core
material.
The present invention will be described in detail partly with
reference to the accompanying drawings in which:
FIG. 1 is a graph showing the amount of energy absorption of the
core material at 50% compression in a compressive
strain-compressive stress curve;
FIG. 2 is a strain-stress curve of a 60 mm-thick test sample
obtained in accordance with Example 4 in a shock resistance
test;
FIG. 3 is a strain-stress curve of a 60 mm-thick test sample
obtained in accordance with Referential Example 2 in a shock
resistance test; and
FIG. 4 is a rough top plan view of the essential parts of an
automobile including a bumper 1 and a body 2.
The core material of this invention can be made from a molded
article obtained, for example, by filling prefoamed particles of a
polyolefin resin in a mold of the desired shape, and heating and
expanding them with steam or the like. Examples of the polyolefin
resin include polyethylene, polypropylene, ethylene/propylene
copolymer, ethylene/vinyl acetate copolymer and a mixture of
ethylene/propylene copolymer with low-density polyethylene and/or
ethylene/vinyl acetate copolymer. Of these, polypropylene,
ethylene/propylene random copolymer and high-density polyethylene
are preferred. In the case of copolymers of an olefin with another
monomer, the proportion of the olefin is preferably at least 95% by
weight. These polyolefin resins may be crosslinked or
non-crosslinked, but crosslinked resins are especially
preferred.
The prefoamed particles of the polyolefin resin can be obtained,
for example, by dispersing particles of the polyolefin resin and a
blowing agent in a dispersion medium such as water in a closed
vessel, heating the resin particles to a temperature above a point
at which they are softened, thereby to impregnate the resin
particles with the blowing agent, then opening one end of the
vessel, and releasing the resin particles and the dispersion medium
into an atmosphere kept at a pressure lower than the pressure of
the inside of the vessel to expand the resin particles.
The core material of the invention has a density .rho. of 0.05 to
0.15 g/cm.sup.3, preferably 0.06 to 0.13 g/cm.sup.3, and also has
the relation represented by the following expression
preferably
wherein E.sub.20 is the amount of energy absorption
(kg-cm/cm.sup.3) when the core material is compressed to 50% at
20.degree. C., and .rho. is the density (g/cm.sup.3) of the core
material.
When the core material has a density of less than 0.05 g/cm.sup.3,
a bumper having a decreased bumper height l cannot be produced
without reducing its shock resistance even if it has the relation
E.sub.20 /.rho..gtoreq.20 kg-cm/g. On the other hand, the core
material having a density of more than 0.15 g/cm.sup.3, has a large
weight even if it has the relation E.sub.20 /.rho..gtoreq.20
kg-cm/g. Consequently, a bumper of a lighter weight cannot be
produced. If the E.sub.20 /.rho. is less than 20 kg-cm/g, even a
core material having a density of 0.05 to 0.15 g/cm.sup.3 is
required to be increased in thickness in order to secure sufficient
shock resistance. As a result, the weight of the core material
increases, and a bumper of a smaller size and a lighter weight
cannot be produced.
As shown in FIG. 1, the amount of energy absorption, E.sub.20
(kg-cm/cm.sup.3), of the core material at 20.degree. C. and 50%
compression can be determined as the area of the hatched portion in
FIG. 1 ranging from a compressive strain of 0 to 50% in the
compressive strain-compressive stress curve of the core material at
20.degree. C.
In order for the core material to have the relation E.sub.20
/.rho..gtoreq.20 kg-cm/g, the prefoamed particles of the polyolefin
resin used for the production of the core material are preferably
those which are nearly spherical in shape, have a particle diameter
of 2 to 15 mm, a cell diameter of 0.10 to 2.00 mm and a proportion
of closed cells of at least 90% and contain air filled within the
cells.
The core material of this invention can be produced, for example,
by subjecting the prefoamed particles of the polyolefin resin to a
pressurizing treatment with an inorganic gas such as air, oxygen,
nitrogen or carbon dioxide or a mixture of the inorganic gas with a
volatile organic blowing agent such as hexane, heptane,
dichlorodifluoromethane and trichlorotrifluoroethane to impart an
internal pressure of about 0.8 to 4.5 kg/cm.sup.2 -G to the
prefoamed particles, thereafter filling the prefoamed particles in
a mold of a desired shape for producing a bumper core material, and
heating the prefoamed particles with steam under a pressure of
about 2.5 to 4.5 kg/cm.sup.2 -G to expand the particles and fuse
the particles to one another.
By using the core material of this invention, there can be produced
a bumper which has a bumper height of 50 to 100 mm and yet shows
good shock resistance.
The following examples illustrate the present invention more
specifically.
EXAMPLES AND COMPARATIVE EXAMPLES
In each run, the prefoamed particles indicated in Table 1 were
pressurized with air to impart an internal pressure (the
pressurizing treatment was not carried out in Comparative Example
3), and then filled in a mold for production of a bumper core
material. The particles were then heated with steam to expand them
and obtain a core material conforming to the shape of the mold.
Table 2 shows the density, the amount of energy absorption E.sub.20
at 50% compression and 20.degree. C., and the E.sub.20 /.rho. value
of the core material. Comparative Example 1 is outside the scope of
the invention in regard to density; Comparative Example 2, in
regard to density and E.sub.20 /.rho.; and Comparative Example 3,
in regard to the type of the base resin.
Table 2 also shows the various properties of the core material.
The shock resistance was tested at 40.degree. C. by using, as
samples, molded articles having a thickness of 60 mm (both 60 mm
and 100 mm in the Comparative Examples) and an area of 40
mm.times.40 mm prepared under the same molding conditions at the
same expansion rate (same density) by using the prefoamed particles
indicated in Table 1.
As referential examples, Table 2 also shows the properties of
commercial bumper core materials made of a polyurethane foam.
The strain-stress curves of the 60 mm-thick samples in the shock
resistance tests in Example 4 and Referential Example 2 are shown
in FIGS. 2 and 3, respectively.
TABLE 1
__________________________________________________________________________
Properties of the prefoamed particles Average Average Base resin
particle cell Apparent Gel fraction Density diameter diameter
density Type (%) (g/cm.sup.3) (mm) (mm) (g/cm.sup.3)
__________________________________________________________________________
Example 1 Ethylene/propylene random copoly- 38 0.908 4.5 0.45 0.06
mer (ethylene content 3.2 wt. %) 2 Ethylene/propylene random
copoly- " " " " 0.09 mer (ethylene content 3.2 wt. %) 3
Ethylene/propylene random copoly- Non-cross- 0.910 5.2 0.65 0.06
mer (ethylene content 3.2 wt. %) linked 4 Ethylene/propylene random
copoly- Non-cross- " " " 0.09 mer (ethylene content 3.2 wt. %)
linked 5 High-density polyethylene 35 0.968 5.8 0.54 0.06 6
High-density polyethylene " " " " 0.10 Comparative Example 1
Ethylene/propylene random copoly- Non-cross- 0.910 4.5 0.83 0.03
mer (ethylene content 3.2 wt. %) linked 2 Low-density polyethylene
62 0.923 6.0 0.74 0.20 3 Polystyrene -- 1.05 4.5 0.21 0.06
__________________________________________________________________________
TABLE 2
__________________________________________________________________________
Heat Oil Overall resis- resis- Shock resistance (*3) evalua-
E.sub.20 E.sub.20 /.rho. tance tance 60 mm-thick 10 mm-thick tion
.rho.(g/cm.sup.3) (kg-cm/cm.sup.3) (kg-cm/g) (*1) (*2) sample
sample (*5)
__________________________________________________________________________
Example 1 0.06 1.8 30.0 O O O -- O 2 0.09 2.9 32.2 O O O -- O 3
0.06 1.7 28.3 O O O -- O 4 0.09 2.7 30.0 O O O -- O 5 0.06 1.4 23.3
O O O -- O 6 0.10 2.5 25.0 O O O -- O Comparative Example 1 0.03
0.9 30.0 O O X O X 2 0.20 3.1 15.5 X O O O X 3 0.06 2.5 41.7 X X X
X X Refer- encial Example 1 0.09 1.1 12.2 O O X (*4) X (*4) X 2
0.22 3.0 13.6 O O X (*4) O (*4) X
__________________________________________________________________________
The various properties shown in Table 2 were measured and
determined by the following methods.
(*1): Heat resistancee
The core material was heated at 100.degree. C. for 24 hours, and
its shrinkage (dimensional change) at this time was measured. The
result was evaluated on the following scale.
: the shrinkage was less than 5%
X: the shrinkage was at least 5%
(*2): Oil resistance
Kerosene at 20.degree. C. was dropped onto the core material, and
the core material was observed 2 hours later. The result was
evaluated on the following scale.
: the core material was not damaged by kerosene
X: the core material was damaged by kerosene
(*3): Shock resistance
A load of 12 kg was let fall from a height of 60 cm onto the core
material sample (60 mm or 100 mm thick) at 40.degree. C. to impart
shock and produce strain. Immediately then, the percent residual
strain was measured, and evaluated on the following scale.
: the percent residual strain was not more than 35%
X: the percent residual strain was more than 35%
(*4): Shock resistance (for Referential Examples)
Samples having the same sizes as in Comparative Examples were
prepared by cutting commercial urethane bumper core materials, and
tested in accordance with (*3) above.
(*5): Overall evaluation
: excellent in regard to all of the above properties
X: inferior in regard to at least one of the above properties
Since the core material of this invention is composed of a molded
article of prefoamed particles of the polyolefin resin and has a
density of 0.05 to 0.15 g/cm.sup.3 and the relation E.sub.20
/.rho..gtoreq.20 kg-cm/g, it has a high energy absorptivity per
unit weight and sufficient energy absorbing property. Moreover,
even when its thickness is decreased, its shock resistance is not
reduced. The height of a bumper made by using this core material
can be decreased as compared with conventional bumpers having
plastic cores, and the passenger occupying space in an automobile
of a fixed length can be increased. Furthermore, since the bumper
height can be decreased, the volume of the bumper can also be
decreased. Consequently, the total weight of the bumper can be
reduced.
* * * * *