JPH02158441A - Core material for automobile bumper - Google Patents

Abstract

PURPOSE:To aim at enhancing the strength, the energy absorbing efficiency and a heat resistance by using a foamed material composed of a random copolymer of propylene 1-butane which has a specific density, a specific compression stress, a specific energy absorbing efficiency (quantity) and a specific 1-butane content. CONSTITUTION:An automobile bumper core material is formed from a specific resin foamed material which is constituted so as to satisfy the following several conditions: That is, there is prepared a random copolymer of propylene 1-butane having the density thereof is 0.02 to 0.08g/cm<3>, a compression stress is less than 2.5kg/cm<2> during compression of 50% (measured at a temperature of 20 deg. C), an energy absorbing efficiency is less than 60%, a ratio (E80/E20) is greater than 0.5 where E20 and E80 are energy absorbing values at temperatures of 20 deg. C and 80 deg. C, respectively, and a content of 1-butane is 3 to 12wt.%. Thereby, it is possible to attain the enhancement of strength, energy absorbing efficiency and heat resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automobile bumper core material that has excellent heat resistance, impact resistance, and strength.

[Prior art]

In order to reduce weight, automobile bumpers are made of resin instead of metal, and the core material is made of resin.
-℃1 A foam bumper with a non-foamed resin outer skin is used. Polyurethane foam, polystyrene, cross-linked polyethylene, and ethylene-propylene random copolymer are used as the material resins for such foam bumper core materials (Foam Times).

July 25, 1956, No. 842, page 29;
No. 163254, USP No. 4,350,378, JP-A-58-221745, JP-A-60-189660).

Density of 0.03 to 0 using ethylene/propylene random copolymer with ethylene content of 1 to 12% by weight as base resin
．． The bumper core material made of in-mold bead molded foam of 065 f/aA is superior to polyurethane foam in terms of lightweight, superior to polystyrene foam in terms of dimensional recovery and heat resistance, and superior in terms of heat resistance and strength. Because cross-linked polyethylene foam has excellent paper properties, demand for it as a bumper core material has been increasing recently.

[Problem to be solved by the invention]

In order to further reduce the weight of automobiles, if the foam exhibits the same strength, it is necessary to use a foam with a lower density.
・ is preferable. Furthermore, automobiles are sometimes exported or used in deserts or tropical regions, and in these cases severe heat resistance is required, and it is desired that the bumper core material function sufficiently even at 80℃. There is.

An object of the present invention is to provide an automobile bumper core material with excellent strength, energy absorption performance, and heat resistance.

[Specific means to solve the problem]

As a bumper core material that achieves the above purpose, the density is 0.02~
0.08 f/cd, compressive stress at 50% compression (2
0℃ measurement) is 2.5 #15 (more than that, the energy absorption efficiency at 20℃ is 60% or more, the ratio of the energy absorption amount E80 at 80℃ to the energy absorption amount Ego at 20℃ (Eeo / E20) is 0.5 butene-1
An automobile bumper core material made of a propylene/1-butene random copolymer foam having a content of 3 to 12% by weight can be used.

(Base resin) The bumper core material of the present invention contains 3 to 12 times of 1-butene! 1
This is an in-mold molded article of foamed propylene resin particles whose main component is propylene with a heavy content of 1. This propylene resin is
Binary random copolymer of 1-butene and propylene, 1
- 3-12% by weight of butene and 0.5-5% by weight of ethylene 7
Ternary random copolymer of 0 and propylene, 3-12% by weight of 1-butene and 4-methylpentene-10,5-5
% by weight and terpolymer of propylene, 1-butene/hexene-1/propylene ternary random copolymer, 1-butene, propylene, ethylene, and 4-methylpentene-1
Alternatively, a quaternary copolymer with hexene-1 can be used.

The crystallinity of this propylene/1-butene random copolymer is 40% or more, and the latent heat of crystal is 6 to 28 cat/f.
Preferably.

The 1-butene content of the copolymer is from 3 to 12% by weight, preferably from 4 to 10% by weight. A copolymer with a 1-butene content of 3% by weight has finer foam cells and a higher melting point, so the heating temperature or heating pressure for producing expanded particles and heat fusing the expanded particles becomes higher. It's too much. 1-
If the butene content exceeds 122% by weight, the compressive strength and heat resistance of the molded product will be poor.

1- of this propylene + 11-butene random copolymer
The butene content was determined by heat pressing the copolymer particles at 190°C.
A 0.5 m thick sheet was obtained by applying a pressure of 2#/cdG for 1 minute and left at 20°C for 1 day as a sample, and the results were determined by infrared absorption spectrum analysis.

If necessary, the propylene/1-butene random copolymer may be blended with other polyolefin resins in an amount not exceeding 50% by weight. For example, homopolypropylene, ethylene-propylene random copolymer, ethylene-propylene block copolymer, ethylene-propylene rubber, high-pressure process low-density polyethylene, linear process process low-density polyethylene, medium- and high-density polyethylene, ethylene-vinyl acetate. copolymer, ethylene/methyl acrylate copolymer, ethylene/ethyl acrylate copolymer,
Ethylene/acrylic acid copolymer, etc. = 5----.

May be added.

Furthermore, the resin may contain inorganic fillers such as zeolite, silica, and talc, pigments, heat stabilizers, dyes, lubricants, and antistatic agents. These should be at most 5% by weight, preferably at most 2% by weight, in order to achieve good fusion when foamed particles are heated with steam to fuse them together to form a molded article.

The weight of one propylene/1-butene random copolymer particle is 0.01 to 2011If. Granulation may be carried out by any method such as a strand cutting method, an underwater cutting method, a sheet cutting method, a freeze-pulverization method, a melt-spraying method, etc., and the method is determined in consideration of productivity, economic efficiency, formability, and quality. In addition, regranulation may be performed.

(Foamed particles) Foamed particles of propylene/1-butene random copolymer are disclosed in Japanese Patent Publication No. 49-2183, No. 57-195131,
No. 58-1732, No. 58-23834, No. 58-
No. 25334, No. 58-33435, No. 58-552
No. 31, No. 58-7-6 2111-6229, No. 58-76231, No. 58-7623
No. 2, No. 58-76233, No. 58-76234,
As described in patent publications such as No. 58-87027 and No. 62-151325, propylene resin particles are dispersed in water in a closed container, then a volatile organic swelling agent is supplied into the closed container, After heating the propylene resin particles to a softening temperature or higher while maintaining the pressure inside the airtight container at the vapor pressure of the expansion agent or higher, the temperature and pressure are maintained for a certain period of time, and then the water level in the airtight container is lowered. Expanded propylene resin particles are produced by opening the discharge port provided at the bottom and simultaneously releasing propylene resin particles containing a volatile expanding agent and water into an atmosphere having a lower pressure than the inside of the container.

Volatile expanding agents include, for example, aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane; halogenated compounds such as trichloromethane, dichlorochloromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride, and methylene chloride; Organic compounds having a boiling point of 80° C. or lower, such as hydrocarbons, can be used alone or in combination of two or more.

The amount of the volatile expanding agent added varies depending on the type of the expanding agent and the bulk density of the intended resin particles, but is usually 10 to 50 parts by weight per 100 parts by weight of the resin particles.

Examples of dispersants for dispersing resin particles in water include inorganic suspending agents such as aluminum oxide, titanium oxide, calcium carbonate, basic magnesium carbonate, tricalcium phosphate, and calcium pyrophosphate; polyvinyl alcohol, methyl carboxycellulose, N- Water-soluble polymeric protective colloid agents such as polyvinylpyrrolidone; anions such as sodium dodecylbenzenesulfonate, sodium alkanesulfonate, sodium alkyl sulfate, sodium olefin sulfate, acylmethyltaurine, sodium dialkylsulfophosphate, etc. Examples include surfactants and the like. Among these, the particle size of inorganic suspending agents is 0.01
It is preferable to use the tricalcium phosphate of ~0.8 micron in combination with the suspension aid sodium dodecylbenzenesulfonate. This fine tricalcium phosphate is obtained by reacting phosphoric acid in water at a ratio of 0.60 to 0.67 mol per mol of calcium hydroxide.

The amount of water in the dispersion medium for 100 parts by weight of resin particles is 150 parts by weight.
~1,000 parts by weight, preferably 200 to 500 parts by weight. If it is less than 150 parts by weight, the resin particles tend to block each other during heating and pressurization.

If the amount exceeds i, o o o parts by weight, the productivity of the expanded particles decreases and is not economical.

A gaseous or liquid expanding agent is supplied to an aqueous dispersion of propylene/1-butene copolymer resin particles dispersed in water by a dispersion medium, and this aqueous dispersion softens the resin in a closed container. The copolymer particles are heated to a temperature higher than the melting point and 20° C. higher than the melting point, and the pressure inside the container increases due to this heating, so that the copolymer particles are impregnated with the swelling agent. The copolymer resin particles are then discharged from the closed container into a low pressure region (generally at atmospheric pressure) along with water through a discharge port such as a slit or nozzle provided at the bottom of the closed container.

By doing so, propylene/1-butene random copolymer foam particles having a bulk density of 8 to 100 #/m' can be produced.

In the production of expanded particles, before or after adding the expanding agent into the closed container, an inorganic gas such as nitrogen, helium, or air is supplied into the closed container to apply pressure.

This inorganic gas may be supplied before or after heating the dispersion.

Supplying an inorganic gas such as air, nitrogen gas, or argon into the closed container facilitates impregnation of the expanding agent into the resin particles, and is useful for obtaining propylene/1-butene copolymer foam particles having a low bulk density.

The heating temperature of the dispersion liquid is determined by determining the peak of crystal melting temperature (so-called melting point) using a differential scanning calorimeter for propylene/1-butene copolymer resin particles, and is approximately 20°C from this peak temperature.
The lower limit is a lower temperature, and the upper limit is a temperature 20° C. higher than this peak temperature, preferably a temperature 3 to 15° C. lower than this peak temperature.

The time for which the dispersion is held in a closed container depends on the pressurizing pressure, holding temperature, and desired expansion ratio, but it may be up to 30
minutes to 12 hours, preferably 1 to 3 hours.

The foamed particles released into the atmosphere are dried (cured) in a room at 30 to 65°C to remove water attached to the surface.
Allotted for molding bumper core material.

As the in-mold bead molding method for molding the bumper core material, various conventionally known methods can be used. An example is shown below.

■ After filling the propylene/1-butene random copolymer foam particles into a mold, the foam particles are compressed to reduce their volume by 15-50%, and then steam of 9/cr/IG is introduced into 1-5. A compression molding method (DO82107683) in which foamed particles are fused together, and then the mold is cooled to obtain a product.

■Pre-expanded particles obtained by pre-impregnating foamed particles with a volatile liquid expanding agent to give them secondary foamability are filled into a mold, heated with steam to cause secondary foaming and fuse the particles together. Get the product by wearing it.

■ 0 foamed particles are placed in a closed chamber, and then inorganic gas such as air or nitrogen gas is forced into the chamber to increase the pressure inside the cells of the foamed particles and give them secondary foaming properties. The applied pre-expanded particles are filled into a mold and heated with steam to cause secondary foaming and fuse the particles together to obtain a product (so-called pressure ripening method; Japanese Patent Publication No. 59-434
No. 92).

■9 In a method of molding a molded foam by filling a mold with foamed particles and fusing the foamed particles with each other by steam heating, the inside of the mold is pressurized to 1.0 to 6.0 #/dG with pressurized gas. Then, the foamed particles were heated at a pressure of 0.5 m/- below the mold pressure.
The pressure inside the mold is kept at the above-mentioned pressure during filling, and the pressure inside the mold is returned to atmospheric pressure after the filling is completed, and then the above-mentioned heating is carried out. The foamed particles are fused together, and the formula of the foamed particles at that time is expressed as follows:

W...Weight of the molded product (f) ■...Capacity of the molded product (t) σ...The compressibility expressed by the bulk density (1't) of the foamed particles in the atmosphere is 40 to 70 In-mold molding method for foamed particles characterized by controlling the
No. 5).

(2) In a method of filling a mold with propylene/1-butene random copolymer foam particles and fusing the foam particles together by steam heating to form a molded foam, pressurized gas is used for 0.5 to s. The above-mentioned foaming is applied with a gas internal pressure obtained by pressurizing the mold with pressure increased to ow/cdG for 1 hour or more using a pressurized gas that is 0.5 kg/cm2 or more higher than the mold internal pressure in advance. The particles were heated to 0.5 below the mold pressure.
Filling using pressurized gas with a pressure higher than kg/cm2,
Continue to maintain the mold internal pressure at the mold internal pressure during the filling,
Next, after filling is completed, the pressure inside the mold is returned to atmospheric pressure, and then the above-mentioned heating is performed to fuse the foamed particles, and the formula of the foamed particles at that time [where W, .

W... Weight of molded product (f) V-1 Capacity of molded product (t) σ... Bulk density of expanded particles in the atmosphere Cf/l))
The compression ratio expressed by is less than 40% (excluding 0%)
An in-mold molding method for foamed propylene/1-butene random copolymer particles, which is characterized in that the propylene/1-butene random copolymer foam particles are controlled to

(Bumper core material) The bumper core material of the propylene/1-butene copolymer foam product molded in this manner has excellent fusion of foamed particles and has high mechanical strength.

The density of this bumper core material is 0.02 to 0.08 f/d1
Preferably it is 0.030 to 0.075 f/cd.

If it is less than o, ozt/-, the energy absorption performance will be poor;
, osr/-, there is no advantage in terms of weight compared to other materials such as propylene-ethylene copolymers.

As a bumper core material, in addition to having a low density in order to reduce weight, (1) it must have high strength in order to reduce the wall thickness (2) it must have an energy absorption efficiency of 60% or more at room temperature (3) It is required to exhibit sufficient energy absorption performance in a high temperature range (4) to have excellent chemical resistance.

The bumper core material of the present invention has a length of 80m and a width of 80s+m.

Height 50w! In the stress/strain curve shown in Figure 1 obtained by cutting out a sample piece of n and compressing it at a speed of 20 cm/min, (i) the compressive stress at 80% strain (point A) was measured at 20°C. It is as high as 2.5 #/d or more.

(11) Energy absorption efficiency (OAH area 10ABC
area) is 60% or more
0/Ezo) is 0.5 or more.

It exhibits physical properties and is stronger than conventional ethylene/propylene random copolymer foam bumper core materials.
a) Under the constraint that the density of the bumper core material is the same, the thickness of the bumper core material can be made thinner. (b) Under the constraint condition that the thickness of the bumper core material is the same, a foam with a smaller density is used. It is possible to make the bumper core material more @
Can be quantified. Furthermore, this bumper core material exhibits sufficient energy absorption performance even with high silver content.

Hereinafter, the present invention will be further explained in detail with reference to Examples. Note that parts and percentages in the examples are based on weight.

Example 1 M with 1-butene content of 5.2% double failure, measured at 230°C
FR is 9.7f/10min, latent heat of crystal is 22.6cat/
Expanded particles were obtained using propylene/l-butene random copolymer particles of f (average weight of one particle was about 1 kg).

That is, in a closed container, 250 parts of water, 100 parts of the above propylene/1-butene copolymer particles, t and o parts of calcium birophosphate, and 0.0 parts of sodium dodecylbenzenesulfonate.
007 parts were charged (filling rate: 62%), nitrogen gas was then pressurized under stirring until the internal pressure of the closed container reached sh/dG, and the supply of nitrogen gas was stopped. Then, inbutane 18
When the sample was supplied into a closed container, heated to 140° C. over 1 hour, and held at the same temperature for 45 minutes, the autocrepe internal pressure showed 26#/iG.

Then, open the discharge nozzle valve at the bottom of the sealed container,
The dispersion was discharged into atmospheric pressure for about 2 seconds to effect foaming. The internal pressure of the sealed container at the moment the final portion after dispersion was released from the sealed container was approximately 10#/-G. Additionally, the temperature of the closed container was maintained at 140° C. during dispersion release.

The thus obtained expanded 10-pyrene/1-butene copolymer particles had a bulk density of 30 ky/d, a particle size of 3.3 m,
The foam cell diameter was 150 microns.

Further, no blocking between foamed particles was observed.

The foamed particles were left to dry in a room at 40°C for 2 days, then filled into a mold with steam holes, the foamed particles were compressed by 50%, and then 3.0 #/mG of steam was introduced. The foamed particles are heated and fused together, and then cooled with water for 10 seconds.
After cooling for 30 seconds, the molded product was removed from the mold and the density was 0.
062 f/L-d, length 1500mm, width 200mm
A bumper core material having a thickness of 150+a+ was obtained.

Length 80 m from this bumper core material, fjQ 80 m,
Cut out a test piece with a height of 50 pieces, find the stress/strain curves at 20°C and 80°C, and calculate the stress at 50 parts strain, energy absorption efficiency, energy absorption needle, and energy absorption ratio at 20°C and 80°C. I asked for it.

The results are shown in Table 1.

Examples 2 to 4, Comparative Examples 1 to 3 Polypropylene resins shown in Table 1, namely 0-globylene-butene-1 random copolymer (BPF) - Propylene-ethylene random copolymer (gPF) - Propylene-ethylene block A bumper core material having the physical properties shown in Table 1 was obtained according to Example 1 using the copolymer (EPB).

(Margin below) 4,

[Brief explanation of the drawing]

FIG. 1 is a graph showing the stress/strain curve of the foam.

Claims (1)

[Claims] Density 0.02-0.08g/cm^3, compressive stress at 50% compression (measured at 20°C) 2.5kg/cm^2 or more,
Energy absorption efficiency at 20℃ is 60% or more, 20
Ratio of energy absorption at 80℃ (E_8_0) to energy absorption at ℃ (E_2_0) (E_8_0/
E_2_0) is 0.5 or more and the 1-butene content is 3 to 12
An automobile bumper core material made of a foam made of a propylene/1-butene random copolymer of % by weight.