JP2675373B2 - Automotive bumper core material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to an automobile bumper core material having excellent heat resistance, impact resistance and strength.

(Prior art)

As a bumper for an automobile, a resin bumper is used instead of a metal bumper, in particular, a resin foam core is used as a core material and a non-foam outer resin is used as a bumper. Polyurethane foam, polystyrene, cross-linked polyethylene, and ethylene / propylene random copolymer are used as the material resin for the foam bumper core material (Form Times, July 25, 1981, No. 842, p. 29; actual development). 55-1632
54, usp4,350,378, JP58-221745, JP60
-189660).

Density of ethylene-propylene random copolymer with ethylene content of 1-12% by weight as base resin 0.03-0.065g
Bumper core material made of in-mold bead molding foam of / cm ³
It is superior to polyurethane foam in terms of lightness, superior to polystyrene foam in terms of dimensional recovery and heat resistance, and superior to cross-linked polyethylene foam in terms of heat resistance and strength, so demand for bumper core material is increasing in recent years. It is growing.

[Problems to be Solved by the Invention] In order to further reduce the weight of automobiles, a foam having the same strength is preferably a foam having a smaller density. In addition, automobiles may be exported or used in the desert or in the tropics. In that case, severe heat resistance is required, and it is desired to exert sufficient bumper core material function even at 80 ° C. There is.

An object of the present invention is to provide a bumper core material for automobiles, which has excellent strength, energy absorption performance and heat resistance.

[Specific means to solve the problem]

As a bumper core material that achieves the above purpose, a density of 0.02 to 0.
08g / cm ^3, 50% -compression of the compressive stress (20 ° C. Measurements) is 2.5 kg / c
m ² or more, energy absorption efficiency at 20 ℃ is 60% or more,
Propylene / 1-butene random copolymer having a butene-1 content of 3 to 12% by weight, in which the ratio (E ₈₀ / E ₂₀ ) of the energy absorption amount E ₈₀ at 80 ° C. to the energy absorption amount E _{20 at} 20 ° C. is 0.5 or more. An automobile bumper core material made of a foamed product can be used.

(Base Resin) The bumper core material of the present invention contains 1 to 1 to 3 to 12% by weight of butene.
It is a propylene-based resin expanded particle type in-molded product containing propylene as a main component. This propylene resin is 1
-A binary random copolymer of butene and propylene, 1-
Tertiary random copolymer of 3-12 wt% butene, 0.5-5 wt% ethylene and propylene, 3-12 wt% 1-butene, 4-methylpentene-1 0.5-5 wt% propylene Terpolymer, 1-butene hexene-1.
A propylene ternary random copolymer, a quaternary copolymer of 1-butene, propylene, ethylene and 4-methylpentene-1 or hexene-1 can be used.

The propylene / 1-butene random copolymer preferably has a crystallinity of 40% or more and a latent heat of crystallization of 6 to 28 cal / g.

The 1-butene content of the copolymer is 3 to 12% by weight, preferably 4 to 10% by weight. A copolymer having a 1-butene content of less than 3% by weight has fine cells and a high melting point, so that the heating temperature or heating pressure for the production of expanded particles and the heat fusion of the expanded particles becomes too high. Will end up. If the 1-butene content exceeds 12% by weight, the molded product has poor compressive strength and heat resistance.

1-of this propylene / 1-butene random copolymer
The butene content is 2 mm / cm ² G pressure at 190 ° C. for 1 minute by hot pressing the copolymer particles to obtain a 0.5 mm thick sheet.
The sample was allowed to stand at 0 ° C. for 1 day, and the sample was determined by infrared absorption spectrum analysis.

If necessary, the propylene / 1-butene random copolymer may be blended with another polyolefin resin in a range not exceeding 50% by weight. For example, homopolypropylene, ethylene-propylene random copolymer, ethylene-propylene block copolymer, ethylene-propylene rubber, high pressure low density polyethylene, straight chain low density polyethylene, medium / high density polyethylene, ethylene / vinyl acetate Copolymer, ethylene / methyl acrylate copolymer, ethylene / ethyl acrylate copolymer,
You may add ethylene-acrylic acid copolymer etc.

Further, the resin may contain an inorganic filler such as zeolite, silica and talc, a pigment, a heat stabilizer, a dye, a lubricant and an antistatic agent. These are 5% by weight or less, preferably 2% by weight or less in order to achieve good fusion when the foamed particles are heated with steam and fused to each other to form a molded body.
Should be:

The weight of one propylene / 1-butene random copolymer particle is 0.01 to 20 mg. For granulation, any method such as strand cutting method, underwater cutting method, sheet cutting method, freeze crushing, and melt spraying method may be used.
Decide in consideration of moldability and quality. Moreover, you may re-granulate.

(Expanded Particles) Expanded particles of a propylene / 1-butene random copolymer are described in JP-B Nos. 49-2183, 57-195131 and 58-1732.
No. 58-23834, No. 58-25334, No. 58-33435,
58-55231, 58-76229, 58-76231, 58
-76232, 58-76233, 58-76234, 58-870
No. 27, No. 62-151325 and the like, propylene-based resin particles are dispersed in water in a closed container as described in Patent Publications,
Then, a volatile organic expander is supplied into the closed container, and while heating the pressure in the closed container to the vapor pressure of the expander or a pressure higher than the softening temperature of the propylene resin particles, The temperature and pressure are maintained for a certain period of time, then the discharge port provided below the water surface in the closed container is opened, and the propylene-based resin particles containing the volatile expanding agent and water are simultaneously released into an atmosphere at a pressure lower than that in the container. As a result, expanded propylene resin particles are produced.

Examples of the volatile expanding agent include aliphatic hydrocarbons such as propane, butane, pentane, hexane and heptane; halogen such as trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride and methylene chloride. Organic compounds having a boiling point of 80 ° C. or lower, such as chemical 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 intended bulk density of the resin particles, but is usually 10 to 50 parts by weight with respect to 100 parts by weight of the resin particles.

As the dispersant for dispersing the resin particles in water, inorganic suspending agents such as aluminum oxide, titanium oxide, calcium carbonate, basic magnesium carbonate, tricalcium phosphate, calcium pyrophosphate, etc .; polyvinyl alcohol, methylcarboxycellulose, N- Water-soluble polymeric protective colloid agent such as polyvinylpyrrolidone; anionic surfactants such as sodium dodecylbenzene sulfonate, sodium alkane sulfonate, sodium alkyl sulfate ester, sodium olein sulfate ester, acylmethyl taurine, sodium dialkylsulfosuccinate Etc. Among them, the particle size of the inorganic suspension agent is 0.01 to 0.
It is preferred to use 8 micron tribasic calcium phosphate in combination with the suspension aid sodium dodecylbenzene sulfonate. This fine tribasic calcium phosphate can be obtained by reacting phosphoric acid in water at a ratio of 0.60 to 0.67 mol with respect to 1 mol of calcium hydroxide.

The amount of water as the dispersion medium is 100 to 1, based on 100 parts by weight of the resin particles.
000 parts by weight, preferably 200 to 500 parts by weight. If it is less than 150 parts by weight, resin particles are likely to block during heating and pressurization. If the amount exceeds 1,000 parts by weight, the productivity of expanded beads decreases, which is not economical.

A gaseous expander or a liquid expander 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. While being heated to a temperature equal to or higher than the point and equal to or lower than 20 ° C. higher than the melting point, the pressure in the container is increased by this heating and the expander is impregnated in the copolymer particles. Then, the bulk density is 8 to 100 kg / by discharging the copolymer resin particles together with water from the discharge port such as a slit and a nozzle provided in the lower part of the closed container into the low pressure region (generally at atmospheric pressure) from the closed container. It is possible to produce m ³ propylene / 1-butene random copolymer expanded particles.

In the production of the expanded beads, an inorganic gas such as nitrogen, helium or air is supplied into the closed container before or after the expansion agent is added into the closed container to apply pressure. The inorganic gas may be supplied before heating the dispersion or after heating it.

The supply of air, nitrogen gas, or an inorganic gas such as argon into the closed container facilitates the impregnation of the expander into the resin particles and serves to obtain the propylene / 1-butene copolymer expanded particles having a low bulk density.

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

The time for holding the dispersion liquid in the closed container is 30 minutes to 12 hours, preferably 1 to 3 hours, although it depends on the pressure applied, the holding temperature and the target expansion ratio.

The expanded particles released into the atmosphere are dried (cured) in a room at 30 to 65 ° C to remove the water adhering to the surface, and then applied to the molding of the 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 expanded particles in the mold, compress it so that the volume of the expanded particles is reduced by 15-50%, and then introduce 1-5 kg / cm ² G of steam to expand the expanded particles. A compression molding method (DOS2107683) to obtain a product by fusing and then cooling the mold.

. The mold is filled with pre-expanded particles obtained by impregnating the expanded particles with a volatile liquid expander in advance and imparting the secondary expandability to the expanded particles, and heating with steam to perform secondary expansion and fuse the particles together. To get the product.

. The expanded particles were placed in a closed chamber, and then an inorganic gas such as air or nitrogen gas was pressed into the chamber to increase the pressure in the cells of the expanded particles to impart secondary foamability, and to impart this secondary foamability. Pre-expanded particles are filled in a mold, heated with steam to secondary-expand, and the particles are fused together to obtain a product (so-called pressure aging method; JP-B-59-43492).
issue).

. In the method of filling the foamed particles in the mold and fusing the foamed particles with each other by steam heating to form a molded product foam, in the mold pressurized to 1.0 to 6.0 kg / cm ² G with a pressurized gas, the The expanded particles are filled while being compressed using a pressurized gas that is 0.5 kg / cm ² or more higher than the in-mold pressure, and the in-mold pressure is continuously maintained at the in-mold pressure during the filling, and then after the filling is completed. After returning the pressure in the mold to atmospheric pressure, the above-mentioned heating is performed to fuse the foamed particles together, and the formula of the foamed particles at that time [In the formula, W, V and σ represent the following, respectively.

W ... weight of molded product (g) V ... capacity of molded product (l) σ ... bulk density (g / l) of foamed particles in the atmosphere] It is necessary to control the compression ratio to 40 to 70%. In-mold molding method of characteristic expanded particles (JP-A-62-151325).

. Propylene / 1-butene Random Copolymer Expanded particles are filled in a mold, and steam heating is used to fuse the expanded particles together to form a molded foam, which is 0.5 to 5.0 kg / cm ² G with a pressurized gas. The foamed particles to which the gas internal pressure was applied, which was obtained by pressurizing the gas for 1 hour or more in advance using a pressurized gas whose pressure was 0.5 kg / cm ² or more higher than the pressure in the mold, Filling with a pressurized gas of 0.5 kg / cm ² or more higher than the in-mold pressure, and keeping the in-mold pressure at the in-mold pressure during the filling, and then the in-mold pressure after completion of the filling. After returning to atmospheric pressure, the above-mentioned heating is performed to fuse the expanded particles, and the formula of the expanded particles at that time [In the formula, W, V and σ represent the following, respectively.

W: Weight of molded product (g) V: Volume of molded product (l) σ: Bulk density of expanded particles in air (g / l)] Compressibility less than 40% (excluding 0%) ) In-mold molding method of expanded propylene / 1-butene random copolymer particles.

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

The density of the bumper core material is 0.02 to 0.08 g / cm ³ , preferably 0.030 to 0.075 g / cm ³ . If it is less than 0.02 g / cm ³ , the energy absorption performance is inferior, and if it exceeds 0.08 g / cm ³ , there is no weight reduction advantage over other materials such as propylene / ethylene copolymer.

As a bumper core material, in addition to having a low density in terms of weight reduction, (1) High strength to reduce the wall thickness (2) Energy absorption efficiency of 60% or more at room temperature (3) Sufficient energy absorption performance at high temperatures (4) Excellent chemical resistance is required.

The bumper core material of the present invention has a length of 80 mm, a width of 80 mm, and a height of 50 mm.
In the stress-strain curve shown in Fig. 1 obtained by cutting the sample piece of No. 1 and compressing it at a speed of 20 mm / min. (I) The compressive stress at 50% strain (point A) was measured at 20 ° C, 2.
It is as high as 5kg / cm ² or more.

(Ii) Energy absorption efficiency (OAB area / OABC area)
60% or more (iii) The ratio (E ₈₀ / E ₂₀ ) of the energy absorption amount (E ₈₀ ) at 80 ° C to the energy absorption amount (E ₂₀ ) at ₂₀ ° C is 0.5 or more.

Since it shows physical properties and has higher strength than the conventional foamed bumper core material of ethylene / propylene random copolymer,
(A) The advantage that the wall thickness of the bumper core can be reduced under the constraint that the density of the bumper core is the same, and (b) the foam having a smaller density can be obtained under the constraint that the thickness of the bumper core is the same. It can be used, and the bumper core material can be made lighter. Furthermore, this bumper core material exhibits sufficient energy absorption performance even at high temperatures.

Hereinafter, the present invention will be described in more detail with reference to Examples. The parts and% in the examples are based on weight.

Example 1 1-butene content was 5.2% by weight and MFR measured at 230 ° C was
9.7 g / 10 minutes, propylene / 1-butene random copolymer particles with a crystal latent heat of 22.6 cal / g (the average weight of one particle is about 1 m
g) was used to obtain expanded particles.

That is, in a closed container, 250 parts of water, 100 parts of the propylene / 1-butene copolymer particles, 1.0 part of calcium pyrophosphate, and 0.007 part of sodium dodecylbenzene sulfonate (0.007 part) are charged (filling rate 62%), and then stirred under nitrogen. The gas was pressurized until the internal pressure of the closed container reached 5 kg / cm ² G, and the supply of nitrogen gas was stopped. Then, 18 parts of isobutane was supplied into a closed container, heated to 140 ° C. over 1 hour, and kept at the same temperature for 45 minutes, and the internal pressure of the autoclave was 26 kg / cm ² G.

Then, the valve of the discharge nozzle at the bottom of the closed container was opened, and the dispersion liquid was discharged into the atmospheric pressure in about 2 seconds for foaming. The internal pressure of the closed container at the moment when the final portion after dispersion was released from the closed container was about 10 kg / cm ² G. Also,
The temperature of the closed vessel was maintained at 140 ° C. during discharge of the dispersion.

The expanded particles of the propylene / 1-butene copolymer thus obtained had a bulk density of 30 kg / m ³ , a particle size of 3.3 mm, and an expanded cell diameter of 150 μm. Moreover, the blocking of foamed particles was not found.

The foamed particles are left to dry in a room at 40 ° C for 2 days, then filled in a mold having steam holes, the foamed particles are compressed by 50%, and then 3.0 kg / cm ² G of steam is introduced, The foamed particles were heated and fused together, then cooled in water for 10 seconds and allowed to cool for 30 seconds, then the molded product was taken out from the mold and had a density of 0.062 g / cm ³ , vertical.
A bumper core material of 1500 mm, width 200 mm, and thickness 150 mm was obtained.

A test piece measuring 80 mm in length, 80 mm in width and 50 mm in height was cut out from this bumper core material, and the stress / strain curve at 20 ° C and 80 ° C was obtained.
The stress at 50% strain, energy absorption efficiency, energy absorption, and the ratio of energy absorption between 20 ° C and 80 ° C were calculated.

 Table 1 shows the results.

Examples 2 to 4 and Comparative Examples 1 to 3 Polypropylene resins shown in Table 1, namely, propylene / butene-1 random copolymer (BPF), propylene / ethylene random copolymer (EPF), propylene / ethylene block. Using the copolymer (EPB), a bumper core material having the physical properties shown in Table 1 was obtained according to Example 1.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing a stress-strain curve of a foam.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Toshio Yagi Toshio Yagi 1000, Kawajiri-cho, Yokkaichi-shi, Mie Mitsubishi Petrochemical Bar Dessie Co., Ltd. (72) Inventor Masanori Saito 1000 Kawajiri-cho, Yokkaichi-shi, Mie Mitsubishi Petrochemical Barditsie Co., Ltd. (72) Inventor Shigeki Matsuno 1000, Kawajiri-cho, Yokkaichi-shi, Mie Mitsubishi Petrochemical Barditsie Co., Ltd. (56) References JP-A-61-254649 (JP, A) JP-A-56-98214 (JP, A) JP-A-62-153334 (JP, A) JP-A-63-43942 (JP, A)

Claims (1)

(57) [Claims] 1. A density of 0.02 to 0.08 g / cm ³ , a compression stress at 50% compression (measured at 20 ° C.) of 2.5 kg / cm ³ or more, an energy absorption efficiency at 20 ° C. of 60% or more, an energy absorption of 20 ° C. the amount (E ₂₀₎ energy absorption of 80 ° C. for percentage (E ₈₀ / E ₂₀₎ is 0.5 or more 1-butene content of 3 to 12% by weight of (E ₈₀₎
A bumper core material for automobiles, which is made of the propylene / 1-butene random copolymer foam.