JPH07137067A - Manufacture of core material for automobile bumper - Google Patents

Abstract

PURPOSE:To obtain a manufacture of a core material for an automobile bumper which is excellent in chemical resistance, heat resistance, lightweight properties, etc., and has dimensional stability and an energy absorbing property at the time of a low s train. CONSTITUTION:After pellets of a 1-butene-propylene random copolymer of which the copolymerization ratio of 1-butene is 2 to 15-wt.% are dispersed in water and deaerated in a pressure-resistant vessel, a foaming agent is added into the pressure-resistant vessel and the pellets are impregnated with the foaming agent by heating. Then, the foaming agent is supplied additionally into the pressure-resistant vessel and the impregnated material is opened under normal pressures while the inside of the vessel is kept at a fixed pressure substantially, whereby preliminary foamed particles are manufactured. Thereafter the preliminary foamed particles thus obtained are filled up in a mold and heated. Thereby a core material for an automobile bumper for which the 1- butene-propylene random copolymer of which the content of the 1-butene is 2 to 15wt.% is used as base resin is manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a core material for a bumper used for manufacturing a bumper of an automobile, more specifically, it has excellent dimensional stability and has a low strain per unit weight. The present invention relates to a method for manufacturing a bumper core material having a significantly improved energy absorption capacity.

[0002]

2. Description of the Related Art In response to the demand for weight reduction of automobiles, in recent years,
Synthetic resin bumpers have been developed, and one of them is a bumper composed of a foamed resin core material and a non-foamed resin skin material encapsulating the core material. The core material in this bumper is an important member that affects the performance as an automobile bumper, and it is not sufficient to simply reduce the weight, and the compressive strength, chemical resistance, heat resistance, etc. required for the core material for bumpers are required. Needless to say, it is necessary that the characteristics of are excellent. Moreover, in addition to these characteristics, the core material for bumpers has excellent energy absorption performance, especially impact energy absorption performance at short strokes, that is, at low strain, from the function of protecting the vehicle body in the event of a collision. Must also be satisfied. Nowadays, as a demand in industry, there is a stricter demand for weight reduction of various members of automobiles, and particularly for core materials for automobile bumpers, it is required to further improve the impact energy absorption capacity at the time of low distortion. Resin foams have been developed.

Conventionally, a polyurethane resin foam or a foam containing polystyrene and polyethylene as components (Japanese Patent Application Laid-Open No. 57-40136) has been used as the core material.
However, the quality of polyurethane resin foams may deteriorate due to hydrolysis due to moisture in the air, etc., although it is extremely gradual, and the energy absorption capacity and dimensional recovery rate of automobile bumpers may deteriorate. There was a maintenance flaw. In order to prevent such deterioration of quality, high density foam (0.1-0.3 g / c
must be m ^3), but this case has a disadvantage weight reduction of the bumper itself is not sufficient.

A foam containing polystyrene and polyethylene as a component does not deteriorate due to hydrolysis and has sufficient compressive strength, energy absorption capacity and dimensional recovery rate even if a foam having a low density is used. Can be made lighter. However, the chemical resistance (gasoline resistance) and heat resistance (heat resistance that does not deform even when exposed to the hot sun, judged by the degree of deformation at 90 ° C) are insufficient, and it is not satisfactory as a core material for bumpers. It was

As these improvements, ethylene-
Foamed moldings using a propylene random copolymer as a base resin (JP-A-58-23834, JP-A-60-1896).
No. 60 and JP-A No. 61-46744) have been proposed. The bumper core material made of such a foamed molded product is superior in properties such as chemical resistance, heat resistance and lightness to conventional foamed molded products. Therefore, the ethylene-propylene random copolymer is widely adopted as a core material for automobile bumpers.

[0006] However, in order to obtain a core material for a bumper having more excellent performance, when it is intended to further improve the compression strength of a foamed molded product using an ethylene-propylene random copolymer as a base resin, the expansion ratio is Lower or lower ethylene content. However, when the expansion ratio is decreased, the weight increases, and when the ethylene content is decreased, the melting point increases, so that it is economically feasible in terms of equipment and utility when manufacturing the pre-expanded particles and the foamed molded product. Will be at a disadvantage.

As a foam material which has improved the above-mentioned drawbacks 1-
Foam molded article using butene-propylene random copolymer as a base resin (JP-A-1-242638, JP-A-3-2)
No. 54930) has been proposed, and it is disclosed that the above-mentioned drawbacks are improved and the compressive strength is improved as compared with the foamed molded product using an ethylene-propylene random copolymer as a base resin.

[0008]

However, although the above-mentioned prior art discloses the characteristics of 1-butene-propylene random copolymer as a base resin, it is difficult to produce pre-expanded particles and foamed molded products. However, there is no disclosure in the manufacturing technology for sufficiently expressing the characteristics of the base resin.

[0009] However, a foamed molded product that fully exhibits the characteristics of the above-mentioned base resin, particularly a foamed molded product excellent in energy absorption performance and dimensional stability at low strain required for a core material for automobile bumpers is obtained. In order to do so, it is necessary to use pre-expanded particles having a small particle size and uniformly impregnated with a foaming agent. However, in the step of producing the pre-expanded particles having a small particle diameter, when the pre-expanded particles are produced by a conventionally known method, it is difficult to uniformly impregnate the pellet having a small particle diameter with a foaming agent. There is a problem that the dimensional stability and the energy absorption performance of the product molded using the expanded beads are deteriorated. Further, the above-mentioned prior art does not disclose any impact (dynamic) energy absorption against a high-speed impact required for a core material for a bumper of an automobile, and it is unknown whether a better core material for a bumper can be manufactured. Met.

Therefore, in order to solve the above-mentioned problems and obtain a more excellent core material for bumpers, the conditions for manufacturing a foamed molded product using a 1-butene-propylene random copolymer as a base resin are limited. As a result of intensive research, the present invention has been completed as a result of discovering a method for producing a core material for an automobile bumper that sufficiently expresses the characteristics of the base resin.

[0011]

The gist of the method for producing a core material for an automobile bumper according to the present invention is to produce a propylene resin foam using a 1-butene-propylene random copolymer as a base resin. In the method, 1-butene-propylene random copolymer pellets having a 1-butene copolymerization ratio of 2 to 15% by weight are dispersed in water in a pressure vessel and deaerated, and then a foaming agent is placed in the pressure vessel. While further heating, the 1-butene-propylene random copolymer pellets are impregnated with a foaming agent, and then a foaming agent is added to the pressure vessel to keep the pressure in the pressure vessel almost constant. The impregnated product is opened under normal pressure to produce pre-expanded particles,
Then, the obtained pre-expanded particles are filled in a mold and heated to form a 1-butene-propylene random copolymer having a 1-butene content of 2 to 15% by weight as a base resin. It is in.

In the method for producing a core material for an automobile bumper, the 1-butene-propylene random copolymer has a particle weight of 50 to 250 mg / 100 particles.

Further, in the method for manufacturing a core material for an automobile bumper, the molded core material for an automobile bumper is molded so that the density is within a range of 0.03 to 0.09 g / cm ^3. is there.

Further, in the method for producing a core material for an automobile bumper, when the pre-expanded particles are produced from the 1-butene-propylene random copolymer pellets, the foaming agent is added at least twice. .

[0015]

In the method for producing a core material for a bumper according to the present invention, 1-butene-propylene random copolymer pellets having a 1-butene copolymerization ratio of 2 to 15% by weight are used in the step of producing the pre-expanded particles. A limited copolymer pellet is used. By using 1-butene-propylene random copolymer pellets having a 1-butene copolymerization ratio of 2 to 15% by weight, it is possible to produce a foamed molded product having high compression strength and high energy absorption at low strain. ,
A core material for a bumper having excellent energy absorption performance can be manufactured. Further, the pre-expanded particles produced by using the above-mentioned copolymer pellets have an appropriate melting point and can form an expanded molded article with an appropriate molding pressure, so that the bumper core does not need special molding equipment. The material can be manufactured.

Further, in the present invention, when the pre-expanded particles are produced, the foaming agent is added twice. That is,
After adding a foaming agent to an aqueous dispersion of small-sized pellets of a specific size, and then impregnating the whole of the small-sized pellets that has been softened by heating with the foaming agent, a foaming agent to maintain a predetermined pressure condition. Is additionally added to impregnate a predetermined amount of foaming agent. By thus adding the foaming agent at least twice, the impregnation rate of the foaming agent is made uniform, and the pressure condition suitable for producing the pre-expanded particles is maintained, so that the pre-foaming with high uniformity is achieved. Particles can be produced. A foam molded article molded using the pre-expanded particles has high uniformity, and a bumper core material having improved energy absorption performance and improved dimensional stability can be manufactured.

Further, by using 1-butene-propylene random copolymer pellets having a very small particle diameter of 50 to 250 mg / 100 grains, which is a very small particle size, the uniformity of the expansion ratio and the expansion ratio can be improved. It is possible to ensure the uniformity of filling, and it is possible to fully express the characteristics of the base resin in a stable state even in a long and complicated foam molding such as a bumper core material, and it has excellent dimensional stability. It is possible to manufacture a high quality bumper core material.

As described above, the core material for an automobile bumper manufactured by the manufacturing method according to the present invention contains 1-butene-propylene random copolymer having a 1-butene content of 2 to 15% by weight as a base resin. Because of the characteristics of the base resin, when the base resin having the same melting point is used, the compression strength of the foam at the same expansion ratio is higher than that using the ethylene-propylene random copolymer. It has the characteristics that it becomes higher and that the amount of energy absorbed in the same amount of strain increases in the drop impact test. This is because the 1-butene-propylene random copolymer has a higher glass transition point (Tg) than the ethylene-propylene random copolymer, and the apparent glass transition point (Tg) further increases at high-speed impact load (that is, It behaves as a harder material), and it is considered that there is a difference in energy absorption in dynamic compression than in static compression.

The core material for automobile bumpers is
Since it comprises a foamed molded product using a butene-propylene random copolymer as a base resin, it has excellent heat resistance and chemical resistance, and is a more excellent core material for automobile bumpers. Furthermore, the density of the core material for automobile bumpers is 0.03 to
The weight of the bumper can be reduced by molding it within the range of 0.09 g / cm ³ .

[0020]

EXAMPLES A method of manufacturing a core material for an automobile bumper according to the present invention will be described below.

First, a method for producing pre-expanded particles will be described. The pre-expanded particles are produced at a copolymerization ratio of 1-butene of 2 to
15 wt% 1-butene-propylene random copolymer pellets are used and the 1-butene-propylene random copolymer pellets are dispersed in water in a pressure vessel. When dispersing 1-butene-propylene random copolymer pellets in water, a dispersant may be present.

With respect to the copolymerization ratio of the 1-butene-propylene random copolymer, the 1-butene copolymerization ratio is preferably 2 to 15% by weight, more preferably 3 to 12% by weight. A copolymer having a 1-butene copolymerization ratio of less than 2% by weight has a high compressive strength and a high energy absorption amount at a low strain, but also has a high melting point and therefore a high molding pressure for a foamed molded product, which causes a problem in molding equipment. It will be a disadvantage. On the other hand, the 1-butene copolymerization ratio is 1
If the amount of the copolymer exceeds 5% by weight, the compression strength and energy absorption of the foamed molded product will be low and the original purpose cannot be achieved.
Further, as the dispersant used here as needed,
Powdered basic tribasic calcium phosphate and sodium n-paraffin sulfonate are preferably used. These dispersants are usually about 0.03 to 100 parts by weight of resin particles.
3.0 parts by weight are used.

The 1-butene-propylene random copolymer pellets have a particle weight of 50 to 250 mg / 100.
It is preferable to use those having a size within the range of grains. Regarding this grain weight, it is generally 1 in the production of resin foam moldings.
Although pellets of about 0 to 800 mg / 100 grains can be used, in the present invention, particularly 100 pellets among such pellets can be used.
Grain weight is 50-250 mg, preferably 100-180
mg small particle size pellets are used.

When 1-butene-propylene random copolymer pellets having a weight of 100 particles of less than 50 mg are used, the expansion ratio of the pellets is not uniform when the pre-expanded particles are produced. Since the particle diameters of the above-mentioned vary greatly, it is not possible to manufacture a core material which is a foam molded article having good characteristics. On the other hand, when 100 pellets weighing more than 250 mg are used,
Since the particle diameter of the pre-expanded particles becomes large, the filling uniformity becomes poor when filling a long and complicated mold such as a bumper core material. Therefore, the core material manufactured from such pre-expanded particles having a large particle diameter has poor product stability, and the manufactured core material varies in size. As described above, the particle size of the small particle size pellets used in the present invention is an extremely important requirement for producing a high-quality core material. That is, the above 50 to 250 mg / 100 grains, preferably 100
By using a pellet having a small particle size of 180 mg / 100 particles, a core material for a bumper having good dimensional stability and energy absorbing ability can be manufactured.

Next, the 1-butene-propylene random copolymer pellets are dispersed in water and deaerated using a vacuum pump while stirring, and then a predetermined amount of a foaming agent is added, and thereafter, The pellets are impregnated with the foaming agent by heating to a temperature not lower than the softening temperature of the 1-butene-propylene random copolymer and allowed to stand for a predetermined time. The heating temperature at this time is usually 120 to 170 ° C.

Examples of the blowing agent used here include aliphatic hydrocarbons such as propane, butane and isobutane, cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane, halogenated trichlorofluoromethane and dichlorofluoromethane. Hydrocarbons and the like can be mentioned. The foaming agent is usually used in the range of 10 to 40 parts by weight with respect to 100 parts by weight of the resin particles. In addition, it is preferable that the foaming agent does not affect the pollution of the air.

In this way, the 1-butene-propylene random copolymer pellets are once impregnated with the foaming agent, and then the foaming agent is additionally added to the pressure vessel under pressure.
Since the pressure in the pressure resistant container is increased by adding the foaming agent additionally, the foaming agent is added while adjusting the supply amount of the foaming agent or the like to a substantially constant pressure with a valve or the like. The pressure in the pressure-resistant container is set to about the vapor pressure of the foaming agent. For example, when isobutane is used as the foaming agent, the pressure is set to about 16 kg / cm ² (G). Here, the foaming agent used is preferably the same as the foaming agent already added to the pressure resistant container.

The additional addition of the foaming agent at least twice is as follows. First, the foaming agent is added to an aqueous dispersion of small-sized pellets of a specific size and then heated to soften it. The entire small particle pellets are impregnated with a predetermined amount of the foaming agent. In this way, the amount of the foaming agent impregnated into the small particle pellets is likely to vary from one small particle pellet to the next, and Foamed particles cannot ensure sufficient uniformity. In addition, the pressure inside the pressure vessel tends to decrease as the foaming agent is impregnated. Therefore, in the present invention, after the foaming agent is once impregnated into the small particle size pellet by heating as described above, the foaming agent is additionally added so as to maintain a predetermined pressure condition.

The additional blowing agent makes the impregnation amount of the blowing agent in the individual small particle size pellets uniform, and
Prevents pressure drop in the pressure vessel. By thus additionally adding the foaming agent, it is possible to impregnate the small-sized pellets with a uniform amount of the foaming agent, and it becomes easy to maintain the pressure condition suitable for producing the pre-expanded particles. That is, by adding the foaming agent at least twice in this way, the foaming agent is likely to be uniformly impregnated during the production of the pre-expanded particles, and the uniformity of the obtained pre-expanded particles is increased. The core material foam-molded by using the pre-expanded particles has high homogeneity, improves energy absorption performance, and improves dimensional stability.

In this way, 1-
The water dispersion of butene-propylene random copolymer pellets is discharged under atmospheric pressure by opening the discharge valve at the bottom of the pressure container while maintaining the pressure inside the pressure container constant, to produce pre-expanded particles. The pre-expanded particles having high uniformity can be produced by such a production process. The pre-expanded particles thus obtained are usually cooled to room temperature.

Regarding the production conditions of the pre-expanded particles,
The conditions can be combined and set so that the density of the core material for automobile bumpers produced by the obtained pre-expanded particles is in the range of 0.03 to 0.09 g / cm ³ .
For example, the density of the produced core material is influenced by the size of the 1-butene-propylene random copolymer pellets used in the step of producing the pre-expanded particles, the amount of the foaming agent, the heating temperature and the pressure, and controls these. By doing so, it can be within the above range. Further, the 1-butene content of the 1-butene-propylene random copolymer for molding the core material is the 1-butene copolymerization amount in the 1-butene-propylene random copolymer pellets used when producing the pre-expanded particles. Can be adjusted within the above range.

Next, the pre-expanded particles obtained in the above step are filled in a mold to manufacture a core material for an automobile bumper in a desired form according to a conventional bead in-mold molding method. For example, as shown in FIG. 1, in an automobile bumper 10, a surface of an automobile bumper core 12 that appears as an external shape is a skin material 14.
The present invention is for manufacturing a core material 12 for an automobile bumper. In addition,
As the skin material 14, for example, a polyurethane resin RIM molded product or a polypropylene copolymer injection molded product is used.

As the in-mold molding method for beads, a pre-expanded molding method and pre-foaming method in which pre-expanded particles are held under pressure in a pressure vessel and air is impregnated inside the particles to increase the cell internal pressure and fill the mold. There is a compression filling molding method in which particles are held under air pressure in a pressure vessel, the cell internal pressure is increased by deformation and volume reduction of the particles, and the particles are filled in a mold under pressure, but there is no limitation to these. is not.

Thus, the 1-butene content is 2-1.
It is molded from 5% by weight of 1-butene-propylene random copolymer and more preferably has a density of 0.03 to
A core material for automobile bumpers in the range of 0.09 g / cm ³ can be obtained.

Although the examples of the method for manufacturing the core material for an automobile bumper according to the present invention have been described above, the present invention is not limited to these examples, and the present invention does not depart from the gist thereof. Within the scope, based on the knowledge of those skilled in the art,
The present invention can be implemented with various improvements, changes and modifications.

Next, the present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples.

Example 1 In a pressure vessel equipped with a stirrer having an internal volume of 1 m ³ ,
Butene-propylene random copolymer pellets (1-butene amount 5% by weight, density 0.90 g / cm ³ , melting point 152 ° C.,
Melt index 8.0g / 10min, grain weight 180mg /
100 parts by weight) was dispersed in 300 parts by weight of water, and 2.0 parts by weight of powdery basic calcium triphosphate and 0.03 parts by weight of n-paraffin sodium sulfonate were added as dispersants.

After degassing the dispersion with a vacuum pump while stirring, 13 parts by weight of isobutane was added as a foaming agent. Then, it is heated to 149 ° C., which is a temperature equal to or higher than the softening temperature of the 1-butene-propylene random copolymer,
The pellets were impregnated by leaving them for 30 minutes.

Then, isobutane, which is the foaming agent, is additionally added to the pressure resistant container, and a predetermined pressure of 16 kg / cm ^{2 is applied.}
While maintaining (G), the discharge valve in the lower part of the pressure vessel is opened to discharge the water dispersion in the pressure vessel under atmospheric pressure through the orifice plate having an opening diameter of 4 mm to obtain pre-expanded particles having a true magnification of 10 times. Obtained.

The obtained pre-expanded particles are filled in a mold, and the pre-expanded particles are molded by a method of impregnating the inside of the particles with air to increase the cell internal pressure according to a conventional bead molding method. A core material for an automobile bumper having a desired shape having a body density of 0.06 g / cm ³ was manufactured.

Regarding the obtained core material for automobile bumpers,
A drop test was performed according to JIS Z 0235-1970 (dynamic compression test method for cushioning material for packaging), and the relationship between compressive strain rate (%) and dynamic compressive stress was determined and shown as a dynamic S-S curve in FIG. It was In addition, the dimensional variation of 100 core materials for automobile bumpers was measured and found to be 0.7% or less.

Comparative Example 1 In the same pressure resistant container as in Example 1, ethylene-propylene random copolymer pellets (ethylene content 2.3% by weight,
Pre-expanded particles were obtained in the same manner as in Example 1 using a density of 0.90 g / cm ³ , a melting point of 152 ° C., a melt index of 8.0 g / 10 minutes, and a grain weight of 180 mg / 100 grains).
Then, the pre-expanded particles were filled in a mold, and a core material for an automobile bumper having a molded body density of 0.06 g / cm ³ was obtained according to a conventional bead molding method.

Regarding the obtained core material for automobile bumpers,
A dynamic SS curve was obtained in the same manner as in Example 1 and is shown in FIG. The dimensional variation of the core material for automobile bumpers was 0.7% or less.

As is apparent from FIG. 2, the foamed molded product using the 1-butene-propylene random copolymer as the base resin has a higher density than the foamed molded product using the ethylene-propylene random copolymer as the base resin. Large compressive stress at low strain,
It is excellent in shock absorption (integrated value of S-S curve), is most suitable as a core material for automobile bumpers, and can be manufactured so that such characteristics can be sufficiently exhibited.

[0045]

The method for producing a core material for an automobile bumper according to the present invention is configured such that the foaming agent is additionally added at least twice, so that the pre-expanded particles are impregnated with the foaming agent. The amount of the pre-expanded particles can be made uniform, and the pressure conditions suitable for producing the pre-expanded particles can be maintained to produce the pre-expanded particles with high uniformity. The characteristics of the polymer can be sufficiently expressed. By the production method of the present invention, the compressive stress at a low strain is large and the shock absorption (the integrated value of the SS curve) is excellent as compared with the foamed molded article using the ethylene-propylene random copolymer as the base resin. It is possible to obtain a core material for an automobile bumper, that is, a core material for an automobile bumper that has excellent energy absorption capacity, which is a necessary performance as a bumper, in particular, an energy absorption rate at low strain, and also has excellent dimensional stability. Obtainable.

In addition, the method for producing a core material for an automobile bumper according to the present invention is prefoamed by using 1-butene-propylene random copolymer pellets having a specific small particle diameter in terms of particle weight. Not only the expansion ratio of the particles is uniform, but also the filling of the pre-expanded particles into the mold can be ensured, making it possible to stabilize even the long and complicated foam moldings such as the core material for automobile bumpers. It can be molded, and the characteristics of the 1-butene-propylene random copolymer that is the base resin can be sufficiently exhibited. That is, the method of the present invention sufficiently develops the characteristics of a foamed molded product using a 1-butene-propylene random copolymer as a base resin, and a quality-stable and lightweight automobile bumper core is produced by such a production method. The material can be obtained.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing an example of an automobile bumper including an automobile bumper core material produced by a method for producing an automobile bumper core material according to the present invention.

FIG. 2 is a dynamic S-representing the relationship between compressive strain rate and dynamic compressive stress.
It is a figure which shows an S curve.

[Explanation of symbols]

 10: Automotive bumper 12: Core material for automobile bumper 14: Skin material

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area B29L 31:00

Claims (4)

[Claims] 1. A method for producing a propylene-based resin foam comprising a 1-butene-propylene random copolymer as a base resin, wherein the 1-butene copolymerization ratio is 2 to 15% by weight. After the copolymer pellets are dispersed in water in a pressure vessel and degassed, a foaming agent is added to the pressure vessel and further heated to add a foaming agent to the 1-butene-propylene random copolymer pellets. Impregnation, then a foaming agent is additionally added to the pressure vessel, the pre-expanded particles are produced by releasing the impregnated material under normal pressure while maintaining the pressure in the pressure vessel almost constant, and thereafter, By filling the obtained pre-expanded particles in a mold and heating, 1-
A method for producing a core material for an automobile bumper, which comprises molding a 1-butene-propylene random copolymer having a butene content of 2 to 15% by weight as a base resin. 2. The method for producing a core material for an automobile bumper according to claim 1, wherein the 1-butene-propylene random copolymer has a particle weight of 50 to 250 mg / 100 particles. 3. The molded core material for an automobile bumper is molded to have a density within the range of 0.03 to 0.09 g / cm ^3. A method for producing a core material for an automobile bumper as described. 4. A foaming agent is added at least twice in the production of pre-expanded particles from the 1-butene-propylene random copolymer pellets, according to any one of claims 1 to 3. A method for producing a core material for an automobile bumper as described in 1.