KR100491243B1 - Car bumper core material - Google Patents

Abstract

The present invention is a polyethylene-based amorphous resin polymerized by a single-site catalyst as a base resin and mixed with additives such as foaming agent, crosslinking agent, crosslinking aid, release agent and the like by melt-kneading to form a primary crosslinked foamed molded article, The present invention relates to a core material for an automobile bumper manufactured by cooling a first crosslinked foamed molded product and then heating and compressing the second molded product.

The bumper core material of the present invention is stable against moisture and has an excellent impact energy absorption capacity at repeated shocks.

Description

Core material for automobile bumper

The present invention relates to a bumper core material (CORE), and more particularly to a bumper core material having an excellent impact energy absorption capacity even in water resistance and repeated impact when applied to a passenger car.

The main function of the bumper for passenger cars is to absorb shocks transmitted to the vehicle and life from big and small accidents. In view of this, in recent years, various moldings have been used as bumper core materials. Among them, polyurethane foams (Japanese Patent Application Laid-Open No. 63-112475, Small 63-00071) and injection molding products of ethylene vinyl acetate (Honeycomb: HONEY COMB) ), Plastic blow moldings, polypropylene foam beads (BEADS) molded articles (KR 90-7527), and the like.

However, the polyurethane foam in the bumper core material has a disadvantage in that its quality is gradually degraded due to its hydrolysis by moisture in the air, thereby degrading shock absorption performance and dimensional stability as an automobile bumper. Increasing interest has been increasingly regulated, and injection molding of ethylene vinyl acetate is used as a structural material to support the bumper carver rather than as a shock absorber as a honeycomb structural material. There is a problem that it is remarkably inferior to this foam molding.

In addition, since the bumper core material by blow molding is shaped like a hollow balloon in the middle, it is crushed once it is impacted and cannot be restored again, and the thickness of each part of the molded article is not formed evenly due to the characteristics of blow molding. Therefore, there is a disadvantage that the thinner the blow molded article tends to rupture during impact of the automobile.

In addition, the polypropylene foam beads molded article is manufactured by using a mold-resistant foam molding method in which polypropylene pre-expanded particles are injected into a mold and then pressurized water vapor is molded into the mold. Unlike the core material described above, it has excellent water resistance and excellent shock absorption ability. However, once the impacted area is not restored, there is a disadvantage that the shock absorbing capacity is lowered when re-impacted.

On the other hand, the present inventor has applied for a bumper core material made of a crosslinked foamed molded article having ethylene vinyl acetate as a main component (Korean Patent Application No. 95-13738) prior to the present invention. However, the bumper core material containing ethylene vinyl acetate as a main component has the disadvantage that the specific density of ethylene vinyl acetate itself is higher than that of polyethylene-based amorphous resins, so that it is heavy in the same foam density body, and at the time of repeated impact, which is the most important characteristic of the bumper core material There was a disadvantage of poor energy absorption.

The present inventors have studied to supplement the above-mentioned disadvantages of the prior art, and as a result, when the crosslinked foamed molded article mainly containing a polyethylene-based amorphous resin polymerized using a single-site catalyst is applied as a bumper core material, it is stable from moisture in the air. In addition, the present invention has been found to be excellent in compressive restoring force and excellent shock absorbing ability even in repeated shocks.

Bumper core material according to the present invention is characterized in that the polyethylene-based amorphous resin polymerized by a single-site catalyst as the primary resin is melt-kneaded with the additive, and then produced by primary crosslinking foam molding and then secondary compression molding. More specifically, the bumper core of the present invention is based on 100 parts by weight of the base resin containing polyethylene-based amorphous resin polymerized by a single-site catalyst, 4 to 6 parts by weight of blowing agent, 0.5 to 0.7 parts by weight of crosslinking agent, 0.2 for crosslinking aid 0.2 ~ 0.3 parts by weight, 0.9 to 1.1 parts by weight of the release agent is mixed and melt kneaded, and then the kneaded product is put into a mold, and then the primary crosslinked foamed molded product is formed by compression foam molding, and the primary crosslinked foamed molded product thus prepared is It is characterized in that it is prepared by cooling the secondary compression molding after cooling.

Hereinafter, the manufacturing method of the bumper core material of the present invention for each process will be described in more detail.

First, a foaming agent and a crosslinking agent, a releasing agent, a crosslinking aid and other additives are mixed with a base resin including a polyethylene-based amorphous resin polymerized by a single-site catalyst as a basic raw material for preparing a primary crosslinked foamed molded product, and then KNEADER and roll mill Melt kneading using (ROLL MILL).

The basic resin may be a polyethylene amorphous resin polymerized with a single-site catalyst alone, or a low density polyethylene, a high density polyethylene, a linear low density polyethylene, a polypropylene, or a polyethylene amorphous resin polymerized with a single-site catalyst. A resin in which at least one selected from ethylene propylene rubber, ethylene propylene diene rubber, natural rubber, isobutyl rubber and styrene butadiene rubber is mixed may be used.

Polyethylene-based amorphous resins polymerized by single-site catalysts are commercially available, such as Engage Series (Grade 8180, 8100, 8200, etc.) by Dow Plastics.

As the blowing agent, a conventional degradable blowing agent can be used, for example azodicarbonamide. The addition amount of the foaming agent is a factor that determines the specific gravity of the foam. 4 to 6 parts by weight is suitable for increasing the expansion ratio and decreasing the specific gravity of the foam.

Generally, the degree of crosslinking is affected by the amount of crosslinking agent added, the crosslinking time and the crosslinking reaction temperature. The crosslinking degree increases as the amount of the crosslinking agent is increased, the higher the temperature and the longer the time. However, at a sufficient crosslinking temperature and time, when a certain amount of crosslinking agent is added, it is difficult to expect as much crosslinking as added. Therefore, it is necessary to determine the appropriate amount of addition according to the given processing conditions. In the present invention, as a crosslinking agent, a conventional crosslinking agent, for example, dicumyl peroxide, may be used, and the amount of the crosslinking agent is 0.5 to 0.7 parts by weight.

Examples of the crosslinking aid include zinc oxide (ZnO), and suitable amounts of 0.2 to 0.3 parts by weight, and suitable release agents include stearic acid and 0.9 to 1.1 parts by weight.

If the melting and kneading time is too long or the processing temperature is too high when forming the first crosslinked foamed molded product, there is a possibility of premature decomposition of the blowing agent and the crosslinking agent. On the contrary, when the temperature is too low or the kneading time is short, It is difficult to obtain a foam having fine dispersion and good bubble structure. Therefore, it is preferable that the temperature of the kneader and the roll mill is controlled in the range of 100 to 130 ° C., and the kneading time is kneaded for 10 to 15 minutes in each step.

The primary crosslinked foamed molded product thus prepared is quenched or cooled in water, and then charged into a mold and heated to second compression molding to complete the manufacture of the bumper core material of the present invention.

In general, the biggest disadvantage of foaming is that it is difficult to manage the dimensions of the foamed product due to the three-dimensional expansion of the resin due to the characteristics of the foaming process. In the present invention, the primary crosslinked foamed foam is compressed by using a secondary press mold. Solved the problem. In general, crosslinked foams are not secondary molding, but in the present invention, the secondary molding defect problem can be solved by controlling the crosslinking ratio of the primary crosslinked foams.

That is, the core technology of the present invention is to control the crosslinking rate of the above-described primary crosslinked foamed molding to foam processing in a state capable of secondary compression molding, and the crosslinking ratio of the primary crosslinked foamed molded product is suitable for 40 to 60%. When the crosslinking rate of the primary crosslinked foamed molded product is 40% or less, it is difficult to form a uniform bubble structure, and when 60% or more, secondary compression molding is not easy in a mold having a complicated structure. The primary crosslinked foamed molded article was air-cooled or water-cooled, cut into a suitable shape to be put into a mold for secondary compression molding, and put into a mold to perform heat compression molding. The foam obtained at this time is called a secondary crosslinked foam, and the crosslinking rate is 70% or more. When the crosslinking rate of the secondary crosslinked foam is lower than 70%, the heat resistance is inhibited.

The present invention is explained in more detail based on the following examples. However, the scope of the present invention is not limited to these embodiments.

Example 1

4 parts by weight of azodicarbonamide, 0.6 parts by weight of crosslinker dicumyl peroxide, 0.3 parts by weight of crosslinking aid zinc oxide (ZnO) and release agent stearic acid based on 100 parts by weight of polyethylene-based amorphous resin (manufactured by Dow Plastics, Engage Series 8180, hereinafter identical) 1 part by weight was melt-mixed and primary crosslinked foamed at 145 ° C. for 25 minutes, the primary crosslinked foam was cooled, and secondly compression molded at 160 ° C. for 20 minutes to prepare a core material for an automobile bumper.

Characterization of the manufactured bumper core material was carried out as follows.

1) Heat resistance evaluation is a method of measuring the shrinkage (%) of the specimen after placing the specimen of width (100mm) × length (100mm) × thickness (3mm) in a high-temperature chamber, leaving it for 6 hours, cooling it in air for 2 hours Was used. At this time, the temperature of the high temperature chamber was 150 degreeC.

The evaluation criteria are Pass: Shrinkage <3 (%) Fail: Shrinkage ≥ 3 (%).

2) The secondary compressive formation of the primary crosslinked foam was evaluated for appearance.

3) The cross-linking rate of the test piece was cut into 2 ~ 3mm ² and then weighed about 3g in a mesh (100mesh) and extracted for 6 hours using xylene. At this time, the initial weight of the test piece The crosslinking ratio was calculated as the weight ratio of the specimen remaining in the mesh after extraction. The formula is as follows.

4) The bubble uniformity of the secondary crosslinked foam is obtained by taking a cross-section of the primary foam under a microscope and measuring the diameter (I) of the inner foam (23-25 mm from the epidermis) and the outer bubble (3-5 mm from the epidermis) of the foam ( 0) was measured 10 times or more, and the average was calculated. When the average diameter ratio (I / 0) of the inner and outer bubbles was less than 2: Passed, and when it was 2 or more, it was determined to fail. At this time, a microscope (magnification: 100 or more) was used for measuring the bubble diameter.

The experimental results of Example 1 are shown in Table 1.

Example 2

5 parts by weight of blowing agent azodicarbonamide, 0.6 parts by weight of crosslinking agent dicumyl peroxide, 0.3 parts by weight of crosslinking aid zinc oxide (ZnO) and 1 part by weight of release agent stearic acid were melt-kneaded with respect to 100 parts by weight of polyethylene-based amorphous resin for 25 minutes at 145 ° C. After primary crosslinked foaming and cooling of the primary crosslinked foam, the core material for an automobile bumper was manufactured by second compression molding at 160 ° C. for 20 minutes.

The results of experiments evaluated in the same manner as in Example 1 are shown in Table 1.

Example 3

6 parts by weight of blowing agent azodicarbonamide, 0.6 parts by weight of crosslinking agent dicumyl peroxide, 0.3 parts by weight of crosslinking aid zinc oxide (ZnO) and 1 part by weight of release agent stearic acid were melt-kneaded with respect to 100 parts by weight of polyethylene-based amorphous resin for 25 minutes at 145 ° C. After primary crosslinking foaming, the first crosslinking foam was cooled, and then compression molding was performed for 2 minutes at 160 ° C. for 20 minutes to prepare a bumper core material.

The results of experiments evaluated in the same manner as in Example 1 are shown in Table 1.

Example 4

5 parts by weight of blowing agent azodicarbonamide, 0.5 parts by weight of crosslinking agent dicumyl peroxide, 0.3 parts by weight of crosslinking aid zinc oxide (ZnO) and 1 part by weight of release agent stearic acid were melt-kneaded with respect to 100 parts by weight of polyethylene-based amorphous resin for 25 minutes at 145 ° C. After primary crosslinking foaming, the primary crosslinked foamed product was cooled, and further compression molded at 160 ° C. for 20 minutes to prepare a core material for an automobile bumper.

The results of experiments evaluated in the same manner as in Example 1 are shown in Table 1.

Example 5

5 parts by weight of blowing agent azodicarbonamide, 0.7 parts by weight of crosslinking agent dicumyl peroxide, 0.3 parts by weight of crosslinking aid zinc oxide (ZnO) and 1 part by weight of release agent stearic acid were melt-kneaded with respect to 100 parts by weight of polyethylene-based amorphous resin for 25 minutes at 145 ° C. After primary crosslinking foaming, the primary crosslinked foam was cooled, and second compression molding was performed at 160 ° C. for 20 minutes to prepare a core material for an automobile bumper.

The results of experiments evaluated in the same manner as in Example 1 are shown in Table 1.

Example 6

5 parts by weight of blowing agent azodicarbonamide, 0.6 parts by weight of crosslinking agent dicumyl peroxide, 0.2 parts by weight of crosslinking aid zinc oxide (ZnO) and 1 part by weight of release agent stearic acid were melt-kneaded with respect to 100 parts by weight of polyethylene-based amorphous resin for 25 minutes at 145 ° C. After primary crosslinking foaming, the primary crosslinked foam was cooled, and second compression molding was performed at 160 ° C. for 20 minutes to prepare a core material for an automobile bumper.

The results of experiments evaluated in the same manner as in Example 1 are shown in Table 1.

Comparative Example 1

3 parts by weight of blowing agent azodicarbonamide, 0.6 parts by weight of crosslinking agent dicumyl peroxide, 0.3 parts by weight of crosslinking aid zinc oxide (ZnO) and 1 part by weight of release agent stearic acid were melt-kneaded with respect to 100 parts by weight of polyethylene-based amorphous resin for 25 minutes at 145 ° C. After primary crosslinking foaming, the primary crosslinked foam was cooled, and second compression molding was performed at 160 ° C. for 20 minutes to prepare a core material for an automobile bumper.

The results of experiments evaluated in the same manner as in Example 1 are shown in Table 1.

Comparative Example 2

7 weight part of blowing agent azodicarbonamide, 0.6 weight part of crosslinking agent dicumyl peroxide, 0.3 weight part of crosslinking aid zinc oxide (ZnO), and 1 weight part of release agent stearic acid were melt-kneaded with respect to 100 weight part of polyethylene-type amorphous resins, for 25 minutes at 145 degreeC After primary crosslinking foaming, the primary crosslinked foam was cooled, and second compression molding was performed at 160 ° C. for 20 minutes to prepare a core material for an automobile bumper.

The results of experiments evaluated in the same manner as in Example 1 are shown in Table 1.

Comparative Example 3

5 parts by weight of blowing agent azodicarbonamide, 0.4 parts by weight of crosslinking agent dicumylperoxide, 0.3 parts by weight of crosslinking aid zinc oxide (ZnO) and 1 part by weight of release agent stearic acid were melt-kneaded with respect to 100 parts by weight of polyethylene-based amorphous resin for 25 minutes at 145 ° C. After primary crosslinking foaming, the primary crosslinked foam was cooled, and second compression molding was performed at 160 ° C. for 20 minutes to prepare a core material for an automobile bumper.

The results of experiments evaluated in the same manner as in Example 1 are shown in Table 1.

Comparative Example 4

5 parts by weight of blowing agent azodicarbonamide, 0.8 parts by weight of crosslinking agent dicumyl peroxide, 0.3 parts by weight of crosslinking aid zinc oxide (ZnO) and 1 part by weight of release agent stearic acid were melt-kneaded with respect to 100 parts by weight of polyethylene-based amorphous resin for 25 minutes at 145 ° C. After primary crosslinking foaming, the primary crosslinked foam was cooled, and second compression molding was performed at 160 ° C. for 20 minutes to prepare a core material for an automobile bumper.

The results of experiments evaluated in the same manner as in Example 1 are shown in Table 1.

Comparative Example 5

5 parts by weight of blowing agent azodicarbonamide, 0.6 parts by weight of crosslinking agent dicumyl peroxide, 0.1 parts by weight of crosslinking aid zinc oxide (ZnO) and 1 part by weight of release agent stearic acid were melt-kneaded with respect to 100 parts by weight of polyethylene-based amorphous resin for 2 minutes at 145 ° C. After primary crosslinking foaming, the primary crosslinked foam was cooled, and second compression molding was performed at 160 ° C. for 20 minutes to prepare a core material for an automobile bumper.

The results of experiments evaluated in the same manner as in Example 1 are shown in Table 1.

Comparative Example 6

5 parts by weight of blowing agent azodicarbonamide, 0.6 parts by weight of crosslinking agent dicumylperoxide, 0.4 parts by weight of crosslinking aid zinc oxide (ZnO) and 1 part by weight of release agent stearic acid were melt-kneaded with respect to 100 parts by weight of polyethylene-based amorphous resin for 25 minutes at 145 ° C. After primary crosslinking foaming, the primary crosslinked foam was cooled, and second compression molding was performed at 160 ° C. for 20 minutes to prepare a core material for an automobile bumper.

The results of experiments evaluated in the same manner as in Example 1 are shown in Table 1.

Table 1. Bumper Core Property Evaluation

Experimental Example

The impact energy absorption rate of the bumper core prepared in Example 1, the conventional polypropylene beads foam, the polystyrene beads foam, and the ethylene vinyl acetate honeycomb was measured, and the density of the ethylene acetate crosslinked foam and the foam of the present invention was measured in the following method. Measured by

The impact energy absorption capacity is expressed as the energy absorption rate (a) by the following equation, and the energy absorption rate measurement specimens were used for the width (50 mm) × length (50 mm) × thickness (40 mm) specimens, and UTM (UNIVERSAL) as the test equipment. TESTING MACHINE) was used, and the test piece was compressed at 80% of the specimen thickness at a speed of 200 mm / sec to obtain a compressive stress-strain curve as shown in FIGS. 1 and 2 to calculate energy absorption. The repeated shock absorbing ability is expressed as the ratio Ra between a and a '. In the following equation, the area A or A ', S or S' shown in Figs. 1 and 2 is used as a factor.

Where a = energy absorption rate in one compression

    a '= energy absorption after 2 compressions

    A, A ', S, S' = Area

    Ra = repeated impact energy absorption

The evaluation criteria are the energy absorption rate during the first compression: ○: a≥70 ×: a <70

Energy absorption rate at 2nd compression: ○: a'≥63 ×: a '<63

Impact energy absorption rate at repeated compression: ○: Ra≥90 ×: Ra <90

Was determined.

The results are shown in Table 2.

Table 2. Impact energy absorption test

The density of the foam was measured by the submerged method, and the average density value was compared three times for one specimen by setting a comparison specimen having the same average diameter of bubbles, and the results are shown in Table 3.

Evaluation criteria judged the test piece with the small average density value at the time of relative comparison as the pass.

Table 3. Density Testing of Foams

* Ethylene vinyl acetate crosslinked foam is prepared in the same manner as in Example 1 except for using ethylene vinyl acetate in place of the polyethylene-based amorphous resin in the composition of Example 1.

As mentioned above, according to this invention, the core material for automobile bumpers excellent in heat resistance, moldability, density uniformity, and impact energy absorption capability is provided.

1 and 2 show examples of compressive stress-strain curves at the time of primary and secondary compression for the calculation of energy absorption in the shock absorption capacity test of the bumper core material carried out in the experimental example of the present invention.

Claims (3)

4 to 6 parts by weight of foaming agent, 0.5 to 0.7 part by weight of crosslinking agent, 0.2 to 0.3 part by weight of crosslinking aid and release agent based on 100 parts by weight of the base resin of polyethylene-based amorphous resin polymerized by single-site catalyst and additives. After mixing 0.9-1.1 parts by weight to melt-kneading, to form a primary crosslinked foamed molding having a cross-linking rate of 40 to 60%, and to cool the molded primary crosslinked foamed molded product after heating to secondary compression molding Core material for automobile bumpers. The method of claim 1, wherein the base resin is at least one selected from among low density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, ethylene propylene rubber, ethylene propylene diene rubber, natural rubber, isobutyl rubber and styrene butadiene rubber Car bumper core material comprising a. 2. The bumper core material according to claim 1, wherein the second compression molded final foam has a crosslinking rate of 70% or more.

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