Core material for automobile bumper

Abstract

To provide a novel core material for an automobile bumper.SOLUTION: A bumper core material (1) comprises a polycarbonate-based resin foam molded body having a density of 24.0 kg / m3 to 75.0 kg / m3 and a closed cell ratio of 70% or more, wherein the polycarbonate-based resin foam molded body has a value of 0.6 or less as determined by dividing the absolute value of the difference between the 50% compressive stress at -30°C and the 50% compressive stress at 80°C by the 50% compressive stress at 23°C.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a core material for an automobile bumper. [Background technology]

[0002] For the sake of automobile safety, energy absorbing components such as bumper core materials must be able to perform at both low and high temperatures. Generally, polypropylene resin foam (EPP) and polystyrene resin foam (EPS) are used as materials for energy absorbing components such as bumper core materials. Polypropylene resin foam has the problem of exhibiting a significant change in strength due to temperature between -30°C and +80°C, and exhibiting behavior that reduces strength in the high temperature range. On the other hand, polystyrene resin foam has the problem of being difficult to use due to problems with heat resistance and crack resistance.

[0003] As a technique for solving the above problems, for example, Patent Document 1 discloses an energy absorbing member for automobiles made of a foam molded product of polycarbonate resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-287277 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even with the technology of Patent Document 1, there is still room for improvement in terms of physical properties, and there is a demand for the development of a new core material for automobile bumpers.

[0006] An object of one aspect of the present invention is to provide a novel core material for automobile bumpers. [Means for solving the problem]

[0007] In order to solve the above problems, one aspect of the present invention is as follows.

[0008] [1] Density is 24.0 kg / m 3 ~75.0Kg / m 3 A core material for automobile bumpers, comprising a polycarbonate-based resin foam molded body having a closed cell rate of 70% or more, wherein the absolute value of the difference between the 50% compressive stress at -30°C and the 50% compressive stress at 80°C divided by the 50% compressive stress at 23°C is 0.6 or less.

[0009] [2] The core material for an automobile bumper according to [1], wherein the polycarbonate resin foam molded article contains, as a base resin, a polycarbonate resin having a melt flow rate (MFR) of 2.4 g / 10 min to 20 g / 10 min.

[0010] [3] The core material for an automobile bumper according to [1] or [2], wherein the polycarbonate resin foam molded article contains a foaming agent of a hydrocarbon having 3 to 6 carbon atoms.

[0011] [4] The core material for an automobile bumper according to [3], wherein the foaming agent is an aliphatic hydrocarbon and / or an alicyclic hydrocarbon and has a boiling point of 30°C or higher.

[0012] [5] The core material for an automobile bumper according to [3] or [4], wherein the foaming agent is cyclopentane.

[0013] [6] The core material for an automobile bumper according to any one of [3] to [5], wherein the polycarbonate resin foam molded article further contains ethyl chloride as another foaming agent. [Effects of the Invention]

[0014] According to one aspect of the present invention, a novel core material for automobile bumpers can be realized. [Brief explanation of the drawings]

[0015] [Figure 1]1 is a side view showing a schematic configuration of an automobile equipped with a bumper having a bumper core material according to an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view showing a schematic configuration of the bumper shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to these, and various modifications are possible within the scope of the description. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments and examples are also included in the technical scope of the present invention. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and less than B)."

[0017] Fig. 1 is a side view showing a schematic configuration of an automobile equipped with a bumper 10 having a bumper core material according to this embodiment. Fig. 2 is a perspective view showing a schematic configuration of the bumper 10 shown in Fig. 1.

[0018] As shown in Fig. 1, a bumper 10 is attached to the front of an automobile body. As shown in Fig. 2, the bumper 10 includes a bumper core material 1 and a skin material 2. The bumper core material 1, with its surface covered with the skin material 2, etc., is attached to a backup beam (not shown) of the automobile body to form the bumper 10.

[0019] In this embodiment, the bumper core material 1 for automobiles includes a polycarbonate-based resin foam molded body, and is preferably made of a polycarbonate-based resin foam molded body. The polycarbonate-based resin foam molded body has a density of 24.0 kg / m 3 ~75.0Kg / m 3and a closed cell ratio of 70% or more. Furthermore, in the polycarbonate resin foam molded product, the absolute value of the difference between the 50% compressive stress at -30°C and the 50% compressive stress at 80°C divided by the 50% compressive stress at 23°C is 0.6 or less. Therefore, the automobile bumper core material 1 according to this embodiment differs from conventional ones and can be said to be a novel automobile bumper core material.

[0020] Furthermore, in the automotive energy absorbing member of Patent Document 1, carbon dioxide gas is used as a foaming agent for the polycarbonate resin foam molded body. As a result, the polycarbonate resin foam molded body constituting the automotive energy absorbing member has a low expansion ratio. Therefore, the automotive energy absorbing member of Patent Document 1 has room for improvement in terms of weight reduction. In other words, compared to the automotive energy absorbing member of Patent Document 1, there is room for improvement in terms of realizing a core material for automotive bumpers that is relatively lightweight and has little temperature dependency in impact energy absorption performance.

[0021] According to the bumper core material 1 of this embodiment, the polycarbonate-based resin foam molded body has a density of 24.0 kg / m 3 ~75.0Kg / m 3 Since the closed cell rate is 70% or more, a bumper core material 1 with excellent weight reduction can be realized.

[0022] Furthermore, in the bumper core material 1 according to this embodiment, the polycarbonate-based resin foam molded body has a value of 0.6 (60%) or less when the absolute value of the difference between the 50% compressive stress at -30°C and the 50% compressive stress at 80°C is divided by the 50% compressive stress at 23°C. Therefore, the polycarbonate-based resin foam molded body has a small difference in compressive stress in a wide temperature range from high to low. Therefore, the bumper core material 1 according to this embodiment has a small temperature dependency of impact energy absorption performance and can be used as an energy absorber over a wide temperature range. The polycarbonate-based resin foam molded body that constitutes the bumper core material 1 will be described in detail below.

[0023] The polycarbonate-based resin foam constituting the bumper core 1 can be any foam that uses a polycarbonate-based resin as a base resin. Preferably, the polycarbonate-based resin foam is a polycarbonate-based resin foam bead molded product (hereinafter referred to as a PC foam molded product). A PC foam molded product can be produced by in-mold molding of polycarbonate-based pre-expanded resin particles (hereinafter referred to as PC pre-expanded resin particles) that are pre-expanded from polycarbonate-based expandable resin particles (hereinafter referred to as PC expandable resin particles).

[0024] In this embodiment, the polycarbonate-based resin is usually in the form of polycarbonate-based resin particles in advance so as to be in the form of foamed particles in the PC foamed molded article. The polycarbonate-based resin particles are obtained by melting the polycarbonate-based resin using an extruder, kneader, Banbury mixer, roll, etc., and molding and processing it into a desired particle shape such as a cylindrical, elliptical, spherical, cubic, or rectangular parallelepiped shape.

[0025] The polycarbonate resin has a polyester structure of carbonic acid and glycol or dihydric phenol, and is particularly preferably one containing an aromatic group. Examples of polycarbonate resins containing an aromatic group include aromatic polycarbonates derived from bisphenols, such as 2,2-bis(4-oxyphenyl)propane, 2,2-bis(4-oxyphenyl)butane, 1,1-bis(4-oxyphenyl)cyclohexane, 1,1-bis(4-oxyphenyl)butane, 1,1-bis(4-oxyphenyl)isobutane, and 1,1-bis(4-oxyphenyl)ethane. These polycarbonate resins are preferred because of their excellent heat resistance.

[0026] Furthermore, without departing from the object and effect of the present invention, the bumper core material 1 may be formed from a resin foam containing a polycarbonate-based resin and other resins. Examples of other resins include polypropylene-based resins, acrylic-based resins, saturated polyester-based resins, acrylonitrile butadiene styrene (ABS)-based resins, polystyrene-based resins, and polyphenylene oxide-based resins. The polycarbonate-based resin foam constituting the bumper core material 1 preferably contains 50% by weight or more of polycarbonate-based resin.

[0027] The first method for producing PC expandable resin particles is a method comprising the following steps (1) to (3): (1) Using an extruder, resin components including a polycarbonate resin, a blowing agent, and, if necessary, additives are melt-kneaded. (2) The molten mixture is extruded into a cutter chamber filled with pressurized circulating water through a die with many small holes attached after the extruder. (3) Immediately after extrusion, the molten mixture is cut by a rotating cutter in contact with the die and cooled and solidified by the pressurized circulating water.

[0028] The second method for producing PC expandable resin particles is as follows: resin particles containing a resin component including a polycarbonate resin and, if necessary, additives are suspended in water, and a blowing agent is supplied to the resin particles to incorporate the blowing agent into the resin particles, thereby obtaining expandable resin particles.

[0029] From the viewpoint of simplicity of equipment and ease of production, the first method for producing PC expandable resin particles is more preferred.

[0030] The blowing agents used to obtain PC expandable resin particles can be volatile and / or inorganic blowing agents. Specific examples of volatile blowing agents include aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, aliphatic alcohols, aliphatic ketones, and halogenated hydrocarbons. Aliphatic hydrocarbons include propane, n-butane, i-butane, n-pentane, i-pentane, and hexane. Alicyclic hydrocarbons include cyclopentane, cyclohexane, and cycloheptane. Aromatic hydrocarbons include benzene, toluene, and xylene. Aliphatic alcohols include methanol, ethanol, and propanol. Aliphatic ketones include acetone and methyl ethyl ketone. Halogenated hydrocarbons include 1-chloro-1,1-difluoroethane, pentafluoroethane, 1,1,1,2-tetrafluoroethane, and 1,1-difluoroethane. Inorganic blowing agents include inorganic gases such as carbon dioxide (CO2), nitrogen gas (N2), and air. In this embodiment, the above-mentioned foaming agents can be used alone or in combination of two or more. For example, different types of foaming agents, such as an inorganic foaming agent and a volatile foaming agent, can be used in combination. The amount of foaming agent used is appropriately determined depending on the type of foaming agent and the desired expansion ratio. When the amount of foaming agent used is determined depending on the desired expansion ratio, the density of the PC foam molded product is determined by the expansion ratio, so the amount of foaming agent used is determined mainly by the desired density of the PC foam molded product.

[0031] Among the blowing agents exemplified above, the PC foam molded product preferably contains a blowing agent of a hydrocarbon having 3 to 6 carbon atoms. The blowing agent is more preferably an aliphatic hydrocarbon and / or an alicyclic hydrocarbon, and has a boiling point of 30°C or higher. Examples of aliphatic hydrocarbons having a boiling point of 30°C or higher include pentane and hexane, and examples of alicyclic hydrocarbons having a boiling point of 30°C or higher include cyclopentane, cyclohexane, and cycloheptane. It is even more preferable that the blowing agent be cyclopentane. Use of such a blowing agent can further lower the density (higher expansion ratio) of the PC foam molded product. The above-mentioned blowing agent of a hydrocarbon having 3 to 6 carbon atoms remains in the PC foam molded product. Therefore, by post-mortem analysis of the PC foam molded product, it is possible to determine whether the PC foam molded product contains a blowing agent of a hydrocarbon having 3 to 6 carbon atoms.

[0032] In addition to the above-mentioned foaming agents, the PC foam molded article preferably further contains ethyl chloride as another foaming agent, which has the effect of improving the plasticity of the polycarbonate resin.

[0033] Any known method can be used to pre-expand the PC expandable resin particles. For example, the PC expandable resin particles are expanded with heated steam to a desired expansion ratio to form PC pre-expanded resin particles, which are then cured for a certain period of time as necessary. The resulting PC pre-expanded resin particles are then used for molding.

[0034] In this embodiment, the obtained PC pre-expanded resin particles are heated by steam in a conventional molding machine under normal molding conditions to produce a PC foamed molded article. Specifically, a preferred method for molding a PC foamed molded article is to fill a mold with the PC pre-expanded resin particles and further expand them by steam heating to fuse and integrate the PC pre-expanded resin particles to produce a PC foamed molded article. The reasons for this are as follows: (1) even complex shapes can be produced relatively easily, and (2) the PC foamed molded article has excellent density uniformity, making it easy to obtain relatively uniform mechanical properties. As a result, when comparing foamed molded articles of the same density, it is easier to achieve high compressive stress and high energy absorption performance than foamed molded articles of the same density obtained by methods other than in-mold molding.

[0035] In this embodiment, the PC foam molded article may contain additives such as antioxidants, weather resistance improvers, antistatic agents, colorants, flame retardant improvers, and electrical conductivity improvers, as needed.

[0036] These additives may be conventionally known additives that can be used in the production of PC foam molded products. There are no limitations on the colorants listed above as examples of additives. PC foam molded products can be natural in color without the addition of colorants. However, to impart design features or to make stains that accumulate over time less noticeable, colorants such as blue, red, and black can be added to create a desired color.

[0037] In the bumper core material 1 according to this embodiment, the density of the PC foam molded body is 24.0 kg / m 3 ~75.0Kg / m 3 The upper limit of the density of the polycarbonate resin foam molded article is 75.0 kg / m 3 Less than 60.0 kg / m 3 The density is 75.0 kg / m or less. 3 If the density exceeds 24.0 kg / m, the lightweight property of the bumper core material 1 tends to be impaired. In addition, the lower limit of the density of the PC foam molded body is set to 24.0 kg / m from the viewpoint of the closed cell ratio and physical properties. 3More preferably, 30.0 kg / m 3 The density of the PC foam molded article is calculated by the following method: The weight of the PC foam molded article is measured to the nearest 1 / 100 g, and then the PC foam molded article is submerged in water to reduce the volume to 1 / 10 cm 3 Then, divide the weight measurement by the volume measurement to get Kg / m 3 The density of the PC foam molding is calculated by converting it into units of

[0038] In addition, in the bumper core material 1 according to this embodiment, the PC foam molded body preferably contains, as a base resin, a polycarbonate-based resin having a melt flow rate (MFR) of 2.4 g / 10 min to 20 g / 10 min. Polycarbonate-based resins having a melt flow rate (MFR) within the above range are suitable for foaming and tend to be more highly foamed. This allows the PC foam molded body to have a high expansion ratio and be lighter in weight. The melt flow rate (MFR) is more preferably 3.0 g / 10 min to 15 g / 10 min.

[0039] In the bumper core material 1 according to this embodiment, the PC foam molding has a value (hereinafter sometimes referred to as the 50% compressive stress change rate) of 0.6 or less, calculated by dividing the absolute value of the difference between the 50% compressive stress at -30°C and the 50% compressive stress at 80°C by the 50% compressive stress at 23°C.

[0040] The 50% compressive stress change rate will be specifically explained. First, for a polycarbonate resin foam molded article, the compressive stress at 50% compression (50% compressive stress) at -30°C is calculated as C (-30) The compressive stress at 50% compression at 80°C is C (80) The compressive stress at 50% compression at 23°C is C (23) The above 50% compressive stress change rate is C (-30) and C (80) The absolute value of the difference between (23)This is the value obtained by dividing by , and corresponds to the left side of the following formula (1). As shown in the following formula (1), the 50% compressive stress change rate is 0.6 (60%) or less. More preferably, the 20% compressive stress change rate is 0.4 (40%) or less. Furthermore, the smaller the 50% compressive stress change rate, the better, but it is preferably 0.1 or more, and more preferably 0.2 or more. |C (-30) -C (80) | / C (23) ≦0.6 … (1) When the 50% compressive stress change rate is 0.6 or less, the change in 50% compressive stress of the PC foam molded product between low and high temperatures is small, and the 50% compressive stress at room temperature is relatively high. Therefore, the PC foam molded product exhibits little change in 50% compressive stress over a wide range from low to high temperatures (for example, a range of -30°C to 80°C), and can exhibit relatively high energy absorption performance.

[0041] On the other hand, when the 50% compressive stress change rate exceeds 0.6, the superiority of the PC foam molding over conventional polypropylene resin foam moldings in terms of the temperature dependency of compressive stress tends to decrease.

[0042] 50% compressive stress C at -30℃ (-30) The 50% compressive stress C at 80°C is preferably 0.35 MPa to 14.0 MPa, and more preferably 0.42 MPa to 12.0 MPa. (80) The 50% compressive stress C at 23°C is preferably 0.18 MPa to 8.1 MPa, and more preferably 0.23 MPa to 7.0 MPa. (23) The 50% compressive stress C at -30°C is preferably 0.30 MPa to 9.7 MPa, and more preferably 0.40 MPa to 9.3 MPa. (-30) , 10% compressive stress C at 80℃ (80) , and 50% compressive stress C at 23°C (23) When the value of is in the above range, it is possible to obtain the effect of being able to exhibit stable and high impact absorbing performance over a wide temperature range.

[0043] 50% compressive stress C at -30℃ (-30) , 50% compressive stress C at 80℃ (80) , and 50% compressive stress C at 23°C (23) can be measured in accordance with JIS K 7181:2011.

[0044] For example, by using the above-mentioned aromatic group-containing polycarbonate resin, which has high heat resistance, as the raw material for the PC foam molded article, the 50% compressive stress change rate can be reduced to 0.6 or less.

[0045] Furthermore, from the viewpoint of increasing the 50% compressive stress described above, the closed cell ratio of the PC foam molded article is 70% or more, preferably 80% or more, and more preferably 85% or more. [Example]

[0046] The present embodiment will be specifically described below based on examples and comparative examples, but the present invention is not limited to these.

[0047] The measurement and evaluation methods used in the following examples and comparative examples are as follows.

[0048] <Measurement method> [Bulk expansion ratio of pre-expanded particles] The bulk expansion ratio of the pre-expanded particles was calculated by placing the pre-expanded particles in a measuring cylinder so that the volume was 1,000 cc, measuring the weight, and using the following formula. Bulk expansion ratio (cc / g) = 1,000 cc / [weight of pre-expanded particles (g)] ... (2) [density] The density of the foamed molded article was calculated according to the following formula in accordance with JIS K 7222:2005. Density (Kg / m 3 ) = Weight of foamed molded product (Kg) / Volume of foamed molded product (m 3 )…(3) (Evaluation indicators) Excellent: 60Kg / m 3 below Good: 60 kg / m3 Larger: 75Kg / m 3 below Possible: 75Kg / m 3 Larger: 120Kg / m 3 below Not possible: 120Kg / m 3 Greater than.

[0049] [Closed bubble rate] Using the test pieces taken for the evaluation of the expansion ratio, the volume was measured using an air comparison type hydrometer at 23°C ± 2°C in accordance with JIS K 7138:2006, and the volume was also measured using a water displacement type hydrometer at 23°C ± 2°C in accordance with JIS K 7112:1999. The closed cell ratio was then calculated using the following formula (4). Cc=(Va / Vaq)×100 …(4) In equation (4), Cc is the closed cell rate (%), Va is the volume (cm) measured by an air comparison hydrometer. 3 ) and Vaq is the volume (cm ) determined by a water displacement hydrometer. 3 )

[0050] The evaluation index for the closed cell ratio is as follows:

[0051] (Evaluation indicators) Excellent: Closed cell rate 85% or more Good: Closed cell ratio 75% to less than 85% Acceptable: Closed cell ratio 70% or more but less than 75% Unacceptable: Closed cell content less than 70%.

[0052] [50% compressive stress] The resulting foam molded article was cut into a size of 250 mm long x 120 mm wide x 60 mm thick to serve as a test specimen (excluding the foam molded article skin layer). Using a thermostatically controlled tensile / compression universal material testing machine, Technograph (Minebea Co., Ltd.), the test environment temperature was set to -30°C to +80°C, and the test specimen was left in the thermostatic chamber for 3 to 5 hours to adjust the temperature of the test specimen to the test environment temperature. The compressive stress (MPa) was then calculated at 50% compression (12.5 mm displacement) in the temperature range of -30°C to +80°C at a compression rate of 10 mm / min.

[0053] The 50% compressive stress (C) measured at temperatures of -30°C, 23°C, and 80°C (-30) , C (23) , C (80) From this, the 50% compressive stress temperature change rate was calculated based on the following formula (5). 50% compressive stress temperature change rate = |C (-30) -C (80) | / C (23) …(5) The evaluation indexes for 50% compressive stress and 50% compressive stress temperature change rate at 23°C are as follows:

[0054] (Evaluation indicators) <50% compressive stress at 23°C: Evaluation index for energy absorption performance> Excellent: 50% compressive stress at 23°C is greater than 0.5 MPa Good: 50% compressive stress at 23°C is 0.4 MPa or more and 0.5 MPa or less Acceptable: 50% compressive stress at 23°C is 0.3 MPa or more but less than 0.4 MPa Unacceptable: 50% compressive stress at 23°C is less than 0.3 MPa.

[0055] <50% compressive stress change rate: Evaluation index for temperature dependence of compressive stress> Excellent: 50% compressive stress change rate is less than 0.3 Good: 50% compressive stress change rate is 0.3 or more and less than 0.4 Acceptable: 50% compressive stress change rate is 0.4 to 0.6 Unacceptable: 50% compressive stress change rate is greater than 0.6.

[0056] (comprehensive evaluation) Excellent: Either the evaluation of 50% compressive stress at 23°C or the evaluation of the rate of change of 50% compressive stress with temperature is "Excellent", and the other evaluations are "Good" or better, the evaluation of the expansion ratio is "Good" or better, and the evaluation of the closed cell ratio is "Good" or better. Good: Either the evaluation of 50% compressive stress at 23°C or the evaluation of the rate of change of 50% compressive stress with temperature is "Good" or better, the evaluation of the expansion ratio is "Fair" or better, and the evaluation of the closed cell ratio is "Fair" or better. Pass: Either the evaluation of 50% compressive stress at 23°C or the evaluation of the rate of change of 50% compressive stress with temperature is "pass" or higher, the evaluation of the expansion ratio is "pass" or higher, and the evaluation of the closed cell ratio is "pass" or higher Unacceptable: Any of the following evaluations is "unacceptable": 50% compression stress at 23°C, 50% compression stress temperature change rate, expansion ratio, or closed cell rate.

[0057] Example 1 [Formation of expandable resin particles] 80 parts by weight of polycarbonate resin (manufactured by Mitsubishi Engineering Plastics Corporation; NOVAREX M7027BF, MFR = 2.4 g / 10 min), 20 parts by weight of polycarbonate resin (manufactured by Mitsubishi Engineering Plastics Corporation; LUPILON H-4000, MFR = 63 g / 10 min), and 0.5 parts by weight of talc (manufactured by Hayashi Kasei Co., Ltd.; Talcan Powder TP-20) were fed into a 40 mm diameter co-rotating intermeshing twin-screw extruder (first extruder) at a total feed rate of 50 kg / hr. The cylinder temperature after the raw material feed section of the twin-screw extruder was then set to 260 °C, and the feed materials were melt-kneaded. Next, 4.0 parts by weight of ethyl chloride and 4.0 parts by weight of cyclopentane as foaming agents were injected into the cylinder after the raw material feed section of the twin-screw extruder, per 100 parts by weight of the melt obtained by melt-kneading, and further melt-kneaded.

[0058] The resulting melt (melt impregnated with the blowing agent) was then supplied to a 90 mm diameter single-screw extruder (second extruder) through a continuation pipe set at 220°C. A gear pump set at 210°C and a diverter valve were connected to the tip of the single-screw extruder. A die was connected downstream of the diverter valve. The die had 55 small holes with a diameter of 0.65 mm and a land length of 5.0 mm and was set at a temperature of 270°C. The cylinder temperature of the single-screw extruder was then set at 210°C to knead the melt, and the melt obtained by melt kneading was extruded through the die connected to the tip of the single-screw extruder at an extrusion (discharge) rate of 54 kg / hr into pressurized water at a temperature of 94°C and a water pressure of 1.3 MPa.

[0059] Immediately after that, a rotary cutter having four blades was used to cut the melt into particles by rotating the cutter at a rotation speed of 2000 rpm, thereby forming expandable resin particles for molding in a mold.

[0060] [Formation of pre-expanded particles] The resulting expandable resin particles were placed in a pre-expanding machine and expanded by introducing steam at 0.16 MPa for 150 seconds. This resulted in the formation of pre-expanded particles. The bulk expansion ratio of the resulting pre-expanded particles was 30 times (cc / g).

[0061] [Production of foamed bead molded body (PC foamed molded body)] A sample of a PC foam molded article for compressive stress measurement was produced as follows. The obtained pre-expanded particles were filled into a mold (in-mold molding mold) attached to a foamed polypropylene molding machine, and water vapor of 0.12 MPa was introduced for 60 seconds to cause in-mold foaming. The resin foam molded article in the mold was then water-cooled until the pressure pressing the mold down to 0.015 MPa (gauge pressure), producing a PC foam molded article sample. The sample measured 370 mm long x 320 mm wide x 80 mm thick, with a density of 75.0 kg / m. 3 The foamed article was a rectangular parallelepiped foam with an expansion ratio of 16.0 and a closed cell ratio of 75%.

[0062] Test pieces for measuring compressive stress were cut out from the prepared PC foam molded articles. The test pieces were then subjected to compressive stress tests at test temperatures of -30°C, 23°C, and 80°C. In each test, the compressive stress at which the thickness displacement (strain) rate was 50% was determined. The results are shown in Table 1.

[0063] Example 2 Density 60.3Kg / m 3 A sample of a PC foam molded article was obtained in the same manner as in Example 1, except that the foaming ratio was changed to 19.9 times and the closed cell ratio was changed to 72%, and a compressive stress test was carried out. The results are shown in Table 1.

[0064] Example 3 Density 40.3Kg / m 3A sample of a PC foam molded article was obtained in the same manner as in Example 1, except that the foaming ratio was changed to 29.8 times and the closed cell ratio was changed to 70%, and a compressive stress test was carried out. The results are shown in Table 1.

[0065] (Comparative Example 1) Density 177Kg / m 3 A compressive stress test was carried out in the same manner as in Example 1, except that a foamed molded article made of a polypropylene resin (Prime Polypro E228, MFR = 2.0 g / 10 min, manufactured by Prime Polymer Co., Ltd.) with an expansion ratio of 5.1 and a closed cell ratio of 93% was used. The results are shown in Table 1.

[0066] (Comparative Example 2) Expandable resin particles were obtained by injecting 4.0 parts by weight of ethyl chloride and 4.0 parts by weight of mixed pentane as foaming agents, and the density of the resin foamed in the mold by introducing steam at 0.12 MPa for 90 seconds was 39.8 kg / m 3 A sample of a PC foam molded article was obtained in the same manner as in Example 1, except that the foaming ratio was 30.2 times and the closed cell ratio was 35%, and a compressive stress test was carried out. The results are shown in Table 1.

[0067] (Comparative Example 3) As a foaming agent, 4.5 parts by weight of carbon dioxide gas was injected to obtain expandable resin particles, and water vapor at 0.12 MPa was introduced for 60 seconds to cause foaming in the mold, resulting in a density of 174 kg / m 3 A sample of a PC foam molded article was obtained in the same manner as in Example 1, except that the foaming ratio was 6.9 times and the closed cell ratio was 85%, and a compressive stress test was carried out. The results are shown in Table 1.

[0068] [Table 1] [Industrial Applicability]

[0069] The present invention can be used in automobile bumpers. [Explanation of symbols]

[0070] 1. Bumper core material 2 Skin material 10 Bumper

Claims

1. Density is 24.0 kg / m ３ ~75.0 kg / m ３ , a polycarbonate-based resin foam molded article having a closed cell rate of 70% or more, The polycarbonate-based resin foam molded body is a core material for automobile bumpers, in which the absolute value of the difference between the 50% compressive stress at -30°C and the 50% compressive stress at 80°C divided by the 50% compressive stress at 23°C is 0.6 or less.

2. 2. The automotive bumper core material according to claim 1, wherein the polycarbonate-based resin foam molded article contains, as a base resin, a polycarbonate-based resin having a melt flow rate (MFR) of 2.4 g / 10 min to 20 g / 10 min.

3. 2. The core material for an automobile bumper according to claim 1, wherein the polycarbonate-based resin foam molded article contains a foaming agent of a hydrocarbon having 3 to 6 carbon atoms.

4. 4. The automotive bumper core material according to claim 3, wherein the foaming agent is an aliphatic hydrocarbon and / or an alicyclic hydrocarbon and has a boiling point of 30° C. or higher.

5. 4. The automotive bumper core material according to claim 3, wherein the foaming agent is cyclopentane.

6. 4. The automobile bumper core material according to claim 3, wherein the polycarbonate resin foam molded article further contains ethyl chloride as another foaming agent.

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