JPH07117471A - Cushioning member for door of automobile - Google Patents

Abstract

PURPOSE:To obtain a cushioning member for the door of an automobile, having good productivity, light weight, excellent in shock absorbing force, and also excellent in heat resistance under the high temperature and the high humidity. CONSTITUTION:In a cushioning member to be arranged on the back surface side of a door trim base member of a vehicle side part, the cushioning member is a beads foamed body made of styrene group heat resistant resin having the Vicat softening point of 108 deg.C or more, and the compression hysteresis loss of the foamed body is 60% or more and the density is 15 to 120kg/m<3>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cushioning material for automobile doors. More specifically, the present invention relates to a side collision preventing material inside a vehicle door.

[0002]

2. Description of the Related Art As a cushioning material for automobile doors, for example, as described in Japanese Patent Laid-Open No. 339046/1992, an injection port is provided on the back surface of a door trim that covers a door inner panel surface of a door body. By preliminarily fixing and arranging a flexible bag body disposed on the outer side of the door trim, attaching the door trim to the door inner panel, and then filling the inside of the bag body with a foam material (urethane resin) through the injection port to foam. It is known that a cushioning material is formed in close contact with the door trim and the door inner panel, and the cushioning material is used to reduce the impact on the occupant to protect the occupant.

Further, Japanese Patent Laid-Open No. 5-65045 describes a hard pad on the back surface of a door trim base material, and a soft pad which is deformed according to the shapes of the hard pad and the back surface of the base material and adheres to the back surface of the base material. A cushioning material that is bonded to a pad is known. Recently, the use of non-crosslinked PP foams has been tried (Chemical Industry Daily; 1993, 5).
(May 27th).

[0004]

However, in the former, when forming a cushioning material (urethane resin foam), a bag is prepared in advance and the bag is filled with the foam material to foam. However, it required a special processing method, so it was very complicated and the productivity was poor. In addition, it is difficult to control the density to a predetermined level by the method of filling and foaming, and there is a concern about the quality of the impact absorbing power. Therefore, there is a problem that the weight is increased in order to set the density higher than necessary. there were. Furthermore, the heat resistance under high temperature and high humidity has a problem that the dimensional change rate is large.

Further, the latter PP foam not only has small impact absorption energy, but also has a problem in high temperature heat resistance. That is, when exposed to a high temperature and high humidity condition which is a practical use condition for a long time, the dimensional change was large and it was unsuitable as a cushioning material for doors. Therefore, the present invention does not require a special processing method and has good productivity, and is lightweight and excellent in shock absorbing power. Furthermore, regarding the heat resistance under high temperature and high humidity,
An object of the present invention is to provide a cushioning material for automobile doors having a small dimensional change rate.

[0006]

According to the present invention, which has solved the above-mentioned problems, in a cushioning material arranged on the back side of a door trim base material on a vehicle side, the cushioning material has a Vicat softening point of 108 ° C.
A cushioning material for automobile doors, which is a foamed bead molding made of the above styrene-based heat-resistant resin, wherein the molding has a compression hysteresis loss of 60% or more and a density of 15 to 120 kg / cm ^3. is there.

In the present invention, since the cushioning material is a bead foam molding made of a styrene-based heat-resistant resin having a Vicat softening point of 108 ° C. or higher, it can be mounted in an arbitrary shape on the back side of the door trim base material and can be heated. We have succeeded in making it usable enough without any deformation. The compacted body has a compression hysteresis loss of 60% or more and a density of 15 to
By being 120 kg / cm ³ , the impact applied to the occupant at the time of a side collision can be mitigated to protect the occupant.

The contents of the present invention will be described in more detail below with reference to the drawings. 1 and 2, 1 is a door inner panel 3
A door body 4 composed of a door outer panel 2 and a door outer panel 2 is a door trim that covers the surface of the door inner panel 3 of the door body 1, and the door cushioning material 5 of the present invention is fixedly arranged on the back surface of the door trim 4.

An essential condition in the present invention is a foamed bead molding made of a styrene-based heat-resistant resin having a Vicat softening point of 108 ° C. or more, and the molding has a compression hysteresis loss of 60% or more and a density of 15 to 120 kg. / M ³ of cushioning material is used. The reason for using a foamed bead made of a styrene-based heat-resistant resin having a Vicat softening point of 108 ° C. or higher is that when the Vicat softening point is lower than 108 ° C., the practical heat resistance is satisfied when used in an automobile. Because I can't. That is, when it is arranged and used in a complicated shape such as the door trim of the present invention, if the dimensional change rate during use becomes large, it may fall off from the use site and the initial purpose may not be achieved. .
It is generally said that this dimensional change rate must be kept within approximately ± 0.5%.

The requirement of the present invention is to use a bead foam molding. This is because, as described above, the conventional drawbacks such as the complexity of foam formation, processing, or mounting are eliminated, productivity is improved, and a cushioning material with less density unevenness as designed is easily obtained. Also, a molded product having a complicated shape such as the cushioning material for doors of the present invention can be arbitrarily obtained according to the characteristics of the original manufacturing method of the bead molded product.

According to the present invention, the molded product has a compression hysteresis loss of 60% or more and a density of 15 to 120 kg / m ^3.
It is an essential requirement to use the cushioning material. The reason is that if the compression hysteresis loss is 60% or less, the ability to absorb the impact energy of the human body at the time of collision is insufficient. A cushioning material with a small compression hysteresis loss, specifically, an elastic foam such as the above-mentioned polyolefin resin such as PP, causes a displacement when the impact energy at the time of collision is applied, but has a small energy absorption rate. Since the recovery force is strong, that is, the compression hysteresis loss is small, the total energy absorption amount of the cushioning material becomes small, and it may be bounced back with almost the same force in the vehicle after the collision, and the impact on the occupant is mitigated. The ability is low. Therefore, the larger the value of this compression hysteresis loss, the better.

Further, it is a requirement to use a cushioning material having a density of 15 to 120 kg / m ³ . Density is 15k
If it is less than g / m ³ , the energy absorption rate becomes extremely small, and it is not practical to use it as a cushioning material for automobile doors. That is, if the energy absorption rate is small, it is necessary to dispose the cushioning material very thick in order to match the total energy absorption amount of the cushioning material for absorbing impact energy at the time of impact, and it is not possible to fit it in the door trim. This is because the thickness will be appropriate. On the contrary, it is possible to consider using a larger area to absorb impact energy, but this is naturally limited because it is related to the area of the human body.

When the density is 120 kg / m ³ or more, the energy absorption rate increases, but it is not practical for use as a cushioning material for automobile doors. In other words, since the set value of the total energy absorption amount of the cushioning material is too large compared to the impact energy generated when the human body collides, the displacement at the time of collision becomes small and a high impact value is generated, which is a sufficient cushioning property to protect the human body. Because I can't get it. From these, the foam density is practically 15 to 120 kg.
/ M ³ is considered, but preferably 20 to 80 kg / m
^{Is 3} . The density distribution value of the molded product is preferably 5% or more.

The styrene-based heat-resistant resin referred to in the present invention is a general term for a resin in which a styrene-based resin is used as a base resin and a heat-resistant resin component is copolymerized or mixed with the resin by a known method. A resin obtained by copolymerizing a styrene monomer and a heat resistant monomer system by a known method, for example, a styrene-acrylonitrile copolymer resin, or a copolymer resin of styrene and an unsaturated carboxylic acid system, for example, styrene-methacrylic acid. System copolymer resin, styrene-acrylic acid copolymer resin, styrene-maleic anhydride copolymer resin, etc., and heat-resistant monomer, copolymer resin with a comonomer may be used as long as it is not particularly limited. Not a thing. Further, instead of styrene, isopropyl styrene, paramethyl styrene, alpha methyl styrene, tertiary butyl styrene, etc. may be used.

Further, a mixed resin of two or more components of a single styrene resin and a single heat resistant resin is also included. For example, a mixed resin of a styrene resin and a polyphenylene ether resin, and the heat resistant resin mixed at this time may be a styrene heat resistant resin as described above.

The polyphenylene ether resin referred to in the present invention means, for example, poly (2,6-dimethylphenylene-1,
4-ether), poly (2,6-diethylphenylene-
1,4-ether), poly (2,6-dichlorophenylene-1,4-ether), poly (2,6-dibromophenylene-1,4-ether), poly (2, methyl-6-
Ethylphenylene-1,4-ether), poly (2, chloro-6-methylphenylene-1,4-ether), poly (2, methyl-6-isopropylphenylene-1,4)
-Ether), poly (2,6-di-n-propylphenylene-1,4-ether), poly (2, bromo-6-methylphenylene-1,4-ether), poly (2, chloro-6- Bromphenylene-1,4-ether), poly (2, chloro-6-ethylphenylene-1,4-ether) and the like.

The degree of polymerization is practically in the range of 10 to 5,000. Further, it is possible to use syndiotactic polystyrene alone as the styrene-based heat-resistant resin, and to use it in combination with the styrene-based resin as described above. In any case, it is a requirement that the Vicat softening point of the styrene-based heat-resistant resin is 108 ° C. or higher according to the present invention.
Further, if necessary, a light stabilizer, an antistatic agent, a colorant, a nucleating agent, a flame retardant, etc. may be added within a range satisfying the requirements of the present invention.

The bead foam molding referred to in the present invention is
Obtaining expandable resin particles impregnated with a foaming agent, obtaining primary expanded particles by pre-expanding the resin particles, and then aging and then fusion-molding in a predetermined mold by a heat molding device. It is a molded product. At this time, the method of obtaining the expandable resin particles is a method called polymer impregnation method, that is, a method of adding a foaming agent during or during the polymerization to obtain granular (bead-like) expandable particles. Alternatively, a method referred to as a post-impregnation method, that is, a method of impregnating particles obtained by extruding a strand shape in advance with an extruder and then cutting, or particles obtained by polymerizing a resin with a foaming agent in a subsequent step. Further, there is an extrusion impregnation method or the like in which a foaming agent is kneaded and impregnated at the time of extrusion, extruded in a strand shape, rapidly cooled with water, and then cut to obtain expandable particles.

The Vicat softening point referred to in the present invention is JI.
Measured according to the standard defined by the test method of SK-7206.

FIG. 3 is for explaining the compression hysteresis loss referred to in the present invention, and is obtained by the compression test of the molded body. In the figure, the horizontal axis X represents the compression ratio (%) with respect to the thickness of the test product, the vertical axis Y represents the load (kg), and D represents the position where the compression ratio is 75%. O is the compression start point, A is the compression curve, point C is the load at a compression ratio of 75%, B is the load-displacement curve when releasing the load, and point E is the no-load point when opening. ing. In the present invention, a test piece having a thickness of 80 mm and an 8 cm square is cut out from the molded body, and the test piece is cut into 2 pieces.
75% compression rate at a speed of 10 mm / min in an atmosphere of 4 ° C
Immediately after applying the load up to, the operation of releasing the load at the same speed was immediately performed, and FIG. 3 showing the relationship between the compressibility and the load during that period was drawn, and the compression hysteresis loss was determined by the following equation. First, let O be the area formed by O, A, C, D, and O, and let O, A, C,
When the area formed by B, E, and O is b, (b / a) × 10
0 was defined as the compression hysteresis loss (%).

[0021]

EXAMPLES The contents of the present invention will be described in more detail below with reference to Examples and Comparative Examples in Table 1. First, the test methods and evaluation methods used in the examples and comparative examples will be summarized.

1) Foam density (Test method and test conditions) The density was determined as follows from a test molded body of 30 cm square and 80 mm thickness. <Average Density> The weight of the entire test molded body of 30 cm square and 80 mm thickness described above was weighed, the volume was determined from the dimensions, and the density was calculated to be the average density. This value is shown in Table 1 as the foam density.

<Surface Density> 10 mm cut pieces were taken from the front and back surface portions in the thickness direction of the above-mentioned test molded body, the density was calculated by the same method as described above, and the average value of the front and back surfaces was taken as the surface density. <Internal Density> Similarly to the above, a 10 mm thick cut piece at the center portion in the thickness direction was sampled, and the density was calculated to be the internal density. <Density distribution value> The density was calculated according to the following formula from the density calculated above. Distribution value (%) = ((surface density-internal density) / average density)
× 100

2) Heat resistance against dry heat (Test method and test conditions) Test pieces of 20 mm square having a thickness of 80 mm sampled from various molded bodies were adjusted for one day in an atmosphere of 24 ° C., and then the distance between opposite sides of each test piece. Was measured with a caliper to 2 digits after the decimal point, and the average value was used as the initial dimension. After that, the test piece was exposed to a thermo-hygrostat adjusted to 80 ° C and 5% relative humidity for 400 hours, and then at 24 ° C. After left in the atmosphere for 1 day, the dimension measured in the same manner as above was used as the dimension after heating, and the dimensional change rate was calculated by the following calculation formula. Heating dimensional change rate (%) = ((initial dimension-after heating) ÷
Initial dimension) × 100 (Evaluation criteria) ○: Heating dimensional change rate is within ± 0.5% ×: Heating dimensional change rate is ± 0.5% or more.

3) Humidification heat resistance (Test method and test conditions) As described above, 24 test pieces each having a thickness of 80 mm and a size of 20 cm were sampled from various molded bodies.
After adjusting for 1 day in an atmosphere of ° C, the initial value is the average value of the dimensions of the opposite sides of the test piece measured with a caliper.
Then, after exposing the test piece to a thermo-hygrostat adjusted to 80 ° C. and 95% relative humidity for 48 hours, the test piece was left in an atmosphere of 24 ° C. for 1 day, and then the values measured in the same manner as above were heated. The size was determined, and the dimensional change rate was calculated by the following calculation formula. Heating dimensional change rate (%) = ((initial dimension-after heating) ÷
Initial dimension) × 100 (Evaluation criteria) ○: Heating dimensional change rate is within ± 0.5% ×: Heating dimensional change rate is ± 0.5% or more

4) Energy Absorption Rate The energy absorption rate was calculated by calculating the compression hysteresis loss diagram obtained by converting the load into the compression stress in the above-mentioned method of determining the compression hysteresis loss, and integrating the compression hysteresis loss region in the present invention. The value was defined as the energy absorption rate.
That is, compressive stress (kg / cm ² ) × compressive strain (cm /
The integrated value of (cm) is the energy absorption rate (kg · cm / cm
³ ) (Evaluation criteria) ○: Energy absorption rate is 0.8 to 15 kg · cm / cm
³ ×: Energy absorption rate is 0.8 kg · cm / cm ³ or less, or 15 kg · cm / cm ³ or more

5) Total Energy Absorption Amount of total energy absorbed by the cushioning material having an area of 200 cm ² of 80 mm thickness (corresponding to the chest pressure receiving area of the human body at the time of collision) is compressed by 75%. . That is, it is determined by the following formula using the value of the energy absorption rate. The total amount of energy absorption (kg · cm) = rate of energy absorption ^{(kg · cm / cm 3)} × 200cm 2 × 8 (c
m) × 0.75 (cm / cm). (Evaluation Criteria) ○: Total energy absorption amount is 900 to 20000 kg · c
m x: Total energy absorption is 900 kg · cm or less or 20000 kg · cm or more

Example 1 100 parts of polystyrene resin (Styron-666, manufactured by Asahi Kasei Corporation) and polyphenylene ether resin [poly (2,6-dimethylphenylene-1,4-ether)]
(Polymerization degree: 200) manufactured by Asahi Kasei Kogyo Co., Ltd.] 35 parts was melt-mixed and extruded in advance with a twin-screw extruder (PCM 45 mm extruder manufactured by Ikegai Tekko KK) to obtain resin pellets. The Vicat softening point of the resin pellet was calculated to be 1 as shown in Table 1.
A value of 29 ° C was shown. Next, 100 parts by weight of the mixed resin pellets was formulated with 10 parts by weight of iso-pentane (foaming agent), and an unexpanded foam of 1 mm diameter × 3 mm length was formed by extrusion impregnation method using a 30 mm extruder. Particles were obtained.

Next, the expandable particles were heated at a steam gauge pressure of 0.5 kg / cm ² for 30 seconds to obtain pre-expanded particles. After aging the expanded beads for 1 day, the density was measured and found to be 45 kg / m ³ . Then, a 80 mm-thick 30 cm square molded body was obtained using a steam molding machine. At this time, the steam gauge pressure for molding fusion during molding is 1.8 kg.
Was / cm ² . The obtained molded body was aged at 50 ° C. for 3 hours, and its density was measured. The average density was 30 kg / m ³ , the surface density was 32 kg / m ³ , the internal density was 28.5 kg / m ³ ,
The density distribution value was 11.7%. 1 at room temperature
After aging for days, the compression hysteresis loss was evaluated by the method described in the present invention. The results are shown in Table 1- (1), 1-
As shown in (2), the value was 86%.

When the heat resistance was evaluated by the method described in the present invention, it was 0.29 at 80 ° C. dry heat resistance.
%, The heat resistance to humidification at 80 ° C. was 0.22%, which was sufficiently satisfactory for practical heat resistance. Further, when the compression energy absorption rate was measured and evaluated, 1.8 kg · cm /
shows cm ^3, the total amount of energy absorption is 2160kg · c
m, which was practically usable as the door cushioning material of the present invention. When the expandable particles obtained in Example 1 were used to mold and mount a cushioning material for doors as shown in FIG. 1, they could be easily and surely attached in close contact with each other, and the shock absorbing ability was excellent. There was no problem.

Examples 2 to 3 Using the expandable particles of Example 1, molded articles having average densities of 115 kg / m ³ and 18 kg / m ³ were obtained according to Example 1. Each density distribution value is 11.4%, 11.
It was 1%. After aging these molded bodies at room temperature for 1 day, the compression hysteresis loss was evaluated in the same manner as above. The results are 94% and 65% as shown in Tables 1- (1) and 1- (2).
The value of was shown. From these results, it can be seen that the higher the density, the higher the compression hysteresis loss. On the contrary, when the density is low, it can be seen that the compression hysteresis loss is generally low. The heat resistance was also evaluated in the same manner.
The values shown in (1) and 1- (2) are shown. Although the molded product having the lower density showed a slightly large dimensional change rate, it still satisfied practical heat resistance.

Further, when the compression energy absorption rate was measured and evaluated in the same manner, 13.2 kg · cm / cm ³ , respectively,
It showed 0.9 kg · cm / cm ³ . The total energy absorption is 15840 kg · cm and 1080 kg, respectively.
・ Indicated cm. As can be seen from these values, it can be seen that when the density is high, the compression energy absorption rate is high, and when the density is low, only the compression energy absorption rate is low. However, in this range, the total energy absorption amount is still within the allowable range, and it can be seen that it can be practically used as the door cushioning material of the present invention.

Example 4 Expandable particles were obtained in the same manner as in Example 1 from a styrene-acrylonitrile copolymer resin (Styrac AS-783, manufactured by Asahi Kasei Kogyo; Vicat softening point 112 ° C.) as a base resin. Then, according to Example 1, an average density of 3
A molded body having 0 kg / m ³ and a density distribution value of 11.1% was obtained.
Similar to the above, the molded body was evaluated for compression hysteresis loss, heat resistance, energy absorption rate, and total energy absorption amount, and Table 1- (1), 1-
The result is (2). As the Vicat softening point is low,
Although the dimensional change rate in the heat resistance evaluation was rather high, all values satisfied the practicality of the present invention.

Comparative Examples 1-2 Using the expandable particles of Example 1, molded articles having the densities shown in Tables 1- (1) and 1- (2) were obtained according to Example 1. After aging these molded bodies for one day at room temperature, the compression hysteresis loss was measured and evaluated in the same manner as above. The results are shown in Table 1.
As shown in-(1) and 1- (2), the values were 57% and 95%. From these results, when the density is very low as in Comparative Example 1, a low compression hysteresis loss of less than 60% is exhibited, and conversely, when the density is very high as in Comparative Example 2, 10
It can be seen that it exhibits a very high compression hysteresis loss close to 0%.

Heat resistance, energy absorption rate, and total energy absorption of these molded products were evaluated in the same manner as in Example 1, and the results shown in Tables 1- (1) and 1- (2) were obtained. As a result, in Comparative Example 1, the heat resistance, the energy absorption rate, and the total energy absorption amount were values that did not satisfy the practical use. The reason for this is that the density of the foamed molded product is too low despite the fact that the resin composition has a high Vicat softening point, and therefore the foam film of the foamed product becomes thin and the rigidity decreases during the heat resistance test, resulting in a dimensional change rate. It is expected to grow. Also, by reducing the density,
As a matter of course, the compressive stress decreases and the energy absorptivity does not satisfy the practicability. In Comparative Example 2, since the density of the molded body is very high, the dimensional change rate of heat resistance is very small and there is no practical problem, but the energy absorption rate is very high and the total energy absorption is also It can be seen that the value no longer shows practically sufficient impact absorption.

Comparative Example 3 A styrene resin (Styron-666, manufactured by Asahi Kasei; Vicat softening point 101 ° C.) was used as a base resin.
The expandable particles were obtained by the same method as described in. Then, according to Example 1, a molded product having an average density of 50 kg / m ³ was obtained. When the molded body was evaluated for compression hysteris loss, heat resistance, energy absorption rate, and total energy absorption, respectively, as in the above, the results shown in Tables 1- (1) and 1- (2) were obtained. It was found that the lower the Vicat softening point, the higher the dimensional change rate in the heat resistance evaluation, and the practicality was not satisfied.

Reference Example 1 A first component of polyisocyanurate and a second component consisting of a polyol, a foaming agent (Freon 11), a catalyst and a surfactant were mixed by stirring and poured into a mold by a so-called one-shot method. A molded body having the same size as in Example 1 was obtained. Average density 80k
g / m ³ , surface density 112 kg / m ³ , internal density 47 k
It had a g / m ³ and a density distribution value of 81%.

After this molded body was aged at room temperature for one day, the compression hysteresis loss was evaluated by the method described in the present invention. The result showed a value of 95%. Further, when the heat resistance was evaluated by the method described in the present invention, it was 0.51% in heat resistance at 80 ° C. dry heat and 2.51% in heat resistance at 80 ° C. humidification (only this value showed the rate of change of the expansion agent. , And all other values shown in Tables 1- (1) and 1- (2) are the rate of change on the shrinkage side.)
It was found that the practical heat resistance was not satisfied. This was considered to be due to the phenomenon that the strength of the urethane resin forming the foam decreased due to hydrolysis.

Reference Example 2 An ethylene-propylene random copolymer resin (Tm = 150 ° C. was used as a base resin, pre-expanded particles were obtained by a known method, and thereafter molded to obtain a molded product having a density of 30 kg / m ^3. These molded bodies were aged at room temperature for 1 day, and then the compression hysteresis loss was measured and evaluated in the same manner as described above.The result showed a value of 51% .The unrecovered amount at this time was 18%. The unrecovered amount of the shown molded body of Example 1 was 41%, and the energy absorption rate was 0.7 kg · c.
It was m / cm ³ .

From these results, it was found that the compression hysteresis loss was lower than that of the examples of the present invention, and the unrestored amount was small and the elastic force was high. Therefore, when such a cushioning material is used for the purpose of the present invention, since the energy absorption rate at the time of collision is small and the recovery force is strong, the total energy absorption amount of the cushioning material is small, and the force is almost the same again in the vehicle after the collision. It may be bounced off by, and its ability to absorb impact on passengers is low. Furthermore, when the heat resistance was evaluated in the same manner as in Example 1, the dimensional change rate of 0.85% at 80 ° C. dry heat resistance and the value of 911% at 80 ° C. humidification heat resistance were shown. From these results, it was found that the heat resistance was extremely poor and it was not suitable for practical use.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

EFFECTS OF THE INVENTION The present invention does not require a special processing step and can be mounted in the back side of the base material of an automobile door trim in any shape with high productivity, is lightweight, has excellent shock absorbing ability, and is practical. It is possible to provide a cushioning material for an automobile door trim that also has sufficient heat resistance.

[Brief description of drawings]

FIG. 1 is a sectional view taken along line ZZ of FIG. 2 showing an embodiment of the present invention.

FIG. 2 is a side view of the vehicle door of the embodiment as seen from the passenger compartment side.

FIG. 3 is an example diagram showing a relationship between a compression rate and a load for explaining a compression hysteresis loss of the present invention.

[Explanation of symbols]

 1 door body 2 door outer panel 3 door inner panel 4 door trim 5 cushioning material A compression curve B recovery curve

Claims (3)

[Claims] 1. A cushioning material arranged on the back side of a door trim base material on a vehicle side, wherein the cushioning material is a bead foam molding made of a styrene-based heat-resistant resin having a Vicat softening point of 108 ° C. or higher. A cushioning material for automobile doors, which has a compression hysteresis loss of 60% or more and a density of 15 to 120 kg / m ³ . 2. The cushioning material for an automobile door according to claim 1, wherein the styrene-based heat-resistant resin comprises a mixed resin of a polystyrene-based resin and a polyphenylene ether resin. 3. The cushioning material for an automobile door according to claim 1, wherein the styrene-based heat-resistant resin comprises a styrene-acrylonitrile-based copolymer resin.