JP2009241691A - Automobile interior part - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automobile interior part having an improved sound-absorbing performance while maintaining a shock absorbing characteristic equal to that of the conventional one. <P>SOLUTION: The automobile interior part such as a tibia pad or a bulk-increasing material is formed of a polyolefin based resin foam where an air flow resistance value per unit thickness is >3,000 N×s/m<SP>4</SP>and <50,000 N×s/m<SP>4</SP>, and the ratio of the static compression stress in a distortion rate of 50% and the static compression stress in a distortion rate of 10% is 0.3 to 0.6. The static compression stress in the distortion rate of 5% of the automobile interior part is ≥0.1 MPa and <2.2 MPa. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an automobile interior part such as a tibia pad, which is a lower limb protection member of an automobile occupant, and a raising member installed on a floor of a passenger compartment.

Tibia pads are used as automotive interior parts. A conventional tibia pad is shown below.
As a lower limb protection member for the occupant of the front seat (30), a tibia pad (6) made of foamed resin as shown in FIG. 7 is provided in contact with the peripheral wall (33) in the passenger compartment (3) (patent) Reference 1). As the foamed resin, for example, a foamed resin of a styrene-modified polyethylene resin is used, which is molded by filling a mold with a resin that has been pre-foamed into particles of a predetermined particle size and heating.

An automobile interior part such as the tibia pad (6) is required to have a shock absorbing characteristic as a footrest. Furthermore, in view of quietness in the vehicle, sound absorption performance characteristics are also required (see Patent Document 2). As a value for evaluating the sound absorption performance characteristic, there is an air flow resistance value. The lower the air flow resistance value, the better the sound absorption performance characteristic. Automobile interior parts disclosed in Patent Document 2 is formed of a polypropylene resin, the air flow resistance value is greater than 50000N · s / m ³ or less 3000N · s / m ³ thickness of the test piece at 0.02m there were. In addition, as a method for evaluating the impact absorption characteristics, a method for obtaining a ratio of a static compressive stress having a strain rate of 10% and a static compressive stress having a strain rate of 50% as defined in JIS K6767 “Testing method for foamed plastic and polyethylene”. There is. Patent Document 2 discloses that the ratio of automobile interior parts is 0.3 or more and 0.5 or less.

  The automobile interior parts in which such foamed resin is used are not only tibia pads but also a raised material (see FIG. 8) that is arranged on the floor (4) surface of the automobile and sets the height of the rear seat (31). 1) (see Patent Document 3). A carpet (5) is laid on the raising material (1).

JP 2007-98964 A JP 2007-45979 A JP 2000-280809 A

The value of the airflow resistance of the automobile interior parts disclosed in Patent Document 2, the thickness of the test piece was 50000N · s / m ³ or less larger than 3000N · s / m ³ at 0.02 m. Here, since the air flow resistance value varies depending on the thickness of the test piece, in order to objectively evaluate the sound absorption performance characteristics, it is necessary to use the unit thickness air flow resistance value obtained by dividing the air flow resistance value by the thickness. There is.
The unit thickness air flow resistance value of the automobile interior part disclosed in Patent Document 2 is larger than 150,000 N · s / m ⁴ obtained by dividing the air flow resistance value by the thickness of 0.02 m and not more than 2500,000 N · s / m ⁴ .
The applicant tried to improve the sound absorption performance characteristic from the value disclosed in Patent Document 2 while maintaining the shock absorption characteristic, assuming that the shock absorption characteristic is equivalent to the value disclosed in Patent Document 2. Specifically, if the foam is prevented from expanding, the resulting foamed molded product is considered to have air permeability.
An object of the present invention is to provide an automobile interior part with improved sound absorption performance characteristics while maintaining shock absorption characteristics equivalent to the conventional one.

Automobile interior parts, unit thickness value of the airflow resistance is at large 50000N · s / m ⁴ or less than 3000N · s / m ^4, and static compressive stress when the strain rate of 50%, the strain rate of 10% of the static It is formed from a thermoplastic resin foam having a ratio to the compressive stress of 0.3 or more and 0.6 or less.

Applicant, polyolefin resin foam is a thermoplastic resin foam obtained from the various experiments, unit thickness value of the airflow resistance is at large 50000N · s / m ⁴ or less than 3000N · s / m ^4, Sound absorption performance characteristics can be greatly improved compared to conventional products. In addition, the ratio of the static compressive stress at the strain rate of 50% and the static compressive stress at the strain rate of 10% is 0.3 or more and 0.6 or less, and the shock absorption characteristics can be maintained at the same level as the conventional one. did it. That is, it was possible to obtain an automobile interior part with improved sound absorption performance characteristics while maintaining shock absorption characteristics equivalent to the conventional one.

Hereinafter, an embodiment of the present invention will be described in detail. The raising material (1) and the tibia pad (6) have the same shape as in the prior art, but the polyolefin resin is a styrene-modified polyethylene foaming resin.
First, the metal mold | die which shape | molds this foamable resin is demonstrated. 1 (a) and 1 (b) are cross-sectional views of the mold (7). As is well known, the mold (7) is constructed by abutting a male mold (70) and a female mold (71). A foamable resin is introduced into the cavity (72) between the two molds (70) (71). The movable mold (70) moves left and right, but the female mold (71) may move.
A first heating chamber (73) and a second heating chamber (74) into which heating steam is introduced are formed outside the female mold (71) and the male mold (70), respectively. ) Is the first steam introduction cylinder (75) and the first drain valve (76) from which the steam is discharged, and the second heating chamber (74) is the second steam introduction cylinder (77) and the second drain from which the steam is discharged. Each has a valve (78). Foamed resin particles are supplied into the cavity (72) from the supply cylinder (79).
The female mold (71) and the male mold (70) have micropores (not shown) through which steam can pass, and the diameter of the micropores is smaller than the diameter of the foamable resin to be molded. Resin does not fall out of the micropores.

At the time of molding, there are four steps of “mold heating”, “one side heating”, “reverse one side heating”, and “both sides heating”.
“Mold heating” means that the first and second heating chambers (73, 73) from the first and second steam introduction cylinders (75) and (77) are respectively heated for the purpose of warming the mold (7) that is cooled before the start of molding. ) (74) refers to a process in which heated steam is introduced, and both drain valves (76) and (78) are open. Therefore, the steam that has entered the first and second heating chambers 73 and 74 warms the mold 7 and eliminates excess air in the mold, and is discharged from the drain valves 76 and 78. The
The “one-side heating” is a process of closing the first drain valve (76) and introducing the heating steam from the first steam introducing cylinder (75) into the first heating chamber (73). 78) is open. The heated steam is discharged from the second drain valve (78) after heating the foamed molded body in the cavity (72).

“Reverse one-sided heating” is the next step after “one-sided heating”, in which the second drain valve (78) is closed and the heated steam is transferred from the second steam introduction cylinder (77) to the second heating chamber (74). The first drain valve (76) is closed. The heating steam heats the foam molded body in the cavity (72) from the second heating chamber (74) side.
“Double-sided heating” is a process after “reverse one-sided heating”, in which both drain valves (76), (78) are closed and heated steam is first supplied from both steam introducing cylinders (75), (77). This is a step of introducing the second heating chamber (73) (74). The heated steam heats the foam molded body in the cavity (72) and promotes the extension of the surface of the foam molded body.

  Further, a technique called cracking is used when a foamed molded article is molded using the mold (7). This is because the male mold (70) and the female mold (71) are brought into contact with each other to fill the foam (72) with particles of the foamable resin to be a foam-molded product. Thereafter, as shown in FIG. 1 (b). Furthermore, it means that the male mold (70) is slightly separated from the female mold (71) to such an extent that the foamable resin particles do not leak. The distance separating the male mold (70) from the female mold (71) (L in FIG. 1 (b)) is called the cracking amount. This is a technique for solving such a shortage of filling in which a portion of the cavity (72) that is not filled with foamable resin particles may be generated at some points. Through various experiments, the applicant has found that the breathability of the foamable resin to be molded can be changed by adjusting the amount of cracking.

The applicant uses the above-described mold (7) to provide five types of styrene-modified polyethylene resins as samples for measuring the sound absorption coefficient, unit length air flow resistance, and static compressive stress of automobile interior parts. A foamed molded body was prepared, and this was designated as Example 1 to Example 4. Example 1 The foamed molded product of Example 4 has air permeability. Further, a foamed molded article having no gap between the particles and having no air permeability was prepared and used as a comparative example. In general, when the heating time is lengthened, the foamable particles swell greatly, so that a foamed molded product having no gap can be obtained. Each of the foam molded bodies is a plate-like base material (described later) having a thickness of 0.03 m.
In Example 1, a foamed molded article having air permeability was obtained even under the same molding conditions as in the comparative example by using a material whose foaming force was suppressed during molding with the raw material.
In Example 2-4, as in the comparative example, the raw material used was a foaming raw material at the time of molding, and the heating time was shorter than that of the comparative example, thereby suppressing the foam from expanding and having air permeability. A molded body was obtained.
In the comparative example, a raw material having the same foaming force as that of Example 2-4 was used as a raw material, and a foamed molded body having no gap was obtained by sufficiently heating.
The manufacturing method of the foaming molding of Example 1-Example 4 and the foaming molding of a comparative example is described below.

Production Method of Foam Molded Body of Example 1 Ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVA) (trade name “NUC-3450” manufactured by Nihon Unicar Co., Ltd., vinyl acetate content: 5% by weight, melting point: 107 ° C., Melt flow rate: 0.5 g / 10 min, density: 0.93 g / cm ³ ) is supplied to an extruder, melted and mixed, granulated by an underwater cutting method, and oval spherical (egg) EVA resin particles (Polyethylene resin particles) were obtained. The average weight of the EVA resin particles was 0.6 mg. The melt flow rate and density of EVA are values measured according to JIS K6992-2.
Next, 0.8 parts by weight of magnesium pyrophosphate and 0.02 parts by weight of sodium dodecylbenzenesulfonate were dispersed in 100 parts by weight of water to obtain a dispersion medium. A suspension was obtained by dispersing 100 parts by weight of the EVA resin particles in a dispersion medium.
Further, 0.19 parts by weight of benzoyl peroxide and 1.5 parts by weight of dicumyl peroxide as a polymerization initiator were dissolved in 200 parts by weight of styrene monomer to prepare a styrene monomer.
The suspension containing EVA resin particles is adjusted to a temperature of 90 ° C., and the styrene monomer is continuously added dropwise at a rate of 50 parts by weight per hour to polymerize the EVA resin particles while impregnating the EVA resin particles. I let you.

Next, the temperature of the reaction system was raised to 140 ° C. and held for 3 hours to crosslink the EVA resin to obtain styrene-modified EVA resin particles. The degree of crosslinking (gel content) of the obtained resin particles was 55%.
Subsequently, 100 parts by weight of the modified resin particles, 0.15 parts by weight of stearic acid monoglyceride and 0.5 parts by weight of diisobutyl adipate are fed to a sealed pressure-resistant V-type rotary mixer having an internal volume of 1 m ³ and rotated. However, 14 parts by weight of butane (n-butane: I-butane = 7: 3) was injected at room temperature. Then, the inside of the rotary mixer was heated to 70 ° C., held for 4 hours, impregnated with butane, and then cooled to 25 ° C. to obtain expandable resin particles.
The obtained expandable resin particles were immediately prefoamed with water vapor to a bulk density of 30 kg / m ³ to obtain prefoamed particles. Next, the pre-expanded particles are filled into the foam molding machine. At this time, the cracking amount is set to 3 mm and the mold is opened slightly, and steam with a steam pressure of 0.08 MPa is used. First, mold heating for 7 seconds, then one heating for 15 seconds, then reverse one heating for 7 seconds, then double-sided heating for 10 seconds, and then water-cooled to form a foamed base material having air permeability Was taken out.
The following foam molding machine was used for foam molding.
Molding machine used: ACE-3SP (manufactured by Sekisui Koki Co., Ltd.)
Mold size: 300 × 400 × 30mm

Production method of foam molded article of Example 2 EVA resin particles were obtained in the same manner as in Example 1 to obtain a suspension.
Further, 0.19 part by weight of t-butyl peroxybenzoate as a polymerization initiator was dissolved in 40 parts by weight of styrene monomer to prepare a styrene monomer.
The suspension containing EVA resin particles was adjusted to a temperature of 60 ° C., and the styrene monomer was added in a fixed amount over 30 minutes, and then stirred for 1 hour to impregnate the styrene monomer in the EVA resin particles.
Next, the temperature of the reaction system was raised to 130 ° C. and maintained for 3 hours, and the styrene monomer was polymerized in the EVA resin particles.
Next, a styrene monomer in which 0.19 part by weight of t-butyl peroxybenzoate was further dissolved in 160 parts by weight of styrene monomer as a polymerization initiator was continuously added at a rate of 50 parts by weight per hour. The styrene monomer was polymerized while being impregnated with EVA resin particles to obtain styrene-modified EVA resin particles.
Subsequently, 100 parts by weight of the modified resin particles, 0.15 parts by weight of stearic acid monoglyceride and 0.5 parts by weight of diisobutyl adipate are fed to a sealed pressure-resistant V-type rotary mixer having an internal volume of 1 m ³ and rotated. However, 14 parts by weight of butane (n-butane: I-butane = 7: 3) was injected at room temperature. Then, the inside of the rotary mixer was heated to 70 ° C., held for 4 hours, impregnated with butane, and then cooled to 25 ° C. to obtain expandable resin particles.

The obtained expandable resin particles were immediately prefoamed with water vapor to a bulk density of 30 kg / m ³ to obtain prefoamed particles. Next, the pre-expanded particles are filled into the foam molding machine. At this time, the cracking is set to 2 mm and the mold is slightly opened, and steam with a steam pressure of 0.08 MPa is used. First, mold heating was performed for 7 seconds, then one heating for 15 seconds, then reverse one heating for 0.5 seconds, and then double-sided heating for 0.5 seconds, followed by water cooling to take out the foamed molded product.
The following foam molding machine was used for foam molding.
Molding machine used: ACE-3SP (manufactured by Sekisui Koki Co., Ltd.)
Mold size: 300 × 400 × 30mm
The base material which is the obtained foam was a foamed molded article having air permeability.

A foamed molded article having air permeability, that is, a base material, was obtained in the same manner as in Example 2 except that the manufacturing cracking amount of the foamed molded article of Example 3 was set to 3 mm.
A foamed molded product having air permeability, that is, a base material, was obtained in the same manner as in Example 2 except that the manufacturing cracking amount of the foamed molded product of Example 4 was set to 7 mm.

Except that the heating time at the time of molding of the foamed molded product of the comparative example was first mold heating 7 seconds, then one heating 15 seconds, then reverse one heating 7 seconds, then double-sided heating 10 seconds In the same manner as in No. 2, a foamed molded product having a low air permeability, that is, a base material was obtained. That is, by making the reverse one-side heating and the double-sided heating longer than those in Example 2, a foamed molded article with less air permeability was obtained.

As shown in FIG. 2, the sample (2) was punched out from the base material (20) which is the foam molded body of Examples 1-4 and Comparative Examples. The thickness of each sample (2) was measured with an electronic caliper, the weight was obtained with an electronic balance, and the density was calculated.
The applicant measured the sound absorption coefficient (unit:%), unit length air flow resistance value (unit: N · s / m ⁴ ), and static compressive stress (unit: MPa) for each sample (2).

Measurement of Sound Absorption Rate FIG. 3 is a diagram of an apparatus for measuring the sound absorption rate. Sample (2) has a diameter of 29.7 mm and a thickness of 30 mm. The sample (2) is attached to the distal end portion of the impedance tube (21), and the speaker (22) is attached to the proximal end portion of the impedance tube (21). A sine wave generator (24) is attached to the input side of the speaker (22) via an amplifier (23), and a microphone (25) and an amplifier (26) are connected to the output side of the speaker (22). An analyzer (27) is attached. A 1 kHz signal from the sine wave generator (24) passes through the impedance tube (21) and enters the sample (2) perpendicularly, and the signal reflected by the sample (2) is picked up by the microphone (25) and amplifier (26 ) Through an analyzer (27). In the analyzer (27), the maximum sound pressure value and the minimum sound pressure value of the signal reflected by the sample (2) are defined in JIS A1405 “Sound absorption coefficient and impedance measurement using impedance tube—standing wave ratio method”. The calculation was applied to the formula. The higher the sound absorption coefficient, the better the material can improve the quietness in the vehicle.

Unit Length Air Flow Resistance Measurement The unit length air flow resistance value is determined based on the air flow resistance value measured by the ISO9053A method with the apparatus shown in FIG. A sample (2) for measuring an air flow resistance value is attached to the measuring tube main body (8), and compressed air is sent to the sample (2) from the compressor (80) via the flow rate regulator (81). Sample (2) has a diameter of 40 mm and a thickness of 30 mm.
The pressure difference between the air entering the sample (2) and the air passing through the sample (2) is measured by the micro differential pressure gauge sensor (82), and the value of the sensor (82) is measured by the micro differential pressure gauge reading unit (83) After reading, the differential pressure signal was sent to the measurement controller (84) to determine the air flow resistance value. The air flow resistance value (unit: N · s / m ³ ) obtained in this way is divided by 0.03 m which is the thickness of the sample (2) to obtain a unit length air flow resistance value (unit: N · s). / M ⁴ ).
The inner diameter of the measurement tube main body (8) was 40 mm, and silicon grease was applied to the gap between the periphery of the sample (2) and the inner surface of the measurement tube main body (8) to fill the gap.

Measurement of Static Compressive Stress Static Compressive Stress is measured based on JIS K 6767 “Foamed Plastics-Polyethylene Test Method” by applying a static compressive load on the sample, A ratio with a static compressive stress of 50% was obtained. In addition, a static compressive stress with a strain rate of 5% was determined. The sample size was 50 × 50 × 25 mm, and the compression speed of the sample was 0.01 m / min.
The data of the sound absorption coefficient, unit length air flow resistance, and static compressive stress are shown in the table of FIG. 5, and the graph with the static compressive stress on the vertical axis and the strain rate on the horizontal axis is shown in FIG.
The sample (2) of Example 1-4 has a better sound absorption rate than the sample (2) of the comparative example. Also, samples of Examples 1-4 (2), the unit thickness value of the airflow resistance is at large 50000N · s / m ⁴ or less than 3000N · s / m ^4, greatly improved the sound absorption performance characteristics than conventional products I can see that I was able to. As can be seen from the table of FIG. 5, the static compressive stress at a strain rate of 5% was 0.1 MPa or more and 0.2 MPa or less, that is, 0.1 MPa or more and less than 2.2 MPa.
The ratio of the static compressive stress when the strain rate was 50% and the static compressive stress when the strain rate was 10% was 0.3 or more and 0.6 or less. It can be considered that this ratio of 0.3 or more and 0.6 or less indicates that the impact absorption characteristics are equivalent to the conventional one.

As can be seen from the table in FIG. 5 and the graph in FIG. 6, the styrene-modified polyethylene resin, which is a polyolefin resin foam obtained by the applicant from various experiments, has a unit thickness air flow resistance value of 3000 N · s. It was larger than / m ⁴ and 50000 N · s / m ⁴ or less, and the sound absorption performance characteristics could be greatly improved as compared with the conventional product. In addition, the ratio of the static compressive stress at the strain rate of 50% and the static compressive stress at the strain rate of 10% is 0.3 or more and 0.6 or less, and the shock absorption characteristics can be maintained at the same level as the conventional one. did it. That is, it was possible to obtain an automobile interior part with improved sound absorption performance characteristics while maintaining shock absorption characteristics equivalent to the conventional one.

As the raw material of the foamed molded product of the above-mentioned Examples, pre-expanded particles of about 1 mm to 5 mm obtained by pre-expanding the expandable synthetic resin particles 3 to 50 times can be used.
The expandable synthetic resin particles are obtained by impregnating a synthetic resin with a physical foaming agent and foam by heating, and include those pre-foamed. In the embodiment of the present invention, pre-expanded so-called pre-expanded particles are mainly used. Examples of the synthetic resin constituting the foamable synthetic resin particles include styrene-modified polyethylene resin, polystyrene, high impact polystyrene, styrene-ethylene copolymer, styrene-maleic anhydride copolymer, and styrene-acrylonitrile copolymer. And polystyrene resins such as polymethyl methacrylate resin, polyolefin resins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer, and polyester resins such as polyethylene terephthalate. Mixtures of these synthetic resins and copolymer of monomers can also be used.
Examples of the physical foaming agent include aliphatic hydrocarbons such as propane, butane, pentane and hexane, aliphatic cyclized hydrogens such as cyclopentane and cyclobutane, and inorganic gases such as carbon dioxide, nitrogen and air. Can be mentioned. These physical foaming agents may be used alone or in combination of two or more.

  The above description of the embodiments is for explaining the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope thereof. In addition, the configuration of each part of the present invention is not limited to the above embodiment, and various modifications can be made within the technical scope described in the claims.

(a), (b) is sectional drawing of the metal mold | die which shape | molds a foamable resin. It is a perspective view of a sample and a base material. It is a figure of the apparatus which measures a sound absorption coefficient. It is a figure of the apparatus which measures an air flow resistance value. It is a table | surface which shows the data of a sound absorption coefficient, unit length airflow resistance value, and a static compressive stress. It is the graph which made the static compressive stress the vertical axis and made the distortion rate the horizontal axis. It is a perspective view of the conventional tibia pad. It is sectional drawing of a raising material.

Explanation of symbols

(2) Sample
(3) Car compartment
(6) Tibia pad
(7) Mold

Claims (4)

The ratio of unit thickness value of the airflow resistance is at large 50000N · s / m ⁴ or less than 3000N · s / m ^4, and static compressive stress when the strain rate of 50%, the strain rate of 10% of the static compressive stress An automobile interior part formed from a thermoplastic resin foam having a value of 0.3 or more and 0.6 or less. The automobile interior part according to claim 1, wherein a static compressive stress at a strain rate of 5% is 0.1 MPa or more and less than 2.2 MPa. The automotive interior part according to claim 1 or 2, wherein the thermoplastic resin foam is a styrene-modified polyolefin resin. The automobile interior part according to claim 3, wherein the styrene-modified polyolefin resin foam has a styrene component of 50% or more.

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