Soundproof material for vehicle

Abstract

This soundproof material for a vehicle comprises a polyurethane foam. The average cell diameter of the polyurethane foam is 50-200 μm, the ventilation resistance is 0.2-5 kPa ⋅ s / m, and the Asker C hardness is 45 or more. When the normal incidence sound absorption coefficient of the polyurethane foam is measured using a disc-shaped sample having a diameter of 30 mm and a thickness of 10 mm, the sound absorption coefficient at a frequency of 800 Hz is 0.30 or more, and the sound absorption coefficient at a frequency of 5000 Hz is 0.50 or more. The polyurethane foam has a desired rigidity and excellent sound absorbency in both the low frequency range and the high frequency range.

Description

Soundproofing material for vehicles

[0001] This disclosure relates to soundproofing materials for vehicles, such as those used in the engine compartment of a vehicle.

[0002] In vehicles such as automobiles, various measures are taken to reduce noise leaking outside the vehicle or into the passenger compartment. For example, in the engine compartment of a vehicle, soundproofing materials such as engine covers, side covers, and oil pan covers are placed around the engine to reduce the noise radiated from the engine, which is the source of the noise. This type of soundproofing material is composed of a hard cover member made of resin or the like, and a soft polyurethane foam placed on its back side, as described in Patent Document 1, for example, and is attached to the mating member by fastening the cover member with bolts or the like.

[0003] Japanese Patent Publication No. 2004-44526 Japanese Patent Publication No. 2024-14696

[0004] Generally, flexible polyurethane foam has high breathability and sound absorption properties, but its low rigidity makes it unsuitable for independent use. Therefore, considering factors such as ease of attachment to mating components, it is often used in conjunction with a rigid cover component. However, using a cover component increases mass and cost. On the other hand, to give polyurethane foam independence and enable its use independently, one could consider making the polyurethane foam itself rigid. However, rigidifying polyurethane foam makes it difficult to maintain cell (air bubble) connectivity, resulting in reduced sound absorption.

[0005] For example, Patent Document 2 describes a sound-absorbing material for vehicles that is thin and has sound-absorbing performance over a wide frequency range, with an average cell diameter of 2000 μm or more, an Asker C hardness of 20 to 100, an average sound absorption coefficient of 0.6 or more from 1000 Hz to 3500 Hz, an average sound absorption coefficient of 0.5 or more from 1000 Hz to 2000 Hz, and an air permeability of 0.1 to 100 cm. ３ / cm ２ A flexible polyurethane foam with / sec is described. As described in paragraph

[0039] of Patent Document 2, in the flexible polyurethane foam described in the same document, the average sound absorption coefficient in a specific frequency range is increased by adding a predetermined amount of defoaming agent to coarseen the cells.

[0006] As described in Patent Document 2, using a foam-breaking agent to merge minute cells and increase the cell diameter may improve air permeability and thus enhance sound absorption in certain frequency ranges. However, increasing the cell diameter shortens the sound propagation path, thus reducing sound absorption in the low-frequency range below 1000 Hz. Furthermore, electric vehicles, which have become increasingly popular in recent years, require sound absorption in the high-frequency range of around 5000 Hz generated by motors and other components.

[0007] This disclosure has been made in view of the above circumstances, and aims to provide a soundproofing material for vehicles using polyurethane foam that has desired rigidity and excellent sound absorption in both low-frequency and high-frequency ranges.

[0008] (1) The soundproofing material for vehicles according to the present disclosure is a soundproofing material for vehicles comprising polyurethane foam, wherein the average cell diameter of the polyurethane foam is 50 μm or more and 200 μm or less, the air permeability resistance is 0.2 kPa·s / m or more and 5 kPa·s / m or less, the Asker C hardness is 45 or more, and when the normal incidence sound absorption coefficient of the polyurethane foam is measured using a disc-shaped sample with a diameter of 30 mm and a thickness of 10 mm, the sound absorption coefficient at a frequency of 800 Hz is 0.30 or more and the sound absorption coefficient at a frequency of 5000 Hz is 0.50 or more.

[0009] In order to solve the above problems, the inventors have conducted extensive research and have found that by adopting a specific cell structure, they have been able to achieve both rigidity and sound absorption in polyurethane foam. First, in the polyurethane foam constituting the soundproofing material for vehicles of this disclosure (hereinafter sometimes referred to as "the polyurethane foam of this disclosure"), the framework is made rigid to achieve a rigidity of Asker C hardness of 45 or higher. As mentioned above, simply making the framework rigid makes it difficult for the foam film to break, making it difficult to connect the cells. However, in the polyurethane foam of this disclosure, the cell diameter is reduced and a continuous cell structure is realized. Reducing the cell diameter lengthens the sound propagation path, improving sound absorption. Lengthening the sound propagation path is particularly effective for sound absorption in the long wavelength (low frequency) range. In addition, by adopting a continuous cell structure, the airflow resistance does not increase even with a small cell diameter. As a result, the polyurethane foam of this disclosure has a normal incidence sound absorption coefficient of 0.30 or higher at a frequency of 800 Hz and a normal incidence sound absorption coefficient of 0.50 or higher at a frequency of 5000 Hz, making it possible to achieve high sound absorption in both the low-frequency and high-frequency ranges.

[0010] In a vehicle's engine compartment, not only radiated noise from noise sources but also reverberating noise within the space needs to be reduced. The polyurethane foam of this disclosure has the desired rigidity and can be used independently without support from rigid cover members. In this case, sound absorption is exhibited on both sides of the polyurethane foam (the side facing the noise source and the opposite side), further improving its effectiveness as a soundproofing material. Furthermore, by not using rigid cover members, the weight of the vehicle soundproofing material of this disclosure can be reduced, and it can be fixed to the mating member using a simple method such as clips.

[0011] (2) In the above configuration, the density of the polyurethane foam is 90 kg / m³ ３ More than 1600kg / m ３The following configuration is also possible. For example, increasing the density of polyurethane foam can reduce the cell diameter, but this reduces the air layer, thus decreasing sound absorption. With this configuration, the cell diameter can be reduced while keeping the density relatively low, so the sound absorption is less likely to decrease.

[0012] The soundproofing material for vehicles disclosed herein exhibits high sound absorption in both the low-frequency and high-frequency ranges. Furthermore, the soundproofing material for vehicles disclosed herein enables weight reduction and cost reduction.

[0013] This graph shows the normal incidence sound absorption coefficient of polyurethane foam in the examples and comparative examples.

[0014] The embodiments of the soundproofing material for vehicles described herein will be described below. However, the embodiments are not limited to those described below, and can be implemented in various modified and improved forms as possible for those skilled in the art. In the numerical ranges described stepwise in this specification, the upper and lower limits described individually can be combined arbitrarily. Furthermore, the upper and lower limits of the numerical ranges can be replaced with the values ​​shown in the examples.

[0015] In the soundproofing material for vehicles disclosed herein, the composition other than polyurethane foam is not particularly limited. The soundproofing material for vehicles disclosed herein may consist solely of polyurethane foam, or it may be composed of polyurethane foam in combination with other materials. For example, when the soundproofing material for vehicles disclosed herein is implemented in an engine cover, the engine cover may be a single-layer structure of polyurethane foam, or a multi-layer structure having a soundproofing layer made of polyurethane foam and a surface layer covering it. The surface layer may be formed using resin, elastomer, metal, fiber, etc. Furthermore, the term "vehicle" as an application includes not only automobiles but also airplanes, trains, etc. The polyurethane foam constituting the soundproofing material for vehicles disclosed herein will be described below.

[0016] <Physical Properties and Characteristics of Polyurethane Foam> [Average Cell Diameter] The average cell diameter of the polyurethane foam disclosed herein is 50 μm or more and 200 μm or less. If the average cell diameter is less than 50 μm, the airflow resistance becomes excessively large, resulting in reduced sound absorption. More suitable average cell diameters are 70 μm or more, 100 μm or more, and 120 μm or more. On the other hand, if the average cell diameter is greater than 200 μm, the sound propagation path becomes shorter, and sound absorption, especially in the low-frequency range, decreases. More suitable average cell diameter is 180 μm or less. In this disclosure, the average cell diameter is the value measured by the cell structure analysis device "PORE!SCAN" manufactured by Goldluecke. Specifically, the cross-section in the thickness direction of the polyurethane foam (10 mm or more vertically, 50 mm or more horizontally) is image-analyzed, and the arithmetic mean of the obtained cell diameters is taken as the average cell diameter.

[0017] [Air permeability resistance] The air permeability resistance of the polyurethane foam of this disclosure is 0.2 kPa·s / m or more and 5 kPa·s / m or less. If the air permeability resistance is less than 0.2 kPa·s / m, the sound propagation path becomes shorter, and the sound absorption performance, especially in the low-frequency range, decreases. A more preferable air permeability resistance is 0.3 kPa·s / m or more. On the other hand, if the air permeability resistance is greater than 5 kPa·s / m, the sound absorption performance decreases. A more preferable air permeability resistance is 4 kPa·s / m or less. In this disclosure, the value of the air permeability resistance is adopted as the value measured by the air permeability tester "KES-F8" manufactured by Kato Tech Co., Ltd. Specifically, a disc-shaped sample with a diameter of 40 mm and a thickness of 10 mm is tested at a constant flow rate V [m³] at a piston speed of 0.2 cm / s. ３ / (m ２ The pressure difference ΔP [kPa] between the pressure of air passing through the passage and atmospheric pressure is measured, and the value R [kPa·s / m] calculated by the following equation (I) is defined as the airflow resistance. R = ΔP / V ... (I)

[0018] The air permeability resistance of polyurethane foam varies depending on its cell structure. The cell structure can be adjusted by changing the components and mixing ratios of the polyurethane foam raw materials (foamed polyurethane resin raw materials), or by crushing, which involves compressing the polyurethane foam using rolls or the like after foam molding.

[0019] [Asker C Hardness] The Asker C hardness of the polyurethane foam of the present disclosure is 45 or more. If it is less than 45, sufficient rigidity cannot be obtained. A more preferable Asker C hardness is 50 or more, and further 60 or more. On the other hand, if the Asker C hardness is too large, it becomes difficult to connect the cells and it becomes difficult to obtain a desired cell structure. Therefore, the Asker C hardness is desirably 70 or less. In the present disclosure, as the Asker C hardness, based on the spring hardness test type C defined in JIS K7312-1996, the peak value measured by the "Asker rubber hardness meter C type" manufactured by Kobunshi Keiki Co., Ltd. is adopted.

[0020] [Density] The density of the polyurethane foam of the present disclosure is preferably 90 kg / m ３ or more and 1600 kg / m ３ or less. If the density is less than 90 kg / m ３ , it becomes difficult to obtain the desired rigidity. A more preferable density is 100 kg / m ３ or more. On the other hand, if the density exceeds 1600 kg / m ３ , the air layer decreases and the sound absorption property deteriorates. A more preferable density is 1000 kg / m ３ or less, 500 kg / m ３ or less, 160 kg / m ３ or less. In the present disclosure, as the density, the value calculated by dividing the mass of the polyurethane foam to be measured by its volume is adopted.

[0021] [Normal Incidence Sound Absorption Coefficient] The normal incidence sound absorption coefficient of the polyurethane foam of the present disclosure is 0.30 or more at a frequency of 800 Hz and 0.50 or more at a frequency of 5000 Hz. In the present disclosure, as the normal incidence sound absorption coefficient, the value measured by the method described in JIS A1405-2:2007 using a disc-shaped sample with a diameter of 30 mm and a thickness of 10 mm is adopted. The normal incidence sound absorption coefficient only needs to be 0.30 or more and 0.50 or more at each of the frequencies of 800 Hz and 5000 Hz, but it is also desirable that it is 0.30 or more in the intermediate frequency range (800 Hz or more and 5000 Hz or less) and further in the high frequency range up to 6300 Hz exceeding 5000 Hz.

[0022] [Flame Retardancy] Components placed in the engine compartment of a vehicle are also required to be flame retardant. For this reason, it is desirable that the polyurethane foam of this disclosure has flame retardancy of, for example, UL94 V-2 level. Specifically, the following vertical combustion test of the UL94 standard is performed, and if all of the judgment criteria (1) to (5) are satisfied, it is judged to be V-2 level. Vertical combustion test: The lower end of a sample held vertically is exposed to the flame of a gas burner for 10 seconds. If combustion stops within 30 seconds, the flame is exposed for another 10 seconds. Judgment criteria: (1) The sample does not burn for more than 30 seconds in either of the two exposures. (2) The total burning time from two exposures for each of the five samples does not exceed 250 seconds. (3) No sample burns up to the position of the fixing clamp. (4) There is a dripping of burning particles that ignites cotton placed below the sample. (5) After the second exposure, the sample does not remain red-hot for more than 60 seconds.

[0023] <Method for Manufacturing Polyurethane Foam> The polyurethane foam of this disclosure may be manufactured by foaming and molding a foamed urethane resin raw material composed of an isocyanate component, a polyol component, a catalyst, a blowing agent, etc. Alternatively, the cell structure may be adjusted by crushing after foaming and molding.

[0024] The isocyanate component is not particularly limited as long as it forms a urethane bond through reaction with the polyol component. For example, it can be appropriately selected from tolylene diisocyanate (TDI), phenylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate (MDI), triphenylmethane triisocyanate, polymethylene polyphenyl isocyanate, naphthalene diisocyanate (NDI), and their derivatives. Examples of derivatives include prepolymers obtained by the reaction of isocyanate and polyol, modified polyisocyanates, and polymeric MDI (multinuclear) having three or more isocyanate groups and benzene rings in one molecule.

[0025] The polyol component can be appropriately selected from among polyhydric hydroxy compounds, polyether polyols, polyester polyols, polymer polyols, polyether polyamines, polyester polyamines, alkylene polyols, urea-dispersed polyols, melamine-modified polyols, polycarbonate polyols, acrylic polyols, polybutadiene polyols, phenol-modified polyols, and others.

[0026] Examples of catalysts include amine catalysts such as tetraethylenediamine, triethylenediamine, and dimethylethanolamine, as well as organometallic catalysts such as tin laurate and tin octanoate. Examples of blowing agents include water, methylene chloride, chlorofluorocarbons, and CO2. ２ Examples include gas.

[0027] The foamed urethane resin raw material may further contain foam stabilizers, plasticizers, crosslinking agents, chain extenders, flame retardants, antistatic agents, viscosity reducers, stabilizers, fillers, colorants, etc. Examples of foam stabilizers include silicone-based foam stabilizers. Examples of crosslinking agents include diethylene glycol, triethanolamine, and diethanolamine. Examples of flame retardants include expanded graphite, phosphorus-based, halogen-based, and metal hydroxide-based flame retardants.

[0028] The foamed urethane resin raw material is preferably prepared by adding the isocyanate component to a premixed polyol, which is made by pre-mixing components other than the isocyanate component with the polyol component. In this case, the premixed polyol and the isocyanate component may be mechanically stirred using a propeller or the like, or they may be mixed by discharging the premixed polyol and the isocyanate component separately at high pressure using a high-pressure injector or the like, causing the two components to collide. It is desirable that the premixed polyol and the isocyanate component be blended so that the isocyanate index (equivalents of isocyanate groups / equivalents of active hydrogen groups × 100) is between 100 and 150, preferably between 100 and 120.

[0029] Next, the present disclosure will be described in more detail with reference to examples.

[0030] <Manufacturing of Polyurethane Foam> [Example 1] First, 70 parts by mass of polyether polyol (AGC Inc.'s "Exenol® 837") and 30 parts by mass of polymer polyol (Sanyo Chemical Industries, Ltd.'s "Sannix® KC-900") were added to the mixture as polyol components, along with 1 part by mass of diethanolamine as a crosslinking agent, 3 parts by mass of water as a blowing agent, 0.3 parts by mass of amine catalyst A (EVONIK's "DABCO® 33LV"), and 0.1 parts by mass of amine catalyst B (MOMENTIVE's "Niax® Catalyst A-1"), and mixed to prepare a premix polyol. Next, the prepared premixed polyol and polymeric MDI (BASF INOAC Polyurethane Co., Ltd.'s "Luplanate® M20S") as an isocyanate component were mixed to achieve an isocyanate index of 100, thereby preparing a foamed urethane resin raw material.

[0031] Next, a wax-based water-based release agent was applied to the mold surface of the mold, which had been pre-adjusted to 58°C. The foamed polyurethane resin raw material was then injected into the mold cavity (a rectangular parallelepiped measuring 500 mm in length, 600 mm in width, and 10 mm in thickness), sealed, and foamed for 5 minutes. After that, the polyurethane foam (10 mm thick) was removed from the mold and crushed on both sides by passing it between a pair of rolls. The distance between the pair of rolls used was 1 mm, and the compression ratio of the polyurethane foam during crushing was 90%. In this way, the polyurethane foam of Example 1 was manufactured.

[0032] [Example 2] The polyurethane foam of Example 2 was manufactured in the same manner as in Example 1, except that the amount of water in the foaming agent was increased to 4 parts by mass, and a roll with a spacing of 5 mm was used during crushing to reduce the compression ratio of the polyurethane foam to 50%.

[0033] [Comparative Example 1] Comparative Example 1 polyurethane foam was manufactured in the same manner as in Example 1, except that crushing was not performed after foam molding.

[0034] [Comparative Example 2] As the polyurethane foam of Comparative Example 2, a polyurethane foam "Carmflex (registered trademark) UGR" manufactured by Inoac Corporation was prepared.

[0035] [Comparative Example 3] In the method for producing the polyurethane foam of Example 1, the polyurethane foam of Comparative Example 3 was produced in the same manner as in Example 1 except that the amount of water as the blowing agent was increased to 4 parts by mass.

[0036] [Comparative Example 4] In the method for producing the polyurethane foam of Example 1, the amount of water as the blowing agent was increased to 4 parts by mass, and the compression ratio of the polyurethane foam was set to 50% using a roll with a 5-mm interval during crushing. The polyurethane foam of Comparative Example 4 was produced in the same manner as in Example 1 except for this point. Also, in the production of the polyurethane foam of Comparative Example 4, the number of crushing times was increased and the continuous connection treatment was carried out carefully compared to when the polyurethane foam of Example 2 was produced.

[0037] <Evaluation of Polyurethane Foam> The average cell diameter, air permeability resistance, Asker C hardness, density, and normal incidence sound absorption rate of the produced polyurethane foam were measured, and the rigidity and sound absorption property were evaluated.

[0038] [Measurement Method] (1) Average Cell Diameter The cross-section in the thickness direction (10 mm in length, 50 mm in width) of the polyurethane foam was subjected to image analysis using a cell structure analyzer "PORE! SCAN" manufactured by Goldluecke to measure the average cell diameter.

[0039] (2) Air Permeability Resistance The air permeability resistance of the polyurethane foam was measured using an air permeability tester "KES-F8" manufactured by Kato Tech Co., Ltd. For the measurement, a disk-shaped sample with a diameter of 40 mm and a thickness of 10 mm cut out from the produced polyurethane foam was used, and air with a constant flow rate of 0.4 cc / (cm ２ ·s) (= 4×10 －３ m ３ / (m ２ ·s)) was passed through at a piston speed of 0.2 cm / s.

[0040] (3) The Asker C hardness of the Asker C hardness polyurethane foam was measured using the "Asker Rubber Hardness Tester Type C" manufactured by Polymer Instruments Co., Ltd., and the peak value was read.

[0041] (4) Density: The density of the polyurethane foam was calculated by dividing its mass by its volume.

[0042] (5) Normal incidence sound absorption coefficient Using a disc-shaped sample with a diameter of 30 mm and a thickness of 10 mm cut from the manufactured polyurethane foam, the normal incidence sound absorption coefficient was measured according to the method described in JIS A1405-2:2007. A normal incidence sound absorption coefficient of 0.30 or higher at a frequency of 800 Hz was evaluated as good sound absorption (indicated by ○ in Table 1), and a value less than 0.30 was evaluated as poor sound absorption (indicated by × in the same table). Similarly, a normal incidence sound absorption coefficient of 0.50 or higher at a frequency of 5000 Hz was evaluated as good sound absorption (indicated by ○ in Table 1), and a value less than 0.50 was evaluated as poor sound absorption (indicated by × in the same table).

[0043] [Measurement Results] Table 1 shows the measurement results of the physical properties and characteristics of the polyurethane foams of the examples and comparative examples. Figure 1 shows a graph of the normal incidence sound absorption coefficient of each polyurethane foam against frequency. In Figure 1, the points with a sound absorption coefficient of 0.30 at 800 Hz and the points with a sound absorption coefficient of 0.50 at 5000 Hz are indicated by black circles.

[0044] As shown in Table 1, the polyurethane foams of Examples 1 and 2 satisfied the conditions of an average cell diameter of 50 μm to 200 μm and an air permeability resistance of 0.2 kPa·s / m to 5 kPa·s / m, and also had an Asker C hardness of 45 or higher, thus possessing the desired rigidity. Furthermore, the density was 90 kg / m³. ３ More than 1600kg / m ３The results were as follows: In the polyurethane foam of Example 1, the normal incidence sound absorption coefficient at a frequency of 800 Hz was 0.32 and at a frequency of 5000 Hz was 0.52. In the polyurethane foam of Example 2, the normal incidence sound absorption coefficient at a frequency of 800 Hz was 0.31 and at a frequency of 5000 Hz was 0.52. In both cases, it was confirmed that the foams had high sound absorption properties in both the low-frequency and high-frequency ranges. Furthermore, as shown in Figure 1, the normal incidence sound absorption coefficient was 0.30 or higher throughout the entire range from 800 Hz to 5000 Hz.

[0045] In contrast, the polyurethane foam of Comparative Example 1 had excessively high airflow resistance, resulting in an overflow of 25 kPa·s / m or more. The normal incidence sound absorption coefficient was low at both 800 Hz and 5000 Hz, indicating poor sound absorption. The polyurethane foam of Comparative Example 2 had excessively low airflow resistance, resulting in 0 kPa·s / m. It was too soft, resulting in an Asker C hardness of 0. The normal incidence sound absorption coefficient was 0.50 or higher at 5000 Hz, but less than 0.30 at 800 Hz, indicating poor sound absorption in the low-frequency range. The polyurethane foam of Comparative Example 3 had airflow resistance less than 0.2 kPa·s / m. The normal incidence sound absorption coefficient was 0.50 or higher at 5000 Hz, but less than 0.30 at 800 Hz, indicating poor sound absorption in the low-frequency range. In the polyurethane foam of Comparative Example 4, the airflow resistance was greater than 5 kPa·s / m, and the normal incidence sound absorption coefficient was low at both 800 Hz and 5000 Hz, indicating poor sound absorption.

[0046] The soundproofing material for vehicles disclosed herein is suitable for use as an eAxle (electric drive module integrating motor, transaxle, and inverter) cover, engine cover, timing chain cover, side cover, oil pan cover, inverter cover, compressor cover, dash insulator, floor insulator, rear package tray, wheelhouse liner, and under cover, as well as for use as a soundproofing material placed around the transmission and other components.

Claims

1. A soundproofing material for vehicles comprising polyurethane foam, wherein the average cell diameter of the polyurethane foam is 50 μm or more and 200 μm or less, the air permeability resistance is 0.2 kPa·s / m or more and 5 kPa·s / m or less, the Asker C hardness is 45 or more, and when the normal incidence sound absorption coefficient of the polyurethane foam is measured using a disc-shaped sample with a diameter of 30 mm and a thickness of 10 mm, the sound absorption coefficient at a frequency of 800 Hz is 0.30 or more, and the sound absorption coefficient at a frequency of 5000 Hz is 0.50 or more.

2. The density of the polyurethane foam is 90 kg / m³. ３ More than 1600kg / m ３ The soundproofing material for vehicles according to claim 1, which is as follows:

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