JP7259076B2 - sound absorbing material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sound absorbing material that absorbs noise and the like as a sound insulating material used in vehicles such as automobiles, and more particularly to a sound absorbing material that has excellent sound absorption characteristics in the medium and high frequency range of 1000 to 6000 Hz. be.

2. Description of the Related Art In recent years, noise countermeasures have been emphasized along with weight reduction of vehicles for low fuel consumption. In addition, due to the demand for higher grade, higher performance and comfort of automobiles, improvement of quietness in the vehicle interior is desired. Furthermore, regulations on vehicle exterior noise are becoming stricter, and there is an increasing demand for reduction of vehicle exterior noise emitted from vehicles to nearby residents. Against this background, there is an urgent need for measures to reduce noise in automobiles.
Conventionally, as a measure to reduce the noise phenomenon of automobiles, for example, in order to suppress the leakage of noise generated from the engine, etc., sheet-like materials made of fiber materials such as glass wool and felt or soft urethane foam are used in dash panels and the like A porous sound absorbing material is attached.

In porous sound absorbing materials made of fiber materials such as glass wool and felt and soft urethane foam, for example, if the thickness is as thin as about 10 mm, the sound absorption coefficient in the high frequency range above 4000 Hz is high, but it is lower than that. The sound absorption coefficient in the frequency range was low. By increasing the thickness, creating a multi-layered structure, or providing a back air layer (i.e., by interposing an air layer between the sound absorbing material and the installation surface), the sound absorption coefficient below the middle frequency range is increased. However, due to the bulkiness, the installation space is increased and the weight is increased, which limits the range of application and installation.

For this reason, conventional porous sound absorbing materials made of fiber materials such as glass wool, felt, or soft urethane foam are insufficient to absorb noise over a wide frequency range emitted from automobiles. In particular, in automobiles, the center noise of outside sounds such as engine noise and road noise, the center noise of inside sounds, and the noise during acceleration and transmission fluctuations are outside the high frequency range. Since it is high in the high frequency range (2000 to 6000 Hz), there is a strong demand for a sound absorbing material that exhibits high sound absorption characteristics even in the medium frequency range.

Here, in Patent Literature 1, a structure of a base material resin that forms open cells and expanded organic hollow particles that are dispersed in the base material resin and form independent cells is thin and lightweight, and has high sound absorption in a wide frequency range. It discloses a sound absorbing material that has excellent sound insulation properties. According to the description of Patent Document 1, in Examples, a base material resin forming open cells and expanded organic hollow particles dispersed in the base material resin and forming closed cells and having an average particle size of 0.1 to 3000 μm In the measurement of the normal incident sound absorption coefficient of a test piece in which a 1 mm thick foam film made of (1 mm thick) is adhered to a 10 mm thick nonwoven fabric, the sound absorption coefficient in the frequency range of 2000 to 4000 Hz is 81 to 92%.

JP 2010-2617 A

However, in Patent Document 1, the sound absorption coefficient was measured using a test piece in which a foam film as a sound absorbing material was combined with a non-woven fabric.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a sound absorbing material that has high sound absorbing properties in a wide frequency range from the middle frequency range to the high frequency range even if the thickness is thin.

According to the first aspect of the present invention, there is provided a sound absorbing material having closed cells, which is formed by applying a compressive force to a foam made of resin, elastomer or rubber, which is a mixture of the closed cells and the closed cells which are communicated by the compression. It has a structure.

Here, the foam having closed cells is not limited to those having only closed cells, and may include continuous cells connected by the growth of cells during the foaming process, including closed cells and open cells. In this case, preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more of all cells are closed cells.

Further, the application of the compressive force means that an external force and a pressing force are applied in the thickness direction of the foam made of resin, elastomer or rubber, that is, in the direction perpendicular to the front and back surfaces of the foam. It does not mean that the compressed state is fixed even if the thickness is reduced and is compressed and deformed, and it does not mean that the compressed state is fixed, but it specifies that a compressive load that allows the cells to communicate is applied. The method of applying the compressive force is not particularly limited as long as the bubbles can be communicated. For example, the bubbles can be communicated by mechanical stress such as pressing with a flat plate or a roll. Such communication of air bubbles by mechanical stress enables communication of air bubbles of 100 μm or more, for example. Also, a compressive force may be applied by air pressurization, vacuum suction, or the like. That is, the compressive force is not limited to the load applied by a flat plate press, roll press, or the like, but is a concept of an external force or pressing force in a broad sense, including the load caused by pressurization or pressure reduction, such as air pressurization or vacuum evacuation.

Examples of resins for foams made of the above resins, elastomers or rubbers include thermosetting resins such as silicone resins, epoxy resins, urethane resins, acrylic resins and phenol resins, and thermoplastic resins such as polyethylene resins, polypropylene resins and vinyl chloride resins. A thermoplastic elastomer or the like can be used as the elastomer, and silicone rubber, chloroprene rubber, styrene-butadiene rubber, nitrile-butadiene rubber, ethylene-propylene diene rubber, acrylic rubber, fluororubber, or the like can be used as the rubber. .

And having the bubbles and the closed cells communicated by the compression means that the cells are communicated with each other by breaking the cell wall, the skeleton, and the cell membrane between adjacent cells by applying the compressive force. Bubbles and closed bubbles that did not communicate with adjacent bubbles even when the compressive force was applied, that is, independent bubbles that existed independently before the application of the compressive force are mixed and coexist. This means that some of the air bubbles that existed before the compression are made to communicate by applying the compressive force. When a compressive force is applied to a foam containing closed cells and open cells, the cells that are communicated by compression include communication between open cells, communication between closed cells, or communication between closed cells and open cells. Any form of communication functions as a bubble that improves the sound absorption characteristics in the middle frequency range.

The sound absorbing material of the invention of claim 1 has closed cells and communicating cells, and has a specific gravity of 0.08 or more and 0.4 or less, preferably 0.09 or more and 0.3 or less, more preferably It is in the range of 0.1 or more and 0.25 or less, and the compressive stress at 25% compression is preferably 2 kPa or more and 4.8 kPa or less, more preferably 2.2 kPa or more and 4.7 kPa or less, and further Preferably, it is made of a resin, elastomer or rubber foam having a pressure within the range of 2.5 kPa or more and 4.6 kPa or less.
Here, the compressive stress (kPa) at the time of 25% compression is obtained by using a compression tester to compress a test piece cut into a size of 20 mm square and 10 mm thick with a flat plate (φ15) at a compression speed of 10 mm / min. Measure the stress (N) when compressing 25% (2.5 mm), that is, compressing to 75% thickness (7.5 mm thickness) with respect to the initial thickness, and the stress (N) is a unit It is obtained by converting per area (cm ² ).

Examples of resins for foams made of the above resins, elastomers or rubbers include thermosetting resins such as silicone resins, epoxy resins, urethane resins, acrylic resins and phenol resins, and thermoplastic resins such as polyethylene resins, polypropylene resins and vinyl chloride resins. A thermoplastic elastomer or the like can be used as the elastomer, and silicone rubber, chloroprene rubber, styrene-butadiene rubber, nitrile-butadiene rubber, ethylene-propylene diene rubber, acrylic rubber, fluororubber, or the like can be used as the rubber. .

The sound absorbing material of claim 2 has a compressive stress of 2 kPa or more and 30 kPa or less when compressed by 25%, preferably 3 kPa or more and 25 kPa or less, more preferably 4 kPa or more and 20 kPa or less. The compressive force is applied to the foam inside.
Here, the compressive stress (kPa) at the time of 25% compression is obtained by using a compression tester to compress a test piece cut into a size of 20 mm square and 10 mm thick with a flat plate (φ15) at a compression speed of 10 mm / min. Measure the stress (N) when compressing 25% (2.5 mm), that is, compressing to 75% thickness (7.5 mm thickness) with respect to the initial thickness, and the stress (N) is a unit It is obtained by converting per area (cm ² ).

The compressive force of the sound absorbing material of the invention of claim 3 is preferably 50% or more and 95% or less, more preferably 70% or more and 95% or less, still more preferably , 80% or more and 95% or less.
The compression rate of 50% to 95% means that the thickness (apparent thickness) before applying the compressive force is compressed by 50% to 95%, that is, the thickness before applying the compressive force is 5% to 50%. This means that a compressive force is applied until

The foam of the sound absorbing material according to the invention of claim 4 is formed by foaming and curing a two-component addition reaction curing silicone material, and the two component addition reaction curing silicone material is applied to an object to be coated. After that, the silicone material reacts, foams, and hardens at room temperature or by heat treatment.

A sound absorbing material according to the invention of claim 5 is a sound absorbing material made of resin, elastomer or rubber foam, and has closed cells and interconnected cells. : Scanning Electron Microscope). It consists mainly of air bubbles.
The bubbles having wrinkles or curled parts around the opening, or having an opening shape with corners or cusps, are obtained by scanning electron microscope (SEM) observation. In the image (300x to 2000x), the periphery of the aperture (hole) has double or several layers of streaks, the edge of the periphery of the aperture is curled up, or the aperture shape has a dent. It may have a corner or a pointed head. In particular, the present inventors used a scanning electron microscope ( SEM observation also confirmed that a plurality of fine pores were formed. In addition, the wrinkles or curled portions around the opening of the bubble, and the shape of the opening with corners or cusps, are mainly caused by buckling deformation of the bubble to which a compressive force is applied or by breaking of the bubble wall. It is speculated that
In addition, the bubbles mainly having wrinkles or curled portions around the opening, or having an opening shape with corners or pointed portions are 50% or more, preferably 60% or more, of all the cells. , more preferably 70% or more, is occupied by bubbles having wrinkles or curled portions around the opening, or having an opening shape with corners or cusps. Other than that, they are circular bubbles whose opening shape is generally round as a whole.

The foam of the sound absorbing material of the invention of claim 6 is made of silicone.
The above-mentioned silicone is a polymer having a main chain (inorganic) composed of a siloxane bond composed of silicon and oxygen, and an acid group mainly composed of a methyl group is bonded to the silicon, and is an elastomer having rubber elasticity at room temperature. Or a general term for silicone resins.

In the foam of the sound absorbing material of the invention of claim 7 , the average cell diameter of the closed cells and the continuous cells is preferably 100 μm or more and 2000 μm or less, more preferably 150 μm or more and 1800 μm or less, and further preferably, It is in the range of 200 µm or more and 1500 µm or less, and the average thickness of the cell walls is preferably 0.5 µm or more and 40 µm or less, more preferably 0.6 µm or more and 35 µm or less, and still more preferably 0.7 µm or more. , 30 μm or less.

Here, the average cell diameter of the air bubbles is obtained by observing the cross section of the sound absorbing material with a microscope (100 to 200 times), and measuring the surface layer side and the inner side (for example, in the case of a sound absorbing material with a thickness of 10 mm, Measure the cell diameter (corresponding to the diameter) of 20 arbitrary bubbles from the surface at a depth of about 2 mm and at a depth of about 5 mm), and calculate the average. is. In the case of closed cells, the maximum diameter (maximum width) of the single cell is measured, and in the case of continuous cells, the maximum diameter (maximum width) of the cell unit is measured by considering the communication of the cell unit. Measured.
The average thickness of the bubble wall is also determined by observing the cross section of the sound absorbing material with a microscope (100x to 200x), and measuring the plateau boundary between adjacent bubbles at any 20 locations (however, the plateau boundary where 3 or more bubbles are adjacent) ) are measured and the average is calculated.

The foam of the sound absorbing material of the invention of claim 8 has a normal incident sound absorption coefficient of 0.45 or more in the frequency range of 1250 Hz to 4000 Hz when measured at a thickness of 10 mm, and the frequency range of 1250 Hz to 4000 Hz. has a maximum sound absorption coefficient of 0.5 or more, more preferably 0.85 or more, and exhibits high sound absorption characteristics at frequencies easily audible to the human ear.
The normal incident sound absorption coefficient was measured according to JIS A 1405-2.

According to the sound absorbing material according to the first aspect of the invention, a foam having closed cells is provided with a compressive force, so that it has a cell structure in which interconnected cells and the closed cells are mixed.
The inventors of the present invention have conducted intensive experimental research to obtain a sound absorbing material that exhibits a high sound absorption coefficient even for sounds in the medium frequency range, to which the human ear is highly sensitive. It was found that the sound absorption coefficient in the mid-frequency range is improved by imparting and communicating the air bubbles, and by forming a cell structure of air bubbles and closed cells that are communicated by compression, and based on this knowledge, the present invention was completed. It is what I let you do.

That is, by having a hybrid cell structure of cells that are communicated by compression and independent cells, friction with cell walls, skeleton and cell membranes in cells that are communicated by compression, sound absorption effect due to viscosity and airflow resistance, resin, rubber Alternatively, the vibration of the base material made of elastomer, the sound absorption effect due to resonance, the resonance of air bubbles, especially the sound absorption effect due to film vibration and resonance in air bubbles that are communicated by compression, etc., can improve the sound absorption characteristics in the medium frequency range. A high sound absorbing property can be obtained in a wide frequency range from high frequencies to high frequencies. Furthermore, even if the sound absorption coefficient is increased, the sound insulation coefficient is high because of the cell structure of the cells that are communicated by compression and the closed cells, and the sound absorption coefficient and the sound insulation coefficient are compatible. Therefore, it is possible to effectively prevent the diffusion of noise.

According to the sound absorbing material according to the invention of claim 1 , it has communicating cells and closed cells, has a specific gravity within the range of 0.08 to 0.4, and has a compressive stress of 2 to 4.8 kPa when compressed by 25%. is within the range of
The inventors of the present invention have conducted intensive experimental research to obtain a sound absorbing material that exhibits a high sound absorption coefficient even for sounds in the medium frequency range, to which the human ear is highly sensitive. It is applied to make the bubbles communicate, and has a mixed cell structure of communicated cells and closed cells, and has a specific gravity within the range of 0.08 to 0.4, and a compressive stress when compressed by 25% is 2 to 2. It was found that the sound absorption coefficient in the middle frequency range was improved when the pressure was within the range of 4.8 kPa, and the present invention was completed based on this finding.

That is, it has a mixed cell structure of communicating cells and closed cells, and has a specific gravity within the range of 0.08 to 0.4 and a compressive stress within the range of 2 to 4.8 kPa when compressed by 25%. contains cells that are communicated by compression, friction with cell walls, skeleton and cell membranes in cells that are communicated by compression, sound absorption effect due to viscosity and airflow resistance, base material film made of resin, rubber or elastomer Sound absorption effect due to vibration and resonance, resonance of air bubbles, especially membrane vibration in bubbles communicated by compression, sound absorption effect due to resonance, etc., can enhance sound absorption characteristics in the middle frequency range, and a wide range of frequencies from middle to high frequencies. High sound absorption characteristics are obtained in the range. Furthermore, even if the sound absorption coefficient is increased, the sound insulation coefficient is high because of the cell structure of the cells that are communicated by compression and the closed cells, and the sound absorption coefficient and the sound insulation coefficient are compatible. Therefore, noise diffusion can be effectively prevented.

According to the sound absorbing material according to the invention of claim 2, the compressive force is applied to the foam having a compressive stress in the range of 2 to 30 kPa when compressed by 25%. In addition to the effect of (1), the communication rate of air bubbles can be increased to increase the sound absorption coefficient in the middle frequency range.

According to the sound absorbing material according to the invention of claim 3, since the foam is pressed so that the compression rate is 50 to 95%, in addition to the effects of claim 1 or claim 2, The sound absorption coefficient in the middle frequency range can be further increased.

According to the sound absorbing material according to the invention of claim 4, the foam is formed by foaming and curing a two-liquid addition reaction curing type silicone material. In addition to the effect described in 1., automatic application is possible and the work of construction can be simplified.

According to the sound absorbing material of the invention of claim 5 , the sound absorbing material is made of foamed material of resin, elastomer or rubber, and has independent cells and interconnected cells, and the cells on the surface of the sound absorbing material are examined with a scanning electron microscope. When observed with a SEM (Scanning Electron Microscope), the bubbles are mainly air bubbles that have wrinkles or curled portions around the opening, or have an opening shape with corners or cusps.
The inventors of the present invention have conducted intensive experimental research to obtain a sound absorbing material that exhibits a high sound absorption coefficient even for sounds in the medium frequency range, to which the human ear is highly sensitive. When the bubbles on the surface of the sound absorbing material are observed with a scanning electron microscope (SEM) in a mixed bubble structure of connected and closed cells, openings are observed. It was found that the sound absorption coefficient in the mid-frequency range is improved when the air bubbles mainly have wrinkled parts or curled parts around them, or have an opening shape with corners or pointed parts. The present invention has been completed based on.

That is, it has a hybrid cell structure of communicating cells and closed cells, and when the cells on the surface of the sound absorbing material are observed with a scanning electron microscope (SEM), wrinkles or curls are formed around the opening. or having an open shape with corners or cusps. Friction with the bubble membrane, sound absorption effect due to viscosity and airflow resistance, membrane vibration of the base material made of resin, rubber or elastomer, sound absorption effect due to resonance, resonance of bubbles, especially membrane vibration in bubbles communicated by compression, Due to the sound absorption effect due to resonance, etc., the sound absorption characteristics in the middle frequency range can be enhanced, and high sound absorption characteristics can be obtained in a wide frequency range from the middle frequency to the high frequency. Furthermore, even if the sound absorption coefficient is increased, the sound insulation coefficient is high because of the cell structure of the cells that are communicated by compression and the closed cells, and the sound absorption coefficient and the sound insulation coefficient are compatible. Therefore, noise diffusion can be effectively prevented.

According to the sound absorbing material according to the invention of claim 6 , since it is made of silicone foam, in addition to the effects described in any one of claims 1 to 5 , it has high heat resistance and a high heat source. A high sound absorption effect can be obtained even when construction is performed around Furthermore, the sound absorption coefficient in the middle frequency range is excellent, and the maximum sound absorption coefficient can be increased.

According to the sound absorbing material according to the invention of claim 7 , the average cell diameter of the closed cells and the communicating cells is in the range of 100 to 2000 μm, and the average thickness of the cell walls is in the range of 0.5 to 40 μm. Therefore, it has an appropriate bubble ratio and specific gravity. Therefore, in addition to the effect described in any one of claims 1 to 6 , the sound absorption property and sound insulation property are excellent, and the noise prevention effect can be improved.

According to the sound absorbing material according to the invention of claim 8 , the normal incident sound absorption coefficient in the frequency range of 1250 Hz to 4000 Hz measured at a thickness of 10 mm is 0.45 or more, and in the frequency range of 1250 Hz to 4000 Hz Since the maximum sound absorption coefficient is 0.5 or more, it has high sound absorption characteristics in a frequency band that is easy for humans to hear. Also, it is effective in suppressing diffusion of noise to the surroundings.

FIG. 1 is a CT (computed tomography) image of a cross section of a sound absorbing material of Example 1 according to an embodiment of the present invention. FIG. 2(a) is a microscope image (×100) of a cross section of the sound absorbing material of Example 1 according to the embodiment of the present invention, and FIG. It is a microscope image (×200) of the cross section of the sound absorbing material of Example 1, and FIG. 2C is a microscope image (×100) of the surface of the sound absorbing material of Example 1 according to the embodiment of the present invention. be. FIG. 3 is a microscope image (×100) of the surface of the sound absorbing material of Example 2 according to the embodiment of the present invention. FIG. 4 is a microscope image (×100) of the surface of the sound absorbing material of Example 4 according to the embodiment of the present invention. FIG. 5(a) is a microscope image (×100) of a cross section of the sound absorbing material of Example 5 according to the embodiment of the present invention, and FIG. It is a microscope image (×200) of the cross section of the sound absorbing material of Example 5, and FIG. 5C is a microscope image (×100) of the surface of the sound absorbing material of Example 5 according to the embodiment of the present invention. be. 6(a) is a cross-sectional microscope image (×100) of the silicone foam of Comparative Example 1, and FIG. 6(b) is a cross-sectional microscope image (×200) of the silicone foam of Comparative Example 1. ), and FIG. 6C is a microscope image (×100) of the surface of the silicone foam of Comparative Example 1. 7A is a cross-sectional microscope image (×100) of the silicone foam of Comparative Example 2, and FIG. 7B is a cross-sectional microscope image of the silicone foam of Comparative Example 2 (×200). ), and FIG. 7C is a microscope image (×100) of the surface of the silicone foam of Comparative Example 2. FIG. 8(a) is a microscope image (×100) of the cross section of the EPDM foam of Comparative Example 3, and FIG. 8(b) is a microscope image (×200) of the cross section of the EPDM foam of Comparative Example 3. ), and FIG. 8C is a microscope image (×100) of the surface of the EPDM foam of Comparative Example 3. 9(a) is a cross-sectional microscope image (×100) of the EPDM foam of Comparative Example 4, and FIG. 9(b) is a cross-sectional microscope image (×200) of the EPDM foam of Comparative Example 4. ), and FIG. 9C is a microscope image (×100) of the surface of the EPDM foam of Comparative Example 4. 10 is a microscope image (×100) of a cross section of the melamine foam of Comparative Example 5. FIG. FIG. 11 is a graph showing the measurement results of the normal incident sound absorption coefficients of the sound absorbing materials of Examples 1 to 5 according to the embodiment of the present invention in comparison with Comparative Examples 1 to 6. FIG. FIG. 12 is a graph showing the measurement results of the transmission loss of the sound absorbing material of Example 1 according to the embodiment of the present invention in comparison with Comparative Example 6. FIG. FIG. 13 is a cross-sectional explanatory view of foaming and curing the silicone material in the mold. FIG. 14 is a graph showing the frequency characteristics of the normal incidence sound absorption coefficient of the sound absorbing material when changing the thickness (wet film thickness) of the silicone material foam-hardened in the mold. FIG. 15 is an SEM image (×100) of the surface of a closed-cell silicone foam (corresponding to Comparative Example 1) observed with a scanning electron microscope. FIG. 16 is an SEM image (×400 to 500) of the closed-cell silicone foam (corresponding to Comparative Example 1) when each bubble in the SEM image shown in FIG. 15 is further enlarged and observed with a scanning electron microscope. ). FIG. 17 is an SEM image (×500) of the closed-cell silicone foam (corresponding to Comparative Example 1) when each cell in the SEM image shown in FIG. 15 is further enlarged and observed with a scanning electron microscope. be. FIG. 18 is an SEM image (×500 to 600) of the closed-cell silicone foam (corresponding to Comparative Example 1) when each bubble in the SEM image shown in FIG. 15 is further enlarged and observed with a scanning electron microscope. ). FIG. 19 is an SEM image (×800 to 1000) of the closed-cell silicone foam (corresponding to Comparative Example 1) when each bubble in the SEM image shown in FIG. 15 is further enlarged and observed with a scanning electron microscope. ). FIG. 20 is an SEM image (×1000) of a closed-cell silicone foam (corresponding to Comparative Example 1) when each cell in the SEM image shown in FIG. 15 is further enlarged and observed with a scanning electron microscope. be. FIG. 21 shows the surface of a sound absorbing material according to an embodiment of the present invention (corresponding to Examples 1 to 4) obtained by applying a compressive force to a closed-cell silicone foam with a scanning electron microscope. It is an SEM image (×100) when observed. FIG. 22 shows the SEM image shown in FIG. 21 of the sound absorbing material according to the embodiment of the present invention (equivalent to Examples 1 to 4) obtained by applying a compressive force to a closed-cell silicone foam. 1 is an SEM image (×300) of each bubble observed with a scanning electron microscope at an enlarged scale. FIG. 23 shows the SEM image shown in FIG. 21 of the sound absorbing material according to the embodiment of the present invention (equivalent to Examples 1 to 4) obtained by applying a compressive force to a closed-cell silicone foam. 1 is an SEM image (×400) of each bubble observed with a scanning electron microscope at an enlarged scale. FIG. 24 shows the SEM image shown in FIG. 21 of the sound absorbing material according to the embodiment of the present invention (corresponding to Examples 1 to 4) obtained by applying a compressive force to a closed-cell silicone foam. 1 is an SEM image (×500 to 600) of each bubble observed with a scanning electron microscope at an enlarged scale. FIG. 25 shows the SEM image shown in FIG. 21 of the sound absorbing material according to the embodiment of the present invention (corresponding to Examples 1 to 4) obtained by applying a compressive force to a closed-cell silicone foam. 1 is an SEM image (×600 to 800) of each bubble observed with a scanning electron microscope at an enlarged scale. FIG. 26 shows the SEM image shown in FIG. 21 of the sound absorbing material according to the embodiment of the present invention (corresponding to Examples 1 to 4) obtained by applying a compressive force to a closed-cell silicone foam. 1 is an SEM image (×800 to 1200) of each bubble observed with a scanning electron microscope at an enlarged scale. FIG. 27(a) is an SEM image (×15) of a closed-cell silicone foam (corresponding to Comparative Example 1) when its internal cross section was observed with a scanning electron microscope, and FIG. 27(b). is an SEM image (×50) of a closed-cell silicone foam (corresponding to Comparative Example 1) observed with a scanning electron microscope; FIG. 1 is a SEM image (×100) of the silicone foam (corresponding to Comparative Example 1) observed with a scanning electron microscope. FIG. 28(a) shows a scanning internal cross-section of a sound absorbing material according to an embodiment of the present invention (equivalent to Examples 1 to 4) obtained by applying compressive force to a closed-cell silicone foam. It is an SEM image (x 15) when observed with a type electron microscope, and FIG. Corresponding to Examples 1 to 4) is an SEM image (×50) when the internal cross section was observed with a scanning electron microscope, and FIG. SEM images (×100 ).

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The sound absorbing material according to the embodiment of the present invention is made of a resin, elastomer or rubber foam having a mixed cell structure of open cells and closed cells. It is made to communicate by applying a compressive force.
In the present embodiment, by applying a compressive force at room temperature to a foam containing closed cells by mechanical stress such as flat press or roll press, for example, cells with a cell diameter of 100 μm or more are made to communicate. , the sound absorbing material is made of resin, elastomer or rubber foam having cells that are communicated by the compression and closed cells that are not communicated by the compression.

By applying a compressive force to the foam containing closed cells made of resin, elastomer, or rubber, the cells are made to communicate with each other, and a mixed cell structure of the cells connected by compression and the closed cells is formed. When the sound absorption coefficient of the sound absorbing material is measured, the sound absorption coefficient increases in a wide range of frequencies compared to before applying the compressive force. It showed high sound absorption characteristics in a wide frequency range from the middle frequency range to the high frequency range.

By applying a compression force to the foam having such closed cells, the cells are communicated with each other, and the reason why the sound absorption coefficient in the mid-frequency range is high in the sound absorbing material having the closed cells and the cells that are communicated by compression. is not necessarily clear, but the following can be considered.
That is, due to the presence of communicating bubbles, that is, due to the porous structure, when the sound propagated moves through the communicating bubbles, friction and viscous resistance are generated against the peripheral walls of the bubbles, and the air in the bubbles In addition to attenuating the sound due to the vibration of the base material (resin, elastomer or rubber), the communication bubbles in which the bubbles are communicated by applying a compressive force are, for example, the CT image in FIG. As shown in the microscope image of (b), a thin bubble film 1 having a thickness of, for example, 1 to 20 μm is likely to be formed on both sides of the communicating hole 2 at the interface between communicating bubbles. Sound is attenuated by vibration, resonance, and interference within the communicating bubbles having the bubble film 1, and the presence of the bubble film 1 causes friction and viscous resistance when the sound moves through the communicating bubbles. Furthermore, it is conceivable that sound attenuation occurs due to an increase in airflow resistance or a change in airflow resistance.

In particular, in a foam having closed cells in which a compressive force is applied to make the cells communicate, the solidified polymer phase of the base material existing between adjacent cells is physically stretched by the compressive force. Since the cells are connected by being broken, that is, the cell walls, skeleton, and cell membrane of the hard polymer phase in which the polymer molecular chains are entangled are broken, and the cells are made to communicate with each other. It is presumed that, unlike continuous cells formed by collisions between cells as the cells grow during the process, a thin cell membrane 1 of the polymer phase is likely to be formed at the interface between cells that are communicated by compression. That is, in the present embodiment, when a predetermined compressive load is applied in the thickness direction to a foam having closed cells, the cells approach, contact and collide with each other due to the application of the compressive force, and the contact interface The walls of the cells, i.e., the solidified polymer phase are stretched and gradually become thinner, and finally the walls are broken to form the communication holes 2 and the cells are communicated with each other. Unlike open cells, which are formed by the growth of air bubbles within the polymer material, the solidified polymer phase is stretched and broken. For this reason, a thin bubble film 1 of the polymer phase is likely to be formed at the interface between the bubbles communicating with each other due to the breakage of the solidified polymer phase. It can be assumed that a damping effect is obtained.

In addition, the plasticity of the base material resin, elastomer or rubber, the resonance caused by the elastic body, the membrane vibration, the sound absorption effect due to elastic loss, and the air due to the coexistence of both closed cells and open cells of different sizes There is also a sound absorption effect due to changes in the flow resistance of air bubbles and spatial resonance in air bubbles.

Therefore, due to the interaction of these, that is, by a plurality of sound absorbing mechanisms that absorb sound at different frequencies, it is possible to absorb sound in a wide frequency range from the middle frequency range to the high frequency range. It is thought that high sound absorption characteristics were obtained even in the medium frequency range of 1000 Hz to 4000 Hz due to film vibration and resonance caused by the formation of the bubble film 1 at the interface between communicating bubbles.

Here, in the sound absorbing material of the present embodiment, by applying a compressive force to a foam made of resin, elastomer or rubber having closed cells, the cells are made to communicate, and the connected cells and the closed cells are mixed. Although it has a cellular structure, resins such as silicone, polyethylene, polypropylene, polyvinyl chloride, polyvinyl acetate, vinyl acetate copolymer, (meth)acrylic copolymer, styrene-acrylic copolymer, Olefin polymers such as ethylene propylene copolymers, polyvinyl fluoride, polyisoprene, polystyrene, styrene polymers, phenol, urea, melamine, polyester, polyurethane, polyamide, polyimide, polyetherimide, polyamideimide, polycarbonate, polyphenylene Sulfide, polyurea, etc. can be used, and elastomers such as thermoplastic elastomers and soft urethanes can be used. Isopropylene rubber, natural rubber, etc. can be used.

By foaming a composition containing a resin material, an elastomer material, or a rubber material, a foam made of resin, elastomer, or rubber can be obtained. For example, organic foaming agents such as ADCA, OBSH, and DBT, chemical foaming agents such as bicarbonates and inorganic foaming agents such as carbonates, foaming by microcapsules, self-foaming by gas generated by reaction of predetermined multiple components, and super foaming. There is physical foaming due to criticality, mechanical foaming, etc.

Preferably, it is a resin or rubber foam obtained by foaming a foamable composition containing a synthetic resin or rubber as a main component and containing a chemical foaming agent or a component that generates gas when mixed.
According to the foam formed by foaming with a chemical foaming agent (chemical foaming) or foaming (self-foaming) in which gas is generated by the reaction of components, the skin layer does not become thick, unlike mechanical foaming such as foam molding. Since it is not formed, even when compressive force is applied by a press or the like, which will be described later, the increase in internal pressure is small. Therefore, it is possible to increase the communication of the air bubbles and enhance the effect of improving the sound absorbing property without causing breakage, cracking, breakage, breakage, or the like.

For example, a liquid urethane resin using isocyanate as a urethane resin, a liquid rubber such as ethylene propylene diene rubber, a liquid resin such as a liquid silicone resin, or a liquid rubber is used, and a foaming agent is added thereto, or a self-foaming component is added. If it is a liquid resin composition or a liquid rubber composition, which is blended and optionally blended with an additive such as a surfactant or a filler such as calcium carbonate and mixed, it can be applied to a desired part of a vehicle body such as an automobile ( For example, a wheel house, a dash panel, a floor panel, etc.) can be mechanically coated (automatic coating) by a coating robot or the like, and by curing and foaming after coating, manual labor for pasting to the desired site is required. The foam can be formed without any need, and the foam can be applied efficiently in a short time by automated coating.

That is, after applying a liquid resin or rubber composition as a paint or the like to an object to be coated, it is foamed and cured at room temperature or by heat treatment or heat generated by reaction of materials (reaction heat), or at room temperature or heat treatment. It is preferred that the material reacts with the foam and cures to form a resin or rubber foam. In this way, in the method of forming a foam from a coating type composition, there is no need to form a shape in advance, the shape can be adapted to the shape of the object to be coated, and the shape to be applied is less likely to be restricted. And it becomes suitable not only for the inside of the vehicle body but also for the outside of the vehicle body.

However, when carrying out the present invention, it may be in the form of installation after molding. A sound absorbing material may be formed by applying a compressive force to the foam that has been foamed by bonding it to the object to be coated, or a sound absorbing material formed by applying a compressive force to the foam may be applied to the object. You may join to a coating thing. The bonding at this time is, for example, bonding via a pressure-sensitive adhesive layer, an adhesive layer, or the like, or pasting using release paper.

Then, by selecting a raw material, etc., a foam having closed cells, i.e., single cells that are not communicating with each other, is controlled by controlling the balance between viscosity due to curing of resin, elastomer or rubber material and the amount of gas and pressure for foaming. can be obtained. Here, the foam having closed cells is not limited to a closed cell (single cell) as the cell structure, and may include continuous cells in which cells are connected to each other. Of all cells, preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more are closed cells. In addition, this bubble ratio can be calculated by measuring an arbitrary number of points using, for example, a microscope image, a CT image, or a microscope image, and calculating the average thereof.

In the present embodiment, a compressive load is applied to the foam containing closed cells by foaming a resin, elastomer, or rubber material in this manner by using a press such as a flat plate or a roll to apply a compressive force to the cells. They are made to communicate with each other to form interconnected bubbles. At this time, when a compressive load is applied to a foam having only closed cells, the independent cells become interconnected to form interconnected cells. In addition, in the foaming process, when a compressive load is applied to a foam in which closed cells and continuous cells are formed by the growth of cells, independent single cells, continuous cells, or independent cells The individual cells and the continuous cells are connected to each other.

Here, according to the experimental research of the present inventors, the compressive stress at 25% compression is preferably 2 kPa or more and 30 kPa or less, more preferably 3 kPa or more and 25 kPa or less, still more preferably 4 kPa or more and 20 kPa. By applying a compressive force to the following foam, it is possible to make the cells preferably communicate with each other.
If the compressive stress at 25% compression of the foam to which the compressive force is applied is too small, the communication of cells is not stable, and there is a risk of breakage due to compression. On the other hand, if the compressive stress at the time of 25% compression is too large, the air bubbles cannot be made to communicate even if the compressive force is applied, and the sound absorption characteristic showing a high sound absorption coefficient in the middle frequency range cannot be obtained.
A foam having closed cells with a compressive stress at 25% compression of preferably 2 kPa or more and 30 kPa or less enables stable high communication by applying a compressive load, and has a high sound absorption coefficient even in the medium frequency range. is obtained. It is more preferably 3 kPa or more and 25 kPa or less, and still more preferably 4 kPa or more and 20 kPa or less.

In addition, the compressive force applied to the foam containing closed cells and having a predetermined stress is preferably 50% or more and 95% or less, more preferably 75% or more and 95% of the thickness of the foam before compression. % or less, more preferably 80% or more and 95% or less.
If the compressibility at this time is too small, the air bubbles cannot be sufficiently communicated, and a sound absorption characteristic showing a high sound absorption coefficient in a wide frequency range from the middle frequency range to the high frequency range cannot be obtained. On the other hand, the thickness of the sound absorbing material to be applied is preferably 5 mm to 50 mm in terms of sound absorbing effect. Maximum compression rate.
It is preferably pressed at a compression ratio of 50% or more and 95% or less of the thickness of the foam before compression, that is, the thickness is 5% or more and 50% or less of the thickness of the foam before compression. By compressing and pressing in the above manner, the air bubbles are made to communicate with each other by compression, resulting in a high degree of communication, and a sound absorption characteristic exhibiting a high sound absorption coefficient in a wide range of frequencies from the middle to high frequencies. More preferably, the compression rate is in the range of 75% or more and 95% or less, more preferably 80% or more and 95% or less.

The compression rate referred to here is calculated by the following formula (1).
Compression rate (%) = {(thickness of foam before pressing - thickness of foam in pressed state)/thickness of foam before pressing} x 100 (1)
That is, since the foam recovers its thickness even after being pressed due to the predetermined elastic force of the foam, the compression ratio is not based on comparison of the thickness before and after pressing, but on the thickness compressed when a compressive load is applied. , the compressed thickness recovers when the applied compressive force is released.

In this way, a compressive load is applied to a foam having closed cells and a compressive stress at 25% compression is within a predetermined range, and the cells are communicated. The sound absorbing material has a foam structure mixed with

Thus, the sound absorbing material of the present embodiment has closed cells and closed cells that are communicated by applying a compressive load to a foam having closed cells and having a compressive stress within a predetermined range when compressed by 25%. It is. In particular, as described above, in bubbles that are communicated by compression, thin bubble membranes 1 are likely to occur on both sides of the communication hole 2 at the interface where the communicating bubbles communicate with each other. improves. Due to the presence of such a thin bubble film 1, the sound absorbing material of the present embodiment has a flow resistance (FR) and a degree of labyrinth that are lower than those of a bubble structure in which bubbles are communicated during the foaming process. (Tortuosity: Tor) is expected to increase. In addition, air permeability increases compared to before application of compressive force.

The sound absorbing material of the present embodiment, which has a hybrid cell structure of cells communicated by compression and independent cells, preferably has a compressive stress of 2 kPa or more and 4.8 kPa or less when compressed by 25%. More preferably, it is in the range of 2.2 kPa or more and 4.7 kPa or less, and still more preferably 2.5 kPa or more and 4.6 kPa or less.
If the compressive stress of the sound absorbing material when compressed by 25% is too small, the strength is low and the durability is poor. Also, the sound insulation property is lowered. On the other hand, if the compressive stress at the time of 25% compression is too large, the effect of making the air bubbles communicated by compression, that is, the practical effect of improving the sound absorption characteristics in the middle frequency range cannot be obtained.
If the compressive stress when the sound absorbing material is compressed by 25% is preferably 2 kPa or more and 4.8 kPa or less, it has the necessary strength, and peeling, falling off, and damage are difficult to occur after construction, and the foam is sufficiently compressed. Due to the balance between the number of air bubbles communicating with each other and the number of closed air bubbles, a sound absorption characteristic exhibiting a high sound absorption coefficient in a medium to high frequency range can be obtained stably. More preferably, it is in the range of 2.2 kPa or more and 4.7 kPa or less, and still more preferably 2.5 kPa or more and 4.6 kPa or less.

Further, the sound absorbing material of the present embodiment preferably has a specific gravity of 0.08 or more and 0.4 or less, more preferably 0.09 or more and 0.3 or less, and still more preferably 0.1 or more. , 0.25 or less.
If the specific gravity is too low, the cell rate (foaming rate) is too high, so that the desired strength cannot be obtained, and the sound insulation properties are also lowered. On the other hand, if the specific gravity is too high, the void content is low, and high sound absorbing properties cannot be obtained.
If the specific gravity of the sound absorbing material is in the range of 0.08 or more and 0.4 or less, the necessary strength can be secured, and more air with large viscosity loss is included, high sound absorption characteristics are obtained, and high sound insulation is obtained. properties are obtained. It is more preferably in the range of 0.09 or more and 0.3 or less, and still more preferably in the range of 0.1 or more and 0.25 or less.

Considering the air bubble ratio, that is, the volume of air bubbles occupying the total volume of the sound absorbing material, it is preferably 20% or more and 95% or less, more preferably 30% or more and 90% or less, still more preferably 40% or more, It is within the range of 85% or less.
If the porosity is too high, the desired strength cannot be obtained, and the sound insulation properties are also lowered. On the other hand, if the porosity is too low, the sound absorbing properties will be insufficient.
If the foam ratio of the sound absorbing material is preferably in the range of 20% or more and 95% or less, both high sound absorption properties and sound insulation properties can be achieved, and strength can be ensured. More preferably, it is in the range of 30% or more and 90% or less, still more preferably 40% or more and 85% or less.
Further, among all the cells, if the closed cell rate is preferably within the range of 10% or more and 80% or less and the open cell rate is within the range of 20% or more and 90% or less, the sound absorption characteristics in the medium frequency range are excellent, and , Excellent in both sound absorption and sound insulation properties. More preferably, the closed cell rate is 30% or more and 70% or less, and the open cell rate is 30% or more and 70% or less.

In addition, in a cell structure in which closed cells coexist with cells communicated by applying a predetermined compressive force to a foam having closed cells and by compressing the foam, a solidified polymer phase (resin, elastomer or rubber phase) Since it breaks some of the cell walls, skeleton, and cell membrane to make the cells communicate with each other, compared to foams with a cell structure that includes open cells and closed cells in which the cells are communicated during the foaming process, the continuous Even if the foaming rate and specific gravity of the cell rate and closed cell rate are the same, the compressive stress is low.

The size of a plurality of closed cells or interconnected cells may be uniform or non-uniform, and has a distribution width of approximately 100 μm to 500 μm, for example. In addition, the shape is generally a circular shape such as a circle or an oval, or a shape close to a polygonal shape such as a triangle or a square. It may have an irregular shape.

In the sound absorbing material of the present embodiment, which has a foamed structure having closed cells and closed cells that are communicated by compression of the foam, the average cell diameter of the linked cells and the closed cells is preferably 100 μm to 2000 μm, more preferably. is in the range of 150 μm to 1800 μm, more preferably 200 μm to 1500 μm, and the average cell wall thickness is preferably 0.5 μm to 40 μm, more preferably 0.6 μm to 35 μm, 0.7 μm to 30 μm. is within the range of
Within this range, the cell diameter and the cell wall thickness of the foam structure in which the cells communicated by compression of the foam having closed cells and the independent cells coexist are moderate cell ratios, and from the middle frequency range. In addition to obtaining a high sound absorbing property in a wide frequency range over a high frequency range, an appropriate specific gravity can be obtained, and the sound insulating property is also high.

That is, although conventional porous sound absorbing materials made of fiber materials such as glass wool and felt or soft urethane foam can provide a high sound absorption rate due to the open cells, the open cell structure and low density of the open cells make it difficult to insulate the sound. The characteristics are low, and it is difficult to achieve both sound absorption characteristics and sound insulation characteristics. On the other hand, in the sound absorbing material of the present embodiment, which has a foam structure having closed cells and closed cells that are communicated by compression of the foam, both the linked cells and the closed cells coexist and the interfaces between the linked cells are thin. Due to the sound absorbing effect due to the presence of the bubble film 1, the sound absorption characteristics in the medium frequency range are improved, and a high sound absorption coefficient is obtained in a wide frequency range from the medium frequency range to the high frequency range. Since the density can be increased, a high sound insulation effect can be obtained, and both the sound absorption effect and the sound insulation effect can be achieved. In particular, as described above, stable sound insulation properties and sound absorption properties can be obtained with a predetermined specific gravity, a predetermined cell size, and a cell wall thickness. Therefore, it is also suitable for areas that require both sound absorption and sound insulation properties, such as the dash panel of an automobile. properties and sound insulation at low cost and low weight.

As the sound absorbing material of the present embodiment, it is particularly preferable to use a highly heat-resistant silicone resin or silicone rubber foam (foamed silicone rubber, silicone foam). That is, by applying a predetermined compressive force to a silicone foam (silicone resin, silicone rubber) containing closed cells, the cells are made to communicate, and the cells made to communicate by the compression are mixed with the closed cells to create a cell structure. Especially preferred is a sound absorbing material comprising a silicone foam having A silicone rubber foam having closed cells can be obtained, for example, by curing and foaming a one-component or two-component liquid silicone material. From the standpoint of handling and storage stability, such as not requiring refrigerated storage or hermetically sealed storage, the two-liquid type is preferable.

There are three curing reaction types for silicone: a condensation reaction type that cures by reacting with moisture in the air, an addition reaction type that can be cured in a short time by heating, and a UV reaction type that accelerates curing by ultraviolet irradiation. However, considering the work environment, workability, productivity, etc. when applying to automobile parts, it is possible to perform the curing reaction in a short time, and it does not produce by-products due to the decomposition of organic peroxides. An addition reaction type liquid silicone material that does not shrink on curing is suitable.

Silicone foaming methods include a heat foaming type in which a thermally decomposable foaming agent is added to a silicone material and the decomposition of the foaming agent by heating generates nitrogen gas to form a silicone foam, and a two-liquid mixing reaction of the silicone material. There is a self-foaming reaction type that cures (rubberizes) into an elastomer while generating hydrogen gas by a dehydrogenation reaction, and foams and cures silicone.

In the heat foaming type, for example, polyorganosiloxane (a polymer whose repeating unit is dimethylsiloxy, methylphenylsiloxy, diphenylsiloxy, methylvinylsiloxy, phenylvinylsiloxy, methyl (3,3,3-trifluoropropyl)siloxy, etc.) or copolymer) as a foaming agent for silicone materials such as azodicarbonamide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, 2,5-bis(t-butylperoxy )-2,5-dimethylhexane, 2,5-bis(t-butylperoxy)-2,5-dimethylhexyne, di-t-butylperoxide, t-butylperoxybenzoate, bis(4-t -butyl cyclohexyl) peroxydicarbonate, and any one or more vulcanizing agents, and azobisisobutyronitrile, dinitrosopentamethylenetetramine, benzenesulfone hydrazide, N,N'-dinitroso-N, Foaming can be performed by adding N'-dimethylterephthalamide, pp'-oxy-bis-(benzenesulfonehydrazide), terephthalazide, or the like.
In the self-foaming type, foaming can be achieved by generating hydrogen in the condensation reaction of the silicone material. For example, hydrogen gas is generated by the dehydrogenation reaction caused by the two-liquid mixing reaction of organopolyhydrosiloxane and organopolyhydrogensiloxane. While foaming can be cured.
Silicone foaming methods include thermal foaming and self-foaming, but they do not require high-temperature heating, and problems of toxicity and odor caused by foam decomposition residues and poor curing due to the poisoning of the catalyst can occur. Therefore, the self-foaming reaction type by dehydrogenative condensation reaction is suitable.

Examples of such a self-foaming reaction type liquid silicone include a main agent (this agent) containing a hydroxyl group (hydroxy group)-containing organopolysiloxane, a silanol group-containing organohydrogenpolysiloxane, a catalyst, etc., and a silanol group-containing organopolysiloxane. A curing agent containing hydrogen polysiloxane can be used, and by mixing a silicone compound containing the main agent and the curing agent, a foamed and cured silicone rubber can be formed. For example, TB5277 manufactured by ThreeBond Co., Ltd., SEF-10 manufactured by Toray Dow Corning Silicone Co., Ltd., KE-521AB, KE-524AB, X-31-1075AB, X-32- manufactured by Shin-Etsu Chemical Co., Ltd. Commercially available products such as 1576AB and X-32-1703AB can also be used. Such a two-liquid addition reaction type, in which the main agent and the curing agent are mixed to foam and cure, is excellent in storage stability, and the curing speed can be easily adjusted by changing the temperature, so that the working efficiency is good.

In addition, the main agent and curing agent containing such organopolyhydrosiloxane and organopolyhydrogensiloxane are mixed using known mixing and dispersing and mixing stirrers such as planetary mixers, grain mills, kneaders, attritors, rolls, and dissolvers. The silicone compound prepared and mixed before foaming and curing exhibits moderate fluidity. Preferably, it has a viscosity of 10,000 to 100,000 mPa·sec. Therefore, it can be applied to coating parts that require sound absorption, such as dash panels, engine rooms, around exhaust pipes, around brake carrier pads, etc. Conventionally known coating methods such as airless spray coating, air spray coating, It can be applied by brush coating, roller coating, dip coating, or the like. Forming a foamed cured product from such a liquid silicone has good penetration into details, and even if the painted surface has unevenness or curved surfaces, it has high adhesiveness, adhesion, and adhesion to the painted surface. Adhesion can be secured.

The two-liquid addition reaction type silicone compound applied to the coating site foams and cures at room temperature, or foams and cures when heated at a predetermined temperature, and forms a spongy silicone foam hardening material having rubber elasticity. Become. The foaming and curing at this time usually proceed even if the material is left at room temperature (ordinary temperature) after mixing. C. to 150.degree. C. may be heated. The silicone compound before curing can also be molded using known molding equipment such as injection molding and injection molding.

In the self-foaming reaction type, for example, platinum compounds, aminoxy compounds, organic tin compounds, etc. are used as catalysts. family-based catalysts) are preferably used. Platinum-based catalysts include platinum-based, palladium-based, and rhodium-based catalysts, and are preferably platinum-based. _{( For example , H2PtCl4.nH2O , H2PtCl6.nH2O , NaHPtCl6.nH2O , KHPtCl6.nH2O , Na2PtCl6.nH2O , K2PtCl4.nH 2} O, PtCl ₄ .nH ₂ O, PtCl ₂ , Na ₂ HPtCl ₄ .nH ₂ O (wherein n is an integer of 0 to 6, preferably 0 or 6)), chloroplatinic acid , platinum group metal compounds such as alcohol-modified chloroplatinic acid, or complexes thereof, such as platinum-olefin complexes, platinum-vinyl group-containing silanes (vinylsiloxanes) or siloxane complexes (e.g., divinyltetramethyldisiloxane , 1,3,5,7-tetravinyl-1,3,5,7-tetratimelcyclotetrasiloxane), platinum phosphite complexes, platinum phosphine complexes, and the like can be used. More preferred are platinum black, chloroplatinic acid, alcohol-modified chloroplatinic acid, and complexes of chloroplatinic acid with olefins, aldehydes, vinylsiloxanes or acetylene alcohols. Among these, chloroplatinic acid, platinic chloride, a complex of platinum and an olefin compound, a platinum complex of vinylsiloxane, and a hexahydrate of chloroplatinic acid are preferred from the viewpoint of providing stability before curing and an appropriate foaming rate. and an olefin or divinyldimethylpolysiloxane complex, an alcohol solution of chloroplatinic acid hexahydrate, and the like are preferred. A carrier such as silica, alumina or silica gel on which particulate platinum metal is adsorbed may also be used. Such a platinum group metal-based catalyst is an addition reaction (hydrosilation) between the alkenyl group in the organosilphenylsiloxane and the SiH group in the organohydrogensiloxane, and the hydroxyl group (silanol group) in the organosilphenylsiloxane. and the SiH groups in the organohydrogensiloxane act as a catalyst to promote the dehydrogenative condensation reaction.

For example, the mechanism of foaming and curing when using a platinum group metal-based catalyst is that the addition reaction between the alkenyl group of the organopolysiloxane and the hydrosilyl group (Si—H group) of the organohydrogenpolysiloxane is promoted by the catalyst. The addition reaction of the alkenyl group and the hydrosilyl group (Si-H group) causes the silicone material to cure, and the hydroxyl group (silanol group) of the organopolysiloxane and the hydrosilyl group (Si-H group) of the organohydrogenpolysiloxane The dehydration-condensation reaction is accelerated by the catalyst, and hydrogen gas is generated by the dehydrogenation-condensation reaction, thereby foaming the silicone material.

In addition, if necessary, the main agent (main agent) and curing agent may contain reinforcing fillers (e.g., carbon black, silica, fumed titanium dioxide) and inorganic fillers (e.g., metal hydroxides such as aluminum hydroxide and magnesium hydroxide, metal carbonates, clay, calcium carbonate, diatomaceous earth, iron oxide, titanium oxide, aluminum oxide, aluminum silicate, zinc oxide, calcium silicate, titanium dioxide, ferric oxide, talc, bentonite, glass beads, glass fiber, etc.) and hydroxy group-containing compounds (eg, water, alcohol, etc.). In addition, curing inhibitors (curing retarders) for speed control of the foaming curing reaction, curing accelerators for shortening the foaming curing time, and adhesion properties such as epoxy group-containing polysiloxane compounds and ester siloxane compounds It is also possible to incorporate enhancers. In addition, in the case of the two-liquid addition curing type, in the case of using a platinum group metal as a catalyst, the ratio of the main agent and the curing agent is, for example, 1:1.

By foaming and curing the liquid silicone material in this way, a silicone foam having closed cells (silicone rubber foam) is obtained. By making them communicate with each other, it is possible to obtain a sound absorbing material made of a silicone foam in which cells that are communicated by compression and closed cells are mixed.

In particular, since the base material of the sound absorbing material made of silicone foam is silicone (silicone resin, silicone rubber), it is superior in heat resistance to organic materials such as general organic rubber, so it can be used at high temperatures. Even if it is placed around a heat source, it is highly durable without melting or thermally deteriorating, and can exhibit a stable sound absorption effect over a long period of time. For example, it is suitable for parts in high temperature environments such as the engine room and around exhaust pipes, suitable not only for the inside of the car body but also for the outside of the car body, can be applied to a wide range of parts, and is widely useful for noise control in automobiles and the like.

In addition, silicone (silicone resin, silicone rubber) has stable electrical properties, weather resistance, UV resistance, water resistance (waterproofness), chemical resistance, solvent resistance, oil resistance, ozone resistance, and cold resistance. have sex. Compared to sound absorbing materials such as glass wool, it has excellent water resistance and oil resistance. Suitable for construction.
Furthermore, silicone (silicone resin, silicone rubber) has a low cross-linking density and contains an organic component, so that even a vehicle body surface made of metal such as a steel plate has adhesiveness, adhesion, and adhesion to it. Good adhesion, adhesiveness, and adhesion to the painted surface even after curing just by applying it to the painted part.

Two-liquid addition-curing silicone is easy to apply even to curved or complicated surface shapes. In particular, since it has rubber physical properties, it can ensure elasticity and flexibility that can follow the expansion and contraction due to heat of the application site, and even when applied to an uneven site, a site having a curved surface or a complicated surface shape, etc. Even when it expands due to a thermal load, cracking (cracking), breakage, peeling, etc. are unlikely to occur, and durability is good. Therefore, it is suitable for soundproofing and noise countermeasures for a wide range of parts without limiting the coating conditions such as the coating part and the amount of coating.
Furthermore, if the curing of the silicone material is of the addition reaction type, the curing without shrinkage makes it difficult for the cured silicone foam to crack or swell, and the curing speed can be controlled, resulting in excellent construction efficiency.

Then, such an uncured liquid silicone is applied directly to the coating surface of the desired coating site, foamed and cured to form a foam having closed cells on the coating site, and a predetermined compressive force is applied. A sound-absorbing material is formed on a coated portion as a foam having communication holes 2 formed in the walls of the cells of the foam to communicate with each other and closed cells that are not communicated. In , application by a robot, that is, mechanical application by automatic painting is possible. For example, application is possible using a predetermined application nozzle, and construction can be automated. Therefore, as compared with manual application of sheet-like sound absorbing material, it is difficult to waste scraps, etc., and work accuracy, workability, work efficiency, etc. are greatly improved, and process time can be shortened. . In addition, it is possible to install without creating a gap with respect to the coated surface. In addition, it has excellent conformability to the painted part.

In this way, the sound absorbing material according to the present embodiment has a compressibility in the range of 50 to 95% with respect to the foam having closed cells and having a compressive stress in the range of 2 to 30 kPa when compressed by 25%. By applying a compressive force, the cells are communicated and have a cell structure of communicated cells and independent cells that are communicated by compression, and have a specific gravity within the range of 0.08 to 0.4, when compressed by 25%. The compressive stress of is within the range of 2 to 4.8 kPa. According to such a sound absorbing material according to the present embodiment, even though it is thin and lightweight, it acquires high sound absorbing characteristics in the middle frequency range of 1000 to 4000 Hz, and has sound absorbing characteristics over a wide frequency range of 500 to 6000 Hz. In particular, it achieves a high sound absorbing effect for a wide range of frequencies in the middle and high frequency bands of 1000 to 6000 Hz, which includes the frequency range easily audible to humans.

In addition, according to the sound absorbing material of the present embodiment, since it has a cell structure of open cells and closed cells that are communicated by compression, by controlling the cell rate, the closed cell rate in all cells can be reduced. It is also possible to control the frequency of sound absorption by controlling the ratio of open cells, and it is also possible to easily design a desired sound absorption characteristic. In addition, the control of the cell rate and the control of the ratio of the closed cells and the open cells are, for example, the type and amount of the foaming agent in the foaming process, the type and amount of the resin material, the curing characteristics, the temperature at the time of foaming and curing, and the compression rate. It is possible to control by the compression rate or the like in the force applying process.

And it is a mixture of open cells and closed cells that are communicated by compression, and has a specific gravity within the range of 0.08 to 0.4, so that it not only has excellent sound absorption properties but also excellent sound insulation properties, and is compressed by 25%. Since the compressive stress at time is within the range of 2 to 4.8 kPa, the mechanical strength is also ensured, and the frequency damping effect (sound absorption and sound insulation) due to vibration is stably obtained for a long period of time. Therefore, it is highly effective in preventing and suppressing noise.

The sound absorbing material according to this embodiment is applied to the surface of a vehicle body such as an automobile, such as a dash panel, a bonnet, an engine room, an engine cover, around an exhaust pipe, around a brake carrier, a pillar, a fender liner, an engine, a transmission, and the like. Noise generated from the vehicle, such as engine noise, tire noise, road noise, muffler noise (exhaust noise), wind noise, muffled noise, pebbles, gravel, muddy water, etc. It can improve the sound absorption effect in the middle frequency range of 1000 to 4000 Hz of noise generated by external noise and internal noise such as splash noise, chipping noise, etc. It can exhibit sound absorption characteristics in a wide frequency range from the middle frequency range of 6000 Hz to the high frequency range. Preferably, it is applied as a coating material for automobiles and the like, and is subjected to foaming curing and compressive force imparting treatment to exhibit a high sound absorption coefficient in the medium to high frequency range as a sound absorbing material. The thickness of the sound absorbing material at this time is, for example, about 1 mm to 50 mm. In particular, even a thin single-layer structure with a thickness of 10 mm exhibits a high sound absorption coefficient in the middle frequency range of 1000 to 4000 Hz. In addition, even with a thin thickness, the middle frequency range of 1000 to 4000 Hz can be increased, so the installation space can be reduced, and it can be applied to a wide range of parts of the vehicle body that require sound absorption.
In addition to automobiles, mechanical devices such as parts of tools or their housings, mechanical structures and their housings, internal combustion engines (engines) with technically movable parts, transformers, electric motors, etc. It can be applied as a soundproofing material for structures, buildings, electric appliances, and the like.

Next, specific examples of the sound absorbing material according to the embodiment of the present invention will be described.
For the sound absorbing material according to Example 1, a silicone foam (silicone rubber foam) having an expansion ratio of 10 is obtained by foaming and curing a two-liquid addition reaction/dehydrogenation condensation reaction type liquid silicone material. It is formed by applying a predetermined compressive load, that is, a compressive force, by roll-pressing the foam in the thickness direction at room temperature. In Examples 1 to 5, there was almost no change in thickness before and after compression and almost no creep. That is, it is not plastically deformed.

In Example 1, a silicone foam having an expansion ratio of 10 times obtained by foaming and curing a two-liquid addition reaction/dehydrogenation condensation reaction type liquid silicone material before applying a compressive force was used in Comparative Example 1 described later. As shown in the microscope image of FIG. 6, the foam is closed-cell type and has a compressive stress of 5 kPa when compressed by 25%. In Example 1, 90% of the thickness of the silicone foam having a compressive stress of 5 kPa at 25% compression before applying the compressive force was compressed, that is, the thickness before the compressive force was applied. A sound absorbing material according to Example 1 was obtained by applying a predetermined compressive force up to 10%.

The expansion ratio here is the value obtained by dividing the density of the silicone compound before foaming by the apparent density of the silicone foam after foaming.
In addition, the compressive stress (kPa) at 25% compression is the repulsive load when a compressive load is applied to a thickness of 75% of the initial thickness of the foam, and is compressed by 25% of the initial thickness. It is expressed per unit area by dividing the required compressive load (N) by the cross-sectional area (m ² ).

As shown in the X-ray CT image of FIG. 1 and the microscope images of FIGS. It has a cell structure in which interconnected cells and closed cells are mixed, has a specific gravity of 0.13, and has a compressive stress of 2.8 kPa when compressed by 25%. In addition, the measurement of bubbles using a microscope image shows that the diameter and volume of the bubbles are relatively non-uniform, the cell unit of the bubbles is distributed in, for example, 100 to 600 μm, and the wall thickness of the bubbles is, for example, It was distributed around 1 μm. The average cell diameter of the cells (average cell diameter) was about 200 μm, and the average thickness of the cell walls was about 1 μm. Note that the compressive stress when the sound absorbing material is compressed by 25% is about 0.56 times that before applying the compressive force because the air bubbles are communicated by applying the compressive force.

In the sound absorbing material according to Example 2, as in Example 1, a silicone foam having an expansion ratio of 10 was obtained by foaming and curing a two-liquid addition reaction/dehydrogenation condensation reaction type liquid silicone material. The silicone foam is roll-pressed in the thickness direction to apply a predetermined compressive load, that is, a compressive force.

In Example 2, the silicone foam obtained by foaming and curing the two-liquid addition reaction/dehydrogenation condensation reaction type liquid silicone material and having an expansion ratio of 10 before applying a compressive force was also the same as in Example 1. (Refer to the microscope image in FIG. 6 of the foam of Comparative Example 1 described later), and the compressive stress at 25% compression is 5 kPa. In Example 2, compressive force was applied to the silicone foam having a compressive stress of 5 kPa at 25% compression at a compression ratio smaller than that in Example 1. That is, by compressing 80% of the thickness of a silicone foam having a compressive stress of 5 kPa at 25% compression before applying a compressive force, that is, until it reaches 20% of the thickness before applying a compressive force. A sound absorbing material according to Example 2 was obtained by applying a compressive force of .

As shown in the microscope image of FIG. 3, the sound absorbing material according to Example 2 obtained in this way has a cell structure in which cells that are communicated by applying a compressive force and independent cells are mixed. , its specific gravity is 0.13, and its compressive stress at 25% compression is 2.8 kPa. In addition, in Example 2, since the compressibility is smaller than that in Example 1, the rate of air bubbles that are made open by compression is smaller than that in Example 1. In addition, in the sound absorbing material of Example 2, although the bubble communication ratio is lower than that of Example 1, the average bubble size and the average thickness of the bubble walls are similar to those of Example 1 from the microscope image of FIG. Since the difference is about 10 μm or less even if it is approximately equal to or greater than the time, detailed measurement is omitted here.

As in Examples 1 and 2, the sound absorbing material according to Example 3 was obtained by foaming and curing a two-liquid addition reaction/dehydrogenation condensation reaction type liquid silicone resin. It is formed by obtaining a silicone foam before application and applying a predetermined compressive load, that is, a compressive force, by roll-pressing the thickness direction of the silicone foam.

In Example 3, the silicone foam obtained by foaming and curing the two-liquid addition reaction/dehydrogenation condensation reaction type liquid silicone material and having an expansion ratio of 10 before applying a compressive force was also the same as in Example 1. (Refer to the microscope image in FIG. 6 of the foam of Comparative Example 1 described later), and the compressive stress at 25% compression is 5 kPa. In Example 3, a compressive force was applied to the silicone foam having a compressive stress of 5 kPa at 25% compression at a compression ratio smaller than that in Examples 1 and 2. That is, by compressing 70% of the thickness of a silicone foam having a compressive stress of 5 kPa at 25% compression before applying a compressive force, that is, until it reaches 30% of the thickness before applying a compressive force. A sound absorbing material according to Example 3 was obtained by applying a compressive force of .

As shown in the microscope image of FIG. 4, the sound absorbing material according to Example 3 thus obtained has a cell structure in which cells that are communicated by applying a compressive force and independent cells are mixed. , its specific gravity is 0.13, and its compressive stress at 25% compression is 2.8 kPa. In addition, in Example 3, since the compressibility is smaller than those in Examples 1 and 2, the rate of air bubbles which are made to communicate by compression is lower than those in Examples 1 and 2. In addition, even in the sound absorbing material of Example 3, although the bubble communication ratio is lower than that of Example 1, the average bubble size and the average thickness of the bubble walls are the same as those of Example 1 from the microscope image in FIG. , the difference is about 10 .mu.m or less, so detailed measurements are omitted here.

The sound absorbing material according to Example 4 has an expansion ratio of 5 times, which is lower than that of Examples 1 to 3, by foaming and curing a two-liquid addition reaction/dehydrogenation condensation reaction type liquid silicone material. A silicone foam is obtained, and the thickness direction of the silicone foam is roll-pressed to apply a predetermined compressive load, that is, a compressive force.

In Example 4, the silicone foam before application of compressive force and having an expansion ratio of 5 times obtained by foaming and curing the two-liquid addition reaction/dehydrogenation condensation reaction type liquid silicone material was a closed cell type. , the compressive stress at 25% compression is 14 kPa, which is larger than that in Examples 1-3. In Example 4, a compressive force was applied to the silicone foam having a compressive stress of 14 kPa when compressed by 25% at a compressibility of 90%, which is the same as in Example 1. That is, by compressing 90% of the thickness of a silicone foam having a compressive stress of 14 kPa at 25% compression before applying a compressive force, that is, until it reaches 10% of the thickness before applying a compressive force. A sound absorbing material according to Example 4 was obtained by applying a compressive force of .

The sound absorbing material according to Example 4 obtained in this way has a cell structure in which cells communicated by applying a compressive force and independent cells are mixed, and its specific gravity is 0.25. , and the compressive stress at 25% compression is 3.0 kPa. In addition, in Example 4, since the expansion ratio is smaller than that in Examples 1 to 3, the compressive stress is larger than in Examples 1 to 3. Moreover, since the air bubbles are communicated by applying the compressive force, the compressive stress when the sound absorbing material is compressed by 25% is about 0.21 times that before applying the compressive force. Although the cell rate is lower than that of Example 1, the average cell size and the average cell wall thickness are approximately equal to or larger than those of Example 1, but the difference is about 50 µm or less. We omit detailed measurements.

As the sound absorbing material according to Example 5, a commercially available EPDM (ethylene propylene diene rubber) foam (“Epto Sealer” manufactured by Nitto Denko Corporation) was used, and the thickness direction of the EPDM foam was roll-pressed to a predetermined degree. It is obtained by applying a compressive load, that is, a compressive force.

In this Example 5, the EPDM foam before application of compressive force was a semi-closed and semi-open cell type, that is, closed cells and It has continuous cells that are connected to each other by the growth of cells during the foaming process, and has a compressive stress of 6.2 kPa when compressed by 25%. In Example 5, the EPDM foam having a compressive stress of 6.2 kPa at 25% compression before applying the compressive force was compressed by compressing 90% of its thickness, that is, before applying the compressive force. A sound absorbing material according to Example 5 was obtained by applying a predetermined compressive force to 10% of the thickness.

The sound absorbing material according to Example 5 thus obtained has a specific gravity of 0.10 and a compressive stress of 4.2 kPa when compressed by 25%. Considering that it is about 0.68 times the compressive stress at the time of 25% compression, and also from the microscope images of FIGS. The air bubbles are communicated and have a cell structure containing the air bubbles that are communicated by the compression and the air cells that are independent. In addition, measurement of bubbles using a microscope image shows that the diameter and volume of the bubbles are relatively non-uniform, the cell unit of the bubbles is, for example, about 1 mm, and the wall thickness of the bubbles is, for example, 10 to 10. It was distributed at 30 μm. The average cell diameter of the cells (average cell diameter) was about 1 mm, and the average thickness of the cell walls was about 20 μm.

Then, for the sound absorbing materials according to Examples 1 to 5 thus obtained, normal incident sound absorption coefficients were measured. The normal incidence sound absorption coefficient was measured using a normal incidence acoustic measurement system (Acoustic Duct Model 9302) manufactured by Rion Co., Ltd. using a test piece with a thickness of 10 mm. The measurement results of the normal incident sound absorption coefficients of the sound absorbing materials according to Examples 1 to 5 are shown in the graph of FIG.
The vertical incident sound absorption coefficient here is the measurement result of the vertical incident sound absorption coefficient in each frequency range of 500 Hz, 630 Hz, 800 Hz, 1000 Hz, 1250 Hz, 1600 Hz, 2000 Hz, 2500 Hz, 3150 Hz, 4000 Hz, 5000 Hz and 6300 Hz.

For comparison, the foamed materials, porous materials, and fibers according to Comparative Examples 1 to 6 were also measured for the normal incident sound absorption coefficient, and the measurement results are shown in FIG. there is
Here, Comparative Example 1 is the silicone foam before application of compressive force in Examples 1-3. That is, it is a silicone foam having an expansion ratio of 10 times obtained by foaming and curing a two-liquid addition reaction/dehydrogenation condensation reaction type liquid silicone material, and is a silicone foam that has not been subjected to compressive force treatment. As shown in the microscope images of FIGS. 6(a) to 6(c), the silicone foam according to Comparative Example 1 is a closed cell type, has a specific gravity of 0.13, and a compressive stress when compressed by 25%. It is of 5 kPa. From the microscope image in FIG. 6, the average bubble size and the average thickness of the bubble wall are compared to Example 1, because the bubbles are not communicated, the bubble size is approximately equal to or less than that of the bubble. Although the wall thicknesses are approximately the same or greater, the difference between them is about 30 μm or less, so detailed measurements are omitted here.

In Comparative Example 2, a commercially available silicone foam (silicone rubber sponge (SGNL (type)) manufactured by Misumi Co., Ltd.) was used, and the thickness direction of the silicone foam was roll-pressed to a predetermined compressive load, that is, compression. It is obtained by giving power.

In Comparative Example 2, the silicone foam before application of compressive force was a closed cell type, and had a compressive stress of 80 kPa when compressed by 25%. In Comparative Example 2, 90% of the thickness of the silicone foam having a compressive stress of 80 kPa at 25% compression before applying the compressive force was compressed, that is, 10% of the thickness before applying the compressive force. %, a silicone foam according to Comparative Example 2 was obtained.

The thus-obtained silicone foam of Comparative Example 2 has a specific gravity of 0.26 and a compressive stress of 80 kPa when compressed by 25%, which is the same compressive stress as before applying the compressive force. Therefore, the microscopic images of FIGS. 7(a) to 7(c) also show that the cells remain independent cells without communicating or breaking due to the application of the compressive force. When the bubbles were measured using a microscope image, the cell units of the bubbles were distributed, for example, from 200 to 500 μm, and the wall thickness of the bubbles was distributed, for example, from 30 to 60 μm. The average cell diameter of the cells (average cell diameter) was about 250 μm, and the average thickness of the cell walls was about 45 μm.

Comparative Example 3 is the EPDM foam of Example 5 before application of compressive force. That is, it is a commercially available EPDM (ethylene propylene diene rubber) foam (“Eptosealer” manufactured by Nitto Denko Corporation), which is an EPDM foam that has not been subjected to compressive force treatment. The EPDM foam of Comparative Example 3, as shown in the microscopic images of FIGS. It has interconnected cells, has a specific gravity of 0.10, and has a compressive stress of 6.2 kPa when compressed by 25%. From the microscope image in FIG. 8 , the average bubble size and the average thickness of the bubble walls are approximately equal to or less than that of Example 5 because the bubbles are not communicated by compression. Although the thickness of the cell wall is approximately the same or greater, the difference between them is about 30 μm or less, so detailed measurements are omitted here.

In Comparative Example 4, a commercially available EPDM foam (EPDM sponge (SGNP (model)) manufactured by Misumi Co., Ltd.) was used, and the thickness direction of the EPDM foam was roll-pressed to a predetermined compressive load, that is, a compressive force. is obtained by giving

In Comparative Example 4, the EPDM foam before application of compressive force was a closed-cell type, and had a compressive stress of 34 kPa when compressed by 25%. In Comparative Example 4, by compressing 90% of the thickness of the EPDM foam having a compressive stress of 34 kPa at 25% compression before applying the compressive force, that is, 10% of the thickness before applying the compressive force. %, an EPDM foam according to Comparative Example 4 was obtained.

The sound absorbing material according to Comparative Example 4 thus obtained has a specific gravity of 0.11 and a compressive stress of 34 kPa when compressed by 25%, which is the same compressive stress as before applying the compressive force. Therefore, the microscopic images of FIGS. 9(a) to 9(c) also show that the cells remain independent cells without communicating or breaking due to the application of the compressive force. When the bubbles were measured using a microscope image, the cell units of the bubbles were distributed, for example, from 100 to 200 μm, and the wall thickness of the bubbles was distributed, for example, from 10 to 20 μm. The average cell diameter of the cells (average cell diameter) was about 150 μm, and the average thickness of the cell walls was about 15 μm.

Comparative Example 5 is a commercially available melamine foam ("Basotect (registered trademark)" manufactured by BASF), which is not subjected to compressive force treatment. As shown in the microscope images of FIGS. 10(a) and 10(b), the melamine foam of Comparative Example 5 is an open-cell type, has a specific gravity of 0.01, and a compressive stress of 14 kPa when compressed by 25%. belongs to.
Further, Comparative Example 6 is a commercially available glass wool (fiber type sound absorbing material) having a specific gravity of 0.05.

As shown in the graph of FIG. 11 and the measurement results of the sound absorption coefficient in Table 1, the foams, porous bodies, or fibers of Comparative Examples 1 to 6 all have a thickness of 10 mm at a frequency of 1000 to 4000 Hz. The sound absorption coefficient in the middle frequency range is low, and in particular, the average sound absorption coefficient in the frequency band of 1000 to 3150 Hz is 0.445 or less.

That is, Comparative Example 2 in which a compressive force was applied to a closed-cell silicone foam having a compressive stress of 80 kPa at 25%, Comparative Examples 3 and 25 in which a commercial semi-closed and semi-open-cell EPDM foam was applied. In Comparative Example 4, in which a compressive force was applied to a closed-cell EPDM foam having a compressive stress of 34 kPa per hour, the sound absorption coefficient was as low as less than 0.4 in the entire measured frequency range.

In particular, in Comparative Examples 2 and 4, even if a compressive force was applied to the foam having closed cells, the 25% compressive stress before applying the compressive force was 80 kPa and 34 kPa, respectively. Even if a compressive force is applied to the body so that the compressibility is 90%, the air bubbles cannot be made to communicate, and the effect of improving the sound absorption coefficient in the middle frequency range of 1000 to 4000 Hz cannot be obtained. .
In Comparative Example 3, even though the EPDM foam had both closed cells and open cells, the open cells were formed during the foaming process and did not contain cells connected by compression. It does not exhibit high sound absorption characteristics in the medium frequency range of 4000 Hz, and has a low sound absorption coefficient of less than 0.4 over the entire frequency range.

In addition, Comparative Example 5 made of commercially available open-cell melamine foam and Comparative Example 6 made of commercially available open-cell glass wool have high sound absorption coefficients in the high frequency range exceeding 4000 Hz, but In the frequency range, especially in the frequency range of 1000-2000 Hz, a thin thickness of 10 mm does not exhibit sufficient sound absorbing properties.
Furthermore, even in Comparative Example 1, which is made of a closed-cell silicone foam obtained by foaming and curing a two-component addition reaction/dehydrogenation condensation reaction type liquid silicone material, the sound of a specific frequency around 1000 Hz Although the sound absorption coefficient increases, the sound absorption coefficient is greatly reduced in the frequency range of 1250 Hz or higher, which is a low sound absorption coefficient.

On the other hand, in the sound absorbing materials of Examples 1 to 5, the average sound absorption coefficient in the frequency range of 1000 to 3150 Hz is 0.51 or more, and in particular, the average sound absorption coefficient in the middle frequency range of 1000 to 4000 Hz is 0.51. It exhibited a sound absorption coefficient of 4 or more, and the maximum sound absorption coefficient in the middle frequency range of 1000 to 4000 Hz was 0.56 to 0.91.

In particular, as can be seen from the comparison between Examples 1 to 3 and Comparative Example 1, Comparative Example 1 made of a silicone foam having a cell structure of only closed cells, that is, in Examples 1 to 3, before applying a compressive force In Comparative Example 1 made of silicone foam, in the graph of FIG. Although there is a sound absorption effect for frequency sound sources, the sound absorption coefficient is very low at 1250 Hz or higher, and it is not possible to effectively absorb sound in a wide frequency range from medium to high frequencies. In Comparative Example 1, from the sound absorption characteristics only in a specific frequency range, it is presumed that this is due to resonance due to soft materials or the like, and sound absorption due to the membrane vibration system alone.

On the other hand, in contrast to Comparative Example 1, the sound absorbing materials of Examples 1 to 3, in which both the closed cells and the cells that were communicated by applying a compressive force coexisted, in a wide range of medium and high frequencies in the range of 1000 to 6300 Hz. In particular, in the middle frequency range of 1600 to 4000 Hz, the sound absorption coefficient was 0.5 or more, and the sound absorption coefficient was dramatically improved compared to Comparative Example 1, showing a high sound absorption coefficient. As described above, the sound absorption characteristics of the examples include the viscosity of air in open cells, sound absorption due to ventilation resistance, resonance due to flexible materials such as resin and rubber, and sound absorption in membrane vibration systems, as well as closed cells and It is presumed that this is due to the sound absorbing effect of film vibration and resonance due to the coexistence of continuous cells and the formation of a thin cell film 1 on the interface of the continuous cells communicated by compression.

Similarly, from the comparison of Comparative Example 3 and Example 5, Comparative Example 3 made of a semi-closed semi-open cell type EPDM foam, that is, Comparative Example 3 made of an EPDM foam before applying a compressive force in Example 5 , the sound absorption coefficient is low in the entire frequency range. The sound absorption coefficient is improved in the frequency range and exhibits high sound absorption characteristics in a wide range of medium and high frequencies in the range of 1000 to 6300 Hz. It had a sound absorption peak at a frequency of 2000 Hz and a maximum sound absorption coefficient of 0.7.

In particular, in the sound absorbing materials of Examples 1, 2, 4 and 5, in which a foam containing closed cells was compressed to a compression ratio of 80% to 90%, 1600 The maximum sound absorption coefficient is 0.73 or more in the medium frequency range of up to 4000 Hz.
Furthermore, in the sound absorbing materials of Examples 1, 2 and 4, each of which is made of a silicone foam obtained by applying a compressive force to a foam having closed cells so as to have a compressibility of 80% to 90%, also has a sound absorption coefficient of 0.6 or more in the middle frequency range of 1600 to 4000 Hz, a sound absorption peak in the middle frequency region of 2000 to 3150 Hz, and a maximum sound absorption coefficient of 0.85 or more.

From a comparison of Examples 1 to 3, at a compression ratio of 70% to 90%, the higher the compression ratio, the higher the sound absorption coefficient in the frequency range of 1250 to 6300 Hz, and the communication rate of air bubbles due to compression. By increasing , the sound absorption coefficient can be increased. The thickness of the applied sound absorbing material is preferably 5 mm to 50 mm in terms of sound absorbing effect, and within such a thickness range, the maximum compressibility is about 90% to 95% considering the thickness of the resin and rubber phases. On the other hand, according to the experimental research of the present inventors, preferably, if the compression rate is 50% or more, the sound absorption characteristics are improved in a broad range including the middle frequency range of 1600 to 4000 Hz by making the air bubbles communicated by compression. do. More preferably, the compression rate is 60% or more, and still more preferably 70% or more. Particularly preferably, by applying a compressive force to the foam containing closed cells so that the compression ratio is 80% to 95%, the effect of improving the sound absorption coefficient in the middle frequency range of 1000 to 4000 Hz is increased, and it is excellent. sound absorption coefficient.

In addition, Example 1 obtained by applying a compressive force to a silicone foam with an expansion ratio of 10 times to give a compression ratio of 90% and a silicone foam with an expansion ratio of 5 times have a compression ratio of 90%. A comparison with Example 4, which was obtained by applying such a compressive force, revealed that the higher the proportion of interconnected cells in the total volume of the foam, that is, the higher the rate of interconnected cells communicated by compression, the higher the sound absorption coefficient. It can be seen that the peak of the sound absorption coefficient shifts to the low frequency side as the proportion of cells in the total volume of the foam, that is, the total cell ratio of closed cells and interconnected cells increases. Therefore, by controlling the void ratio of the foam before applying the compressive force, it is possible to control the frequency at which the sound absorbing effect is desired to be enhanced.

According to the experimental research of the present inventors, the expansion ratio of the two-liquid addition reaction/dehydrogenation condensation reaction type silicone foam before application of compressive force is 3 to 20 times, and more preferably 4 times. It is preferably in the range of to 18 times, more preferably 5 times to 15 times.
If the foaming ratio is too low, the mechanical strength and hardness are high, and the void content is also low. A practical effect of improving the sound absorption coefficient in the middle frequency range of 1000 to 4000 Hz cannot be obtained. On the other hand, if the expansion ratio is too high, it is difficult to manufacture, and because of its high elasticity and flexibility, even if a predetermined compression force is applied, a sufficient number of interconnected cells cannot be obtained by compression. There is a possibility that a practical improvement effect of the sound absorption coefficient in the middle frequency range of 1000 to 4000 Hz cannot be obtained.
In the two-liquid addition reaction/dehydrogenation condensation reaction type silicone foam, by applying a predetermined compressive force to the foam having an expansion ratio of 3 to 20 times, sufficient interconnected cells can be obtained. It is possible to obtain a practical improvement effect of the sound absorption coefficient in the middle frequency range of 1000 to 4000 Hz. More preferably, it is in the range of 4 to 18 times, still more preferably 5 to 15 times.

Thus, the sound absorbing materials of Examples 1 to 5 have a compressive stress in the range of 5 to 14 kPa at 25% compression and a compressibility in the range of 70% to 90% with respect to the foam having closed cells. The cells are communicated by applying a compressive force of 25%, and have a cell structure of communicated cells and independent cells communicated by compression, and have a specific gravity within the range of 0.1 to 0.25. The compressive stress during compression is in the range of 2.8 to 4.2 kPa.
In the sound absorbing materials of Examples 1 to 5, even with a thickness of 10 mm, the sound absorption characteristics are improved in the entire frequency range compared to before the application of the compressive force, and in particular, the sound absorption characteristics in the medium frequency range of 1000 to 4000 Hz are improved. It is extremely high and exhibits high sound absorption characteristics in a wide frequency range from the middle frequency range of 1000 to 6300 Hz to the high frequency range. In this way, even without increasing the thickness, for example, even with a thin single layer structure of 10 mm thickness, it exhibits high sound absorption characteristics against medium frequency noise of 1000 to 4000 Hz, so it can be installed in a small space and can be applied to a wide range of parts. make it applicable.

Even if the sound absorbing coefficient is increased in this way, the sound absorbing material having the cell structure of the open cells and the independent cells that are communicated by compression has a high sound insulating coefficient. That is, the sound absorption coefficient can be improved without impairing the sound insulation.
Just to make sure, a 10 mm thick test piece of the sound absorbing material made of the silicone foam of Example 1 and a 15 mm thick test piece made of the glass wool of Comparative Example 6 were measured for their transmission loss (dB). The results are shown in FIG. shown in the graph. The measurement of the transmission loss at this time is also made at the same frequency as in the measurement of the normal incidence sound absorption coefficient described above. As shown in FIG. 12, in Example 1, the transmission loss (dB) is 14.0 or more in the entire measured frequency range, and the transmission loss (dB) is higher than that of Comparative Example 6, that is, the sound insulation effect is high. ing.
It should be noted that the transmission loss at this time is obtained by measuring the normal incidence sound transmission loss of an acoustic tube according to ASTM E2611-09. That is, a test piece was set in a predetermined acoustic tube, a speaker was used to generate sound toward the inside of the acoustic tube from one opening surface of the acoustic tube, and four microphones directed inward from the peripheral surface of the acoustic tube were used. was used for measurement by the transfer function method.

In this way, a sound absorbing material having a cell structure of open cells and closed cells that are communicated by compression provides a high sound insulation rate even if the sound absorption rate is increased, and has sound insulation properties that achieve both sound absorption rate and sound insulation rate. can get. Therefore, the effect of suppressing noise is excellent and the effect of suppressing noise diffusion is enhanced by the synergistic effect of the sound absorbing property and the sound insulating property.

That is, the sound absorbing material of the present embodiment does not have a composite or multi-layered structure used in combination with other sound insulating materials, etc., but even if it is constructed as a single structure using a single foam, it has a high sound absorption rate and a high sound insulation rate. A noise suppression effect can be exhibited. Therefore, there is no need for a joining process to form a composite or multi-layered structure, and workability and workability for imparting a soundproofing effect are simple and can be completed in a short process time, so that the productivity of the vehicle can be increased. However, when carrying out the present invention, it is also possible to use it in combination with other sound insulating materials or the like. Moreover, it is good also as a structure which provides several through-holes.

In Examples 1 to 4 above, a compression force was applied to a closed-cell foam obtained by foaming and curing a two-liquid addition reaction curing silicone material. When foaming and curing the silicone foam (130 mm × 45 mm x 10 mm thick). Incidentally, the thickness (wet film thickness) of the silicone material to be foamed and cured at this time was 3.2 to 3.8 mm. In Examples 1 to 4, the foamed and cured silicone foam was dried (150° C.×20 minutes), and then given a predetermined compressive force to obtain a sound absorber. A test piece obtained by cutting the central portion of the obtained sound absorber is used for the measurement of the sound absorption coefficient and the like.

Here, as described above, in the sound absorbing material of the present embodiment, it is possible to control the frequency at which the sound absorbing effect is desired to be enhanced by controlling the bubble rate and ratio of the closed cells and the open cells. When obtaining a sound absorbing body from a silicone foam made by foaming and curing an addition reaction curing silicone material, the silicone material is placed in a mold during the foaming and curing process, and the silicone material is foamed and cured, and then put into the mold. The amount (volume) of the silicone material, particularly the thickness (wet film thickness), makes it possible to control the bubble rate and ratio of closed cells and open cells, and to control the frequency characteristics of the sound absorption coefficient.

Specifically, the change in frequency characteristics when the thickness (wet film thickness) of the silicone material to be foamed and cured in the mold is changed will be described with reference to FIG. The present inventors used the same silicone material on the side of the two-liquid addition reaction/dehydration condensation reaction as used in Examples 1 to 4 above, and measured the thickness (wet film) when foaming and curing the silicone material. Thickness) was varied to make multiple 10 mm thick silicone foams. Then, by applying a predetermined compressive force (compressibility of 90%) to the silicone foam, samples of the sound absorbing material were obtained, and their sound absorption coefficients were measured.

At this time, as shown in FIG. 13, the silicone material was foamed and cured in a state surrounded by an upper jig J1, a lower jig J2 and spacers S1, S2, R1 and R2, that is, inside a mold. That is, a pair of spacers S1 and S2 having a predetermined thickness corresponding to the thickness of the silicone material (wet film thickness) is placed in parallel on the lower jig J2 (70 mm×150 mm). Pour the silicone material on the side of the two-liquid addition reaction/dehydration condensation reaction, furthermore, place a pair of spacers R1 and R2 with a thickness of 10 mm outside the pair of spacers S1 and S2, and place the spacers R1 and R2 on top. A jig J1 (70 mm×150 mm) was placed. Note that the spacers S1 and S2 and the spacers R1 and R2 are arranged only on two opposing long sides of the upper jig J1 and the lower jig J2. The silicone material surrounded by the upper jig J1, the lower jig J2, and the spacers S1, S2, R1, and R2 is regulated to a thickness of 10 mm when foamed and cured. Become.

Here, the thickness (wet film thickness) of the silicone material put into the spacers S1 and S2 on the lower jig J2 is 3.0 mm, 3.2 mm, and 3.8 mm, and silicone materials with different thicknesses are used. Each was foamed and cured to produce a silicone foam of 45 mm×130 mm×10 mm thick. Then, the silicone foam was released from the mold, dried (150 ° C. x 20 minutes), and then subjected to a predetermined compression force (compression rate of 90%) to obtain a sound absorbing material sample. Measurements were made in the same manner as in Examples. The sound absorption coefficient was measured by dividing the sample of the sound absorbing material into three equal parts in the longitudinal direction, and measuring the end part side and the center part in the longitudinal direction. The graph of FIG. 14 shows the results of measurement of the frequency characteristics of the sound absorption coefficient for each sound absorber sample obtained from silicone materials with different thicknesses.

As shown in FIG. 14, under the thickness control, the larger the thickness of the silicone material to be foamed and cured (the wet film thickness before foaming), the higher the sound absorption coefficient near 1000 Hz and the lower the peak frequency of the sound absorption coefficient. moving to the side. This is because when the thickness of the silicone material to be foamed and cured (wet film thickness before foaming) is large, the thickness of the skin layer of the obtained silicone foam is large and the specific gravity is high, resulting in surface air bubbles. It is presumed that the sound absorption characteristics due to membrane vibration are enhanced due to the communication of the membrane and the small number of communication bubbles, and therefore the sound absorption coefficient is high around 1000 Hz, and the peak frequency of the sound absorption coefficient appears on the low frequency side. In other words, if the thickness of the silicone material to be foamed and cured (wet film thickness before foaming) is thin, the thickness of the skin layer of the resulting silicone foam is thin, and the specific gravity is small, so that the number of surface cells is small. It is presumed that the sound absorption coefficient is low near 1000 Hz, and the maximum peak frequency of the sound absorption coefficient appears on the high frequency side because of the large number of communication and communication bubbles. This can be inferred from the fact that the peak frequency of the sound absorption coefficient is on the low frequency side on the edge side rather than on the center side. That is, on the center side, the thickness of the skin layer is thinner than that on the end side, the cells are dense, and the compressive stress tends to concentrate, so the cells are easily interconnected and the number of interconnected cells increases. , the sound absorption coefficient near 1000 Hz is lower than that on the end side, and the peak frequency of the sound absorption coefficient is presumed to be closer to the high frequency.

As described above, according to the sound absorber obtained by applying a predetermined compressive force to the silicone foam obtained by foaming and curing the two-liquid addition reaction curing silicone material, the silicone material is placed in a mold, foamed and cured. By controlling the thickness, it is possible to control the communication of compressed air bubbles by controlling the thickness of the skin layer and the foaming, thereby facilitating the control of the frequency characteristics of sound absorption. Similarly, it is possible to control the frequency characteristics of sound absorption by controlling the dimensions of the mold. However, when carrying out the present invention, a silicone foam is produced by free foaming without restricting the thickness of the silicone material to be foamed and cured, or restricting the width in the direction perpendicular to the thickness direction, and a predetermined It is also possible to use a sound absorber to which a compressive force of .

By the way, a closed-cell foam (corresponding to Comparative Example 1 above) obtained by foaming and curing such a silicone material, and applying a compressive force to such a closed-cell foam to communicate the cells When the surface of the sound absorbing material (corresponding to Examples 1 to 4 above) was observed with a scanning electron microscope (SEM), the closed-cell foam before applying a compressive force showed a As shown in FIGS. 15 to 20, there are no wrinkled parts or curled parts around the opening, and there are no corners or cusps, and the opening is generally circular. As shown in FIGS. 21 to 26, the sound absorbing material obtained by applying a predetermined compressive force to a closed-cell foam has wrinkles a and curls b around the opening, corners d, and so on. The bubbles B mainly have an opening shape with a pointed head d.

That is, when the surface of the closed-cell foam before application of a compressive force was observed with a scanning electron microscope (SEM), expansion of the cells in the SEM image (×100) of FIG. 15 was shown in FIGS. As shown in the SEM images of No. 20 (×300 to ×1000), the opening is higher than the bubble B, which has wrinkles and curled parts around the opening, and has an opening shape with corners and cusps. There are many bubbles A which have no wrinkles or curls around them, and which have a circular opening with no corners or cusps.
On the other hand, when the surface of the sound absorbing material obtained by applying a compressive force to the closed-cell foam was observed with an electron microscope (SEM), the cells in the SEM image (x 100) of FIG. As shown in the enlarged SEM images (×300 to×1500) of FIGS. There are more bubbles B that have a wrinkled part a or a curled part b around the opening, or an opening shape with a corner part d or a pointed head d than bubbles A that have a shape. account for more than 50% of Preferably, it is 60% or more, more preferably 70% or more.

16 to 20 and FIGS. 22 to 26, the air bubble A (judgment column A) or air bubble B (judgment column B) was identified by an in-house monitor (N = 8) as an opening (hole). There are double or several creases (crack marks, etc.) around the opening (creased part a), the peripheral edge of the opening is rolled up (curved part b), and the opening shape has a dent If the bubble has a dovetail corner c or a pointed head d, it is called bubble B, and if the other opening is entirely round and circular, it is called bubble A. A bubble A is judged to be bubble A by 50% or more of the judges, and a bubble B is judged to be bubble B by 50% or more of the judges.

In this way, in the sound absorbing material of the present embodiment, which is obtained by applying a compressive force to the foam having closed cells, when the cells on the surface are observed with a scanning electron microscope (SEM), the openings are generally circular. Rather than the bubble A, which is , the bubble B mainly has a wrinkled part a or a curled part b around the opening, or has an opening shape with a corner part d or a pointed head part d. This is due to the buckling deformation and breakage of the bubbles due to the application of compressive force that makes the bubbles communicate, which causes wrinkles a and curled portions b at the opening edge of the bubbles, and the opening shape is changed to the corner c. , or transformed into one with a pointed head d.

In this manner, in the sound absorbing material of the present embodiment, which is obtained by applying a compressive force to the foam having closed cells, by applying a compressive force that makes the cells communicate, the cells on the surface of the sound absorbing material can be observed with a scanning electron microscope (SEM). Observation shows that the bubbles B mainly have wrinkles a and curled parts b around the opening, and have an opening shape with corners d and pointed parts d.

Observation of the surface of such a sound absorbing material with an electron microscope (SEM) reveals that bubbles B have wrinkles a and curled parts b around the opening, and have an opening shape with corners d and pointed parts d. In the sound absorbing material of this embodiment, which is the main component, as described above, the friction with the cell walls, the skeleton and the cell membrane 1 in the cells communicating by compression, the sound absorbing effect due to the viscosity and airflow resistance, the base material (resin, rubber or elastomer) membrane vibration, sound absorption effect due to resonance, air bubbles, especially membrane vibration in interconnected bubbles having a bubble membrane 1 due to communication by compression, sound absorption effect due to resonance, etc., even with thin thickness and light weight, in the middle frequency range The sound absorption characteristics can be enhanced, and high sound absorption characteristics can be obtained in a wide frequency range from medium to high frequencies.

As shown in FIG. 27, in the silicone foams of Examples 1 to 3 (equivalent to Comparative Example 1) having a closed-cell structure before application of a compressive force, a scanning electron microscope (SEM) observation of the cross section revealed that: Rounded cells were confirmed as a whole, and no breakage of cells was observed in the skin layer of the cross section or inside. Corresponding to Examples 1 to 4), as shown in FIG. 28, observation of the cross section with a scanning electron microscope (SEM) shows that the bubbles undergo buckling deformation and burst when compression is applied. Partially broken air bubbles P on the surface layer and inside of the cross section of the sound absorbing material, and voids Q formed by broken air bubbles inside the sound absorbing material are confirmed. Therefore, it can be inferred that the non-uniform presence of broken cell walls in the polymer phase and the presence of voids in the polymer phase are also factors that contribute to the high sound absorption coefficient in the medium frequency range.

As described above, the sound-absorbing material according to the present embodiment is a sound-absorbing material obtained by applying a compressive force to a foam having closed cells. have.

According to the sound absorbing material according to the present embodiment, since the cell structure is a mixture of cells that are communicated by compression and independent cells, the friction with the cell wall, the skeleton, and the cell film 1 in the cells that are communicated by compression, and the viscosity・Sound absorption effect due to ventilation resistance, film vibration of base material (resin, rubber or elastomer), sound absorption effect due to resonance, sound absorption effect due to air bubbles, especially film vibration and resonance in interconnected bubbles having a bubble membrane 1 due to communication by compression Thus, even with a small thickness and light weight, the sound absorbing property in the middle frequency range can be enhanced, and high sound absorbing property can be obtained in a wide frequency range from the middle frequency to the high frequency. Furthermore, even if the sound absorption coefficient is increased, the sound insulation coefficient is high because of the cell structure of the cells that are communicated by compression and the closed cells, and the sound absorption coefficient and the sound insulation coefficient are compatible. Therefore, noise diffusion can be effectively prevented.

In particular, by applying a compressive force to a foam having a compressive stress in the range of 2 to 30 kPa when compressed by 25%, the communication rate of the cells is increased and the sound absorption rate in the medium frequency range is stabilized. can be enhanced.
Furthermore, by pressing the foam so that the compressibility is 50 to 95%, the sound absorption coefficient in the middle frequency range can be further increased.

Further, the above embodiment has communicating cells and closed cells, has a specific gravity in the range of 0.08 to 0.4, and has a compressive stress in the range of 2 to 4.8 kPa when compressed by 25%. It can also be regarded as the invention of sound absorbing materials.

That is, it has a hybrid cell structure of communicating cells and closed cells, and has a specific gravity within the range of 0.08 to 0.4 and a compressive stress within the range of 2 to 4.8 kPa when compressed by 25%. Friction with cell walls, skeleton and bubble film 1 in cells communicated by compression, sound absorption effect due to viscosity and airflow resistance, base material (resin, rubber or elastomer). sound absorption effect due to membrane vibration and resonance, air bubbles, especially membrane vibration in interconnected bubbles having a bubble membrane 1 due to communication by compression, sound absorption effect due to resonance, etc. A high sound absorbing property can be obtained in a wide frequency range over high frequencies. Furthermore, even if the sound absorption coefficient is increased, the sound insulation coefficient is high because of the cell structure of closed cells and closed cells that are communicated by compression and the specific gravity is high. Therefore, noise diffusion can be effectively prevented. In addition, since the compressive stress at 25% compression is within the range of 2 to 4.8 kPa, the mechanical strength is also maintained, and the vibration and noise caused by sound propagation in the medium to high frequency range can be effectively suppressed for a long period of time. It is possible to absorb and block.

In particular, when the sound absorbing material is made of silicone foam, it has high heat resistance, so that the application range can be widened, and a high sound absorbing effect can be obtained even when the sound absorbing material is applied around a high heat source. In addition, since the physical properties of the silicone phase (silicone resin phase, silicone rubber phase) are less likely to change due to changes in temperature, a stable sound absorption coefficient can be obtained. Furthermore, the sound absorption coefficient in the middle frequency range is excellent, and the maximum sound absorption coefficient can be increased.

In addition, a sound absorbing material having open cells and closed cells is produced by foaming and curing a two-liquid addition reaction curing silicone material to form a foam having closed cells and applying a compressive force to the foam. , Automatic application using a coating device such as a coating robot is possible, simplifying the work of construction. Furthermore, it can be formed into an arbitrary coating shape, is easy to adjust the shape after coating, is easy to handle, and does not waste scraps. In addition, it can be foamed and cured in an open mold without being molded in a specific closed mold. In particular, a liquid silicone material that is applied to a desired site, then foamed and cured enables a high filling rate and high adhesion in a closed space, and reduces noise due to resonance in the closed space. The effect of suppressing the increase is also obtained.

In addition, when the average cell diameter of the closed cells and the open cells is within the range of 100 to 2000 μm and the average thickness of the cell walls is within the range of 0.5 to 40 μm, the viscous loss can be minimized with an appropriate cell rate. Since a large amount of air is included, the sound absorption coefficient in the medium frequency range can be stably increased, the sound insulation effect is excellent, and the compatibility between sound absorption and sound insulation is excellent.

Then, if the normal incident sound absorption coefficient in the frequency range of 1250 Hz to 4000 Hz measured at a thickness of 10 mm is 0.45 or more, and the maximum sound absorption coefficient in the frequency range of 1250 Hz to 4000 Hz is 0.5 or more, Due to its high sound absorption characteristics in a frequency band that is easy for humans to hear, it is also effective against external noise in automobiles and the like, and has a high effect of suppressing the diffusion of noise to the surroundings.

In particular, when the sound absorbing material is made of silicone foam, the compressive stress when the foam that imparts compressive force is compressed by 25% is preferably 2 to 20 kPa, more preferably 3 to 15 kPa, still more preferably 4 Within the range of up to 10 kPa, the rate of open air bubbles can be increased by applying a compressive load, and sound absorption characteristics showing a high sound absorption coefficient can be stably obtained in a wide frequency range from the middle frequency range to the high frequency range. .
The sound absorbing material made of silicone foam to which a compressive force is applied and the cells are communicated has a specific gravity of preferably 0.1 to 0.3, more preferably 0.11 to 0.28, and still more preferably , is in the range of 0.13 to 0.25, and the compressive stress at 25% compression is preferably 2.5 to 4 Kpa, more preferably 2.6 to 3.5 Kpa, still more preferably, If it is within the range of 2.8 to 3 Kpa, a moderate cell rate is obtained, and the cell rate that is made open by applying a compressive load is high, and is high in a wide frequency range from the middle frequency range to the high frequency range. A sound absorption characteristic indicating a sound absorption coefficient can be stably obtained.
Furthermore, when the sound absorbing material is made of silicone foam, the average cell diameter of the cells is preferably in the range of 100 to 500 μm, more preferably 100 to 400 μm, still more preferably 100 to 300 μm, and the cell wall is preferably in the range of 0.5 to 10 μm, more preferably 0.6 to 5 μm, and even more preferably 0.8 to 3 μm, medium frequencies including frequency bands that are easy for humans to hear It can exhibit stable and excellent sound absorption characteristics in a wide frequency band from low to high frequencies, and also has excellent sound insulation effect.

Further, in the above embodiment, the sound absorbing material made of resin, elastomer or rubber foam has closed cells and interconnected cells, and the cells on the surface of the sound absorbing material are observed with a scanning electron microscope (SEM). In fact, it can be regarded as an invention of a sound absorbing material mainly composed of bubbles B having wrinkles a and curled parts b around the opening, and having an opening shape with corners d and pointed parts d. .

That is, when the bubbles on the surface of the sound-absorbing material are observed with a scanning electron microscope (SEM), the bubbles have a wrinkled part a or a curled part b around the opening, in a mixed bubble structure of communicating bubbles and closed cells. Those mainly composed of bubbles B having an opening shape with a corner d or a pointed head d include bubbles that are communicated by compression. Friction with the membrane 1, sound absorption effect due to viscosity/air resistance, membrane vibration of the base material (resin, rubber or elastomer), sound absorption effect due to resonance, bubbles, especially in communication bubbles having a bubble membrane 1 due to communication by compression Due to the sound absorbing effect of membrane vibration and resonance, etc., the sound absorbing property in the middle frequency range can be enhanced, and high sound absorbing property can be obtained in a wide frequency range from the middle frequency to the high frequency. Furthermore, even if the sound absorption coefficient is increased, the sound insulation coefficient is high because of the cell structure of closed cells and closed cells that are communicated by compression and the specific gravity is high. Therefore, noise diffusion can be effectively prevented.
In addition, there is flexibility and elasticity due to the mixed cell structure of communicating cells and closed cells, and there are also flexibility and elasticity due to the base material resin, elastomer or rubber, so resonance, membrane vibration, and elastic loss In addition to the sound absorbing effect, there is also a change in air flow resistance due to the coexistence of both closed cells and open cells of different sizes, and a sound absorbing effect due to spatial resonance in the cells.

In carrying out the present invention, the configuration, components, composition, manufacturing method, and the like of other parts of the sound absorbing material are not limited to the above examples.
Further, all of the numerical values given in the embodiments and examples of the present invention do not indicate critical values, and certain numerical values are values determined from manufacturing costs, forms that are easy to manufacture, etc. Since these are preferred values, even if the above numerical values are slightly changed within the permissible values, the implementation thereof is not denied.

Claims (8)

A sound absorbing material obtained by applying a compressive force to a foamed body made of resin, elastomer or rubber having closed cells,
Having the closed cells and the connected cells in which the cells are connected by applying the compressive force,
A sound absorbing material having a specific gravity within a range of 0.08 to 0.4 and a compressive stress within a range of 2 to 4.8 Kpa when compressed by 25%. 2. The sound absorbing material according to claim 1, wherein the compressive force is applied to the foam having a compressive stress in the range of 2 to 30 kPa when compressed by 25%. 3. The sound absorbing material according to claim 1, wherein the compressive force is applied to the foam so that the compressibility is 50 to 95%. The sound absorbing material according to any one of claims 1 to 3, wherein the foam is formed by foaming and curing a two-liquid addition reaction curing silicone material. A sound absorbing material made of resin, elastomer or rubber foam,
having closed cells and communicating cells,
When the bubbles on the surface of the sound absorbing material are observed with a scanning electron microscope, the bubbles mainly have wrinkles or curled portions around the opening, or have an opening shape with corners or cusps. A sound absorbing material characterized by: 6. The sound absorbing material according to claim 1, wherein said foam is made of silicone. The closed cells and the continuous cells have an average cell diameter in the range of 100 to 2000 μm, and an average cell wall thickness in the range of 0.5 to 40 μm . 7. The sound absorbing material according to any one of items 6 . Furthermore, the normal incident sound absorption coefficient in the frequency range of 1250 Hz to 4000 Hz when measured at a thickness of 10 mm is 0.45 or more, and the maximum sound absorption coefficient in the frequency range of 1250 Hz to 4000 Hz is 0.5 or more. The sound absorbing material according to any one of claims 1 to 7, characterized by:

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