JP6916878B2 - Sound absorbing materials, vehicle parts and automobiles - Google Patents

Description

The present invention relates to sound absorbing materials, vehicle parts and automobiles.

Vehicles such as automobiles are machines that have a power source such as an engine and can be moved by human operation, and generate various vibrations and noises. The sound transmitted to the inside of the vehicle includes not only the sound generated by the power source but also the sound generated outside the vehicle such as road noise, tire pattern noise, wind noise, etc. generated when the vehicle is running. .. If these sounds are transmitted to the inside of the vehicle, it causes discomfort to people. Therefore, soundproofing materials are used in the engine, engine room, interior, body, exhaust pipe area, etc. Measures are being taken.

In addition, with the technological improvement of automobiles, there is a need for new soundproofing measures for automobiles. For example, lowering the center of gravity and ground clearance of automobiles is being considered as one of the measures to improve the fuel efficiency of automobiles. By lowering the center of gravity of the vehicle, the stability and operability of the vehicle can be improved, and by lowering the minimum ground clearance, air resistance can be reduced. However, as the minimum ground clearance of the vehicle becomes lower, the viscosity of the air flowing between the vehicle and the road surface during traveling increases. Then, noise generated from the road surface during running, such as tire pattern noise (frequency range of 500 to 3000 Hz, also simply referred to as pattern noise), is difficult to be reflected and diffused to the surroundings under the vehicle body, and the degree of noise entering the vehicle is high. Is estimated to be high. Similar problems can occur in electric vehicles.

Therefore, if the center of gravity and ground clearance of a car are lowered in order to improve the fuel efficiency of the car, it is assumed that the noise that was conventionally diffused outside the car will be transmitted to the person in the car. .. In particular, it is considered that these noises are likely to enter from the rear part of the vehicle and the bottom of the lower part of the luggage room (underfloor space) where the accommodation space is arranged. Since these noises include noises in the frequency range of 500 to 2000 Hz, which are unpleasant for humans, countermeasures are required.

Patent Document 1 describes an introduction passage that opens on one side of a flexible porous foam formed by foam molding, and a hollow portion that is formed in the back of the introduction passage and has a cross-sectional area larger than that of the introduction passage. A sound absorbing material having a large number of resonance chambers is disclosed.

Patent Document 2 discloses a sound absorbing / insulating structure comprising a resin molded body having a plurality of independent blind cavities having openings on the front surface or the back surface and a sound absorbing material, and having a specific 100 Hz to 10 kHz resonance sound absorbing peak frequency. Has been done.

Japanese Unexamined Patent Publication No. 08-260589 Japanese Unexamined Patent Publication No. 2001-249666

Here, the sound absorbing material described in Patent Document 1 and the resin molded product described in Patent Document 2 are formed with holes called a Helmholtz resonance structure.

Here, the Helmholtz resonance structure will be described.
20 (a) is a perspective view schematically showing a general Helmholtz resonance mechanism, FIG. 20 (b) is a sectional view taken along line AA of FIG. 20 (a), and the Helmholtz resonance mechanism resonates. The state of doing is schematically shown.
As shown in FIG. 20A, a general Helmholtz resonance mechanism 500 includes a columnar introduction passage 510 and a hollow portion 520.
The introduction passage 510 is columnar and has a diameter d ₅₁₀ , a length L _510, and a cross-sectional area S ₅₁₀ . Further, the hollow portion 520 has a volume V ₅₂₀ .
_{Further, air A 510} is present in the introduction passage 510, _{and air A 520} is present in the hollow portion 520.

Here, the case where the sound reaches the introduction passage 510 of the general Helmholtz resonance mechanism 500 will be described.
First, the air _{A 520} in the hollow portion 520 can not exit to the outside from the other inlet passage 510. Further, as shown in FIG. 20B, when the air A ₅₁₀ of the introduction passage 510 tries to enter the hollow portion 520, the air A ₅₂₀ in the hollow portion 520 is an elastic body, so that the air A _{510 of the introduction passage 510 is formed.} Try to push it out. That is, the air _{A 520} in the hollow portion 520 will serve as a spring.
Here, reach the sound inlet passage 510, when air _{A 510} of the introduction passage 510 is about to enter the hollow portion 520, given the air _{A 510} of the introduction passage 510 and rigid, the air _{A 510} of the introduction passage 510 The motion can be expressed as a simple vibration motion, and the frequency f at that time can be approximately calculated by the following equation (2).

（式（２）中、ｃは音速である。）

(In equation (2), c is the speed of sound.)

Further, at this frequency (that is, the resonance frequency), the sound reaching the introduction passage 510 is resonated and canceled.
This is the principle that sound is absorbed by the Helmholtz resonance mechanism.

In reality, the air A ₅₁₀ in the introduction passage 510 is not a rigid body, and the surrounding air also _{affects the air A 510} in the introduction passage 510.
Therefore, the above equation (2) is corrected as in the following equation (3) to calculate the resonance frequency.

（式（３）中、ｃは音速である。）

(In equation (3), c is the speed of sound.)

However, even if the Helmholtz resonance mechanism is designed so that the resonance frequency becomes a desired frequency based on the above equation (3), the sound absorption frequency of the actual sound absorbing material may deviate from the calculated resonance frequency. ..
Therefore, there is a problem that the noise in the frequency range of 500 to 2000 Hz, which is unpleasant for humans, cannot be sufficiently absorbed.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a sound absorbing material capable of taking measures against noise in the frequency range of 500 to 2000 Hz, which is unpleasant for humans. ..

The present inventors have found that the cause of the deviation between the calculated resonance frequency of the Helmholtz resonance mechanism and the sound absorption frequency of the actual Helmholtz resonance mechanism is due to the surface roughness of the introduction passage, and completed the present invention. ..

That is, the sound absorbing material of the present invention is a sound absorbing material having a non-through hole, and the non-through hole of the sound absorbing material is a hollow portion connected to the outside through an introduction passage opening on the surface and the introduction passage. When the Helmholtz resonance structure is formed, the equivalent circle diameter of the introduction passage is d, the length is L, the opening area is S, the surface roughness is Ra, and the volume of the hollow portion is V. The circle-equivalent diameter d is 1 to 30 mm, the length L is 1 to 20 mm, and 500 Hz ≦ f ≦ 2000 Hz holds for f (Hz) obtained by the following formula (1). And.

（式（１）中、音速ｃは３４０００ｃｍ／ｓｅｃであり、Ｒａが０μｍを超え、０．１μｍ以下の場合にはαは１．１０であり、Ｒａが０．１μｍを超え、２．０μｍ以下の場合にはαは１．１５であり、Ｒａが２．０μｍを超える場合にはαは１．１８である。）

(In the formula (1), the speed of sound c is 34000 cm / sec, Ra is more than 0 μm and 0.1 μm or less, α is 1.10, Ra is more than 0.1 μm and 2.0 μm or less. In the case of, α is 1.15, and when Ra exceeds 2.0 μm, α is 1.18.)

In a sound absorbing material having a Helmholtz resonance structure, the surface roughness of the introduction passage is a factor that affects the movement of air existing in the introduction passage.
Therefore, it is necessary to correct the calculation formula for obtaining the resonance frequency due to the difference in surface roughness.
The sound absorbing material of the present invention is designed based on the calculation formula with such correction.
Therefore, in the sound absorbing material of the present invention, the actual sound absorbing frequency is set between 500 Hz and 2000 Hz by designing the sound absorbing material so that the value of f (Hz) calculated by the equation (1) is 500 Hz to 2000 Hz. It can be adjusted and can reliably absorb noise in the frequency band of 500 Hz to 2000 Hz, which is unpleasant for humans.

The circle-equivalent diameter is the diameter when the cross-sectional area of the introduction passage is replaced with a perfect circle having the same area when the introduction passage is cut in a direction perpendicular to the length direction. If the introduction passage is a perfect circle, the diameter may be used as it is as the diameter equivalent to the circle.

Note that c in the equation (1) is the speed of sound, and in the present invention, the speed of sound c = 34000 cm / sec is used as a constant in the equation (1).

In the sound absorbing material of the present invention, it is desirable that the introduction passage is cylindrical.
It is advantageous that the introduction passage is columnar because there is no anisotropy in the sound absorption characteristics.

The sound absorbing material of the present invention is preferably made of a resin and / or a fibrous material. The resin is preferably an elastomer such as a foamed resin or rubber.
If the sound absorbing material is made of resin, it is easy to reduce the weight, which is particularly desirable as a vehicle part.
Further, when the resin is a foamed resin, its weight can be made lighter, and it can contribute to the improvement of fuel efficiency when it is used as a vehicle component.
In the present invention, it may be a composite material of resin and fiber. As a method of compounding, the resin and the fiber may be mixed, or the resin and the fiber may be combined in a block shape.

The vehicle component of the present invention is characterized by comprising the sound absorbing material of the present invention.
Since the sound absorbing material of the present invention has excellent soundproofing performance, it is excellent as a vehicle component.
Examples of vehicle parts provided with the sound absorbing material of the present invention include a raising material, a partition member, a luggage box, and the like.

The automobile of the present invention is characterized in that the introduction passage of the sound absorbing material of the present invention is arranged toward the road surface.
By arranging the sound absorbing material of the present invention in such an orientation, it is possible to absorb the noise of the tire pattern noise transmitted from the road surface and prevent the noise from being transmitted to the inside of the vehicle.

FIG. 1 is a cross-sectional view schematically showing an example of the sound absorbing material of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of the sound absorbing material of the present invention. FIG. 3A is an explanatory view schematically showing an example of a portion where the sound absorbing material of the present invention is arranged, and FIG. 3B is a partial enlargement of the region shown by the broken line portion in FIG. 3A. It is a figure. FIG. 4A is a perspective view schematically showing an example of a mold used in the method for producing a sound absorbing material of the present invention, and FIG. 4B is a cross-sectional view taken along the line BB of FIG. 4A. Is. FIG. 5 is an explanatory diagram schematically showing an example of a step of producing a foamed resin in the method for producing a sound absorbing material of the present invention. 6 (a) to 6 (c) are explanatory views schematically showing an example of a step of extracting protrusions from the foamed resin in the method for producing a sound absorbing material of the present invention. FIG. 7 is an explanatory diagram schematically showing a method of measuring the reverberation room sound absorption coefficient with respect to the sound absorbing material. FIG. 8 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-1. FIG. 9 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-2. FIG. 10 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-3. FIG. 11 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-4. FIG. 12 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-5. FIG. 13 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-6. FIG. 14 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-7. FIG. 15 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Comparative Example 1. FIG. 16 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Comparative Example 2. FIG. 17 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Comparative Example 3. FIG. 18 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 2-1. FIG. 19 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 3-1. 20 (a) is a perspective view schematically showing a general Helmholtz resonance mechanism, FIG. 20 (b) is a cross-sectional view taken along the line AA of FIG. 20 (a), and the Helmholtz resonance mechanism resonates. The state of doing is schematically shown.

(Detailed description of the invention)
Hereinafter, the present invention will be specifically described. The present invention is not limited to the following description, and can be appropriately modified and applied without changing the gist of the present invention.

The sound absorbing material of the present invention is a sound absorbing material having a non-through hole, and the non-through hole of the sound absorbing material comprises an introduction passage opening on the surface and a hollow portion connected to the outside through the introduction passage. It has a Helmholtz resonance structure, and when the equivalent circle diameter of the introduction passage is d, the length is L, the opening area is S, the surface roughness is Ra, and the volume of the hollow portion is V, the circle. The equivalent diameter d is 1 to 30 mm, the length L is 1 to 20 mm, and 500 Hz ≦ f ≦ 2000 Hz holds for f (Hz) obtained by the following formula (1). ..

（式（１）中、音速ｃは３４０００ｃｍ／ｓｅｃであり、Ｒａが０μｍを超え、０．１μｍ以下の場合にはαは１．１０であり、Ｒａが０．１μｍを超え、２．０μｍ以下の場合にはαは１．１５であり、Ｒａが２．０μｍを超える場合にはαは１．１８である。）

(In the formula (1), the speed of sound c is 34000 cm / sec, Ra is more than 0 μm and 0.1 μm or less, α is 1.10, Ra is more than 0.1 μm and 2.0 μm or less. In the case of, α is 1.15, and when Ra exceeds 2.0 μm, α is 1.18.)

In the present invention, it is presumed that the reason why the f (Hz) of the formula (1) satisfies 500 Hz to 2000 Hz makes it easier to absorb noise having a frequency of 500 Hz to 2000 Hz, which is unpleasant for humans, as follows.
In a sound absorbing material having a Helmholtz resonance structure, the surface roughness of the introduction passage is a factor that affects the movement of air existing in the introduction passage.
Therefore, it is considered necessary to correct the calculation formula for obtaining the resonance frequency due to the difference in surface roughness.
The sound absorbing material of the present invention is designed based on the calculation formula with such correction.
Therefore, in the sound absorbing material of the present invention, there is little deviation between f (Hz) calculated by the equation (1) and the actual sound absorbing frequency. Therefore, by setting the value of f (Hz) to 500 to 2000 Hz, which is a frequency band in which the value of f (Hz) is desired to be absorbed, noise in the band can be reliably absorbed.

In the sound absorbing material of the present invention, the equivalent circle diameter d is preferably 1 to 30 mm, and more preferably 3 to 25 mm.
The desirable size of the opening area S can be calculated from the length of the circle equivalent diameter d, but specifically, ^{it is preferably 0.8 to 706.8 mm 2} , and 7.1 to 490.9 mm. It is more desirable to be ^2.

In the sound absorbing material of the present invention, the length L is preferably 1 to 20 mm, more preferably 3 to 15 mm.

In the sound absorbing material of the present invention, the surface roughness Ra is preferably more than 0 and 15 μm or less, and more preferably 0.01 to 10 μm.
In the present invention, the surface roughness Ra of the introduction passage means the arithmetic mean roughness defined by JIS B 0601 (2001), and means a value measured by the following method.
First, the 10%, 30%, 50%, 70%, and 90% portions are set as the surface roughness measurement reference points in the direction from the hollow portion side end portion to the opposite end portion of the introduction passage.
Next, the surface roughness Ra in a square region centered on each surface roughness measurement reference point is measured using a laser type surface roughness measuring device (model name: KEYENCE product name: VX-9700). .. The measurement is performed as follows. First, prepare a measuring piece cut in the direction perpendicular to the cross section of the introduction passage. Next, the surface of the introduction passage of the measuring piece is turned to the upper surface, and the measuring device is fixed to the measuring device. Laser measurement is performed. At this time, the surface roughness curve of the surface is measured and drawn at an interval of 10 μm in a square area with a length of 100 μm and a width of 100 μm around the measurement reference point (thus, 10 surface roughness curves are drawn). Ra is calculated from each surface roughness curve, and the average of these 10 Ra values is defined as the surface roughness Ra of the measurement reference point. The same measurement is performed at each measurement reference point, and the average value of the measured values of the five measurement reference points is defined as the surface roughness Ra of the introduction passage.

In the sound absorbing material of the present invention, the volume V of the hollow portion is preferably a 24～329,860Mm ^3, and more desirably a 257~246,766mm ^3.

In the sound absorbing material of the present invention, the volume of the introduction passage is represented by the opening area S × the length L.
Theoretically, in the Helmholtz resonance structure, when the equation for obtaining the resonance frequency holds, the volume of the hollow portion is sufficiently larger than the volume of the introduction passage.

In the sound absorbing material of the present invention, the introduction passage is preferably cylindrical, and when the introduction passage is cylindrical, it is desirable that the cross-sectional shape in the direction perpendicular to the length direction is a perfect circle.
It is advantageous that the introduction passage is columnar because there is no anisotropy in the sound absorption characteristics.

In the sound absorbing material of the present invention, the shape of the hollow portion is not particularly limited, and may be a spherical hollow shape or a columnar hollow shape. Among these, a columnar hollow shape is desirable, and a columnar hollow shape is more desirable.
When the hollow portion has a columnar hollow shape, its height is preferably 1 to 20 mm, and more preferably 3 to 15 mm.

In the sound absorbing material of the present invention, the thickness of the sound absorbing material is preferably 10 to 120 mm. It is more desirable that the thickness of the sound absorbing material is 20 to 100 mm.
When the thickness of the sound absorbing material is less than 10 mm, it becomes difficult to form a non-through hole in which the Helmholtz resonance structure functions.
If the thickness of the sound absorbing material exceeds 120 mm, the sound absorbing material becomes too large and it becomes difficult to arrange it in a desired space.

The sound absorbing material of the present invention is preferably made of a resin and / or a fibrous material. The resin is preferably an elastomer such as a foamed resin or rubber.
If the sound absorbing material is made of resin, it is easy to reduce the weight, which is particularly desirable as a vehicle part.
Further, when the resin is a foamed resin, its weight can be made lighter, and it can contribute to the improvement of fuel efficiency when it is used as a vehicle component.
In the present invention, it may be a composite material of resin and fiber. As a method of compounding, the resin and the fiber may be mixed, or the resin and the fiber may be combined in a block shape.

The resin is preferably any of a foamed resin composed of foamable resin particles (beads), a foamed resin having bubbles, a fiber, a thermoplastic resin, and a thermosetting resin.
It is preferable that the resin has a density ρm of 0.01 to 1 g / cm ³ , and more preferably a density ρm of 0.02 to 0.1 g / cm ³ . When the resin is a foamed resin, the density of the resin refers to the density of the foamed resin that has been foam-molded.
When the density of the resin is within the above range, it is easy to obtain the strength required as a sound absorbing material.
On the other hand, if the density of the resin ^{is less than 0.01 g / cm 3} , sufficient mechanical strength as a sound absorbing material may not be obtained. Further, when the density of the resin ^{exceeds 1 g / cm 3} , the weight of the sound absorbing material increases, which hinders the weight reduction of the vehicle.
Further, the resin is more preferably a foamed resin composed of foamable resin particles (beads). When the resin is a foamed resin composed of foamable resin particles (beads), the weight of the sound absorbing material can be reduced while maintaining the strength, which can contribute to the improvement of fuel efficiency when used for vehicle parts. ..
The foamed resin is obtained by foaming and molding foamable resin particles.

The foamable resin particles (beads) used in the sound absorbing material of the present invention are particles containing a foaming agent inside the resin particles, and known particles can be preferably used.
Examples of the resin component constituting the foamable resin particles include olefin resins such as polyethylene and polypropylene, and styrene resins such as polystyrene.
Examples of the styrene resin include a styrene homopolymer and a copolymer obtained by copolymerizing styrene and a monomer (or a derivative thereof) copolymerizable with styrene. The styrene copolymer may be a block copolymer, a random copolymer, or a graft copolymer.
Examples of the foaming agent include hydrocarbons such as propane, butane, and pentane.

The foamable resin particles used in the sound absorbing material of the present invention include flame retardants, flame retardants, processing aids, fillers, antioxidants, light-resistant stabilizers, antistatic agents and colorings, if necessary. Known additives such as agents may be added. As an example of the use of additives, if a black colorant is used, stains will not be noticeable.

Flame retardants include metal hydrated flame retardants such as aluminum hydroxide and magnesium hydroxide, phosphoric acid flame retardants such as red phosphorus and ammonium phosphate, tetrabromobisphenol A (TABB), brominated polystyrene, and chlorinated paraffin. Halogen-based flame retardants such as, ammonium carbonate, nitrogen-based flame retardants such as melamine cyanurate, and the like can be mentioned.
Examples of the flame retardant aid include antimony trioxide and antimony pentoxide.
Examples of the processing aid include stearate, liquid paraffin, olefin wax, stearylamide compound, epoxy compound and the like.
Examples of the filler include silica, talc, calcium silicate and the like.
Examples of the antioxidant include alkylphenols, alkylenebisphenols, alkylphenol thioethers, β, β-thiopropionic acid esters, organic phosphite esters, phenol-nickel complexes and the like.
Examples of the light resistance stabilizer include benzotriazole-based ultraviolet absorbers and hindered amine-based stabilizers.
Examples of the antistatic agent include low molecular weight antistatic agents such as fatty acid ester compounds, aliphatic ethanolamine compounds and aliphatic ethanolamide compounds, and high molecular weight antistatic agents.
Examples of the colorant include dyes and pigments.

The average particle size of the foamable resin particles used in the sound absorbing material of the present invention is preferably 300 μm to 2400 μm, and more preferably 800 μm to 2000 μm.
The foaming ratio of the foamable resin particles is preferably 10 to 60 times.
By setting the foaming ratio in the range of 10 to 60 times, it becomes easy to adjust ^{the density of the resin in the range of 0.02 to 0.1 g / cm 3.}
On the other hand, when the foaming ratio is less than 10 times, the sound absorbing material may become too hard or too heavy. If the foaming ratio exceeds 60 times, the strength of the sound absorbing material may be insufficient.

As the foamed resin having bubbles used in the sound absorbing material of the present invention, polyurethane or the like can be used. By mixing polyurethane, a foaming agent, etc. as a main agent, foaming, and molding, a foamed resin having air bubbles can be obtained, and a sound absorbing material can be produced by this.

The resin used in the sound absorbing material of the present invention may be a thermoplastic resin or a thermosetting resin.
As the thermoplastic resin used in the sound absorbing material of the present invention, polypropylene resin, polyethylene resin, polyester resin, polystyrene resin and the like can be used. A sound absorbing material can be produced by molding a thermoplastic resin as a resin pellet, heating the resin pellet, and performing a molding process such as injection molding or extrusion molding.
As the thermosetting resin used in the sound absorbing material of the present invention, melamine resin, urea resin, polyurethane, polyurea, polyamide, polyacrylamide and the like can be used. A sound absorbing material can be produced by preheating a thermosetting resin, putting it in a mold, pressurizing it, raising the mold temperature, and curing it.

The fibers used in the sound absorbing material of the present invention are preferably organic fibers and inorganic fibers, and polyester, polyamide, acetate and the like can be used as the organic fibers. As the inorganic fiber, alumina, silica, and mullite fiber are desirable. It is desirable to bond the fibers together with a binder to form a felt.

Further, the portion other than the non-through hole portion of the sound absorbing material of the present invention may be made of a material such as an inorganic material or a metal material in addition to the resin material.

In the sound absorbing material of the present invention, the arrangement pattern of the non-through holes opened on the surface may be a square arrangement in which the non-through holes are arranged at the vertices of the square on a plane in which the squares are continuously arranged vertically and horizontally, and an equilateral triangle is formed. It may be a staggered arrangement in which non-through holes are arranged at the vertices of a triangle in a plane arranged continuously in the vertical and horizontal directions.
Among these, a staggered arrangement is desirable. When the arrangement pattern of the non-through holes is a staggered arrangement, all the adjacent non-through holes tend to be evenly spaced, so that the sound absorption effect is improved.

An example of such a sound absorbing material of the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view schematically showing an example of the sound absorbing material of the present invention.

As shown in FIG. 1, the sound absorbing material 100 is a sound absorbing material having a non-through hole 101.
The non-through hole 101 of the sound absorbing material 100 has a Helmholtz resonance structure including an introduction passage 110 opening on the surface and a hollow portion 120 connected to the outside via the introduction passage 110.
In the sound absorbing material 100, the introduction passage 110 is a columnar shape having _{a diameter d 110} and a length L _110.
The area of the opening of the introduction passage 110 is S ₁₁₀ , and the surface roughness of the introduction passage 110 is Ra ₁₁₀ .
In the sound absorbing material 100, the hollow portion 120 has a columnar hollow shape having _{a volume V 120.}

（式（１´）中、音速ｃは３４０００ｃｍ／ｓｅｃであり、Ｒａ_１１０が０μｍを超え、０．１μｍ以下の場合にはαは１．１０であり、Ｒａ_１１０が０．１μｍを超え、２．０μｍ以下の場合にはαは１．１５であり、Ｒａ_１１０が２．０μｍを超える場合にはαは１．１８である。）In the sound absorbing material 100, the diameter d ₁₁₀ is 1 to 30 mm, and the length L ₁₁₀ is 1 to 15 mm.
Then, 500 ≦ f ≦ 2000 holds for f (Hz) obtained by the following formula (1 ′).

(In the equation (1'), the speed of sound c is 34000 cm / sec, Ra ₁₁₀ exceeds 0 μm, and when it is 0.1 μm or less, α is 1.10 and Ra ₁₁₀ exceeds 0.1 μm, 2 When it is 0.0 μm or less, α is 1.15, and when Ra ₁₁₀ exceeds 2.0 μm, α is 1.18.)

The surface condition of the wall surface of the introduction passage is not flat but has irregularities. This unevenness differs depending on the material, molding process, and the like. Therefore, the length of the introduction passage is not the same as the length in the cross section of the introduction passage. Therefore, the resonance frequency calculated by the above equation (3) may deviate from the sound absorption frequency of the actual sound absorbing material. Therefore, it is presumed that the deviation between the calculated resonance frequency and the actual sound absorption frequency of the sound absorbing material can be eliminated by correcting with the correction coefficient α due to the surface roughness of the introduction passage and using Eq. (1). NS.

By the way, in the sound absorbing material of the present invention, n introduction passages (n is a natural number of 2 or more) having the same shape may be formed in one hollow portion.
In this case, when the sound reaches each introduction passage of the sound absorbing material, the air in each introduction passage is simultaneously pushed toward the hollow portion. Since the air in the hollow part is an elastic body, it tries to push the air in the introduction passage to the outside.
The force that pushes the air out of the introduction passage depends on the volume of air in the hollow portion, in which case the Helmholtz resonance mechanism has a hollow portion with a volume of V / n in one introduction passage. It can be considered that there are n pieces.
That is, the force for pushing air out to one introduction passage can be approximately calculated based on the value obtained by dividing the volume of air in the hollow portion by the number of introduction passages.
That is, in the above equation (1), f can be calculated by calculating V as a value obtained by dividing the volume V of the entire hollow portion by n.

An example of such a sound absorbing material of the present invention will be described below with reference to the drawings.
FIG. 2 is a cross-sectional view schematically showing an example of the sound absorbing material of the present invention.

As shown in FIG. 2, the sound absorbing material 200 is a sound absorbing material having a non-through hole 201.
The non-through hole 201 of the sound absorbing material 200 has a Helmholtz resonance structure composed of n introduction passages 210 (n is a natural number of 2 or more) opening on the surface and a hollow portion 220 connected to the outside via the introduction passage 210. is doing.
In the sound absorbing material 200, the introduction passage 210 is a columnar shape having _{a diameter d 210} and a length L _210.
The area of the opening of the introduction passage 210 is S ₂₁₀ , and the surface roughness of the introduction passage 210 is Ra ₂₁₀ .
In FIG. 2, the volume of the entire hollow portion 220 is indicated by reference _{numeral V 220.}

In the sound absorbing material 200, the diameter d ₂₁₀ is 1 to 30 mm, and the length L ₂₁₀ is 1 to 15 mm.

As shown in FIG. 2, it can be considered that the sound absorbing material 200 has n Helmholtz resonance structures having a _{hollow portion having a volume of V 220 / n.}
Therefore, in the above equation (1), f can be calculated by calculating _{V as V 220 / n.}

An example in which the sound absorbing material of the present invention is used as a vehicle component and an example of an automobile in which the sound absorbing material of the present invention is arranged will be described with reference to FIGS. 3 (a) and 3 (b).
FIG. 3A is an explanatory view schematically showing an example of a portion where the sound absorbing material of the present invention is arranged, and FIG. 3B is a partial enlargement of the region shown by the broken line portion in FIG. 3A. It is a figure.
As shown in FIG. 3A, the automobile 1 includes a luggage room 3 behind the rear seat 2. A plate-shaped floor member 4 is laid under the luggage room 3, and an underfloor space 5 exists under the floor member 4.
Under the underfloor space 5, the sound absorbing material 100 is arranged in the automobile so that the open surface of the non-through hole 101 faces the road surface direction.

The sound absorbing material 100 of the present invention is designed so that f (Hz) is 500 ≦ f ≦ 2000 in consideration of the surface roughness of the introduction passage 110.
Therefore, it is possible to prevent noise in the frequency range of 500 to 2000 Hz, which makes people feel uncomfortable, from entering the vehicle interior, and it is possible to reduce that people in the vehicle interior feel uncomfortable.

Subsequently, a method for producing the sound absorbing material of the present invention will be described.
The sound absorbing material of the present invention can be produced by forming a non-through hole having a Helmholtz resonance structure in the resin layer.
The method for forming the non-through hole in the resin layer of the sound absorbing material of the present invention is not particularly limited, but for example, the through hole may be manually formed in the resin layer using a tool such as a cutter.
Further, in the case of industrial mass production, a method of arranging a protrusion having a shape of an introduction passage and a hollow portion in a mold, forming a resin layer in the mold, and then removing the protrusion can be mentioned. An example of such a method will be described below.

In the method for producing a sound absorbing material of the present invention, first, a foamed resin is produced by a bead method in which foamable resin particles are filled in a mold formed by arranging a plurality of protrusions protruding inside and heated and foamed.
Next, non-through holes can be formed in the foamed resin by extracting the protrusions from the foamed resin.

In the above method, a foamed resin is produced by a bead method in which foamed resin particles are filled in a mold and foamed by a method such as steam heating.
Since a plurality of protrusions protruding inward are arranged in the mold, the foamed resin particles are not filled in the protrusions. Therefore, by extracting the protrusion from the foamed resin, a non-through hole corresponding to the shape of the protrusion can be formed in the foamed resin.

The material of the protrusion is not particularly limited, but it is desirable that at least a part thereof is made of a resin elastic body.
When at least a part of the protrusion is made of a resin elastic body, the protrusion is deformed when the protrusion is pulled out from the foamed resin, and the protrusion becomes easy to pull out.

Further, it is desirable that the protrusion has a substantially mushroom shape including a shaft portion and an umbrella portion, and the shaft portion is fixed to the mold.
When the protrusion has a substantially mushroom shape consisting of a shaft portion and an umbrella portion and the shaft portion is fixed to the mold, the foamed resin is formed with an introduction passage corresponding to the shape of the shaft portion to form the shape of the umbrella portion. Correspondingly, a hollow portion will be formed.

In the protrusion, it is desirable that the shaft portion is made of metal and the umbrella portion is made of the resin elastic body.
When the shaft of the protrusion is made of metal, the mechanical strength is high, so that the protrusion is less likely to be damaged by repeated use, the life of the protrusion can be maintained for a long time, and a highly durable mold can be obtained. ..
Further, when the umbrella portion of the protrusion is made of a resin elastic body, only the umbrella portion can be deformed, so that the protrusion can be easily pulled out from the foamed resin.

In the protrusions, it is desirable that the heat resistant temperature of the resin elastic body is higher than the temperature of heat foaming of the foamable resin particles.
If the heat-resistant temperature of the resin elastic body is higher than the heat-foaming temperature of the foamable resin particles in the bead method, the shape of the protrusions is less likely to be deformed by the heat when the foamable resin particles are foamed, and the durability against repeated use. Is obtained.
Since the heating temperature of the foamable resin particles in the bead method is 80 to 150 ° C., it is desirable that the heat resistant temperature of the resin elastic body is higher than the above temperature, specifically 100 to 180 ° C. , 155 to 180 ° C. is more desirable.

In the protrusions, it is desirable that the A hardness of the resin elastic body is 50 ° or less.
When the A hardness of the resin elastic body is 50 ° or less, the shape of the non-through hole can be sufficiently maintained during molding of the foamed resin by heat foaming, and when the protrusions are removed from the foamed resin after molding, the protrusions are formed. It deforms and becomes easy to pull out.
The A hardness means the hardness using a type A durometer measured in accordance with JIS K 6253-3 (2012).

In the protrusions, the resin elastic body is preferably a silicone resin or a silicone gel.
When the resin elastic body is a silicone resin or a silicone gel, the heat-resistant temperature of the resin elastic body is high, so that the shape of the protrusions is not easily deformed during heating and foaming, and the resin elastic body has high durability in repeated use. Further, it is easily deformed when the protrusions are pulled out from the foamed resin, and the protrusions can be easily pulled out from the foamed resin. Further, even when a protrusion having a shape that forms a Helmholtz resonance structure is used, the protrusion (capsule portion) forming the hollow portion is deformed so that it can pass through the introduction passage, so that the protrusion is formed of foamed resin. The protrusions can be removed from the foamed resin without damaging the Helmholtz resonance structure.

An example of a method for manufacturing such a sound absorbing material will be described with reference to the drawings.

FIG. 4A is a perspective view schematically showing an example of a mold used in the method for producing a sound absorbing material of the present invention, and FIG. 4B is a cross-sectional view taken along the line BB of FIG. 4A. Is.
In the method for manufacturing the sound absorbing material, first, a mold 50 as shown in FIG. 4A is prepared.
The mold 50 has a plurality of protrusions 60 inside the mold 50. As shown in FIG. 4B, the protrusion 60 has a substantially mushroom shape including a shaft portion 61 and an umbrella portion 62, and the shaft portion 61 is fixed to the mold 50.

FIG. 5 is an explanatory diagram schematically showing an example of a step of producing a foamed resin in the method for producing a sound absorbing material of the present invention.
Next, as shown in FIG. 5, the foamed resin 102 is produced by a bead method in which the mold 50 is filled with foamable resin particles and heated and foamed.

6 (a) to 6 (c) are explanatory views schematically showing an example of a step of extracting protrusions from the foamed resin in the method for producing a sound absorbing material of the present invention.
As shown in FIG. 6A, a protrusion 60 composed of a shaft portion 61 and an umbrella portion 62 is embedded in the foamed resin 102 after foam molding, and the umbrella portion 62 is made of a resin elastic body.
When the protrusion 60 is pulled out from the foamed resin 102, the umbrella portion 62 is deformed as shown in FIG. 6 (b). This is because the umbrella portion 62 is made of a resin elastic body and is easily deformed, and the foamed resin 102 is not deformed. The protrusion 60 can be pulled out from the foamed resin 102 by passing the umbrella portion 62 while deforming.
When the protrusion 60 is pulled out from the foamed resin 102, the shape of the umbrella portion 62 returns to the original shape as shown in FIG. 6C, and the space in which the protrusion 60 is buried becomes the non-through hole 101. Of the non-through holes 101, the shape of the introduction passage 110 that opens to the surface corresponds to the shape of the shaft portion 61, and the shape of the hollow portion 120 connected to the outside via the introduction passage 110 corresponds to the shape of the umbrella portion 62. do.
A sound absorbing material can be manufactured through such a process.

In the sound absorbing material of the present invention, the surface roughness Ra of the introduction passage can be adjusted by adjusting the processing conditions of the introduction passage, for example, the hardness of the protrusion 60. Further, it can be adjusted by a polishing treatment, a roughening treatment such as sandblasting, or the like.

(Example)
Specific examples for explaining the present invention in more detail will be shown below, but the present invention is not limited to these examples.

(Example 1-1)
(Making a protrusion unit)
An aluminum substrate was prepared by drilling 10 holes (diameter 3 mm, depth 5 mm) so that the distance between the side surfaces of the hollow portions adjacent to the surface of the aluminum plate having a thickness of 10 mm was 10 mm in a staggered arrangement.
Subsequently, an acrylic mold was prepared for producing a protrusion to be attached to the aluminum substrate.
The acrylic mold can be divided into two (one is a male mold and the other is a female mold). The shape of a cylinder having a length of 10 mm has a substantially mushroom-shaped cavity in which the central axes of the cylinders are aligned and connected. In order to obtain a cavity of this shape, the surface of each divided mold was machined. On the surfaces of the male and female molds, dents (cavities) corresponding to the shapes obtained by dividing the above-mentioned substantially mushroom shape into two along the length direction are formed, respectively.
0.5 part of the curing agent [Shin-Etsu Chemical Co., Ltd., CAT-RM] is mixed with 100 parts of the main agent of the silicone resin [Shin-Etsu Chemical Co., Ltd., KE-17], and vacuum defoaming (defoaming) is performed. After performing foaming time (20 minutes), it was poured into the cavities of the female mold and the female mold, and the female mold and the female mold were combined and fixed with a rubber band, and cured at 70 ° C. for 20 minutes. After curing, the female mold and the female mold are separated, the cured product is taken out, and burrs are removed so that a cylinder having a diameter of 10 mm and a length of 10 mm and a cylinder having a diameter of 3 mm and a length of 15 mm align the central axes of each cylinder. A connected substantially mushroom-shaped molded body was obtained. The A hardness of the resin elastic body constituting the molded body was 50 °.
Subsequently, a protrusion unit in which 10 protrusions were fixed on the aluminum substrate was prepared by inserting an end portion having a diameter of 3 mm of the molded product into a hole in the aluminum substrate to a depth of 5 mm. The protrusion was composed of a cylindrical shaft portion having a diameter of 3 mm and a length of 10 mm and a cylindrical umbrella portion having a diameter of 10 mm and a length of 10 mm.

(Effervescent resin foam)
The protrusion unit is attached to the die holder to prepare the mold, and the pre-foamed primary foam particles (made of polypropylene, average particle diameter 3.5 mm, foaming agent: carbon dioxide) are filled in the mold and foamed with heated steam. A plate-shaped perforated foamed resin was prepared by molding (143 ° C., 10 seconds), removing it from the mold, and drying it at 80 ° C. for 12 hours. At this time, the foaming ratio of the foamed resin was 30 times.

(Separation of protrusion unit)
After foam molding, the foamed resin and the protrusion unit were taken out in an integrated state, and the foamed resin and the protrusion unit were separated.
As a result, a sound absorbing material having a non-through hole formed of an introduction passage and a hollow portion was produced.

In the sound absorbing material according to Example 1-1, the inner diameter d of the introduction passage was 3 mm, the length L was 10 mm, the opening area S was 7.1 mm ² , and the surface roughness Ra was 1.02 μm.
The volume V of the hollow portion was 785 mm ³ .
The surface roughness is a laser-type surface roughness measuring device (model name) with five measurement reference points of 10%, 30%, 50%, 70%, and 90% with respect to the length direction of the introduction passage. : Measured using KEYENCE product name: VX-9700). Before measurement, prepare a measuring piece cut along the cross section of the introduction passage. The surface of the introduction passage of the measuring piece is turned to the upper surface, the set is set, the magnification of the microscope of the laser type surface roughness measuring device is set to 50 times, the measurement reference point is focused, and the measurement is performed by the laser. At this time, the surface roughness Ra was measured in a square region with a length of 100 μm and a width of 100 μm around the measurement reference point, and as a result, Ra at the 10% position was 1.10 μm and Ra at the 30% position. : 0.97 μm, Ra at 50% position: 1.08 μm, Ra at 70% position: 1.00 μm, Ra at 90% position: 1.07 μm, and the average value of these 5 points was calculated. The surface roughness Ra was set to 1.02 μm.

(Examples 1-2 to 1-7, Example 2-1 and Example 3-1 and Comparative Examples 1 to 3)
Examples 1-2 to Examples are the same as in Examples 1-1, except that a mold is used so that the inner diameter of the hollow portion and the surface roughness Ra of the introduction passage are the values shown in Tables 1 and 2. The sound absorbing materials according to 1-7, Example 2-1 and Example 3-1 and Comparative Examples 1 to 3 were obtained.

(Sound absorption frequency measurement experiment)
Sound absorption by measuring the sound absorption coefficient of the sound absorbing materials of Examples 1-1 to 1-7, Example 2-1 and Example 3-1 and Comparative Examples 1 to 3 while changing the frequency. The frequency was measured.

The sound absorption coefficient was measured by the reverberation room method sound absorption coefficient test. The measurement was performed according to JIS A 1409-: 1998 "Measurement method of reverberation room sound absorption coefficient".
FIG. 7 is an explanatory diagram schematically showing a method of measuring the reverberation room sound absorption coefficient with respect to the sound absorbing material.
As shown in FIG. 7, when measuring the sound absorption coefficient, the sound absorbing material 300 according to each Example and each Comparative Example is placed on the floor surface 81 of the reverberation room 80 with the opening of the introduction passage facing up. Electrical noise is radiated from the noise signal generator 82 through the speaker 83 in the reverberation room 80. Next, the radiation of the sound is stopped, the sound is measured by the microphone 84, and the attenuation process is analyzed by the signal analyzer 85. The reverberation time, T1 [sec. ], The reverberation time, which is the time for the sound to be attenuated by 60 dB from the measured attenuation curve in the state after the test piece is placed on the floor surface, T2 [sec. ] Is asked. The measurement is performed at 300-5000 Hz.

(Calculation of reverberation room method sound absorption coefficient)
From the reverberation time obtained by the analysis and the surface area S of the test piece, the reverberation room method sound absorption coefficient αs is calculated by the following formula (4).

（式（４）中、Ｖ：室容積〔ｍ^３〕、ｃ：３４０００ｃｍ／ｓｅｃ（音速））

(In equation (4), V: chamber volume [m ³ ], c: 34000 cm / sec (sound velocity))

In the obtained sound absorption coefficient chart, the maximum value of the peak in the region where the sound absorption coefficient becomes large was defined as the sound absorption frequency.

The results of the absorption sound absorption length measurement experiment are shown in FIGS. 8 to 19 and Tables 1 and 2.
FIG. 8 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-1.
FIG. 9 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-2.
FIG. 10 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-3.
FIG. 11 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-4.
FIG. 12 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-5.
FIG. 13 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-6.
FIG. 14 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 1-7.
FIG. 15 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Comparative Example 1.
FIG. 16 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Comparative Example 2.
FIG. 17 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Comparative Example 3.
FIG. 18 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 2-1.
FIG. 19 is a graph of frequency-sound absorption coefficient of the sound absorbing material according to Example 3-1.

The sound absorbing material of each embodiment has a sound absorbing frequency in the range of 500 to 2000 Hz. Therefore, it is possible to absorb noise in the frequency range of 500 to 2000 Hz, which is an unpleasant frequency range for humans.

1 Automobile 2 Rear seat 3 Luggage room 4 Floor member 5 Underfloor space 50 Mold 60 Protrusion 61 Shaft 62 Umbrella 80 Reverberation room 81 Floor 82 Noise signal generator 83 Speaker 84 Microphone 85 Signal analyzer 100, 200, 300 Sound absorption Material 101, 201 Non-through hole 102 Foamed resin 110, 210, 510 Introduction passage 120, 220, 520 Hollow part 500 Helmholtz resonance mechanism

Claims (6)

A sound absorbing material with non-through holes
The non-through hole of the sound absorbing material has a Helmholtz resonance structure including an introduction passage opening on the surface and a hollow portion connected to the outside through the introduction passage.
The circle-equivalent diameter of the introduction passage is d, the length is L, the opening area is S, and the surface roughness is Ra.
When the volume of the hollow portion is V,
The circle equivalent diameter d is 1 to 30 mm.
The length L is 1 to 20 mm.
A sound absorbing material characterized in that 500 (Hz) ≤ f ≤ 2000 (Hz) holds for f (Hz) obtained by the following formula (1).

(In the formula (1), the speed of sound c is 34000 cm / sec, Ra is more than 0 μm and 0.1 μm or less, α is 1.10, Ra is more than 0.1 μm and 2.0 μm or less. In the case of, α is 1.15, and when Ra exceeds 2.0 μm, α is 1.18.) The sound absorbing material according to claim 1, wherein the introduction passage is cylindrical. The sound absorbing material according to claim 1 or 2, wherein the sound absorbing material is made of a resin and / or a fibrous material. The sound absorbing material according to claim 3, wherein the resin is a foamed resin. A vehicle component comprising the sound absorbing material according to any one of claims 1 to 4. An automobile according to any one of claims 1 to 4, wherein the introduction passage of the sound absorbing material is arranged toward the road surface.

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