JP2016177117A - Thin plate-like sound absorbing structure and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin plate-like sound absorbing structure that absorbs low and high frequency noise from a sound generating source, and a method of consecutively and inexpensively manufacturing the sound absorbing structure.SOLUTION: A thin plate-like sound absorbing structure includes: a porous sheet provided with a large number of through holes; an airtight sheet that blocks passage of air; and a center seat having a pulsed side surface interposed between the porous sheet and the airtight sheet. The center sheet has a plurality of different half-value widths. In the sound absorbing structure, an elongated converging space and an enclosed space are repeated while being in parallel in a length direction, and a large number of through holes are provided in one side wall of the individual enclosed space.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a thin plate-like sound absorbing structure that absorbs low-frequency and high-frequency noise from a sound generation source, and further relates to a method for continuously manufacturing a long sound-absorbing structure at a low cost.

  The sound absorbing material is an indispensable commodity for a city person to spend a comfortable day in a city where various noise sources exist. For example, the sound absorbing material disclosed in Japanese Patent Application Laid-Open No. 2002-243111 has a structure in which a plurality of Helmholtz resonators are formed inside a sound insulation cover that covers a compressor of an air conditioner, so that the sound absorbing material can be disposed on the outer periphery of the compressor. The sound insulation cover is formed in a cylindrical shape. JP 2008-138505 A and JP 2010-61078 A are installed around railway facilities and highways in order to prevent noise generated from trains and automobiles as sound insulation walls.

  In some cases, the sound absorbing material is incorporated into the walls of various buildings, and in concert halls and conference rooms, it is possible to prevent unnecessary interference of musical sounds and to prevent voice sound leakage to adjacent rooms. This type of sound-absorbing material generally has a thickness of about 5 cm, but if it is a thin plate with a thickness of about 0.5 mm, it is laid on the inner wall of a PC case where the sound from a CPU fan, hard disk fan or video card fan is loud. It can also be installed inside devices such as vacuum cleaners and lawn mowers that are individual noise sources.

JP 2002243321 A JP 2008-138505 A JP 2010-61078 A

  In the sound absorbing material disclosed in Japanese Patent Laid-Open No. 2002-243211, a plurality of inner cases provided with orifice holes are installed inside the sound insulating cover, and the thickness of the sound absorbing material itself is not so large. The inner case resonates and absorbs sound of a specific frequency band by Helmholtz resonance theory, and can absorb sound of individual frequency bands by changing the thickness of the orifice hole and the volume of the air chamber inside the case. This sound-absorbing material is complicated and expensive because it produces individual inner cases with different dimensions and attaches them to the sound insulation cover. In addition, it absorbs sound using Helmholtz's resonance theory alone and absorbs air vibration. Is hardly attenuated, it is difficult to sufficiently absorb the noise generated from the motor.

  On the other hand, Japanese Patent Application Laid-Open No. 2008-138505 and Japanese Patent Application Laid-Open No. 2010-61078 are composed of a box body that stores a plurality of rectangular frame materials having different heights, and the total thickness of the box body is the sum of the thicknesses of the frame materials used. . In Japanese Patent Application Laid-Open No. 2008-138505, for example, the thicknesses of three frame members are 15 mm, 30 mm, and 53 mm, and the total thickness is 98 mm, and the total thickness of the box reaches 100 mm when the plate thickness is added. In Japanese Patent Application Laid-Open No. 2010-61078, the side wall widths of the two frame members are h3 and h4. Even if the specific numerical values are unknown, the total thickness of the box is considerably increased by adding the plate thickness. Can be estimated.

  Since the sound absorbing material has a considerably large thickness as described above, its use will be limited to the sound insulation wall installed around the highway. In addition, since this sound absorbing material sandwiches the periphery of a porous plate such as an aluminum plate between two rectangular frame members, the size of the sound absorbing material is limited to a certain extent, and is large enough to reach several meters in length. It is practically difficult to manufacture. For this reason, when applied to a sound insulation wall on a road, it is necessary to arrange a plurality of sound absorbing materials in combination, and even a single sound absorbing material is a considerable manufacturing cost, so the sound insulating wall as a whole is very expensive. It becomes high.

  The present invention has been proposed in order to improve the above-mentioned problems associated with conventional sound-absorbing materials, and has a thin plate-like structure. Therefore, the present invention is disposed inside the walls of vehicles and vehicles such as automobiles in addition to sound-insulating walls of roads. It is an object of the present invention to provide an inexpensive sound absorbing structure that can be attached to absorb noise from a sound source. Another object of the present invention is to provide a sound absorbing structure that effectively absorbs noise in which low to high frequency sounds exist. Another object of the present invention is to provide a method of manufacturing a sound absorbing structure that can be efficiently manufactured to a final product even with a large size.

  The thin plate-like sound absorbing structure according to the present invention includes a porous sheet provided with a large number of through holes, an airtight sheet that blocks passage of air, and the center of a pulsed side surface interposed between the porous sheet and the airtight sheet. A sheet. The central sheet has a plurality of different half-value widths, and by adhering the central sheet to the perforated sheet and the airtight sheet in parallel lines, the elongated converging space and the surrounding space are arranged in parallel in the length direction inside the sound absorbing structure. However, a number of through holes are provided in one side wall of each surrounding space.

  In the sound-absorbing structure of the present invention, it is preferable to use a sheet having an uneven surface as the porous sheet. A third air layer exists between the concave back surface of the porous sheet and the upper plane of the center sheet. The presence can absorb relatively high frequency sound. Preferably, the porous sheet has a through hole having an arbitrary shape with a width of 0.3 to 1 mm, and the opening ratio of the porous sheet is 70 to 80%, while on the side wall of the surrounding space of the sound absorbing structure. Provides a circular through hole with a diameter of 0.5 to 1 mm, and the opening ratio of the side wall is set to 40 to 50%. Further, the side surface of the center sheet is a trapezoidal, corrugated or rectangular sheet, and the total thickness of the sound absorbing structure is 3 to 6 mm.

  In the method for producing a sound absorbing structure according to the present invention, a flat thin sheet is passed between a pair of perforating rollers, and a group of through holes are repeatedly provided in a parallel strip shape on the sheet, and then the thin sheet is heated. Then, the sheet is passed through a pair of tooth-shaped rollers, and the sheet is bent into an uneven shape to produce a center sheet. As a result, a through-hole exists only on one side wall of the half width portion of the center sheet, and a porous sheet is fed into the center sheet from above and an airtight sheet from below. Adhere to each airtight sheet.

  In the method for producing a sound-absorbing structure of the present invention, it is preferable that the porous sheet is passed through a pair of annular groove rollers to form an uneven surface, and the uneven porous sheet is sent to the central sheet and bonded.

  The sound absorbing structure according to the present invention has a total thickness of 3 to 6 mm and is much thinner than a conventional sound absorbing material having a thickness of around 5 cm. For this reason, the sound absorbing structure of the present invention can be used not only as a sound insulation wall around a railway facility or highway, but also as an interior soundproof part such as an automobile or a train, a soundproof material in the wall of a building, etc. It can also be laid on the inner wall of the case or installed inside equipment such as a vacuum cleaner or lawn mower.

  In the sound absorbing structure of the present invention, not only a flat sheet but also a sheet having an uneven cross section can be used. When a porous sheet having a concavo-convex cross section is bonded, a third air layer is formed between the concave back surface and the upper plane of the center sheet, and the presence of this air layer reflects the sound that enters the sound absorbing structure of the present invention. Refraction is increased, and high frequency sounds around 4 kHz can be sufficiently absorbed. For example, since the main frequency band of a noise source is 400 to 4 kHz in a railway train and the main frequency band is 250 to 4 kHz in a highway, noise is generated when sound in these bands is absorbed by the sound absorbing structure of the present invention. Can be sufficiently reduced.

  The sound-absorbing structure according to the present invention can be manufactured even with a size of about 2 × 500 m, for example, and by increasing the size, the number of use can be reduced even in a place with a large area such as a sound insulation wall. Since no construction is possible, installation work becomes easy. Further, if the sound absorbing structure of the present invention is made of soft plastic, it can be bent to some extent because it is thin, and can be deformed into a cylindrical shape surrounding the curved portion of the road sound insulating wall and the entire noise source.

  In the manufacturing method according to the present invention, the sound absorbing structure can be manufactured continuously, and can be continuously manufactured even when its length reaches about 500 m, and the parts such as plate materials used for the manufacturing are relatively inexpensive. Yes, the number of parts may be small. Therefore, when the manufacturing method of the present invention is used, it can be manufactured much more quickly than in the case of manufacturing a box-shaped sound absorbing material as in the prior art, and can be manufactured at an overwhelmingly low cost.

It is an expanded sectional view showing an example of a sound absorption structure concerning the present invention. It is a side view which shows the sound-absorbing structure which adhere | attached the surface porous sheet of the pulse-shaped side surface as a modification of this invention. It is the end elevation which looked at the sound absorption structure of Drawing 2 from the front. It is a top view which shows the porous sheet which has the checkered pattern-like uneven | corrugated surface. It is a schematic explanatory drawing which shows the process processed into a center sheet | seat of a trapezoid side surface from a thin sheet | seat. It is a schematic explanatory drawing which shows the process of adhere | attaching a porous sheet and an airtight sheet | seat on the upper and lower surfaces of the center sheet | seat of a trapezoid side surface. It is a fragmentary top view which shows the thin sheet after passing a pair of punching rollers, and this thin sheet becomes a center sheet after uneven | corrugated processing. It is a schematic explanatory drawing which shows until it manufactures a sound absorption structure from the center sheet | seat of a pulse-shaped side surface. It is a graph which shows the sound absorption rate regarding the sound absorption structure in the Example of this invention.

  As shown in FIG. 1, the sound absorbing structure 1 according to the present invention includes a porous sheet 3 provided with a large number of through holes 2, an airtight sheet 5 that blocks passage of air, and a porous sheet 3 and an airtight sheet 5. It consists of a central sheet 7 with a pulse-like side surface interposed therebetween. The thickness of the porous sheet 3, the airtight sheet 5 and the center sheet 7 is determined according to the frequency band of the sound to be absorbed, and is usually a thin plate material having the same or different thickness of about 0.2 to 0.5 mm. .

  The material of the porous sheet 3, the airtight sheet 5 and the center sheet 7 is made of polyolefins such as polypropylene and polyethylene, polyamide, polyester, or other flame retardant plastic such as FRP, metal plate such as aluminum or stainless steel plate, paperboard For example, thin wood. The sheet material to be used is determined according to the environment in which the sound absorbing structure 1 is installed. For example, a flame retardant plastic or a metal plate is used in a high temperature environment, and a polyolefin such as polypropylene is used if cost is important.

  In the sound-absorbing structure 1 of FIG. 1, it is preferable that the flat porous sheet 3 is provided with a large number of through holes 2 having a width of 0.3 to 1 mm, and the planar shape of the through holes is an arbitrary shape such as a circle or a square. In addition, a plurality of planar through holes may be mixed. When the width of the through hole 2 is less than 0.3 mm, the sound passing through the porous sheet 3 is reduced, and when the width exceeds 1 mm, the sound is likely to go straight and the refraction and reflection of the sound are reduced. The aperture ratio of the porous sheet 3 is 70 to 80% over the entire surface of the sheet. If the aperture ratio is less than 70%, the sound absorption rate of the sound with a predetermined frequency cannot be increased to a certain level, and the aperture ratio is 80%. Exceeding this makes it difficult to increase the attenuation of air vibration due to refraction of sound.

  The porous sheet 3 is adhered to the central sheet 7 in a parallel line shape, so that when the sound passes through the through hole 2, the porous sheet 3 is securely held by the central sheet, Vibration is suppressed, and a decrease in sound absorption performance can be prevented. Further, the airtight sheet 5 is not provided with a through-hole because it is necessary to block the passage of air, and is usually made of the same thickness and material as the porous sheet 3.

  The central sheet 7 has a pulse-shaped side surface as shown in the figure, and the side surface shape may be any of a trapezoidal shape, a corrugated shape, a triangular waveform, and a square shape, and the pulse-shaped side surface is formed in the longitudinal direction or the crossing direction as shown in FIG. do it. The center sheet 7 shown in FIG. 1 has a trapezoidal side surface, and adheres to the porous sheet 3 at the flat portion of the top vertex 8 thereof. Therefore, in the case of the porous sheet, the hole area ratio decreases at the time of bonding. The standing wall portion of the center sheet 7 preferably has an angle of about 60 degrees with respect to the horizontal plane, but the sound is easy to pass from the convergence space 12 to the surrounding space 14, but it is 90 ° with respect to the horizontal plane like a rectangular side surface. Even if the angle is at a degree, the sound wave entering the converging space 12 from the perforated sheet 3 is refracted when passing through a narrow gap, which is a small-diameter through-hole 16, so if this refraction is used, the sound is bent even if the side wall is at right angles. Can be used as the center sheet 7.

  The central sheet 7 is bonded in parallel lines to the porous sheet 3 at the upper vertex 8 and is bonded to the airtight sheet 5 in the lower vertex 10 so as to be elongated in the interior of the sound absorbing structure 1. 12 and the surrounding space 14 are repeated in parallel in the length direction. Each surrounding space 14 has both side walls 16, 18. A large number of through holes 20 are provided only on one side wall 16, and the surrounding space 14 communicates with the converging space 12 through the through holes. For this reason, the group of the through-holes 20 is provided in a part of the center sheet 7 in a horizontal band shape (see FIG. 7).

  The convergence space 12 and the surrounding space 14 are arranged in parallel in the length direction of the sound absorbing structure 1 to maintain the thinness of the structure. The convergence space 12 and the surrounding space 14 have a length corresponding to the lateral width (for example, 2 m) of the sound absorbing structure although the unit area is small due to the small thickness of the sound absorbing structure 1. The amount is almost the same as the conventional sound absorbing material. The surrounding space 14 communicates with the converging space 12 through a large number of through holes 20 to increase reflection and refraction of sound entering the converging space and increase attenuation due to air vibration.

  A through hole 20 having a diameter of 0.5 to 1 mm is provided in the side wall 16 of the surrounding space 14, and the through hole is preferably a circular plane. If the diameter of the through hole 20 is less than 0.5 mm, it is difficult for sound to flow from the converging space 12 to the surrounding space 14, and if it exceeds 1 mm, sound refraction in the converging space 12 decreases. The opening rate of the side wall 16 is preferably set to 40 to 50%. When the opening rate is less than 40%, sound flows from the convergence space 12 into the surrounding space 14 less, and when the opening rate exceeds 80%, a predetermined amount is obtained. The sound absorption rate of the frequency sound cannot be increased beyond a certain level.

  Since the central sheet 7 on the pulse-shaped side surface has a plurality of different half widths, the individual converging space 12 and the surrounding space 14 may be a combination of a plurality of different lateral widths. For example, in order to absorb sound having a frequency band of 100 to 1 kHz, the convergence space 12 determines a, b, c, and d in increments of 0.5 mm from the lower lateral width of 1.3 to 2.0 mm, and the convergence space. The surrounding space 14 that communicates with each other may be determined by increasing e, f, g, and h in increments of 0.5 mm from an upper horizontal width of 0.8 to 1.5 mm, and repeats in the length direction with this vertical width. In general, the surrounding space 14 has a smaller unit area than the convergence space 12, thereby further increasing the refraction of sound in the air layer of the surrounding space 14.

  Regarding the convergence space 12 and the surrounding space 14, the lower width and the upper width of the individual are determined within the above-described increased width range, and it is not necessary to increase or decrease the vertical width in order. In the air chambers of the converging space 12 and the surrounding space 14, a resonance phenomenon occurs in a direction orthogonal to the direction in which the sound travels. However, the sound having a specific resonance frequency can be resonantly absorbed by the Helmholtz resonance theory. Furthermore, when the central sheet 7 has a plurality of different half-value widths, the volumes of the converging space 12 and the surrounding space 14 are different from each other, and the sound of each frequency band is absorbed by an air chamber of a specific volume, the Helmholtz resonance principle The number of resonance frequencies that can be absorbed increases, and as a whole, sounds in a wide frequency band can be absorbed.

  Further, since the convergence space 12 and the surrounding space 14 communicate with each other through a large number of through holes 20, the resonance phenomenon is alleviated and the performance can be further improved. Sound that does not pass through the through-hole 20 in the convergence space 12 has a half-wave width of the convergence space 12, and sound that passes through the through-hole 20 has a frequency equal to or lower than the frequency that makes the width of the surrounding space 14 half-wave. The sound travels through the through hole 20 to prevent the sound from spreading.

  In the converging space 12 and the surrounding space 14 that are air layers, the parameters including the thickness of the space layer, the opening ratio of the side wall 16, the plate thickness, and the diameter of the through hole 20 are the same as those for the through hole 2 and the through hole 20 of the porous sheet 3. It is defined to cause the viscous action of air due to refraction and reflection of sound to the passing air. As a result, when a viscous damping action occurs in the air passing through the through-hole 20, the air vibration is converted into thermal energy, resulting in the damping of the air vibration, resulting in a high sound absorption effect in a relatively wide frequency band. Demonstrate.

  Since the overall thickness of the sound absorbing structure 1 is 3 to 6 mm, the sound absorbing structure 1 is laid not only on a sound insulation wall such as a road but also on an interior of a car or a train, an inner wall surface of a personal computer case, or attached to the inside of a motor using device. be able to. The sound absorbing structure 1 can also be increased in overall thickness as desired. Since the sound absorbing structure 1 includes the elongated converging space 12 and the surrounding space 14 repeatedly in parallel, the sound absorbing structure 1 can sufficiently absorb sound in a frequency band of 1 kHz or less in the noise source even if the thickness is thin.

  2 and 3, the sound absorbing structure 21 uses a porous sheet 22 having irregularities. As in the case of the central sheet 7, the porous sheet 22 has a checkered pattern in which peaks and valleys are alternately formed as shown in FIG. May be provided. The uneven surface of the porous sheet 22 intersects with the uneven surface of the center sheet 7 at an angle that is orthogonal or somewhat oblique. For example, as shown in FIG. 8, a corrugated side surface may be formed in the porous sheet 22 in a direction intersecting the longitudinal direction, and the corrugated side surface may be orthogonal to the uneven surface of the center sheet 7. Moreover, the pulse-shaped side surface of the porous sheet 22 may be formed in the longitudinal direction and intersected with the central sheet in which the uneven surface is formed in the direction intersecting the longitudinal direction.

  The perforated sheet 24 shown in FIG. 4 has a pyramidal crest 26 and a pyramidal trough 28 formed continuously by thermoforming or embossing, and has a checkered pattern with a triangular cross section and an uneven surface. The porous sheet 24 may be formed with fine pores before or simultaneously with the thermoforming or embossing. The perforated sheet 24 can be bent relatively easily by forming the pyramid crest portions 26 and the pyramid trough portions 28 alternately, and can be bent or depressed even when the thickness of the perforated sheet is thin. Less is.

  The corrugated side porous sheet 22 shown in FIGS. 2 and 3 can achieve sound absorption from a low frequency to a high frequency by reflection of the surface due to the shape of the surface. When the porous sheet 22 is bonded to the upper surface of the center sheet 7, an elongated third air layer 30 (FIG. 3) is formed between the concave back surface of the porous sheet 22 and the upper plane of the center sheet 7. Due to the presence, the refraction of the sound entering the porous sheet 22 increases, and it is possible to absorb a large amount of sound of relatively high frequency. The elongated third air layer 30 communicates with the elongated converging space 12 in a crossing manner, and most of the sound that has entered the porous sheet 22 is repeatedly reflected and refracted from the third air layer 30 to the converging space 12, A viscous damping effect is generated in the air, and the sound absorbing effect is exhibited in a wide frequency band.

  In the corrugated side porous sheet 22, when the height of the unevenness is increased, the sound absorption rate of the high frequency sound is increased, and when the unevenness is small and approaches flat, the sound absorption rate of the high frequency sound is decreased. When the unevenness height of the porous sheet 22 is about the same as the unevenness height of the center sheet 7, that is, a height of 2.5 to 5 mm, reflection and refraction of sound entering the porous sheet 22 increase, and a high frequency around 4 kHz. Can also be absorbed (see FIG. 8). Since the noise of railway trains and automobiles is mainly in the frequency band of 250 to 4 kHz, noise can be sufficiently reduced by absorbing sound in these bands with the sound absorbing structure 21 of the present invention.

  Although not shown, it is possible to interpose another porous sheet or thin net between the porous sheet 22 and the center sheet 7. Further, as the unevenness of the porous sheet 22 becomes smaller and approaches flat, the sound absorption of the high-frequency sound can be achieved even if the sound absorption from the low frequency of about 100 Hz to the high frequency of about 4 kHz can be achieved as in the case of the porous sheet 3. The rate is relatively low.

  When the sound absorbing structure 1 is manufactured, as shown in FIG. 5, a flat thin sheet 32 made of plastic or metal is used. The thin sheet 32 has a thickness of 0.2 to 0.5 mm, and the porous sheet 3 and the airtight sheet 5 have the same thickness. The thin sheet 32 can have a width of 1.5 to 2 m and a length of about 1500 m, and the porous sheet 3 and the airtight sheet 5 have the same width as the thin sheet 32 and a length of 1000 m or less. Good. In order to manufacture the porous sheet 3 from a thin sheet, it is possible to pass the thin sheet through a pair of perforating rollers (not shown) in which needles are implanted on the entire peripheral surface so that the aperture ratio is 70 to 80%. is there.

  The thin sheet 32 is passed between a pair of perforating rollers 34, 34 in which needle rows 35 are intermittently planted in FIG. 5, and the group of through holes 20 is repeatedly provided in a parallel strip shape on the sheet (FIG. 7). reference). In the case of plastic sheets, the perforating rollers 34 and 34 are preferably drilled while heating the rollers themselves.

  In the perforating rollers 34, 34, one is a roller in which three or more narrow needle rows 35 are implanted, and the other is a roller in which a blind hole row 36 into which each needle row enters is engraved. In the perforating roller 34 in which a plurality of needle rows 35 are implanted, the center sheet 7 having a plurality of different half-value widths can be obtained by different intervals between the needle rows 35 and 35.

  The thin sheet 32a in which the group of through holes 20 is formed at a predetermined different interval is passed between a pair of tooth-shaped rollers 37, 37, and the sheet is bent into a concavo-convex shape at a predetermined interval to obtain a central sheet 7 on the pulse side surface. Get. In the case of a plastic sheet, the tooth-shaped rollers 37 and 37 are preferably drilled while heating the roller itself.

  The tooth-shaped rollers 37 and 37 have concave and convex peripheral surfaces meshing with each other, and rotate in synchronization with the perforating rollers 34 and 34 accurately. In the tooth profile rollers 37, 37, the width of each tooth tip and the width of the bottom of the teeth are different, and the thin sheet 32a that passes therethrough is, as shown in FIG. 7, a pair of valley fold lines 38, 38 and mountain fold lines 40, 40. Are repeatedly formed while changing the width. If the distance between the valley fold lines 38 and 38 is defined as a, b, c, and d, a <b <c <d, and the distance between the mountain fold lines 40 and 40 is defined as e, f, g, and h, e <F <g <h.

  The center sheet 7 having a trapezoidal side surface in FIG. Next, in FIG. 6, the obtained center sheet 7 is coated with a liquid adhesive by rollers 42 and 44 on the upper and lower surfaces thereof, and then the porous sheet 3 and the lower roll 48 from the upper roll 46 to the center sheet. Then, the airtight sheet 5 is sequentially fed, and the perforated sheet 3 and the airtight sheet 5 are bonded to the center sheet 7, respectively, and then dried through a far-infrared drying oven 50 or the like.

  When the center sheet 7, the porous sheet 3 and the airtight sheet 5 are resin sheets, they can be welded by high frequency, dielectric heating or ultrasonic waves. In this case, the coating rollers 42 and 44 and the drying furnace 50 are It is unnecessary. If these sheets are made of metal, spot welding and brazing are also possible.

  FIG. 8 shows an example in which the corrugated side porous sheet 22 shown in FIGS. 2 and 3 is manufactured. The lateral width of the porous sheet 22 is determined so as to substantially match the width of the center sheet and the airtight sheet after the formation of the irregularities. In order to manufacture the porous sheet 22 from a flat thin sheet, the thin sheet is passed through a pair of perforating rollers (not shown) on the peripheral surface of the needle to obtain a flat porous sheet, The corrugated side surface may be formed in the crossing direction through the pair of annular groove rollers 52 and 52. The rollers 52 and 52 have a depth and a width of an annular groove corresponding to a desired corrugated side surface, the width corresponds to the width of the center sheet and the airtight sheet, and in addition to the corrugated side surface, a trapezoidal, triangular corrugated or rectangular side surface It may be.

  Although not shown in the figure, the corrugated side porous sheet 22 is applied with a liquid adhesive on the upper surface of the center sheet, and then sequentially fed and bonded to the center sheet from above, and further, the airtight sheet is fed from below and bonded. The obtained sound absorbing structure porous sheet 22 is dried again in a far-infrared drying furnace or the like.

  Next, the present invention will be described based on examples, but the present invention is not limited to the examples. A polypropylene sheet having a thickness of 0.4 mm is used as a material for the sound absorbing structure. The flat perforated sheet 3 is provided with a large number of through holes 2 in this polypropylene sheet. The through holes have a diameter of 0.5 mm and the opening ratio of the entire sheet is 80%. The airtight sheet 5 uses this polypropylene sheet as it is.

  With respect to the center sheet 7, a 0.4 mm thick polypropylene sheet has a group of through holes 20 formed between the pair of perforating rollers 34, 34 (FIG. 5) in a horizontal band shape at predetermined different intervals. The center sheet 7 on the trapezoidal side surface is obtained by bending the sheet between the tooth-shaped rollers 37 and 37 and bending the sheet into an uneven shape. Next, the perforated sheet 3 and the airtight sheet 5 are sent from above to the center sheet and bonded at high frequency.

  In FIG. 1, the center sheet 7 is bonded to the porous sheet 3 in parallel lines at the upper vertex 8, and is bonded to the airtight sheet 5 in parallel lines at the lower vertex 10. As a result, a large number of elongated converging spaces 12 and surrounding spaces 14 are juxtaposed in the longitudinal direction inside the sound absorbing structure 1. In the convergence space 12, the lower lateral width is a = 1.5 mm, b = 2.0 mm, c = 2.5 mm, and d = 3.0 mm, while in the surrounding space 14, the upper lateral width is e = 1.25 mm, f = 1.75 mm, g = 2.25 mm, h = 2.75 mm, and the lower horizontal width of the convergence space 12 and the upper horizontal width of the surrounding space 14 are repeated.

  The obtained sound absorbing structure has an overall thickness of 4 mm, and the standing wall portion of the center sheet 7 is at an angle of about 60 degrees with respect to the horizontal plane. Each surrounding space 14 has a large number of through holes 20 on one side wall 16 thereof, and the surrounding space 14 communicates with the converging space 12 through the through holes. The through hole 20 having a circular plane has a diameter of 0.5 mm, and the opening rate of the side wall 16 is set to 50%.

  The sound absorption rate of the obtained sound absorbing structure is measured. The normal incident sound absorption coefficient is defined in JIS A 1405-1 and 2 “Measurement of sound absorption coefficient and impedance by acoustic tube” (2) (3). In the measurement of the normal incident sound absorption coefficient, it is also referred to as a standing wave method, an acoustic tube method, or an in-tube method, and a sound wave is perpendicularly incident on the sample surface. This JIS requires an acoustic tube that satisfies the condition that the wavelength λ of the sound wave radiated from the speaker in the tube and the inner diameter d (m) of the tube is d <0.59λ (in the case of a circular tube), and has a low frequency. A plurality of acoustic tubes having different inner diameters are used to measure sound in a wide frequency band from to high frequencies.

If the maximum value Pmax and the minimum value Pmin of the sound pressure amplitude of the standing wave are obtained, the normal incident sound absorption coefficient α ₀ can be obtained from the standing wave ratio n.
Standing wave ratio n = Pmax / Pmin
Normal incident sound absorption coefficient α ₀ = 1− (n−1 / n + 1) ²

  With respect to the sound absorbing structure of Example 1, the measurement result of the normal incident sound absorption coefficient is shown by a dotted line in FIG. From this result, even when the sound absorbing structure is 4 mm thick, it can sufficiently absorb sound in a frequency band of 1 kHz or less in the noise source, and its absorption is slightly reduced when it becomes a high frequency sound near 4 kHz.

  As the material of the sound absorbing structure, the same polypropylene sheet as in Example 1 is used. The center sheet 7 and the airtight sheet 5 are processed and used in the same manner as in Example 1.

  A flat perforated sheet is provided with a large number of through holes 2 in a thin sheet, the through holes having a diameter of 1.0 mm and an open area ratio of 70%. When this flat perforated sheet is passed through a pair of annular groove rollers 52 and 52 (FIG. 8) to form a corrugated surface in the longitudinal direction, the lateral width of the perforated sheet 22 substantially matches the width of the center sheet 7 and the airtight sheet 5. . The corrugated perforated sheet 22 is coated with a liquid adhesive on the upper and lower surfaces of the center sheet 7, then fed to the center sheet from above and bonded together with the airtight sheet 5 fed from below.

  The obtained sound absorbing structure has an overall thickness of 7 mm. Each surrounding space 14 has a large number of through holes 20 on one side wall 16 thereof. The through hole 20 having a circular plane has a diameter of 0.5 mm, and the opening ratio of the side wall 16 is set to 40%.

  With respect to the sound absorbing structure of Example 2, the measurement result of the normal incident sound absorption coefficient is shown by a solid line in FIG. From this result, even if the sound absorbing structure is 7 mm thick, it can sufficiently absorb sound in a frequency band of 1 kHz or less in the noise source, and can also sufficiently absorb high frequency sound around 4 kHz.

DESCRIPTION OF SYMBOLS 1 Sound absorption structure 2 Through-hole 3 Porous sheet 5 Airtight sheet 7 Center sheet 12 Convergence space 14 Enclosure space 20 Through-hole 22 Porous sheet 22 of a pulse-shaped side surface
30 Third Air Layer 32 Thin Sheet 34, 34 Hole Roller 37, 37 Tooth Profile Roller

Claims (7)

  A porous sheet provided with a large number of through holes, an airtight sheet that blocks passage of air, and a central sheet on a pulse-shaped side surface interposed between the porous sheet and the airtight sheet, the central sheet being a plurality of different By adhering the central sheet to the perforated sheet and the airtight sheet in parallel lines, the narrow converging space and the surrounding space are repeated in parallel in the length direction inside the sound absorbing structure, A thin plate-like sound absorbing structure in which a large number of through holes are provided on one side wall in a space.   A sheet having a concavo-convex surface is used as the porous sheet, and a third air layer exists between the concave back surface of the porous sheet and the upper plane of the center sheet, and relatively high frequency sound can be absorbed by the presence of the third air layer. The sound absorbing structure according to claim 1.   The porous sheet has a through hole of an arbitrary shape with a width of 0.3 to 1 mm, and the porosity of the porous sheet is 70 to 80%. On the other hand, the diameter of the porous sheet is 0 on the side wall of the surrounding space of the sound absorbing structure. 2. The sound absorbing structure according to claim 1, wherein a circular through hole of 5 to 1 mm is provided and the opening ratio of the side wall is set to 40 to 50%.   The sound absorbing structure according to claim 1, wherein the center sheet is a trapezoidal, corrugated or square sheet on its side surface.   The sound absorbing structure according to claim 1, wherein the entire thickness of the sound absorbing structure is 3 to 6 mm.   A flat thin sheet is passed between a pair of perforating rollers, and a group of through holes is repeatedly provided in a parallel strip shape in the sheet, and then the thin sheet is heated and passed between a pair of tooth-shaped rollers. By bending the sheet into a concavo-convex shape to produce the center sheet, a through hole exists only on one side wall of the half width portion of the center sheet. A method for producing a thin plate-like sound absorbing structure in which an airtight sheet is fed and the central sheet is bonded to a porous sheet and an airtight sheet, respectively.   The manufacturing method according to claim 6, wherein the porous sheet is passed through a pair of annular groove rollers to form an uneven surface, and the uneven porous sheet is fed to the central sheet and bonded.

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