JP2009056947A - Sound absorption structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure the rigidity of a sound absorption structure by restricting reduction in the strength of an outer layer while improving a sound absorption coefficient at a low pitched sound zone. <P>SOLUTION: A sound absorption structure 1 comprises a clearance layer 10 having a clearance and an outer layer 11 covering the clearance layer 10. The outer layer 11 has holes 13 communicating with the clearance of the clearance layer 10. Cylindrical members 3 formed to be longer than the thickness size of the outer layer 11 are fitted into the holes 13. The cylindrical member 3 has an outer side contact part 14 extending along the surface of the outer layer 11. An inner hole 3a of the cylindrical member 3 communicates with the clearance in the clearance layer 10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sound absorbing structure in which a void layer having voids is covered with an outer surface layer, and a hole portion communicating with the voids of the void layer is formed on the outer surface layer.

  Conventionally, for example, as disclosed in Patent Document 1, a void layer having a void and an outer surface layer covering the void layer are provided, and a hole portion communicating with the void of the void layer is formed in the outer surface layer. A resin-made sound absorbing structure is known. This sound absorbing structure is manufactured by a manufacturing apparatus having a fixed mold and a movable mold. The movable mold has a facing mold facing the fixed mold and a back mold positioned on the back side of the facing mold so that a cavity is formed between the facing mold and the fixed mold when the mold is closed. It has become. The facing mold is formed with many communication holes communicating with the cavity, and the back mold is formed with a resin reservoir communicating with each communication hole. The communication hole is formed to have a larger diameter as it approaches the resin reservoir. When a sound absorbing structure is manufactured with this manufacturing apparatus, first, a resin material mixed with fibers is supplied to the cavity in a state where the movable mold and the fixed mold are clamped. This resin material is accumulated in the resin reservoir through the face-to-face communication hole. Since the resin accumulated in the communication hole and the resin reservoir becomes larger as the inner diameter of the communication hole approaches the resin reservoir, the anchor shape is obtained. Then, by retracting the movable mold to enlarge the cavity volume, a springback phenomenon is caused by the fibers mixed in the resin material, and a void layer is formed. Thereby, the intermediate molded product provided with the space | gap layer which has a space | gap, and an outer surface layer is obtained. Thereafter, the anchor-shaped resin tab solidified in the communication hole and the resin reservoir is moved away from the main body portion of the intermediate molded product by moving the facing mold and the back mold in the movable mold. Then, the trace from which the resin tab is detached becomes a hole communicating with the gap of the gap layer, and a sound absorbing structure is obtained.

In such a sound absorbing structure, the frequency at which the sound absorption coefficient reaches a peak can be changed by changing the volume of the void layer, the length of the hole in the axial direction, and the like.
JP 2005-349758 A

  By the way, for example, a sound absorbing structure like Patent Document 1 may be attached to a vehicle. In this case, there is a demand for increasing the sound absorption rate of low-frequency noise that is likely to cause discomfort to the passenger. In order to improve the sound absorption coefficient in the low frequency range, the volume of the gap layer may be increased. However, if the volume of the gap layer is increased, the sound absorbing structure is enlarged and securing the space required for mounting becomes a problem. . Therefore, it is conceivable to make the outer layer thinner and to increase the volume of the void layer as much as possible. However, if the outer surface layer is made thinner, the strength of the outer surface layer is lowered, and as a result, the rigidity of the sound absorbing structure cannot be secured. In addition, as the outer surface layer becomes thinner, the axial length of the hole formed in the outer surface layer becomes shorter. The length of the hole in the axial direction affects the sound absorption coefficient, and when this length is shortened, the sound absorption coefficient particularly in the low sound range is lowered.

  The present invention has been made in view of such a point, and the object of the present invention is to ensure the rigidity of the sound-absorbing structure so that the lowering of the strength of the outer surface layer can be suppressed while increasing the sound-absorbing rate in the low-frequency range. There is.

  In order to achieve the above object, according to the first aspect of the present invention, a void layer having voids and an outer surface layer covering the void layer are provided, and a hole portion communicating with the voids of the void layer is formed in the outer surface layer. In the sound absorbing structure, a tubular member formed longer than the thickness of the outer surface layer is fitted into the hole, and the tubular member has a front side contact portion along the surface of the outer surface layer. The structure is formed.

  In 2nd invention, it is set as the structure by which the back side contact part in alignment with the back surface of an outer surface layer is formed in the cylindrical member in 1st invention.

  According to a third aspect of the present invention, there is provided a sound absorbing structure including a void layer having a void and an outer surface layer covering the void layer, wherein the outer surface layer has a hole communicating with the void of the void layer. A cylindrical portion protruding to at least one of the front side and the back side of the outer surface layer is integrally formed at the peripheral edge portion of the hole portion of the outer surface layer.

  According to the first invention, since the cylindrical member longer than the thickness dimension of the outer surface layer is fitted into the hole portion of the outer surface layer, the inner hole of the cylindrical member communicates with the gap of the gap layer. The length of the inner hole is longer than the thickness dimension of the outer surface layer. Therefore, even if the thickness of the outer surface layer is reduced, the sound absorption coefficient in the low frequency range can be improved. Furthermore, in a state where the cylindrical member is fitted in the hole of the outer surface layer, the front side contact portion of the cylindrical member contacts the surface of the outer surface layer, and the outer surface layer partially has a double structure. Thereby, an outer surface layer can be reinforced and the rigidity of a sound absorption structure can be ensured.

  According to the second invention, the front-side contact portion and the back-side contact portion of the tubular member are in contact with the front surface and the back surface of the outer-surface layer, respectively, in a state where the tubular member is fitted into the hole portion of the outer-surface layer. Therefore, the outer surface layer can be reinforced from both the front side and the back side, and the rigidity of the sound absorbing structure can be further improved.

  According to the third invention, since the cylindrical portion protruding to at least one of the front side and the back side of the outer surface layer is integrally formed on the peripheral edge portion of the hole portion of the outer surface layer, the inner hole and the outer surface layer of the cylindrical portion are formed. The hole is in a state of communicating with the voids of the void layer. Since the length of the inner hole of the cylindrical portion and the length of the hole portion of the outer surface layer is longer than the thickness of the outer surface layer, even if the outer surface layer is made thinner, the sound absorption in the low frequency range is reduced. The rate can be improved. Furthermore, a thick-walled part can be formed in a part of the outer surface layer by integrally forming the cylindrical portion on the outer surface layer. Thereby, an outer surface layer can be reinforced and the rigidity of a sound absorption structure can be ensured.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

Embodiment 1 of the Invention
FIG. 1 shows a sound absorbing structure 1 according to an embodiment of the present invention. The sound absorbing structure 1 is formed by expanding and molding a resin material, and can be used as, for example, an interior material attached to a vehicle interior side of a vehicle body constituent member of an automobile. As shown in FIG. 2, the sound absorbing structure 1 includes a plate-like main body 2 and a large number of cylindrical members 3, 3,. As the resin material constituting the main body 2, for example, a material obtained by mixing glass fiber with polypropylene can be used, but is not limited thereto.

  The inside of the main body 2 is composed of a void layer 10 having voids throughout. The gap layer 10 is formed by the springback phenomenon of glass fiber, and has a low resin density. The void layer 10 is covered with a solid outer surface layer 11 having a resin density higher than that of the void layer 10. Further, the thickness of the outer surface layer 11 is set thin in order to increase the volume of the gap layer 10. Specifically, it is 1.0 mm or less. The main body 2 can be obtained by the expansion molding method disclosed in Patent Document 1.

  .. Are formed in the outer surface layer 11 so as to communicate with the voids of the void layer 10. Each hole 13 is substantially circular. For example, the hole 13 may be formed in a mold as in Patent Document 1 described above, or after forming the gap layer 10 and the outer surface layer 11, a punching tool (not shown) is used. You may make it form. The size, shape, arrangement, and number of the holes 13 can be arbitrarily set. The size and shape of the hole 13 may be different from each other.

  As shown in FIG. 3, the tubular member 3 is fitted in the hole 13 of the main body 2. Each cylindrical member 3 is formed by molding a resin material such as polypropylene, and has a cylindrical shape as a whole. The material constituting the cylindrical member 3 and the material constituting the main body 2 may be the same or different. The length of the cylindrical member 3 in the axial direction is set longer than the thickness dimension of the outer surface layer 11. The tubular member 3 protrudes toward the front side and the back side of the outer surface layer 11 in a state of being fitted into the hole 13.

  The outer diameter of the cylindrical member 3 is set to be substantially the same as the inner diameter of the hole 13. Moreover, the inner hole 3a of the cylindrical member 3 is set to the same diameter over both axial ends. As shown in FIGS. 3 and 4, a front-side contact portion 14 that comes into contact with the surface of the outer surface layer 11 is provided at one end portion in the axial direction of the cylindrical member 3 (upper end portion in FIGS. 3 and 4). The front side contact portion 14 protrudes from the outer peripheral surface of the tubular member 3 outward in the radial direction, and has a circular bowl shape extending continuously over the entire circumference. A contact surface 14 a with the outer surface layer 11 in the front side contact portion 14 is formed flat so as to follow the surface of the outer surface layer 11. Moreover, the surface located on the opposite side to the outer surface layer 11 in the front side contact portion 14 is an inclined surface 14b that is inclined so as to approach the outer surface layer 11 as it goes to the outer edge portion. Therefore, the front side contact portion 14 has its outer edge. The thickness becomes thinner as it goes to the part.

  On the outer peripheral surface of the cylindrical member 3, two back side contact portions 15, 15 that contact the back surface of the outer surface layer 11 are provided so as to protrude. These back side contact portions 15, 15 are arranged closer to the front side contact portion 14 than the other axial end portion (the lower end portion in FIGS. 3 and 4) of the tubular member 3, and are separated from each other in the circumferential direction of the tubular member 3. ing. The contact surface 15 a with the outer surface layer 11 in each back side contact portion 15 extends flat along the back surface of the outer surface layer 11. The separation distance between the contact surface 15a of the back side contact portion 15 and the contact surface 14a of the front side contact portion 14 is set to be the same as the thickness dimension of the outer surface layer 11 or slightly shorter than the thickness dimension of the outer surface layer 11. The cylindrical member 3 is prevented from rattling with the cylindrical member 3 fitted in the hole 13. The surface located on the opposite side to the outer surface layer 11 in the back side contact portion 15 is configured by an inclined surface 15 b that is inclined so as to approach the outer surface layer 11 as it goes to the front end portion in the protruding direction of the back side contact portion 15. Therefore, the back side contact part 15 is pointed toward the protrusion direction front end side.

  When the cylindrical member 3 is fitted into the hole 13 of the main body 2, first, as shown in FIG. 3A, the cylindrical member 3 is arranged so that the other end faces the hole 13. To do. Thereafter, the cylindrical member 3 is pushed into the hole 13 from the other end side. Then, the inclined surface 15b of the back side contact portion 15 is brought into sliding contact with the peripheral portion of the hole portion 13, and the peripheral portion of the back side contact portion 15 and the hole portion 13 is elastically deformed so that the back side contact portion 15 changes the peripheral portion of the hole portion 13. It gets over and is located on the back side of the outer surface layer 11. Thereby, as shown in FIG.3 (b), the front side contact part 14 and the back side contact part 15 of the cylindrical member 3 will be in the state which each contacted the surface and the back surface of the outer surface layer 11, and the drop-off | omission of the cylindrical member 3 is prevented. Is done. As described above, the front side contact portion 14 and the back side contact portion 15 of the cylindrical member 3 come into contact with the outer surface layer 11, so that a part of the outer surface layer 11 has a multiple structure. In addition, the inner hole 3a of the cylindrical member 3 fitted in the hole portion 13 communicates with the gap of the gap layer 10 and thus has a structure capable of absorbing noise.

  Here, the length of the inner hole 3a is changed by changing the length of the cylindrical member 3 in the axial direction. By fitting the cylindrical members 3 having different lengths into the holes 13, the frequency at which the sound absorption coefficient reaches a peak can be changed. This will be described based on the measurement results shown in the graph of FIG. Although not shown, this measurement result shows a change in sound absorption rate when sound of 1600 Hz to 100 Hz is radiated from a speaker in a state where the sound absorbing structure 1 is placed in a predetermined container.

  As is apparent from this graph, when the cylindrical member 3 having an axial length of 2 mm is fitted in the hole 13 (measurement results are indicated by broken lines), the frequency at which the sound absorption coefficient peaks is about 900 Hz. In addition, when the cylindrical member 3 having an axial length of 4 mm is fitted in the hole 13 (measurement result is indicated by a one-dot chain line), the frequency at which the sound absorption coefficient peaks is about 820 Hz. When the cylindrical member 3 having an axial length of 6 mm is fitted into the hole 13 (the measurement result is indicated by a two-dot chain line), the frequency at which the sound absorption coefficient peaks is about 740 Hz. When the cylindrical member 3 is not fitted (measurement result is indicated by a solid line), the frequency at which the sound absorption coefficient reaches a peak is about 1000 Hz. That is, by fitting the tubular member 3 into the hole 13, the frequency at which the sound absorption coefficient reaches a peak is lowered, so that it is possible to absorb a large amount of noise in the low frequency range of 900 Hz or less that makes the passenger feel uncomfortable. Become. Furthermore, the longer the axial length of the cylindrical member 3 is, the lower the frequency at which the sound absorption coefficient is peaked. Therefore, when it is desired to further reduce the peak frequency, the cylindrical member longer than 6 mm is provided with a hole. 13 may be fitted. The diameters of the inner holes 3a of the measured 2 to 6 mm cylindrical members 3 are the same, and the inner diameters of the holes 13 when the cylindrical members 3 are not fitted are the same. 3 has the same diameter as the inner hole 3a.

  As described above, according to the sound absorbing structure 1 of the first embodiment, the tubular member 3 longer than the thickness of the outer surface layer 11 is fitted into the hole 13 of the outer surface layer 11, thereby The inner hole 3a that is longer than the thickness dimension is in communication with the gap of the gap layer 10, so that the sound absorption coefficient in the low frequency range can be improved. Furthermore, the outer surface layer 11 can be partially made into a multiple structure by bringing the front side contact portion 15 of the cylindrical member 3 into contact with the surface of the outer surface layer 11 in a state where the cylindrical member 3 is fitted in the hole 13 of the outer surface layer 11. . Thereby, the outer surface layer 11 can be reinforced and the rigidity of the sound-absorbing structure 1 can be ensured.

  Further, with the tubular member 3 fitted in the hole 13 of the outer surface layer 11, the front side contact portion 14 and the back side contact portion 15 of the cylindrical member 3 come into contact with the front surface and the back surface of the outer surface layer 11, respectively. As a result, the outer surface layer 11 can be reinforced from both the front side and the back side, and the rigidity of the sound absorbing structure 1 can be further improved.

  Moreover, since the cylindrical member 3 separate from the main body 2 is fitted into the hole 13, the length of the cylindrical member 3 fitted into the hole 13 is changed after the main body 2 is formed. Thus, the frequency at which the sound absorption coefficient reaches a peak can be easily changed.

  Moreover, since the front side contact part 14 of the cylindrical member 3 has comprised the bowl shape, the peripheral part of the hole 13 is covered over the perimeter. Thereby, the appearance of the sound absorption structure 1 can be made favorable, without processing the peripheral part of the hole part 13 separately.

  In the first embodiment, the same cylindrical member 3 is fitted in all the holes 13, but the present invention is not limited to this, and the cylindrical members 3 having different lengths may be fitted. Moreover, the length of the cylindrical member 3 should just be longer than the thickness dimension of the outer surface layer 11, and may be 2 mm or less.

  Moreover, the shape of the cylindrical member 3 is not restricted to the above-mentioned shape, For example, you may abbreviate | omit the back side contact part 15 of the cylindrical member 3 like the modification 1 shown in FIG.

  Further, as in Modification 2 shown in FIG. 7, the cylindrical member 3 may be formed so as to largely protrude from the outer surface layer 11 to the front side. An annular front contact portion 16 that contacts the surface of the outer surface layer 11 is formed on the outer peripheral surface of the cylindrical member 3. The cylindrical member 3 is formed with two projecting portions 17 and 17 projecting in the axial direction. These protrusions 17 and 17 are formed at intervals in the circumferential direction of the cylindrical member 3. Claw portions 17 a and 17 a that protrude outward in the radial direction of the cylindrical member 3 are formed at the distal ends of the protruding portions 17 and 17. The claw portions 17 a and 17 a are back side contact portions that come into contact with the back surface of the outer surface layer 11.

  Moreover, you may form the front side contact part 18 in the intermediate part of the axial direction of the cylindrical member 3 like the modification 3 shown in FIG. The front-side contact portion 18 has an annular shape that protrudes from the outer peripheral surface of the cylindrical member 3 and continuously extends in the circumferential direction.

  The cylindrical member 3 may be welded to the main body 3 or may be bonded with an adhesive. Further, screw portions that are screwed to each other are formed on the outer peripheral surface of the cylindrical member 3 and the inner peripheral surface of the hole portion 13 of the main body portion 3, and the screw portion of the cylindrical member 3 is used as the screw portion of the main body portion 3. You may make it screw in.

  Moreover, you may provide the front side contact parts 14, 16, and 18 intermittently, without setting it as the shape which continues to the perimeter of the cylindrical member 3. FIG. The front side contact portions 14, 16, and 18 can have various shapes such as a star shape, a rhombus shape, a triangle shape, and an oval shape other than a circular shape. By setting it as such a shape, the designability of the sound-absorbing structure 1 can be improved.

<< Embodiment 2 of the Invention >>
FIG. 9 is a cross-sectional view of the sound absorbing structure 1 according to Embodiment 2 of the present invention. The sound absorbing structure 1 of the second embodiment is different from that of the first embodiment in that a separate cylindrical member is not provided. Hereinafter, the same parts as those of the first embodiment are denoted by the same reference numerals, description thereof will be omitted, and different parts will be described in detail.

  That is, the outer surface layer 11 of the sound absorbing structure 1 according to the second embodiment is integrally formed with a cylindrical portion 20 that protrudes to the front side at the peripheral portion of the hole portion 13. The diameter of the inner hole 20 a of the cylindrical portion 20 is set to be the same as the diameter of the hole 13. The front end surface in the protruding direction of the cylindrical portion 20 extends in a direction orthogonal to the axis of the hole 13. The peripheral surface of the cylindrical part 20 is comprised by the taper surface which becomes small diameter, so that it goes to the protrusion direction front end side.

  Next, the manufacturing apparatus 30 for the sound absorbing structure 1 configured as described above will be described. As shown in FIG. 10, the manufacturing apparatus 30 includes a molding die 31 and a resin injection machine (not shown). The mold 31 includes a fixed mold 32 and a movable mold 33. The movable mold 33 is driven by a driving device (not shown) so as to come into contact with and away from the fixed mold 32, and in the clamped state, a cavity is formed by the molding surface of the fixed mold 32 and the molding surface of the movable mold 33. It is like that.

  The fixed mold 32 is formed with a pin mold arrangement hole 32a so as to open to the cavity. The pin type arrangement hole 32 a is positioned so as to correspond to the cylindrical portion 20 of the sound absorbing structure 1. A pin mold 35 for forming the cylindrical portion 20 and the hole portion 13 is disposed in the pin mold disposing hole 32a. The pin mold 35 has a bottomed cylindrical shape, and its bottom portion faces the cavity. Formed on the bottom of the pin mold 35 are a molding surface 35 a for molding the cylindrical portion 20 and a pin 35 b for molding the hole 13. Further, a passage R to which a cooling medium is supplied is formed inside the pin mold 35 as a cooling means. As the cooling medium, for example, cooling water or the like can be used.

  Next, the case where the sound-absorbing structure 1 is manufactured using the manufacturing apparatus 30 configured as described above will be described. First, the fixed mold 32 and the movable mold 33 of the mold 31 are clamped to form a cavity, and polypropylene and reinforcing glass fibers are kneaded by a resin injection machine to obtain a molten resin material. This molten resin material is injected into the cavity of the mold 31 from the nozzle of a resin injection machine. At this time, the volume of the cavity is reduced by using the movable die 33 as the advance position, and a compressive force is applied to the molten resin material.

  When the outer surface layer 11 is formed after a predetermined time has elapsed from the injection of the molten resin material, the movable mold 33 is retracted. This causes a so-called springback phenomenon. Due to this springback phenomenon, the reinforcing glass fiber that has received the compressive force in the cavity is restored by its elastic force, and the molten resin material other than the outer surface layer 11 expands. Thereby, as shown in FIG.10 (b), the space | gap layer 10 which has a space | gap is formed, and the sound-absorbing structure 1 is obtained. By removing the sound absorbing structure 1, the trace of the pin 35b of the pin mold 35 becomes the hole 13 of the outer surface layer 11 and the inner hole 20a of the cylindrical part 20, and these hole 13 and inner hole 20a are voids. It will be in the state connected to the space | gap of the layer 10. FIG.

  In the sound absorbing structure 1 obtained in this way, the tubular portion 20 is integrally formed with the outer surface layer 11 by providing the pin mold 35 with the passage R to which the cooling water is supplied. A part of the layer 11 can be surely made thick. Therefore, the total length of the inner hole 20a of the cylindrical portion 20 and the length of the hole portion 13 of the outer surface layer 11 is longer than the thickness dimension of the outer surface layer 11, and the shape can be stably obtained. Therefore, as in the first embodiment, it is possible to improve the sound absorption coefficient in the low frequency range.

  Furthermore, by changing the shape of the molding surface 35a at the bottom of the pin mold 35, the length of the cylindrical portion 20 in the axial direction can be changed, and the frequency at which the sound absorption coefficient peaks can be arbitrarily changed. It becomes possible. Therefore, when changing the length of the cylindrical part 20, it is only necessary to replace the pin mold 35, and the mold cost can be reduced.

  As described above, according to the sound absorbing structure 1 of the second embodiment, since the cylindrical portion 20 is integrally formed with the peripheral edge portion of the hole portion 13 of the outer surface layer 11, the inner hole 20a of the cylindrical portion 20 is a hole. It becomes the state connected to the space | gap of the space | gap layer 10 through the part 13. FIG. Since the combined length of the inner hole 20a of the cylindrical portion 20 and the length of the hole portion 13 of the outer surface layer 11 is longer than the thickness dimension of the outer surface layer 11, the sound absorption coefficient in the low frequency range is improved. Can do. Furthermore, a thick portion can be formed on a part of the outer surface layer 11 by integrally forming the cylindrical portion 20 on the peripheral edge portion of the hole 13 of the outer surface layer 11. Thereby, the outer surface layer 11 can be reinforced and the rigidity of the sound-absorbing structure 1 can be ensured.

  In addition, you may form the cylindrical part 25 in the back surface side of the outer surface layer 11, like the modification 1 of Embodiment 2 shown in FIG. Part of the outer surface layer 11 of the first modification (upper part in FIG. 11) has a double structure of an outer part 11a and an inner part 11a. As shown in FIG. 12, the fixed die 32 of the forming die 31 according to the first modified example is provided with a bottomed cylindrical tubular die 40 and a pin die 41 in a pin die arrangement hole 32a. . The bottom of the cylindrical mold 40 faces the cavity. Formed on the bottom portion are a molding surface 40a for molding the cylindrical portion 20 on the front side of the outer surface layer 11, and an insertion hole 40b through which the pin 41a of the pin mold 41 is inserted. The pin mold 41 is formed in a bottomed cylindrical shape, and is arranged inside the cylindrical mold 40 so that the bottom portion faces the cavity. A pin 41a is formed at the bottom. Cooling water is supplied into the pin mold 41. The pin mold 41 is advanced and retracted in the moving direction of the movable mold 33 by a driving device (not shown). Further, the resin injection machine of the manufacturing apparatus 30 can perform primary injection and secondary injection.

  The case where the sound-absorbing structure 1 which concerns on the modification 1 is manufactured using this manufacturing apparatus 30 is demonstrated. First, the fixed mold 32 and the movable mold 33 of the mold 31 are clamped to form a cavity, and primary injection is performed by a resin injection machine. As shown in FIG. 12 (a), when the primary injected molten resin material is solidified, the outer portion 11a of the outer surface layer 11 is formed, and the front side cylindrical portion 20 is formed by the cylindrical mold 40. In addition, the inner hole 20a is formed by the pin 41a.

  Thereafter, as shown in FIG. 12B, the movable die 33 is separated from the fixed die 32 to increase the volume of the cavity, and the pin die 41 is advanced. Then, secondary injection is performed by a resin injection machine. The resin material injected secondarily is integrated with the outer portion 11a of the outer surface layer 11 formed by the first injection to form the inner portion 11b.

  After a predetermined time has elapsed since the secondary injection, as shown in FIG. 12C, the movable mold 33 is moved backward to cause a springback phenomenon. Thereby, the sound absorption structure 1 is obtained. Further, since the pin mold 40 is cooled by the cooling water, the resin around the pin 41a is quickly solidified on the back side of the outer surface layer 11, and the cylindrical portion 25 on the back side is formed. By removing the sound absorbing structure 1, the traces of the pins 41a of the pin mold 41 are formed on the inner hole 20a of the front cylindrical portion 20, the hole 13 of the outer surface layer 11, and the rear cylindrical portion 25. It becomes the inner hole 25a. The hole 13 and the inner holes 20 a and 25 a are in communication with the gap of the gap layer 10.

  Note that the front cylindrical portion 20 of the outer surface layer 11 may be omitted, and only the rear cylindrical portion 25 may be formed.

  In the first modification of the second embodiment, in order to ensure communication between the inner hole 20a and the gap of the gap layer 10, the pin mold 41 is directed toward the gap layer 10 after the completion of molding and before demolding. You may make it advance.

  Further, the pin mold 35 of the mold 31 according to the second embodiment may be replaced with the pin mold 40 of the first modification. Thus, after the movable die 33 is retracted and expanded, the pin die 41 can be advanced toward the gap layer 10 in order to ensure communication between the inner hole 20a and the gap layer 10. .

  Further, as in Modification 2 of Embodiment 2 shown in FIG. 13, when a part of the outer surface layer 11 has a double structure of the outer portion 11a and the inner portion 11b, the cylindrical portion 20 is formed only on the outer portion 11a. May be provided. The molding die 31 according to the second modification has the same structure as the molding die 31 used at the time of manufacturing the sound absorbing structure 1 according to the first modification.

  The case where the sound-absorbing structure 1 which concerns on the modification 2 is manufactured using this shaping | molding die 31 is demonstrated. First, the fixed mold 32 and the movable mold 33 are clamped to form a cavity, and primary injection is performed by a resin injection machine. As shown in FIG. 13 (a), when the primary injected molten resin material is solidified, the outer portion 11a of the outer surface layer 11 is formed, and the tubular portion 20 is formed by the tubular mold 40. The inner hole 20a is formed by the pin 41a.

  Thereafter, as shown in FIG. 13B, the movable mold 33 is separated from the fixed mold 32 to increase the volume of the cavity. At this time, the pin type 41 does not move. Then, secondary injection is performed by a resin injection machine. The resin material secondarily injected is integrated with the outer portion 11a of the outer surface layer 11 formed by the primary injection.

  After a predetermined time has elapsed since the secondary injection, as shown in FIG. 13C, the movable die 33 is moved backward to cause a springback phenomenon. Furthermore, by advancing the pin mold 41, the inner portion 11b of the outer surface layer 11 formed by the secondary injection is pierced by the tip end portion of the pin 41a, and the inner hole 20a becomes the gap of the gap layer 11. It will surely communicate. The timing at which the pin mold 41 is advanced may be the same as the start of the retraction of the movable mold 33 or may be after the retreat of the movable mold 33 is started. Further, since the pin mold 40 is cooled, the resin around it can be solidified reliably, and the length of the hole 13 can be set as intended.

  As described above, the sound-absorbing structure according to the present invention is suitable for being disposed, for example, in a passenger compartment of an automobile.

It is a perspective view of the sound absorption structure concerning Embodiment 1 of the present invention. It is the II-II sectional view taken on the line in FIG. It is a partial expanded sectional view of a sound absorption structure, (a) shows the state before fitting a cylindrical member in a main part, and (b) shows the state where a cylindrical member was inserted in a main part. It is a perspective view of a cylindrical member. It is a graph which shows the relationship between the sound absorption rate of a sound absorption structure, and a frequency. FIG. 6 is a diagram corresponding to FIG. 4 according to a first modification of the first embodiment. FIG. 5 is a diagram corresponding to FIG. 4 according to a second modification of the first embodiment. FIG. 6 is a view corresponding to FIG. 4 according to a third modification of the first embodiment. It is a fragmentary sectional view of the sound-absorbing structure of Embodiment 2. FIG. 3 shows a mold for a sound absorbing structure according to Embodiment 2, wherein (a) shows a state where injection of a resin material is completed, and (b) shows a state where a void layer is formed. 6 is a partial cross-sectional view of a sound absorbing structure according to Modification 1 of Embodiment 2. FIG. The shaping | molding die of the sound-absorbing structure which concerns on the modification 1 of Embodiment 2 is shown, (a) shows the state which the primary injection of the resin material was completed, (b) shows the state which the secondary injection of the resin material was completed. (C) shows a state in which a void layer is formed. FIG. 13 is a diagram corresponding to FIG. 12 according to a second modification of the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sound absorption structure 2 Main body part 3 Cylindrical member 3a Inner hole 10 Gap layer 11 Outer surface layer 13 Hole part 14 Front side contact part 15 Back side contact part 20 Cylindrical part 20a Inner hole

Claims (3)

A sound-absorbing structure comprising a void layer having voids and an outer surface layer covering the void layer, wherein the outer surface layer is formed with holes communicating with the voids of the void layer,
A cylindrical member formed longer than the thickness of the outer surface layer is fitted into the hole, and a front side contact portion along the surface of the outer surface layer is formed on the cylindrical member. Sound absorbing structure. The sound absorbing structure according to claim 1,
A sound absorbing structure characterized in that a back side contact portion along the back surface of the outer surface layer is formed on the tubular member. A sound-absorbing structure comprising a void layer having voids and an outer surface layer covering the void layer, wherein the outer surface layer is formed with holes communicating with the voids of the void layer,
A sound absorbing structure, wherein a cylindrical portion protruding to at least one of a front side and a back side of the outer surface layer is integrally formed at a peripheral edge portion of the hole portion of the outer surface layer.

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