Manufacturing method of soundproof sheet, and soundproof sheet

Abstract

This invention provides a method for manufacturing a sound-absorbing sheet, and the sound-absorbing sheet itself. The method for manufacturing the sound-absorbing sheet (S) is characterized by comprising: a first stacking step (S12) for producing a sheet (W1) composed of a mixture of a plurality of first fibers (23A) and a plurality of second fibers (23B), wherein the first fibers (23A) are natural fibers, and the second fibers (23B) include a first core (231) and a first coating layer (232) covering the first core (231) and having a first melting point; and a heating step (S13) for heating the sheet (W1) to make the first coating layer (23B)... 32) Melting occurs; First cooling step (S14), cooling the sheet (W1) while the first coating layer (232) is molten to solidify the first coating layer (232); Pressurization and heating step (S15), heating the sheet (W1) to melt the first coating layer (232) and applying a predetermined compressive force to the sheet (W1); Second cooling step (S16), cooling the sheet (W1) after the pressurization and heating step (S15) to a point below the first melting point to solidify the first coating layer (232).

Description

Technical Field

[0001] This invention relates to a method for manufacturing a soundproof sheet, and the soundproof sheet itself. Background Technology

[0002] Sound-absorbing sheets containing natural fibers such as cellulose fibers and resins have been known for a long time. For example, Patent Document 1 discloses a plate-shaped fiber substrate containing natural fibers and synthetic resins, wherein the content of each material varies in the thickness direction.

[0003] However, in the fiber substrate described in Patent Document 1, there is a problem that it is difficult to easily control the internal structure. Specifically, in order to form a structure in which the content ratio of each material varies, the fiber aggregate is produced by stacking the materials in a manner that gradually changes the content ratio. This method easily leads to increased intervals and increased complexity of the manufacturing process, thus affecting manufacturing costs. Therefore, there is currently a need for a method for manufacturing a sound-damping sheet that allows for easy control of its internal structure.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2017-48475 Summary of the Invention

[0005] The method for manufacturing a sound-absorbing sheet is characterized by comprising: a first stacking step, wherein a first stacked fiber body composed of a mixture of a plurality of first fibers and a plurality of second fibers is produced, wherein the first fibers are natural fibers, and the second fibers include a first core and a first coating layer covering the first core and having a first melting point; a heating step, wherein the first stacked fiber body is heated to melt the first coating layer; a first cooling step, wherein the first stacked fiber body is cooled while the first coating layer is molten to solidify the first coating layer; a pressurized heating step, wherein the first stacked fiber body is heated to melt the first coating layer and a predetermined compressive force is applied to the first stacked fiber body; and a second cooling step, wherein the first stacked fiber body after the pressurized heating step is cooled to a temperature below the first melting point to solidify the first coating layer.

[0006] The method for manufacturing a sound-absorbing sheet is characterized by comprising: a first stacking step, wherein a first stacked fiber body is formed by mixing a plurality of first fibers and a plurality of second fibers, wherein the first fibers are natural fibers, and the second fibers include a first core and a first coating layer covering the first core and having a first melting point; a second stacking step, wherein a second stacked fiber body is formed by mixing a plurality of first fibers and a plurality of third fibers, wherein the third fibers include a second core and a second coating layer covering the second core and having a second melting point higher than the first melting point; and a heating step, wherein the first stacked fiber body and the second stacked fiber body are overlapped and heated, thereby causing the first coating layer to... The process involves: 1) melting the first and second coating layers; 2) a first cooling step, in which the first and second coating layers are molten, cooling the overlapping first and second stacked fiber bodies to a point below the first melting point to solidify the first and second coating layers; 3) a pressurizing and heating step, heating the overlapping first and second stacked fiber bodies to a point above the first melting point and below the second melting point, and applying a predetermined compressive force to the overlapping first and second stacked fiber bodies; and 4) a second cooling step, cooling the overlapping first and second stacked fiber bodies to a point below the first melting point to solidify the first coating layer.

[0007] The soundproof sheet is characterized in that it is manufactured using the aforementioned method for manufacturing soundproof sheets. Attached Figure Description

[0008] Figure 1 This is a schematic enlarged view of the soundproof sheet according to the first embodiment.

[0009] Figure 2 for Figure 1 The cross-sectional view of line segment AA in the diagram.

[0010] Figure 3 for Figure 1 The cross-sectional view of line segment BB in the diagram.

[0011] Figure 4 A flowchart illustrating the manufacturing method of the soundproof sheet.

[0012] Figure 5 This is a schematic diagram illustrating the structure of a device for manufacturing soundproof sheets.

[0013] Figure 6 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet.

[0014] Figure 7 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet.

[0015] Figure 8 A block diagram illustrating the structure of the pressurized heating section, etc.

[0016] Figure 9 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet.

[0017] Figure 10 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet.

[0018] Figure 11 A graph representing the soundproofing properties resulting from the density of the soundproofing sheet.

[0019] Figure 12 This is a schematic enlarged view of a low-density area of ​​the soundproof sheet according to the second embodiment.

[0020] Figure 13 for Figure 12 A cross-sectional view of line segment CC in the diagram.

[0021] Figure 14 A flowchart illustrating the manufacturing method of the soundproof sheet.

[0022] Figure 15 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet.

[0023] Figure 16 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet.

[0024] Figure 17 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet.

[0025] Figure 18 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet.

[0026] Figure 19 A graph representing the soundproofing properties achieved by the internal structure of the soundproofing sheet.

[0027] Figure 20 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet according to the third embodiment.

[0028] Figure 21 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet.

[0029] Figure 22 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet.

[0030] Figure 23 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet.

[0031] Figure 24This is a schematic diagram illustrating the manufacturing method of the soundproof sheet according to the fourth embodiment.

[0032] Figure 25 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet.

[0033] Figure 26 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet.

[0034] Figure 27 This is a schematic diagram illustrating the manufacturing method of the soundproof sheet. Detailed Implementation

[0035] In the embodiments described below, a sound-absorbing sheet S containing natural fibers, etc., and its manufacturing method are illustrated, and the description is provided with reference to the accompanying drawings. In the following figures, the XYZ axes, serving as coordinate axes, are labeled as needed, and the direction indicated by the arrow is designated as the + direction, and the direction opposite to the + direction is designated as the - direction. Sometimes the +Z direction is referred to as upward, and the -Z direction as downward. Furthermore, in Figure 5 In the middle, the -Z direction is consistent with the vertical direction.

[0036] Furthermore, for ease of illustration, the sizes of the components are made different from the actual size. In the manufacturing apparatus 10 for the soundproof sheet S, the target side of the conveying direction of the sheet W1, the soundproof sheet S, etc., is sometimes referred to as downstream, and the side of the back conveying direction is referred to as upstream. The thickness of the sheet W1, etc., or the soundproof sheet S refers to the distance along the Z-axis, and the thickness direction refers to the direction along the Z-axis.

[0037] 1. First Implementation Method

[0038] The sound-damping sheet S involved in this embodiment is manufactured by the manufacturing method of the sound-damping sheet S described below. Figure 1 As shown, the sound-absorbing sheet S, as a raw material, comprises a plurality of first fibers 23A and a plurality of second fibers 23B. The plurality of first fibers 23A and the plurality of second fibers 23B are not oriented in a specific direction, but are intertwined. The joints of the first fibers 23A and the second fibers 23B, as well as the joints of the second fibers 23B with each other, are bonded together by a first coating layer 232 of the second fibers 23B, which will be described later.

[0039] In the first fiber 23A, there is approximately one or more contact points with the second fiber 23B. In the second fiber 23B, there is also approximately one or more contact points with the first fiber 23A or other second fibers 23B. The contact points of the first fibers 23A with each other are not bonded, but there are also approximately one or more contact points. Thus, in the soundproof sheet S, a plurality of first fibers 23A and a plurality of second fibers 23B are joined together.

[0040] The soundproof sheet S possesses the flexibility and strength derived from the aforementioned methods. Applications of the soundproof sheet S include soundproofing materials for residences, offices, shops, factories, and music studios; and sound insulation materials for vehicles such as automobiles, ships, and airplanes.

[0041] The first fiber 23A is a natural fiber. In this embodiment, cellulose fiber is used as the first fiber 23A. Cellulose fiber is a relatively abundant natural material derived from plants, thus it is relatively inexpensive and readily available.

[0042] Cellulose fibers are obtained by defibrillating raw materials such as paper, corrugated cardboard, pulp, pulp sheets, sawdust, shavings, and wood. Cellulose fibers are substances mainly composed of cellulose, but may also contain components other than cellulose. Examples of components other than cellulose include hemicellulose and lignin.

[0043] The average fiber length of the first fiber 23A is preferably 10 μm or more and 50 mm or less, more preferably 20 μm or more and 5 mm or less. This allows the multiple first fibers 23A and multiple second fibers 23B to be easily wound together, thereby improving the mechanical properties of the sound-absorbing sheet S, such as strength. The average fiber length of the first fiber 23A and the second fiber 23B is measured using a length distribution diagram method.

[0044] like Figure 2 As shown, the second fiber 23B includes a first core 231 and a first coating layer 232 covering the first core 231. The first coating layer 232 is thermoplastic and has a first melting point. The first coating layer 232 is melted by heating during the manufacturing process of the sound-absorbing sheet S, described later. Figure 2 The image shows the state in which the junction of the first fiber 23A and the second fiber 23B is bonded together by the first coating layer 232, which has melted and solidified.

[0045] The first core 231 is made of organic fiber. Examples of organic fibers include natural fibers such as cellulose fibers described above, as well as synthetic fibers such as polyester and rayon. In this embodiment, polyethylene terephthalate (PET) is used as the first core 231. PET has high heat resistance due to its crystallinity, and thus has advantages such as ease of recycling from plastic bottles.

[0046] The first coating layer 232 is a thermoplastic resin. Examples of thermoplastic resins include styrene-butadiene resin, polypropylene, polyvinyl chloride, polyurethane, polystyrene, acrylic resin, and polyvinyl acetate. In this embodiment, polyethylene is used as the first coating layer 232. The average molecular weight of polyethylene can be easily changed during the manufacturing stage, allowing for more flexible setting of its melting point.

[0047] The first melting point of the first coating layer 232 is preferably about 20°C lower than the melting point of the first core 231. Therefore, during the manufacture of the sound-absorbing sheet S, it becomes easier to melt the first coating layer 232 without melting the first core 231. The melting point of the first coating layer 232 is preferably 100°C or higher and 200°C or lower, more preferably 100°C or higher and 150°C or lower. The melting points of the first coating layer 232 and the second coating layer 234, described later, are measured using JIS K0064:1992 (Method for measuring the melting point and melting range of chemical products).

[0048] The average fiber length of the second fiber 23B, i.e. the average fiber length of the first core 231, is preferably 100 μm or more and 5 mm or less, and more preferably about 1 mm. This allows the multiple second fibers 23B to be easily wound with the multiple first fibers 23A, thereby improving the mechanical properties of the soundproof sheet S, such as its strength.

[0049] The ratio of the diameter D1 of the first core 231 to the thickness E1 of the first coating layer 232 is preferably 0.2 or more and 2.0 or less, and more preferably 0.5 or more and 1.5 or less. As a result, during the heating process when manufacturing the soundproof sheet S, deformation of the first core 231 can be suppressed and the first coating layer 232 can be melted and solidified.

[0050] like Figure 3 As shown, the first coating layer 232 also bonds the joints of the second fibers 23B together. The joints of the second fibers 23B are bonded together by the mutual first coating layer 232, which melts and solidifies through heating during the manufacturing process. Since the joints of the first fibers 23A and the second fibers 23B, as described above, and the joints of the second fibers 23B together, are bonded together by the first coating layer 232, the shape of the sound-damping sheet S becomes easier to maintain. Furthermore, the sound-damping properties and strength of the sound-damping sheet S can be improved.

[0051] like Figure 4 As shown, the manufacturing method of the soundproof sheet S involved in this embodiment includes a first mixing process S11, a first stacking process S12, a heating process S13, a first cooling process S14, a pressurized heating process S15, a second cooling process S16, and a cutting process S17.

[0052] In the manufacturing method of the sound-damping sheet S, the sound-damping sheet S is manufactured by proceeding through each process in the above-described order, from the upstream first mixing process S11 to the downstream cutting process S17. Furthermore, the manufacturing method of the sound-damping sheet of the present invention includes a first stacking process S12, a heating process S13, a first cooling process S14, a pressurized heating process S15, and a second cooling process S16; other processes are not limited to the above. In addition, the sound-damping sheet of the present invention can also be rolled into a roll for storage and sale while the second cooling process S16 is completed and the cutting process S17 is not completed.

[0053] A specific example of the manufacturing method of the sound-damping sheet S will be described together with the manufacturing apparatus 10 of the sound-damping sheet S. The manufacturing apparatus 10 of the sound-damping sheet S described below is an example and is not limited thereto.

[0054] like Figure 5 As shown, the manufacturing apparatus 10 includes, from upstream to downstream, a mixing section 11, a stacking section 100, a sheet conveying section 120, a humidifying section 130, a heating section 140, a cooling section 150, a pressurized heating section 160, a cooling section 170, a cutting section 180, and a tray 190 serving as a storage section. Although not shown in the figure, the manufacturing apparatus 10 also includes a device control section for uniformly controlling the operation of each of the above structures.

[0055] A first mixing process S11 is performed in the mixing section 11. The mixing section 11 mixes the first fiber 23A and the second fiber 23B in air to generate a first mixture. The mixing section 11 includes a tubular main body 60, hoppers 13 and 14 connected to the main body 60, supply pipes 61 and 62, and valves 65 and 66.

[0056] The hopper 13 is connected to the interior of the main body 60 via a supply pipe 61. A valve 65 is disposed between the hopper 13 and the main body 60 in the supply pipe 61. The hopper 13 supplies first fibers 23A into the main body 60. The valve 65 regulates the quality of the first fibers 23A supplied from the hopper 13 to the main body 60.

[0057] The hopper 14 is connected to the interior of the main body 60 via a supply pipe 62. A valve 66 is disposed between the hopper 14 and the main body 60 in the supply pipe 62. The hopper 14 supplies the second fiber 23B into the main body 60. The valve 66 regulates the mass of the second fiber 23B supplied from the hopper 14 to the main body 60. The mixing ratio of the first fiber 23A and the second fiber 23B is thus adjusted via valves 65 and 66.

[0058] In detail, the first mixture comprising the first fiber 23A and the second fiber 23B forms a sheet W1 as the first stacked fiber body in the stacking section 100 described later. In the sheet W1, the content of the second fiber 23B relative to the content of the first fiber 23A is preferably 12.0% by mass or more and 40.0% by mass or less, more preferably 14.0% by mass or more and 25.0% by mass or less. This allows for the suppression of the content of the first coating layer 232 in the second fiber 23B while improving the mechanical properties of the sound-absorbing sheet S, such as its strength.

[0059] The second fiber 23B is a material produced by another known device and is supplied to the hopper 14. Alternatively, a heated mixer or the like can be arranged upstream of the hopper 14, so that the second fiber 23B produced by the heated mixer is supplied to the hopper 14. In the heated mixer, a first coating layer 232 is formed on the first core 231.

[0060] The first core 231 of the first fiber 23A and the second fiber 23B can also be made from fibers produced by defiberizing waste paper or old cloth. Furthermore, additives can be supplied from either of the hoppers 13 and 14, thereby containing additives in the sheet W1. Examples of additives include colorants, flame retardants, insect repellents, mildew inhibitors, antioxidants, ultraviolet absorbers, agglomeration inhibitors, and release agents.

[0061] The first fiber 23A and the second fiber 23B are mixed while being conveyed from the main body 60 to the stacking section 100 to form a first mixture. To promote the formation of the first mixture in the main body 60 and improve its conveyability, a blower or similar device for generating airflow may be provided in the main body 60. The first mixture is conveyed from the main body 60 to the stacking section 100. Then, it proceeds to the first stacking process S12.

[0062] The first stacking process S12 is performed in the stacking section 100. The stacking section 100 stacks the first mixture in the air, thereby producing a sheet W1 containing a plurality of first fibers 23A and a plurality of second fibers 23B. The stacking section 100 includes a roller section 101. The stacking section 100 is generally box-shaped with an open bottom, and the roller section 101 is disposed at the top of its interior. The stacking section 100 introduces the first mixture from the main body section 60 into the interior of the roller section 101 and stacks it on the mesh belt 122 in a dry manner.

[0063] Below the stacking section 100, there is a sheet conveying section 120 including a mesh belt 122 and a suction mechanism 110. The suction mechanism 110 is positioned opposite the roller section 101 in the direction along the Z-axis, with the mesh belt 122 in between.

[0064] The drum section 101 is a cylindrical sieve that is driven to rotate by a motor (not shown). A mesh functioning as a sieve is provided on the side of the cylindrical drum section 101. The drum section 101 allows particles such as fibers and the first mixture, which are smaller than the mesh size of the sieve mesh, to pass through from the inside to the outside. Intertwined fibers in the first mixture are untangled by the drum section 101 and dispersed into the air within the accumulation section 100.

[0065] The first fiber 23A and the second fiber 23B are dispersed in the air within the stacking section 100 and randomly stacked on the mesh belt 122. Therefore, in the sheet W1, the first fiber 23A and the second fiber 23B are difficult to orient in a specific direction.

[0066] The sieve of the drum section 101 may not have the function of screening larger fibers in the first mixture. That is, the drum section 101 may also break down the fibers of the first mixture and release the entire first mixture into the interior of the accumulation section 100. The first mixture dispersed in the air within the accumulation section 100 is accumulated above the mesh belt 122 by gravity and suction from the suction mechanism 110.

[0067] The sheet conveying unit 120 includes a mesh belt 122 and a suction mechanism 110. The sheet conveying unit 120 promotes the accumulation of the first mixture on the mesh belt 122 by the suction mechanism 110. In addition, the sheet conveying unit 120 conveys the sheet W1 formed by the first mixture downstream by rotating the mesh belt 122.

[0068] A suction mechanism 110 is disposed below the roller section 101. The suction mechanism 110 draws air from the accumulation section 100 through multiple holes in the mesh belt 122. As a result, the first mixture released to the outside of the roller section 101 is drawn downwards along with the air and accumulates on the surface above the mesh belt 122. A known suction device such as a blower can be used in the suction mechanism 110.

[0069] The mesh belt 122 has multiple holes that allow air to pass through, but makes it difficult for the first fiber 23A and the second fiber 23B contained in the first mixture to pass through. The mesh belt 122 is a seamless belt and is supported by three support rollers 121.

[0070] The mesh belt 122 moves downwards by rotating its supporting roller 121. In other words, the mesh belt 122... Figure 5The conveyor belt 122 rotates clockwise. The conveyor belt 122 is rotated by the support roller 121, causing the first mixture to continuously accumulate and form a sheet W1. The sheet W1 contains a large amount of air, making it soft and inflated. The sheet W1 is conveyed downstream along with the movement of the conveyor belt 122.

[0071] A scraper 123 is attached below the scraper 121 located in the +X direction among the three support rollers 121. The scraper 123 contacts the surface of the conveyor belt 122, which has finished conveying the sheet W1. The conveyor belt 122 removes the first mixture remaining on its surface by contacting the scraper 123 while rotating.

[0072] A humidification section 130 is disposed downstream of the stacking section 100. The humidification section 130 humidifies the sheet material W1 on the conveyor belt 122 by spraying water. This suppresses the scattering or dust generation of the first fiber 23A and second fiber 23B contained in the sheet material W1. Furthermore, the water used for humidification can contain water-soluble additives, thereby allowing the additives to be impregnated into the sheet material W1 in parallel with humidification.

[0073] The sheet W1 is conveyed downstream via the mesh belt 122 and peeled off from the mesh belt 122. Then, the sheet W1 is introduced into the interior of the heat radiation section 143 of the heating section 140 via the conveyor roller 147 of the heating section 140. Then, it proceeds to the heating process S13.

[0074] The heating process S13 is performed using a heating unit 140. The heating unit 140 heats the sheet W1 introduced into it to a point above the first melting point of the first coating layer 232 in the second fiber 23B, causing the first coating layer 232 to melt. Thus, the sheet W1 becomes a molten fiber body. The heating unit 140 includes a heat source 141, a heat radiation section 143, an air supply section 145, and a conveying roller 147.

[0075] The heat-radiating section 143 is generally box-shaped, and the heat source section 141 and the air supply section 145 are stored inside it at the upper part. Below the heat-radiating section 143, the material sheet W1 is conveyed from the -X direction to the +X direction by the conveying roller 147.

[0076] The heat source 141 is positioned above the heat radiating section 143 and faces the sheet W1 across the air supply section 145. The heat source 141 radiates heat downward within the heat radiating section 143. The heat source 141 may be a heating device such as an infrared heater. Alternatively, the heating section 140 may be a structure that heats the sheet W1 by contact with it, such as a hot plate, or a constant temperature bath with hot air circulation.

[0077] The air supply unit 145 delivers heat generated by the heat source unit 141 to the sheet W1, which moves downwards within the heat radiation unit 143, via air supply. The sheet W1 is heated non-contactly while being conveyed within the heat radiation unit 143. Therefore, uneven temperature distribution is less likely to occur within the sheet W1, thus suppressing deterioration caused by insufficient heating or uneven heat distribution. The sheet W1 can also be conveyed within the heat radiation unit 143 using a seamless belt or similar material instead of the conveyor roller 147.

[0078] Through the above structure, such as Figure 6 As shown, the sheet W1 in the heating section 140 is heated to a heating temperature T1. The heating temperature T1 of the sheet W1 in the heating process S13 is appropriately set according to the melting point of the first fiber 23A, the melting point of the first core 231 of the second fiber 23B, and the first melting point of the first coating layer 232. That is, the heating temperature T1 of the sheet W1 in the heating section 140 is set to be above the first melting point of the first coating layer 232, and below the melting point of the first fiber 23A and below the melting point of the first core 231. For example, when the melting point of the first core 231 is 260°C and the melting point of the first coating layer 232 is 125°C, the heating temperature T1 is set to 190°C.

[0079] The sheet W1 is formed by mixing and stacking the first fiber 23A and the second fiber 23B in air. Therefore, the sheet W1 arriving at the heating section 140 is not pressurized, and is in a state containing more air and with lower density. By heating the sheet W1 in a lower density state, the heating efficiency can be improved and the energy required for heating can be reduced. Then, it proceeds to the first cooling process S14.

[0080] Return to Figure 5 The first cooling process S14 is performed using a cooling unit 150. The cooling unit 150 introduces a molten sheet W1 of the first coating layer 232 into its interior and cools the sheet W1 to below its first melting point, thereby solidifying the first coating layer 232. As a result, the sheet W1 becomes a bonded fiber body where the joints of the first fiber 23A and the second fiber 23B, as well as the joints of the second fibers 23B to each other, are bonded together. The cooling unit 150 includes a cooling source 151, a cooling chamber 153, an air supply unit 155, and a conveying roller 157.

[0081] The cooling chamber 153 is generally box-shaped, and the cooling source section 151 and the air supply section 155 are stored inside it at the top. Below the cooling source section 151, the material sheet W1 is conveyed from the -X direction to the +X direction by the conveying roller 157.

[0082] The cooling source 151 is positioned above the cooling chamber 153 and faces the sheet W1 across the air supply section 155. The cooling source 151 radiates cold air downwards within the cooling chamber 153. The cooling source 151 may be, for example, a cooling device including a cooler and a capacitor. The cooling section 150 may also be a structure that uses a Peltier element or the like to directly cool the sheet W1 through contact.

[0083] The air supply unit 155 delivers the cold air generated by the cooling source unit 151 to the sheet W1, which moves downwards within the cooling chamber 153. The sheet W1 is cooled non-contactly while being conveyed within the cooling chamber 153. Therefore, uneven temperature distribution is less likely to occur within the sheet W1. A seamless belt or similar material can also be used instead of the conveyor roller 157.

[0084] like Figure 7 As shown, the sheet W1 is conveyed by the conveying roller 157 and cooled to a cooling temperature T2 by the cooling section 150. Since the cooling temperature T2 is less than the first melting point of the first coating layer 232, the joints of the first fiber 23A and the second fiber 23B, and the joints of the second fibers 23B to each other, are bonded together by the first coating layer 232. At this time, since no compressive force is applied to the sheet W1, the density of the sheet W1 hardly changes before and after the first cooling step S14. Then, it proceeds to the pressurization and heating step S15.

[0085] Return to Figure 5 The pressurizing and heating process S15 is performed using a pressurizing and heating unit 160. In the pressurizing and heating process S15, the sheet W1 is heated to melt the first coating layer 232, and a predetermined compressive force is applied to the sheet W1. The pressurizing and heating unit 160 has a first pressurizing and heating unit 161 and a second pressurizing and heating unit 162. The pressurizing and heating unit 160 is, for example, a stamping device capable of simultaneously heating and pressurizing the sheet W1.

[0086] The first pressure heating unit 161 and the second pressure heating unit 162 are positioned opposite each other in the vertical direction. Specifically, the first pressure heating unit 161 is positioned above, and the second pressure heating unit 162 is positioned below. The lower surface of the first pressure heating unit 161 and the upper surface of the second pressure heating unit 162 are formed as approximately flat surfaces and are heated by a heating mechanism (not shown). Examples of such heating mechanisms include electric heaters. The sheet W1 is heated by contacting the lower surface of the first pressure heating unit 161 and the upper surface of the second pressure heating unit 162.

[0087] like Figure 8As shown, the first pressurized heating unit 161 has a first control unit 163, and the second pressurized heating unit 162 has a second control unit 164. Although the figures are omitted, the first control unit 163 and the second control unit 164 each include a CPU (Central Processing Unit), a system bus, ROM (Read Only Memory), RAM (Random Access Memory), etc.

[0088] The first control unit 163 and the second control unit 164 are electrically connected to the third control unit 210, and are controlled uniformly by the third control unit 210. The third control unit 210 is provided on an external device 200 relative to the manufacturing apparatus 10. That is, the pressurized heating unit 160 is controlled by the third control unit 210 of the external device 200. The external device 200 is, for example, an information terminal device such as a personal computer.

[0089] Therefore, since the first pressurizing and heating unit 161 and the second pressurizing and heating unit 162 are independently controlled by the third control unit 210, the compressive force applied to the sheet W1 and the heating temperature T3 (described later) can be precisely and uniformly controlled. Furthermore, the first control unit 163 and the second control unit 164 can also be controlled by the third control unit 210 via the device control unit of the manufacturing apparatus 10 described above.

[0090] The first control unit 163 and the second control unit 164 may also have temperature measurement functions. This allows the actual temperature of the sheet W1, etc., to be sent to the third control unit 210, thereby enabling more precise control of the heating temperature T3 of the sheet W1. Furthermore, the third control unit 210 may also be electrically connected to the heating unit 140 and the cooling units 150 and 170, and adjust the heating temperature T1, the cooling temperature T2, and the cooling temperature T4 (described later).

[0091] The pressure heating section 160 is not limited to the structure described above; for example, it could be a pair of pressure heating rollers. Furthermore, it could also be a structure in which a stamping mechanism or pressure rollers are provided inside a heating device such as the heating section 140.

[0092] More specifically, such as Figure 9 As shown, sheet W1 is sandwiched between the first pressure heating section 161 and the second pressure heating section 162. The heating temperature T3 of sheet W1 is set above the first melting point. At this time, the lower surface of the first pressure heating section 161 is in contact with the upper surface of sheet W1, and the upper surface of the second pressure heating section 162 is in contact with the lower surface of sheet W1.

[0093] When manufacturing a high-density sound-absorbing sheet S, heating is performed before applying a predetermined compressive force to the sheet W1. That is, no compressive force is applied until the interior of the sheet W1 reaches the heating temperature T3, which is above the first melting point. As a result, the melting of the first coating layer 232 is completed, making it easier for the compressive force to reach the interior of the sheet W1, thereby increasing the compressibility of the sheet W1.

[0094] In detail, when the first coating layer 232 is subjected to compressive force while it is in a re-molten state, the adhesion between the joints of the first fiber 23A and the second fiber 23B, as described above, and between the joints of the second fibers 23B to each other, is released. As a result, the mechanical strength of the sheet W1 decreases, and it is easily compressed in the vertical direction by the applied compressive force, thus forming a higher density internal structure.

[0095] In contrast, when manufacturing a lower-density sound-damping sheet S, the aforementioned period for applying compressive force can be advanced, or the method described below can be used. That is, the heating temperature T3 of the sheet W1 is set to be lower than the first melting point of the first coating layer 232. As a result, the solidification of the first coating layer 232 is maintained without melting of the first coating layer 232. Therefore, the sheet W1 becomes difficult to compress due to the applied compressive force. Furthermore, the thickness compression ratio of the sheet W1 in the vertical direction becomes lower, thereby enabling the manufacture of a lower-density sound-damping sheet S. Thus, by adjusting the heating temperature T3, the density of the sound-damping sheet S can also be easily adjusted.

[0096] Next, a predetermined compressive force is applied to the sheet W1 between the first pressurizing heating section 161 and the second pressurizing heating section 162 in a manner that shortens the distance along the Z-axis. The compression ratio of the thickness of the sheet W1 in the vertical direction caused by the predetermined compressive force is preferably 10% or more.

[0097] Therefore, due to the increased density of the sound-damping sheet S, the sound insulation properties within the sound-damping characteristics are improved. Furthermore, by adjusting the compression ratio, the density of the sound-damping sheet S can be changed. That is, increasing the compression ratio increases the density of the sound-damping sheet S, while decreasing the compression ratio decreases the density. The relationship between the density of the sound-damping sheet S and the sound insulation properties will be described later. Then, the process proceeds to the second cooling step S16.

[0098] Return to Figure 5 The second cooling process S16 is performed using the cooling unit 170. In the second cooling process S16, the sheet W1 after the pressurized heating process S15 is cooled to a temperature lower than the first melting point so that the first coating layer 232 is cured.

[0099] The cooling section 170 has the same structure as the cooling section 150 described above. Specifically, the cooling section 170 includes a cooling source section 171, a cooling chamber 173, an air supply section 175, and a conveying roller 177. The cooling source section 171 corresponds to the cooling source section 151, the cooling chamber 173 corresponds to the cooling chamber 153, the air supply section 175 corresponds to the air supply section 155, and the conveying roller 177 corresponds to the conveying roller 157. Each structure of the cooling section 170 has the same manner and function as the corresponding structure of the cooling section 150. Therefore, a detailed description of each structure of the cooling section 170 is omitted.

[0100] like Figure 10 As shown, the sheet W1 is conveyed by the conveying roller 177 and cooled to a cooling temperature T4 by the cooling section 170. The cooling temperature T4 is set to be lower than the first melting point of the first coating layer 232. Therefore, the first coating layer 232 is cured, and the joints of the first fiber 23A and the second fiber 23B, and the joints of the second fiber 23B with each other, are bonded together by the first coating layer 232. Thus, a continuous sheet-shaped sound-absorbing sheet S is formed.

[0101] Because a compressive force is applied to the sheet W1 in the pressurizing and heating process S15, the internal structure of the sheet W1 becomes denser. Furthermore, the pressurizing and heating process S15 to the second cooling process S16 are performed continuously. Then, the process proceeds to the cutting process S17.

[0102] Return to Figure 5 The cutting process S17 is performed using the cutting section 180. The cutting section 180 cuts the continuous, sheet-like soundproof sheet S into the desired shape. Although not shown in the figure, the cutting section 180 includes a longitudinal blade and a transverse blade.

[0103] The longitudinal blade, for example, cuts the continuous, sheet-like sound-damping sheet S along the X-axis. The transverse blade, for example, cuts the continuous, sheet-like sound-damping sheet S along the Y-axis. This produces a roughly rectangular, plate-like sound-damping sheet S, which is then stored in the tray 190.

[0104] Here, the relationship between the density of the soundproof sheet S and the sound insulation properties in the soundproofing characteristics is explained. Figure 11 This illustrates the change in sound transmission loss when sound waves are emitted while the density and thickness of the sound-absorbing sheet S are varied, thus altering the frequency. Figure 11 In the diagram, the horizontal axis represents the frequency of the sound wave [Hz], and the vertical axis represents the transmission loss [dB]. Transmission loss is an indicator of sound insulation performance; the higher the value, the more difficult it is for sound waves to pass through, resulting in superior sound insulation performance.

[0105] exist Figure 11 In the above, levels a and d represent densities set to 0.05 g / cm³.3 For the sample, levels b and e are defined with a density set to 0.10 g / cm³. 3 The sample, with levels c and f, had a density set to 0.15 g / cm³. 3 The thickness of the samples was set to 20mm for levels a, b, and c, and 40mm for levels d, e, and f.

[0106] The theoretical value 1 is at 1000g / m 2 The line segment calculated under the given conditions has a theoretical value of 2 at 2000 g / m. 2 The line segment calculated under the given conditions has a theoretical value of 3 at 4000 g / m. 2 The line segment calculated under the given conditions has a theoretical value of 4 at 6000 g / m. 2 The line segment calculated under the given conditions.

[0107] like Figure 11 As shown, the sound insulation characteristics varied across different levels between approximately 300Hz and 2000Hz. Overall, it can be observed that the level with higher density and greater thickness exhibits superior sound insulation characteristics.

[0108] According to this embodiment, the following effects can be obtained.

[0109] In the sound-damping sheet S, the internal structure can be easily controlled. Specifically, since a compressive force is applied while the first coating layer 232 is melted in the pressure heating process S15, the compression ratio of the sheet W1 can be easily adjusted by regulating this compressive force. Therefore, the thickness and density of the sound-damping sheet S can be easily changed. In other words, a method for manufacturing a sound-damping sheet S with easily controlled internal structure can be provided. Furthermore, since the control of the internal structure is relatively simple, a sound-damping sheet S with a lower cost than previously available can be provided.

[0110] 2. Second Implementation Method

[0111] The sound-damping sheet S according to this embodiment is manufactured by the manufacturing method of the sound-damping sheet S of this embodiment described below. The sound-damping sheet S of this embodiment differs from the sound-damping sheet S of the first embodiment in that it is formed from a sheet W1 as a first stacked fiber body and a sheet W2 as a second stacked fiber body. Hereinafter, descriptions of structures repeated in the first embodiment will be omitted. In the manufacturing method of the sound-damping sheet S of this embodiment, the manufacturing apparatus 10 described above is also used. In the following description, reference is also made to the first embodiment. Figure 5 ...

[0112] The sound-damping sheet S of this embodiment has a high-density region L2 originating from sheet W1 and a low-density region L1 originating from sheet W2, as described later. The high-density region L2 has the same internal structure as the higher-density region in the sound-damping sheet S of the first embodiment.

[0113] like Figure 12 As shown, the low-density region L1 of the sound-absorbing sheet S in this embodiment contains a plurality of first fibers 23A and a plurality of third fibers 23C as raw materials. The plurality of first fibers 23A and the plurality of third fibers 23C are not oriented in a specific direction, but are intertwined. The joints of the first fibers 23A and the third fibers 23C, as well as the joints of the third fibers 23C with each other, are bonded together by a second coating layer 234 of the third fibers 23C, which will be described later.

[0114] In the first fiber 23A, there is approximately one or more contact points with the third fiber 23C. In the third fiber 23C, there is also approximately one or more contact points with the first fiber 23A or other third fibers 23C. The contact points of the first fibers 23A are not bonded to each other, but there are approximately one or more contact points. As described above, in the low-density region L1, multiple first fibers 23A and multiple third fibers 23C are also bonded to each other.

[0115] like Figure 13 As shown, the third fiber 23C includes a second core 233 and a second coating layer 234 covering the second core 233. The second coating layer 234 is thermoplastic and has a second melting point. The second coating layer 234 is melted by heating during the manufacturing process of the sound-absorbing sheet S of this embodiment, as described later. Figure 13 The diagram shows the state in which the joints of the first fiber 23A and the third fiber 23C are bonded together by a second coating layer 234 that has melted and solidified. Although not shown in the diagram, the joints of the third fibers 23C are also bonded together by the second coating layer 234.

[0116] The second core 233 is an organic fiber. Examples of organic fibers include the same material as the first core 231 described above. In this embodiment, polyethylene terephthalate is used as the second core 233.

[0117] The second coating layer 234 is a thermoplastic resin. Examples of thermoplastic resins include those similar to the first coating layer 232 described above. In this embodiment, polyethylene is used as the second coating layer 234.

[0118] The second melting point of the second coating layer 234 is higher than the first melting point of the first coating layer 232. The difference between the second melting point and the first melting point is preferably 3°C or more, and more preferably 5°C or more. Therefore, in the pressure heating process described later in the manufacturing of the soundproof sheet S, the first coating layer 232 can be easily melted without melting the second coating layer 234.

[0119] Furthermore, the second melting point is preferably about 20°C lower than the melting point of the second core 233. Therefore, during the manufacture of the sound-absorbing sheet S, the second coating layer 234 can be easily melted without melting the second core 233. The melting point of the second coating layer 234 is preferably 110°C or higher and 210°C or lower, more preferably 110°C or higher and 160°C or lower.

[0120] The average fiber length of the third fiber 23C, i.e. the average fiber length of the second core 233, is preferably 100 μm or more and 5 mm or less, and more preferably about 1 mm. Therefore, the plurality of third fibers 23C can easily be wound with the plurality of first fibers 23A, thereby improving the mechanical properties of the soundproof sheet S, such as its strength.

[0121] The ratio of the diameter D2 of the second core 233 to the thickness E2 of the second coating layer 234 is preferably 0.2 or more and 2.0 or less, and more preferably 0.5 or more and 1.5 or less. Therefore, during the heating process in manufacturing the soundproof sheet S, deformation of the second core 233 can be suppressed, and the second coating layer 234 can be melted and solidified.

[0122] like Figure 14 As shown, the manufacturing method of the sound-damping sheet S according to this embodiment includes a first mixing step S11 and a first stacking step S12 for producing sheet W1, and a second mixing step S21 and a second stacking step S22 for producing sheet W2. Furthermore, as a subsequent step after producing sheet W1 and sheet W2, the manufacturing method of the sound-damping sheet S includes a heating step S23, a first cooling step S24, a pressurized heating step S25, a second cooling step S26, and a cutting step S27. However, the manufacturing method of the sound-damping sheet S is not limited to the above-described structure.

[0123] The first mixing process S11 and the first stacking process S12 are performed in the same manner as in the first embodiment. In this embodiment, the first mixing process S11 described above and the subsequent first stacking process S12 are performed to manufacture the sheet W1, and the second mixing process S21 and the subsequent second stacking process S22 are performed in parallel with or after these processes to manufacture the sheet W2.

[0124] In the manufacturing apparatus 10 described above, the sheet W1 can be either wound into a roll near the heating section 140, or it can skip the heating section 140 and proceed to the cooling section 170 to be processed into a single sheet W1 in the cutting section 180.

[0125] The second mixing step S21 is performed in the mixing section 11. In the second mixing step S21, the second mixing step is performed in the same manner as the first mixing step S11, except that the second fiber 23B in the first mixing step S11 is replaced with the third fiber 23C. Through the second mixing step S21, a second mixture containing a plurality of first fibers 23A and a plurality of third fibers 23C is produced.

[0126] The second mixture is formed in the stacking section 100 into a sheet W2, which serves as a second stacked fiber body. In the sheet W2, the content of the third fiber 23C relative to the content of the first fiber 23A is preferably 12.0% by mass or more and 40.0% by mass or less, more preferably 14.0% by mass or more and 25.0% by mass or less. This allows for the suppression of the content of the second coating layer 234 containing the third fiber 23C while improving the mechanical properties of the sound-absorbing sheet S, such as its strength.

[0127] The third fiber 23C is a substance produced by another known device and supplied to the hopper 14. Alternatively, a heated mixer or the like can be arranged upstream of the hopper 14 to supply the third fiber 23C produced by the heated mixer to the hopper 14. In the heated mixer, a second coating layer 234 is formed on the second core 233.

[0128] The second core 233, which is the third fiber 23C, can also be made from fibers produced by defiberizing waste paper or old cloth. Additives can also be supplied from either of the hoppers 13 or 14, and the sheet W2 can contain them. Examples of additives include, for instance, colorants, flame retardants, insect repellents, mildew inhibitors, antioxidants, UV absorbers, agglomeration inhibitors, and release agents.

[0129] The first fiber 23A and the third fiber 23C are mixed while being conveyed from the main body 60 to the stacking section 100 to form a second mixture. The second mixture is conveyed from the main body 60 to the stacking section 100 via a blower or the like. Then, it proceeds to the second stacking process S22.

[0130] The second stacking process S22 is performed in the stacking section 100. The stacking section 100 stacks the second mixture in the air, thereby producing a sheet W2 containing a plurality of first fibers 23A and a plurality of third fibers 23C. The stacking section 100 introduces the second mixture from the main body section 60 into the interior of the roller section 101 and stacks it on the mesh belt 122 in a dry manner. The second stacking process S22 is performed in the same manner as the first stacking process S12, except that the sheet W2 is produced by the second mixture.

[0131] The produced sheet W2 can be wound into a roll in the same continuous sheet shape as sheet W1, or it can be made into a single sheet at the cutting section 180, etc. Sheets W2 and W1 are overlapped by bonding their respective main surfaces together. Alternatively, sheet W2 can be produced on the surface above sheet W1 instead of on the mesh belt 122, thus eliminating the need for overlapping. In this case, a mechanism for unwinding the continuous sheet W1 onto the mesh belt 122 can be provided upstream of the sheet conveying section 120. Then, the process proceeds to the heating step S23.

[0132] The heating process S23 is performed using the heating unit 140. For example... Figure 15 As shown, in the heating step S23, sheet W1 and sheet W2 are overlapped and heated in the heating section 140 to melt the first coating layer 232 and the second coating layer 234. The heating temperature T1 of sheet W1 and sheet W2 is set to be above the second melting point of the second coating layer 234. Otherwise, it is performed in the same manner as the heating step S13 of the first embodiment. Then, it proceeds to the first cooling step S24.

[0133] The first cooling process S24 is performed using the cooling unit 150. For example... Figure 16 As shown, the stacked sheets W1 and W2 are cooled to a temperature below the first melting point, i.e., cooling temperature T2. This causes the first coating layer 232 and the second coating layer 234 to solidify.

[0134] While being conveyed by the conveying roller 157, sheet W1 and sheet W2 are cooled to a cooling temperature T2 by the cooling section 150. The cooling temperature T2 is set to be lower than the first melting point of the first coating layer 232. Therefore, in sheet W1, the joints of the first fiber 23A and the second fiber 23B, and the joints of the second fibers 23B to each other, are bonded together by the first coating layer 232. In sheet W2, the joints of the first fiber 23A and the third fiber 23C, and the joints of the third fibers 23C to each other, are bonded together by the second coating layer 234.

[0135] Furthermore, at the interface of the overlapping sheets W1 and W2, the first fiber 23A and the second fiber 23B of sheet W1, and the first fiber 23A and the third fiber 23C of sheet W2 are in contact with each other. Therefore, by curing the molten first coating layer 232 and the second coating layer 234, the interface of sheet W1 and sheet W2 is also bonded together to become a single unit.

[0136] At this point, since no compressive force is applied to sheet W1 and sheet W2, the density of sheet W1 and sheet W2 hardly changes before and after the first cooling step S24. Then, the process proceeds to the pressurization and heating step S25.

[0137] The pressurized heating process S25 is performed using the pressurized heating unit 160. For example... Figure 17 As shown, the stacked sheets W1 and W2 are heated to a temperature above the first melting point and below the second melting point, i.e., heating temperature T3. As a result, the first coating layer 232 of sheet W1 melts, while the second coating layer 234 of sheet W2 remains solidified.

[0138] Heating is performed to a heating temperature T3, and a predetermined compressive force is applied to the stacked sheets W1 and W2. To raise the temperature to T3 up to the interior of sheet W1, sheets W1 and W2 can be sandwiched between the first pressurizing heating section 161 and the second pressurizing heating section 162 for a certain period before applying the compressive force. When the interior of sheet W1 reaches the heating temperature T3, sheets W1 and W2 are compressed by shortening the distance along the Z-axis between the first pressurizing heating section 161 and the second pressurizing heating section 162.

[0139] Because the first coating layer 232 is in a molten state, bonding between the joints of the first fiber 23A and the second fiber 23B, as well as between the joints of the second fibers 23B to each other, is difficult. Therefore, the sheet W1 has low mechanical strength, and is thus compressed in the vertical direction by the applied compressive force, resulting in a higher density internal structure.

[0140] In contrast, the second coating layer 234 remains in a cured state. Therefore, the joints of the first fiber 23A and the third fiber 23C, as well as the joints of the third fibers 23C with each other, are bonded together. Consequently, the sheet W2 has high mechanical strength, making it difficult to compress in the vertical direction under applied compressive force, thus resulting in a lower density internal structure.

[0141] Furthermore, at the interface between the overlapping sheets W1 and W2, the adhesion between sheets W1 and W2 is maintained because the second coating layer 234 remains solidified. Although the first coating layer 232 temporarily melts, it is solidified again in the second cooling process S26 in the next process, which helps to bond sheets W1 and W2.

[0142] The compression ratio of the thickness of sheet W1 and sheet W2 in the vertical direction generated by the predetermined compression force is preferably 10% or more in total. As a result, the density of sheet W1 increases, thus improving sound insulation. Then, the process proceeds to the second cooling step S26.

[0143] The second cooling process S26 is implemented using the cooling unit 170. For example... Figure 18 As shown, in the second cooling process S26, the stacked sheets W1 and W2 are cooled to a cooling temperature T4, which is lower than the first melting point, so that the first coating layer 232 is cured.

[0144] The stacked sheets W1 and W2 are conveyed by the conveying roller 177 and cooled to a cooling temperature T4 by the cooling section 170. Since the cooling temperature T4 is lower than the first melting point of the first coating layer 232, the first coating layer 232 is cured in sheet W1. In contrast, the second coating layer 234 of sheet W2 is also maintained in a cured state in the preceding pressurization and heating process S25.

[0145] Thus, the first coating layer 232, in addition to the second coating layer 234, also becomes cured, and the joints of the first fiber 23A and the second fiber 23B, as well as the joints of the second fibers 23B to each other, are bonded together by the cured first coating layer 232. Therefore, a sound-damping sheet S is formed, comprising a higher-density region L2 originating from sheet W1 and a lower-density region L1 originating from sheet W2. Furthermore, as described above, sheets W1 and W2 are bonded together by the first coating layer 232 and the second coating layer 234 present at their interface. Then, the process proceeds to the cutting process S27.

[0146] The cutting process S27 is performed using the cutting section 180. The sound-damping sheet S can also be wound up while maintaining a continuous, sheet-like state without performing the cutting process S27. Through these methods, the sound-damping sheet S of this embodiment is manufactured.

[0147] Here, the sound absorption characteristics of the soundproofing properties are explained in the soundproofing sheet S, which includes a low-density region L1, a high-density region L2, and a region with intermediate density in its internal structure. Figure 19This paper shows the change in sound absorption rate when a sample with altered configuration of the three regions in the sound-absorbing sheet S is subjected to perpendicular incidence of sound waves onto one side of the main surface, while simultaneously changing the frequency [Hz]. Figure 19 In the diagram, the horizontal axis represents the frequency of the sound wave [Hz], and the vertical axis represents the absorption rate of the incident sound wave, i.e., the perpendicular incidence absorption rate. The absorption rate is an indicator of sound absorption characteristics; the higher the value, the better the sound absorption characteristics.

[0148] The aforementioned region with intermediate density can be formed by means of adjusting the applied compressive force in the pressurization and heating process S25.

[0149] In each sample, three sound-damping sheets S with different densities were overlapped one on top of the other. A density of 0.15 g / cm³ was used as the high-density region L2. 3 Thin sheets H were used as low-density regions L1 with a density of 0.05 g / cm³. 3 Thin sheets L were used, and a density of 0.10 g / cm³ was used as a region with intermediate density. 3 Thin sheet M. Thin sheets H, L, and M are each 20 mm thick.

[0150] Levels g1 and g2 represent samples where thin sheet L is placed on the surface where sound is incident, and thin sheet H or thin sheet M is placed behind thin sheet L. Levels h1 and h2 represent samples where thin sheet M is placed on the surface where sound is incident, and thin sheet L or thin sheet H is placed behind thin sheet M. Levels f1 and f2 represent samples where thin sheet H is placed on the surface where sound is incident, and thin sheet L or thin sheet M is placed behind thin sheet H.

[0151] like Figure 19 As shown, differences in sound absorption characteristics are observed across different levels within a frequency range of approximately 500Hz to 4000Hz. Within this range, sound absorption characteristics are improved at levels h1 and h2 compared to levels f1 and f2, and are even more superior at levels g1 and g2. Generally, it can be observed that the lower the density of the surface on which sound waves are incident, the better the sound absorption characteristics. Therefore, when considering the relationship between density and sound insulation characteristics described above, configuring a low-density region L1 on the incident side of the sound wave and a high-density region L2 on the emitting side of the sound wave can improve both sound absorption and sound insulation characteristics.

[0152] According to this embodiment, the following effects can be obtained.

[0153] In the sound-damping sheet S, the internal structure can be easily controlled. Specifically, by performing the pressure heating process S25 while the first coating layer 232 is melted and the second coating layer 234 is solidified, compression by pressure is easily achieved in the sheet W1, resulting in a higher density internal structure. In contrast, compression by pressure is difficult to achieve in the sheet W2, resulting in a lower density internal structure. Thus, a high-density region L2 and a low-density region L1 can be easily formed in the sound-damping sheet S. That is, a method for manufacturing a sound-damping sheet S with easy control over its internal structure can be provided. Furthermore, since the control over the internal structure is relatively simple, a sound-damping sheet S with a lower cost than before can be provided.

[0154] 3. Third Implementation Method

[0155] The sound-damping sheet S according to this embodiment is manufactured by the manufacturing method of the sound-damping sheet S of this embodiment, which will be described later. The sound-damping sheet S of this embodiment has an internal structure in which a lower density region L1 originating from sheet W2 is sandwiched between a higher density region L2 originating from sheet W1. That is, the sound-damping sheet S of this embodiment differs from the sound-damping sheet S of the second embodiment in that it is manufactured from two sheets W1 and one sheet W2.

[0156] Hereinafter, descriptions of structures that are repeated in the above embodiments will be omitted. In the manufacturing method of the sound-damping sheet S of this embodiment, the manufacturing apparatus 10 described above is also used. In the following description, reference will also be made to the first embodiment. Figure 5 and the second embodiment Figure 14 .

[0157] Sheets W1 and W2 are manufactured in the same manner as in the above embodiment and proceed to the heating step S23. In the heating step S23, as... Figure 20 As shown, in the heating section 140, sheet W1, sheet W2, and sheet W1 are stacked vertically in this order and heated to melt the first coating layer 232 and the second coating layer 234. The heating temperature T1 of sheet W1 and sheet W2 is set to be above the second melting point of the second coating layer 234. Otherwise, it is performed in the same manner as the heating step S13 of the first embodiment. Then, it proceeds to the first cooling step S24.

[0158] In the first cooling process S24, as Figure 21As shown, the two sheets W1 and one sheet W2, which are overlapped, are cooled to a cooling temperature T2, which is lower than the first melting point. As a result, the first coating layer 232 and the second coating layer 234 solidify. Then, the process proceeds to the pressurization and heating step S25.

[0159] In the pressurized heating process S25, such as Figure 22 As shown, the two sheets W1 and one sheet W2 that are overlapped are heated to a heating temperature T3 that is above the first melting point and below the second melting point. As a result, the state in which the first coating layer 232 of sheet W1 melts and the second coating layer 234 of sheet W2 is solidified is maintained.

[0160] Heating is performed to a heating temperature T3, and a predetermined compressive force is applied to the stacked sheets W1 and W2. To raise the temperature to T3 up to the interior of sheet W1, sheets W1 and W2 can be sandwiched between the first pressurizing heating section 161 and the second pressurizing heating section 162 and held for a certain period before applying the compressive force. When the interior of sheet W1 reaches the heating temperature T3, sheets W1 and W2 are compressed by shortening the distance along the Z-axis between the first pressurizing heating section 161 and the second pressurizing heating section 162.

[0161] In sheet W1, because the first coating layer 232 is in a molten state, bonding between the joints of the first fiber 23A and the second fiber 23B, as well as between the joints of the second fibers 23B to each other, is difficult. Therefore, sheet W1 has low mechanical strength, and is thus compressed in the vertical direction by the applied compressive force, resulting in a higher density internal structure.

[0162] In the second coating layer 234 of sheet W2, the second coating layer 234 is maintained in a cured state. Therefore, the joints of the first fiber 23A and the third fiber 23C, as well as the joints of the third fibers 23C with each other, are bonded together. As a result, sheet W2 has high mechanical strength and is difficult to compress in the vertical direction by the applied compressive force, thus resulting in a low-density internal structure. Then, the process proceeds to the second cooling process S26.

[0163] In the second cooling process S26, as Figure 23 As shown, the stacked sheets W1 and W2 are cooled to a cooling temperature T4, which is below the first melting point, so that the first coating layer 232 is cured.

[0164] The stacked sheets W1 and W2 are conveyed by the conveying roller 177 and cooled to a cooling temperature T4 by the cooling section 170. Since the cooling temperature T4 is lower than the first melting point of the first coating layer 232, the first coating layer 232 is cured in sheet W1. In contrast, the second coating layer 234 of sheet W2 is also maintained in a cured state in the preceding pressurization and heating process S25.

[0165] Thus, the first coating layer 232, in addition to the second coating layer 234, also becomes cured, and the joints of the first fiber 23A and the second fiber 23B, as well as the joints of the second fibers 23B to each other, are bonded together by the cured first coating layer 232. Furthermore, the upper and lower surfaces of the sheet W2 are bonded to the adjacent sheet W1 to become a single unit. Then, a sound-damping sheet S is formed, having an internal structure in which a region L2 of higher density originating from sheet W1 holds a region L1 of lower density originating from sheet W2. Then, the process proceeds to the cutting process S27. In the sound-damping sheet S, cutting processing can also be appropriately performed through the cutting process S27.

[0166] According to this embodiment, in addition to the effects of the above-described embodiments, a three-layer structure can be easily formed.

[0167] 4. Fourth Implementation Method

[0168] The sound-damping sheet S according to this embodiment is manufactured by the manufacturing method of the sound-damping sheet S of this embodiment, which will be described later. The sound-damping sheet S of this embodiment differs from the sound-damping sheet S of the first embodiment in that it has an internal structure consisting of a lower-density region L1 and a higher-density region L2 formed from a single sheet W1. Hereinafter, descriptions of structures repeated in the above embodiments will be omitted. In the manufacturing method of the sound-damping sheet S of this embodiment, the manufacturing apparatus 10 described above is also used. In the following description, reference is made to the first embodiment. Figure 4 , Figure 5 .

[0169] The sheet W1 is manufactured in the same manner as in the first embodiment and proceeds to the heating step S13. In the heating step S13, as... Figure 24 As shown, the sheet W1 is heated in the heating section 140, causing the first coating layer 232 to melt. The heating temperature T1 of the sheet W1 is set above the first melting point of the first coating layer 232. Then, the process proceeds to the first cooling step S14.

[0170] In the first cooling process S14, as Figure 25As shown, in the cooling section 150, the sheet W1 is cooled to a cooling temperature T2, which is lower than the first melting point. As a result, the first coating layer 232 solidifies. Since no compressive force is applied to the sheet W1, the density of the sheet W1 hardly changes before and after the first cooling step S14. Then, the process proceeds to the pressurization and heating step S15.

[0171] In the pressurized heating process S15, such as Figure 26 As shown, sheet W1 is sandwiched between the first pressure heating section 161 and the second pressure heating section 162 and heated. At this time, it is assumed that regions with a melting point lower than the first melting point and regions with a melting point higher than the first melting point coexist within sheet W1. That is, regions that are closer to the first pressure heating section 161 and the second pressure heating section 162 and where the first coating layer 232 has solidified, and regions that are farther away from the first pressure heating section 161 and the second pressure heating section 162 and where the first coating layer 232 has melted, are mixed together. Therefore, a predetermined compressive force is applied to sheet W1 before the internal temperature of sheet W1 uniformly and completely rises to the heating temperature T3.

[0172] When the above-described state is achieved, a predetermined compressive force is applied to the sheet W1. As a result, in the sheet W1, compression becomes difficult in areas below the first melting point due to resistance to the compressive force, while compression becomes easier in areas above the first melting point due to the compressive force. Then, the process proceeds to the second cooling step S16.

[0173] In the second cooling process S16, as Figure 27 As shown, in the cooling section 170, the sheet W1 is cooled to a cooling temperature T4, which is a temperature lower than the first melting point. The cooling temperature T4 of the sheet W1 in the second cooling process S16 is set to a temperature lower than the first melting point of the first coating layer 232.

[0174] Therefore, in the sound-damping sheet S, the region below the first melting point becomes the lower density region L1, and the region above the first melting point becomes the higher density region L2. The sound-damping sheet S, having the lower density region L1 and the higher density region L2, is manufactured from a single sheet W1.

[0175] According to this embodiment, in addition to the effects of the first embodiment, it is also possible to easily form an internal structure with a density tilt in a sheet W1.

[0176] Symbol Explanation

[0177] 10… Manufacturing apparatus; 23A… First fiber; 23B… Second fiber; 23C… Third fiber; 160… Pressurized heating section; 161… First pressurized heating section; 162… Second pressurized heating section; 163… First control section; 164… Second control section; 210… Third control section; 231… First core; 232… First coating layer; 233… Second core; 234… Second coating layer; S… Soundproof sheet; S12… First stacking process; S13, S23… Heating process; S14, S24… First cooling process; S15, S25… Pressurized heating process; S22… Second stacking process; S16, S26… Second cooling process; W1… Sheet as the first stacked fiber body; W2… Sheet as the second stacked fiber body.

Claims

1. A method for manufacturing a sound-absorbing sheet, characterized in that, have: The first stacking process involves producing a first stacked fiber body composed of a mixture of multiple first fibers and multiple second fibers, wherein the first fibers are natural fibers, and the second fibers include a first core and a first coating layer that coats the first core and has a first melting point. The second stacking process involves fabricating a second stacked fiber body composed of a mixture of a plurality of first fibers and a plurality of third fibers, wherein the third fibers include a second core and a second coating layer that coats the second core and has a second melting point that is higher than the first melting point. The heating process involves overlapping and heating the first and second stacked fiber bodies to melt the first and second coating layers. In the first cooling process, while the first coating layer and the second coating layer are molten, the overlapping first stacked fiber body and the second stacked fiber body are cooled to a temperature lower than the first melting point, so as to solidify the first coating layer and the second coating layer. In the pressurization and heating process, the first stacked fiber body and the second stacked fiber body to be overlapped are heated to above the first melting point and below the second melting point, and a predetermined compressive force is applied to the first stacked fiber body and the second stacked fiber body. The second cooling process involves cooling the overlapping first and second stacked fiber bodies to below the first melting point to solidify the first coating layer.

2. The method for manufacturing the sound-absorbing sheet as described in claim 1, wherein, The first fiber is a cellulose fiber. The average fiber length of the first fiber is 10 μm or more and 50 mm or less. In the second fiber, the first core is polyethylene terephthalate, and the first coating layer is polyethylene. In the third fiber, the second core is polyethylene terephthalate, and the second coating layer is polyethylene. The average fiber length of the second fiber and the third fiber is more than 100 μm and less than 5 mm.

3. The method for manufacturing the sound-absorbing sheet as described in claim 2, wherein, The difference between the first melting point and the second melting point is greater than 3°C.

4. The method for manufacturing the sound-absorbing sheet as described in claim 3, wherein, In the first stacked fiber body, the content of the second fiber is 12.0% by mass or more and 40.0% by mass or less relative to the content of the first fiber. In the second stacked fiber body, the content of the third fiber is 12.0% by mass or more and 40.0% by mass or less relative to the content of the first fiber.

5. The method for manufacturing the sound-absorbing sheet as described in claim 1, wherein, In the pressurization and heating process, the compression rate achieved by the predetermined compression force is 10% or more.

6. The method for manufacturing the sound-absorbing sheet as described in claim 5, wherein, The pressurization and heating process is implemented using a pressurization and heating unit. The pressurized heating section includes a first pressurized heating section and a second pressurized heating section. The compressive force is applied between the first pressurized heating section and the second pressurized heating section.

7. The method for manufacturing the sound-absorbing sheet as described in claim 6, wherein, The first pressurized heating unit has a first control unit. The second pressurized heating unit has a second control unit. The first control unit and the second control unit are controlled by the third control unit.

8. A soundproof sheet, characterized in that, It is manufactured using the method for manufacturing the soundproof sheet as described in claim 1.

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