Diaphragm for loudspeaker and method for manufacturing diaphragm for loudspeaker

Abstract

Provided is a speaker diaphragm that can uniformly increase rigidity throughout the entire area. A speaker diaphragm 1 of the present invention includes a base material having a resin matrix 2 with a thermoplastic resin as a main component and fibers 3 dispersed in the resin matrix 2, the fibers 3 being poly-p-phenylene benzobisoxazole fibers, the average length of the fibers 3 being 0.5 mm or more and 3.0 mm or less, and the content of the fibers in the base material being 3 mass% or more and 15 mass% or less.

Description

[0001] This application is a divisional application of the invention patent application filed on July 25, 2019, with application number 201980045598.7 and entitled "Vosifying plate for loudspeaker and method of manufacturing virtuous plate for loudspeaker". Technical Field

[0002] This invention relates to a diaphragm for loudspeakers. Background Technology

[0003] For loudspeaker diaphragms, high rigidity is desirable to enable efficient sound production. Furthermore, loudspeaker diaphragms also require good environmental adaptability and high water resistance.

[0004] From this perspective, a loudspeaker diaphragm made of synthetic resin has been proposed to replace the loudspeaker diaphragm made of wood pulp. As such a loudspeaker diaphragm, a loudspeaker diaphragm containing long fibers with a length of 3 mm to 50 mm in the resin has been proposed (see Japanese Patent Application Publication No. 2004-15194).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2004-15194 Summary of the Invention

[0008] The technical problem that the invention aims to solve

[0009] However, if the resin contains long fibers, as described in the aforementioned loudspeaker diaphragm, it is difficult for the fibers to be evenly dispersed in the resin. In particular, in this loudspeaker diaphragm, the higher the fiber content, the more easily the fibers become unevenly distributed in the resin. Therefore, it is difficult to sufficiently increase the rigidity of this loudspeaker diaphragm throughout the entire area.

[0010] The present invention was made in view of the above circumstances, and the object of the present invention is to provide a loudspeaker diaphragm capable of uniformly increasing rigidity over the entire area, and a method for manufacturing the loudspeaker diaphragm.

[0011] Technical solutions for solving technical problems

[0012] In one embodiment of the present invention made to solve the above-mentioned technical problems, a loudspeaker diaphragm includes a substrate having a resin matrix mainly composed of a thermoplastic resin and fibers dispersed in the resin matrix, the fibers being poly(p-phenylenebenzodioxazole) fibers, the average length of the fibers being 0.5 mm or more and 3.0 mm or less, and the content of the fibers in the substrate being 3% by mass or more and 15% by mass or less.

[0013] In another aspect of the present invention, made to solve the aforementioned technical problem, a method for manufacturing a loudspeaker diaphragm includes: a step of extruding a resin composition containing a thermoplastic resin and fibers in a rod shape; a step of cutting the extruded material in the extrusion step into granules; and a step of injection molding the granules obtained in the cutting step; wherein the fibers are poly(p-phenylenebenzodioxazole) fibers, and the average length of the fibers after the cutting step is 0.5 mm or more and 3.0 mm or less. Attached Figure Description

[0014] Figure 1 This is a schematic front view of a loudspeaker diaphragm according to one embodiment of the present invention.

[0015] Figure 2 yes Figure 1 A sectional view of the diaphragm for a loudspeaker along line A-A.

[0016] Figure 3 It means Figure 1 A schematic diagram of the fiber dispersion state in the resin matrix of a loudspeaker diaphragm.

[0017] Figure 4 This is a flowchart illustrating a method for manufacturing a loudspeaker diaphragm according to one embodiment of the present invention. Detailed Implementation

[0018] In one aspect of the present invention, the loudspeaker diaphragm includes a substrate having a resin matrix mainly composed of thermoplastic resin and fibers dispersed in the resin matrix, wherein the fibers are poly(p-phenylenebenzodioxazole) fibers and the average length of the fibers is 0.5 mm or more and 3.0 mm or less.

[0019] In one embodiment of the loudspeaker diaphragm of the present invention, the fibers dispersed in the resin matrix are poly(p-phenylene benzodioxazole) fibers, thus facilitating a substantial increase in rigidity. In particular, in this loudspeaker diaphragm, the average length of the poly(p-phenylene benzodioxazole) fibers is within the aforementioned range, thereby enabling uniform dispersion of the fibers in the resin matrix. As a result, the rigidity of this loudspeaker diaphragm can be uniformly increased throughout the entire area.

[0020] The diaphragm of the loudspeaker can be cone-shaped.

[0021] In this loudspeaker diaphragm, the substrate may have a pair of skin layers constituting its surface side and back side, and a core layer formed between the pair of skin layers.

[0022] The fiber content in the substrate is preferably 3% by mass or more and 30% by mass or less.

[0023] In the diaphragm of this loudspeaker, the resin matrix and fibers may be unbonded at least in a portion.

[0024] In the diaphragm of this loudspeaker, the thermoplastic resin may be polypropylene.

[0025] In another aspect of the present invention, the method for manufacturing a loudspeaker diaphragm includes: a step of extruding a resin composition containing a thermoplastic resin and a fiber in a rod shape; a step of cutting the extruded molded body into granules; and a step of injection molding the granules obtained in the cutting step; wherein the fiber is poly(p-phenylenebenzodioxazole) fiber, and the average length of the fiber after the cutting step is 0.5 mm or more and 3.0 mm or less.

[0026] In another aspect of the present invention, a method for manufacturing a loudspeaker diaphragm is used to injection mold the loudspeaker diaphragm using particles cut from a rod-shaped extruder containing thermoplastic resin and poly(p-phenylene benzodioxazole) fibers. This allows for the manufacture of a loudspeaker diaphragm in which the poly(p-phenylene benzodioxazole) fibers are sufficiently and uniformly dispersed in the thermoplastic resin. Specifically, in this method, the average length of the poly(p-phenylene benzodioxazole) fiber particles is within the aforementioned range, ensuring that the fibers in the resulting loudspeaker diaphragm are uniformly dispersed in the thermoplastic resin without entanglement. If the fibers become entangled, fiber clumps will form, potentially clogging the material flow path in injection molding. Furthermore, since the fiber clumps are not uniformly dispersed in the thermoplastic resin, the rigidity of the loudspeaker diaphragm cannot be improved. On the other hand, by weaving the fibers together, the fibers can be uniformly dispersed in the thermoplastic resin, thereby improving the rigidity of the loudspeaker diaphragm. That is, the manufacturing method of the loudspeaker diaphragm can produce a loudspeaker diaphragm that uniformly improves rigidity throughout the entire area.

[0027] It should be noted that, in this invention, "main component" refers to the component with the highest content by mass, for example, a component with a content of 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more. "Average fiber length" refers to the average length of any 10 fibers. "Surface side" refers to the side facing the sound direction, and "back side" refers to the opposite side. "Surface layer" refers to the area with a depth of 50 μm or less between the surface and back side of the object or layer to which it is applied.

[0028] Hereinafter, embodiments of the present invention will be described in detail with appropriate reference to the accompanying drawings.

[0029] [Speaker diaphragm]

[0030] Figures 1-3 The loudspeaker diaphragm 1 includes a substrate 1a, which has a resin matrix 2 mainly composed of thermoplastic resin and fibers 3 dispersed in the resin matrix 2. The loudspeaker diaphragm 1 is a single unit of the substrate 1a.

[0031] The speaker's diaphragm 1 can be shaped to match the speaker used. Figure 1 and Figure 2 The substrate 1a is cone-shaped. By making the speaker diaphragm 1 cone-shaped, its strength can be increased. Furthermore, the size of the speaker diaphragm 1 can be set according to the speaker used. It should be noted that this speaker diaphragm can also be used in small speakers, such as those found in headphones, in-ear headphones, and portable electronic devices.

[0032] <Substrate>

[0033] The loudspeaker diaphragm 1 includes a substrate 1a, which has a resin matrix 2 and fibers 3 dispersed in the resin matrix 2. The substrate 1a can be formed by injection molding, as described later. The substrate 1a may have a pair of skin layers constituting its surface side and back side, and a core layer formed between the pair of skin layers. That is, a core layer may exist between the pair of skin layers. The pair of skin layers are formed by the resin matrix 2 and fibers 3 flowing in contact with the mold cavity during injection molding. The core layer is formed by the resin matrix 2 and fibers 3 that are not in contact with the mold cavity and are relatively slowly cooled and cured. In the skin layer and core layer of the loudspeaker diaphragm 1, the arrangement direction of the fibers 3 may be different.

[0034] The substrate 1a of the loudspeaker diaphragm 1 (in this embodiment, the loudspeaker diaphragm 1 itself) has a substantially uniform thickness. The lower limit of the average thickness T of the substrate 1a of the loudspeaker diaphragm 1 is preferably 100 μm, more preferably 300 μm. On the other hand, the upper limit of the average thickness T of the substrate 1a of the loudspeaker diaphragm 1 is preferably 800 μm, more preferably 650 μm. If the average thickness T does not meet the lower limit, the loudspeaker diaphragm 1 may lack rigidity or be difficult to form by injection molding. Conversely, if the average thickness T exceeds the upper limit, the loudspeaker diaphragm 1 may become unnecessarily heavy. It should be noted that "substantially uniform thickness" means that the ratio of the maximum thickness to the minimum thickness is greater than 1 and less than 1.20. "Average thickness" refers to the average thickness of any 10 points. It should be noted that the ratio described above regarding "approximately uniform thickness" refers to the ratio for a speaker diaphragm with approximately uniform thickness, and does not apply to speaker diaphragms with specially designed reinforcing ribs, etc.

[0035] (Resin matrix)

[0036] As described above, the resin matrix 2 is mainly composed of a thermoplastic resin. Examples of such thermoplastic resins include polyethylene, polypropylene, polystyrene, fluoropolymers, polycarbonate, polysulfone, polyethersulfone, polybutylene terephthalate, polyamide, polyimide, and acrylonitrile-butadiene-styrene resin. These resins can be used alone or in combination. Polypropylene is preferred as the thermoplastic resin. By using polypropylene as the thermoplastic resin, the vibration attenuation rate (internal loss) at the audible frequency of the speaker diaphragm 1 can be increased. Furthermore, when the thermoplastic resin is polypropylene, as will be described later, the fibers 3 are easily dispersed in a non-bonded state with the resin matrix 2, thereby further increasing the vibration attenuation rate and improving sound reproducibility. It should be noted that the fibers 3 may not be bonded to the resin matrix 2 at least partially, or the entire surface of the fibers 3 may not be bonded to the resin matrix 2.

[0037] (fiber)

[0038] Fiber 3 is poly(p-phenylene benzodioxazole) fiber. In the diaphragm 1 of this loudspeaker, fiber 3 is poly(p-phenylene benzodioxazole) fiber, which can suppress the decrease in vibration attenuation rate and increase rigidity.

[0039] The lower limit for the content of fiber 3 in the substrate 1a (in other words, the content of fiber 3 in the speaker diaphragm 1) is preferably 3% by mass, more preferably 6% by mass. On the other hand, the upper limit for the content of fiber 3 in the substrate 1a is preferably 30% by mass, more preferably 22% by mass, and even more preferably 15% by mass. If the content of fiber 3 does not meet the lower limit, the rigidity of the speaker diaphragm 1 may be insufficient. Conversely, if the content of fiber 3 exceeds the upper limit, the fibers 3 in the resin matrix 2 may become entangled with each other, resulting in insufficient uniform dispersion of the fibers 3 in the resin matrix 2. In addition, if the content of fiber 3 exceeds the upper limit, when heating the resin composition containing fiber 3 and the thermoplastic resin and passing it through the nozzle of the injection molding device, the unevenness of the fibers 3 may cause blockage, making the manufacture of the speaker diaphragm 1 difficult.

[0040] The lower limit for the average length of fiber 3 is 0.5 mm, preferably 1.0 mm. On the other hand, the upper limit for the average length of fiber 3 is 3.0 mm, preferably 2.5 mm, and more preferably 1.5 mm. If the average length of fiber 3 does not meet the lower limit, the effect of increasing rigidity brought about by fiber 3 may be insufficient. Conversely, if the average length of fiber 3 exceeds the upper limit, fiber 3 may easily entangle with each other, and the uniform dispersion of fiber 3 in resin matrix 2 may be insufficient. It should be noted that as long as the average length of each fiber 3 dispersed in resin matrix 2 is within the aforementioned range, it can also be non-uniform.

[0041] The maximum length of the fibers 3 dispersed in the resin matrix 2 is preferably 5.0 mm, more preferably 4.0 mm, and even more preferably 3.0 mm. In this way, by keeping the maximum length of the fibers 3 below the upper limit, it is easy and reliable to prevent the fibers 3 from entangled with each other.

[0042] The lower limit for the average aspect ratio of fiber 3 is preferably 20, more preferably 50. On the other hand, the upper limit for the average aspect ratio of fiber 3 is preferably 300, more preferably 200. If the average aspect ratio does not meet the lower limit, it may be difficult to control the orientation of fiber 3. Conversely, if the average aspect ratio exceeds the upper limit, it may be easy for fiber 3 to entangle with each other. It should be noted that the "average aspect ratio of fiber" refers to the value obtained by averaging the ratio of the length to the diameter of any 10 randomly selected fibers.

[0043] like Figure 3As shown, it is preferable that the resin matrix 2 and the fiber 3 are not bonded at least partially. In other words, it is preferable that the fiber 3 and the resin matrix 2 are in a non-bonded state, that is, the fiber 3 is embedded in the hollow portion 2a of the resin matrix 2 while in close contact with the resin matrix 2. In this case, it is sufficient that the fiber 3 and the resin matrix 2 are not bonded at least partially. As a result, the vibration damping rate of the speaker diaphragm 1 can be increased. In the speaker diaphragm 1, from the viewpoint of increasing rigidity by utilizing the fiber 3, it is preferable that the shape of the hollow portion 2a is the same as the shape of the fiber 3 embedded in the hollow portion 2a. In other words, it is preferable that there is no gap between the resin matrix 2 and the fiber 3. It should be noted that in the speaker diaphragm 1, the fiber 3 is immiscible with the aforementioned thermoplastic resin, and there is no chemical bond between the two, thereby allowing the fiber 3 to be held in a non-bonded state with the resin matrix 2. Furthermore, in the speaker diaphragm 1, even when the fiber 3 is not chemically bonded to the thermoplastic resin, by controlling the content and average length of the fiber 3 within the aforementioned range, the fiber 3 can be uniformly dispersed in the resin matrix 2.

[0044] (Other ingredients)

[0045] The substrate 1a of the loudspeaker diaphragm 1 may contain other components besides the resin matrix 2 and the fiber 3, without affecting the effects of the present invention. Examples of such other components include colorants such as titanium dioxide, ultraviolet absorbers, and compatibilizers.

[0046] <Advantages>

[0047] In this loudspeaker diaphragm 1, the fibers 3 dispersed in the resin matrix 2 of its substrate 1a are poly(p-phenylene benzodioxazole) fibers, thus allowing for easy and sufficient increase in rigidity using these fibers 3. In particular, the average length of the poly(p-phenylene benzodioxazole) fibers in this loudspeaker diaphragm 1 is within the aforementioned range; therefore, by controlling the fiber content within the aforementioned range, the fibers 3 can be uniformly dispersed in the resin matrix 2. As a result, in this loudspeaker diaphragm 1, rigidity can be uniformly increased throughout the entire area.

[0048] [Manufacturing method for loudspeaker diaphragms]

[0049] Next, refer to Figure 4 ,right Figure 1 The manufacturing method of the loudspeaker diaphragm 1 will be described. The manufacturing method of the loudspeaker diaphragm includes a step of extruding a resin composition comprising thermoplastic resin and fiber in the form of a rod (extrusion step), a step of cutting the extruded molded body in the extrusion step into granules (cutting step), and a step of injection molding the granules obtained in the cutting step (molding step).

[0050] (Extrusion process)

[0051] In the extrusion process, a resin composition comprising thermoplastic resin and fiber 3 is extruded in a rod shape while being stirred. This extrusion process can be performed using an extrusion molding apparatus. This apparatus includes, for example, an extruder having a cylinder for guiding the resin composition and a screw mounted within the cylinder for stirring the resin composition; a T-die for extruding the resin composition stirred in the extruder in a rod shape; and a cooling section for cooling the resin composition extruded from the T-die. In the extrusion process, after the resin composition is extruded in a rod shape, it is cooled by the cooling section, thereby solidifying the resin composition in the shape it was extruded into. Thus, a rod-shaped extruded body can be obtained.

[0052] Examples of thermoplastic resins used in the extrusion process include... Figure 1 The aforementioned thermoplastic resin is included as the main component of the resin matrix 2 of the substrate 1a of the loudspeaker diaphragm 1. Among them, polypropylene is preferred as the thermoplastic resin.

[0053] The fiber 3 used in the extrusion process is poly(p-phenylene benzodioxazole) fiber. The length of the poly(p-phenylene benzodioxazole) fiber is not particularly limited; for example, it can be 1 mm or more and 10 mm or less, preferably 3 mm or more and 6 mm or less. The method for manufacturing this loudspeaker diaphragm adjusts the length of the particles through a cutting process described later, thereby adjusting the length of the fiber 3 contained in the substrate 1a of the resulting loudspeaker diaphragm 1 to the aforementioned range.

[0054] The lower limit for the content of fiber 3 in the resin composition is preferably 3% by mass, more preferably 6% by mass. On the other hand, the upper limit for the content of fiber 3 is preferably 30% by mass, more preferably 22% by mass, and even more preferably 15% by mass. If the content of fiber 3 does not meet the lower limit, the rigidity of the resulting speaker diaphragm 1 may become insufficient. Conversely, if the content of fiber 3 exceeds the upper limit, the uniform dispersion of fiber 3 in the resin matrix 2 may be insufficient.

[0055] The resin composition may include, as other components, colorants such as titanium dioxide, ultraviolet absorbers, and solubilizers for making the thermoplastic resin and fiber 3 miscible.

[0056] (Cutting process)

[0057] In the cutting process, the extruded material from the extrusion process is cut at equal intervals along its length to form multiple cylindrical particles. Since the fibers 3 contained in the extruded material tend to align in the extrusion direction, by cutting the extruded material at equal intervals, the average length of the fibers 3 can be suppressed to below the length of the particles. In the cutting process, while forming the particles, poly(p-phenylenebenzodioxazole) fibers of the aforementioned length range are divided into two or more in the length direction, thereby easily adjusting the length of the fibers 3 contained in the substrate 1a of the resulting speaker diaphragm 1 to be non-uniform. In the cutting process, by cutting the extruded material at intervals of, for example, 3 mm or less, multiple cylindrical particles with a length of 3 mm or less are formed.

[0058] The lower limit for the average length of the fibers 3 after the cutting process is 0.5 mm, preferably 1.0 mm. On the other hand, the upper limit for the average length of the fibers 3 after the cutting process is 3.0 mm, preferably 2.5 mm, and more preferably 1.5 mm. If the average length of the fibers 3 does not meet the lower limit, the rigidity of the obtained speaker diaphragm 1 may not be sufficiently improved. Conversely, if the average length of the fibers 3 exceeds the upper limit, the fibers 3 in the substrate 1a of the obtained speaker diaphragm 1 may easily become entangled with each other, and the uniform dispersion of the fibers 3 in the resin matrix 2 may be insufficient.

[0059] (Molding process)

[0060] In the molding process, the substrate 1a of the loudspeaker diaphragm 1 is formed by injection molding of the particles obtained in the cutting process. This molding process can be performed using an injection molding apparatus. This injection molding apparatus includes, for example: a cylinder having a nozzle at its front end; a hopper connected to the cylinder for feeding the particles obtained in the cutting process; a screw mounted within the cylinder; and a mold forming a cavity communicating with the opening of the nozzle. The cavity has a shape matching the substrate 1a of the loudspeaker diaphragm 1. In the cavity, a portion corresponding to the bottom (center portion viewed axially) of the substrate 1a of the loudspeaker diaphragm 1 communicates with the opening of the nozzle. In the molding process, a resin composition (molten material of the particles) is radially filled into the cavity from the portion corresponding to the bottom. Furthermore, in the molding process, after filling the cavity with the resin composition, the cavity is cooled to solidify the resin composition. The molded article after the resin composition has solidified constitutes the substrate 1a of the loudspeaker diaphragm 1.

[0061] The lower limit for the cavity temperature during the molding process is preferably 30°C. Conversely, the upper limit for the cavity temperature is preferably 50°C. If the cavity temperature does not meet the lower limit, the resin flow within the cavity may be insufficient, making it difficult to control the orientation of the fibers 3. Conversely, if the cavity temperature exceeds the upper limit, it may be difficult to adequately cool the resin composition after filling the cavity, making it difficult to remove the resulting speaker diaphragm substrate 1a from the cavity.

[0062] The lower limit of the injection speed of the resin composition in the molding process is preferably 80 mm / s, and more preferably 100 mm / s. On the other hand, the upper limit of the injection speed is preferably 200 mm / s, and more preferably 150 mm / s. If the injection speed does not meet the lower limit, the fluidity of the resin composition within the cavity becomes insufficient, and it may be difficult to control the orientation direction of the fibers 3 within the cavity. Conversely, if the injection speed exceeds the upper limit, the fluidity of the resin composition within the cavity becomes excessive, and it may be difficult to control the orientation direction of the fibers 3 within the cavity.

[0063] <Advantages>

[0064] In this method for manufacturing a loudspeaker diaphragm, particles obtained by cutting a rod-shaped extruder containing thermoplastic resin and poly(p-phenylene benzodioxazole) fibers are used to injection mold the substrate 1a of the loudspeaker diaphragm. This allows the production of a loudspeaker diaphragm in which the poly(p-phenylene benzodioxazole) fibers are sufficiently and uniformly dispersed in the thermoplastic resin. Specifically, in this method, if the average length of the poly(p-phenylene benzodioxazole) fiber particles is within the aforementioned range, and the content of the poly(p-phenylene benzodioxazole) fibers in the resin composition is controlled within the aforementioned range, then in the resulting substrate 1a of the loudspeaker diaphragm, these fibers can be uniformly dispersed in the thermoplastic resin without entanglement. As a result, this method for manufacturing a loudspeaker diaphragm enables the production of a loudspeaker diaphragm 1 with uniformly increased rigidity throughout the entire area.

[0065] [Other Implementation Methods]

[0066] The embodiments described herein do not limit the structure of the present invention. Therefore, in the embodiments described herein, the omission, substitution, or addition of various constituent elements of the embodiments can be based on the description in this specification and common technical knowledge, and such omissions, substitutions, or additions should all be interpreted as falling within the protection scope of the present invention.

[0067] For example, the diaphragm of the loudspeaker does not necessarily have to be conical; it can be flat, for example.

[0068] Example

[0069] The present invention will now be described in detail based on embodiments, but this is not intended to limit the scope of the invention.

[0070] [No.1]

[0071] A resin composition comprising polypropylene (manufactured by PIGMENT Corporation of Japan) as a thermoplastic resin and poly(p-phenylene benzodioxazole) fibers with a fiber length of 6 mm ("Zhailong" manufactured by Toyobo Corporation) is stirred and extruded in rod form using a single-screw extruder. The extruded resin composition is then cooled to solidify in the shape it was extruded (extrusion process). The resin composition contains 94% polypropylene by mass and 6% poly(p-phenylene benzodioxazole) fibers by mass. The extrusion conditions are: discharge rate 3 kg / h, screw speed 17 rpm, and extrusion temperature 165°C–185°C.

[0072] The extruded material from the extrusion process is cut into granules with a length of 3 mm (cutting process). Furthermore, the cylindrical granules obtained from the cutting process are injection molded using an injection molding apparatus to obtain the No.1 speaker diaphragm (monomer of the substrate). This injection molding apparatus includes: a cylinder with a nozzle at its front end; a hopper connected to the cylinder, into which the granules obtained in the cutting process are fed; a screw installed within the cylinder; and a mold forming a cavity communicating with the opening of the nozzle. The cavity has a conical internal space, and the opening of the nozzle communicates with the bottom of this internal space. The injection molding conditions are: cylinder temperature 200°C–210°C, mold temperature 40°C, injection speed 100 mm / s, injection pressure 50 MPa, and back pressure 2 MPa.

[0073] (The shape of the fiber)

[0074] The average length of the poly(p-phenylenebenzodioxazole) fibers in the diaphragm of the No.1 loudspeaker was determined according to the following steps.

[0075] First, the speaker diaphragm of No. 1 was heated in a muffle furnace at 450°C for 4 hours to melt the thermoplastic resin (polypropylene). Poly(p-phenylene benzodioxazole) fibers were then removed from the diaphragm. After cooling the heated diaphragm for 10 hours, the poly(p-phenylene benzodioxazole) fibers were dispersed in water. The length of any 10 fibers was measured using a fiber tester manufactured by Lorentzen & Wettre. The average length of the fibers was calculated to be 1.35 mm. The maximum value (maximum fiber length) was 3.2 mm. Furthermore, the average diameter and average straightness of the poly(p-phenylene benzodioxazole) fibers were calculated using the same procedure. The results were: an average diameter of 17.4 μm (aspect ratio 77.6) and an average straightness of 90%. It should be noted that the "average straightness" is calculated as the average distance between fiber ends / average fiber length × 100.

[0076] [No.2]

[0077] As for the poly(p-phenylene benzodioxazole) fiber, Zyron with a fiber length of 3 mm is used. Except that the polypropylene content in the resin composition is 90% by mass and the poly(p-phenylene benzodioxazole) fiber content is 10% by mass, the speaker diaphragm (monomer of the substrate) is manufactured under the same conditions as No.1.

[0078] For the diaphragm of the loudspeaker No.2, the average length, maximum length, average diameter, and average straightness of the poly(p-phenylenebenzodioxazole) fiber were calculated using the same procedure as for No.1. The results were: average length of 0.97 mm, maximum length of 1.6 mm, average width of 17.9 μm (aspect ratio of 54.2), and average straightness of 85.5%.

[0079] [No.3]

[0080] As for the poly(p-phenylene benzodioxazole) fiber, Zyron with a fiber length of 1 mm is used. Except that the polypropylene content in the resin composition is 85% by mass and the poly(p-phenylene benzodioxazole) fiber content is 15% by mass, the speaker diaphragm (monomer of the substrate) is manufactured under the same conditions as No.1.

[0081] [No.4]

[0082] As for the poly(p-phenylene benzodioxazole) fiber, Zyron with a fiber length of 3 mm was used. The speaker diaphragm (monomer of the substrate) was manufactured under the same conditions as No. 1, except that the polypropylene content in the resin composition was 78.6% by mass and the poly(p-phenylene benzodioxazole) fiber content was 21.4% by mass. It should be noted that the average length, average diameter, and average straightness of the poly(p-phenylene benzodioxazole) fiber in the speaker diaphragm of No. 4 are the same as those in No. 2.

[0083] [No. 5]

[0084] As for the poly(p-phenylene benzodioxazole) fiber, Zyron with a fiber length of 1 mm is used. Except that the polypropylene content in the resin composition is 90% by mass and the poly(p-phenylene benzodioxazole) fiber content is 10% by mass, the speaker diaphragm (monomer of the substrate) is manufactured under the same conditions as No.1.

[0085] [No. 6]

[0086] Except that the polypropylene content in the resin composition is 90% by mass and the poly(p-phenylene benzodioxazole) fiber content is 10% by mass, the loudspeaker diaphragm (monomer of the substrate) is manufactured under the same conditions as No.1. It should be noted that the average length, average diameter, and average straightness of the poly(p-phenylene benzodioxazole) fiber in the loudspeaker diaphragm of No.6 are the same as those in No.1.

[0087] [No.7]

[0088] As poly(p-phenylene benzodioxazole) fiber, Zyron with a fiber length of 1 mm is used. The speaker diaphragm (monomer of the substrate) is manufactured under the same conditions as No.1, except that the polypropylene content in the resin composition is 80% by mass and the poly(p-phenylene benzodioxazole) fiber content is 20% by mass.

[0089] [No. 8]

[0090] As for the poly(p-phenylene benzodioxazole) fiber, Zyron with a fiber length of 1 mm is used. Except that the polypropylene content in the resin composition is 70% by mass and the poly(p-phenylene benzodioxazole) fiber content is 30% by mass, the loudspeaker diaphragm (monomer of the substrate) is manufactured under the same conditions as No.1.

[0091] (Energy storage modulus)

[0092] The storage modulus [GPa] of loudspeaker diaphragms No. 2, No. 5 to No. 8 at 250 Hz and 1000 Hz was measured. For this storage modulus, rectangular samples with a width of 5 mm, a length of 40 mm, and a thickness of 0.5 mm were cut and measured in tensile mode using a dynamic viscoelasticity measuring device (DMA+150) manufactured by Metravib at a temperature of 23 ± 2 °C. The measurement results are shown in Table 1.

[0093] (Loss Modulus)

[0094] The loss modulus [GPa] of loudspeaker diaphragms No. 2, No. 5 to No. 8 at 250 Hz and 1000 Hz was measured. The loss modulus was measured using the same sample and measuring apparatus as the storage modulus, under the same measurement conditions. The results are shown in Table 1.

[0095] (Internal losses)

[0096] The internal loss (tanδ) of the diaphragm plates for loudspeakers No. 2, No. 5 to No. 8 was measured at 250 Hz and 1000 Hz. The internal loss was measured using the same sample and measuring apparatus as the storage modulus, under the same measurement conditions. The results are shown in Table 1.

[0097] (Fiber bonding state)

[0098] In the diaphragms of loudspeakers No.1 to No.8, a portion of the poly(p-phenylene benzodioxazole) fibers can be pulled out from the resin matrix, and the resin matrix and the poly(p-phenylene benzodioxazole) fibers are not bonded in at least a portion.

[0099] [Table 1]

[0100]

[0101] [Evaluation Results]

[0102] The average length of the poly(p-phenylene benzodioxazole) fibers in the speaker diaphragms of No. 1 to No. 8 is between 0.5 mm and 3.0 mm. When visually inspected, all the poly(p-phenylene benzodioxazole) fibers in the speaker diaphragms of No. 1 to No. 8 are uniformly dispersed in a resin matrix composed of polypropylene. Therefore, it can be considered that the rigidity of the speaker diaphragms of No. 1 to No. 8 is uniformly improved throughout the entire region. It should be noted that, in addition to polypropylene and poly(p-phenylene benzodioxazole) fibers, the resin composition may also contain titanium dioxide as a colorant and / or a compatibilizer.

[0103] As shown in Table 1, comparing No. 2, No. 5, and No. 6, where the content of poly(p-phenylene benzodioxazole) fiber in the diaphragm of a loudspeaker is 10% by mass, it can be seen that the storage modulus and loss modulus remain approximately constant regardless of the change in the average length of the poly(p-phenylene benzodioxazole) fiber. Furthermore, comparing No. 2, No. 5, and No. 6, it can be seen that when the average length of the poly(p-phenylene benzodioxazole) fiber is 1.35 mm or more (No. 6), the internal loss tends to decrease. Conversely, when the average length of the poly(p-phenylene benzodioxazole) fiber is 0.97 mm or less (No. 2 and No. 5), even if the average length of the poly(p-phenylene benzodioxazole) fiber increases, the internal loss remains at the same level.

[0104] Furthermore, as shown in Table 1, a comparison of No. 5, No. 7, and No. 8, where the average length of the poly(p-phenylene benzodioxazole) fibers was the same and the content of the poly(p-phenylene benzodioxazole) fibers was varied, reveals that the storage modulus and loss modulus increased approximately proportionally with the increase in the content of the poly(p-phenylene benzodioxazole) fibers, while the reduction in internal loss caused by the increase in the content of the poly(p-phenylene benzodioxazole) fibers was suppressed to a relatively small extent.

[0105] Industrial applicability

[0106] As described above, the speaker diaphragm of the present invention can uniformly improve rigidity throughout the entire area, and is therefore suitable for use as a rigid and relatively inexpensive diaphragm.

[0107] Explanation of reference numerals in the attached figures

[0108] 1…loudspeaker diaphragm, 1a…substrate, 2…resin matrix, 2a…hollow part, 3…fiber.

Claims

1. A loudspeaker diaphragm comprising a substrate having a resin matrix primarily composed of a thermoplastic resin and fibers dispersed therein. The fiber is poly(p-phenylenebenzodioxazole) fiber. The average length of the fibers is greater than 0.5 mm and less than 3.0 mm. The fiber content in the substrate is 3% by mass or more and 15% by mass or less. The fibers dispersed in the resin matrix are not of uniform length. The average aspect ratio of the fiber is greater than 20 and less than 300. The average aspect ratio refers to the average value obtained by taking the ratio of the length to the diameter of any 10 randomly selected fibers.

2. The loudspeaker diaphragm according to claim 1, The average length of the fiber is less than 2.5 mm.

3. The loudspeaker diaphragm according to claim 1 or 2, The diaphragm for the loudspeaker is a single unit of the substrate.

4. The loudspeaker diaphragm according to claim 1 or 2, The internal loss at 250Hz, i.e., tanδ, is above 0.

068.

5. The loudspeaker diaphragm according to claim 1 or 2, The internal loss at 250Hz, i.e., tanδ, is above 0.

079.

6. The loudspeaker diaphragm according to claim 1 or 2, The average thickness of the substrate is above 100 μm and below 800 μm.

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