Speaker diaphragm and speaker

Abstract

The speaker diaphragm includes a substrate having a resin matrix containing a thermoplastic resin as a main component and fibers dispersed in the resin matrix. The fibers have a plurality of loss regions where the fibers are locally bent and broken, or a plurality of loss regions having a diameter 5% to 50% larger than the average diameter of the fibers.

Description

[Technical field]

[0001] The present disclosure relates to a speaker diaphragm and a speaker. This application claims priority based on Japanese Patent Application No. 2023-142350, filed September 1, 2023, the disclosure of which is incorporated herein in its entirety. [Background technology]

[0002] It is desirable for speaker diaphragms to have high rigidity so as to generate sound efficiently, and also for them to have excellent environmental resistance, and therefore high water resistance. From this viewpoint, various speaker diaphragms made of synthetic resin have been proposed today in place of the speaker diaphragms made of wood pulp paper.

[0003] As an example of a synthetic resin speaker diaphragm, a diaphragm made by injection molding polyparaphenylenebenzoxazole fiber having a high tensile modulus and polypropylene into a cone shape is known (see Patent Document 1). Also known is a diaphragm that is injection molded by incorporating long fibers of 3 to 5 mm into a resin and positioning the long fibers radially from the center of a conical diaphragm toward the periphery (see Patent Document 2). Furthermore, a speaker diaphragm made of a resin reinforced with polybenzazole fibers having a void diameter of 25 Å or less is known (see Patent Document 3). Furthermore, a speaker diaphragm is known that includes a substrate having fibers dispersed in a resin matrix, the fibers being polyparaphenylene benzobisoxazole fibers, and the average length of the fibers being 0.5 mm or more and 3.0 mm or less (see Patent Document 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-284884 [Patent Document 2] JP 2004-15194 A [Patent Document 3] Japanese Patent Application Publication No. 6-253389 [Patent Document 4] Republished WO2020 / 022459 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, various speaker diaphragms are available. However, the speaker diaphragms according to the conventional techniques have a problem that it is unclear whether a user can experience high quality reproduced sound.

[0006] An object of the present disclosure is to provide a speaker diaphragm and a speaker that can achieve crisp, clear sound quality. [Means for solving the problem]

[0007] (1) A speaker diaphragm according to a first aspect of the present disclosure comprises a substrate having a resin matrix containing a thermoplastic resin as a main component and fibers dispersed in the resin matrix, the fibers having a plurality of loss regions where the fibers are locally bent and broken, or a plurality of loss regions having a diameter 5% to 50% larger than an average diameter of the fibers.

[0008] (2) A speaker according to a second aspect of the present disclosure includes the speaker diaphragm described above. Effect of the Invention

[0009] According to the present disclosure, it is possible to provide a speaker diaphragm that can achieve crisp, clear sound quality. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic front view of a speaker diaphragm according to a first embodiment of the present disclosure. [Diagram 2]2 is a cross-sectional view taken along line AA of the speaker diaphragm shown in FIG. 1. [Diagram 3] 2 is an enlarged schematic diagram of the structure of the speaker diaphragm shown in FIG. 1. [Figure 4] FIG. 2 is a flow diagram showing a method for manufacturing a speaker diaphragm according to an embodiment of the present disclosure. [Diagram 5] 1 is a photograph showing an electron microscope image of fibers used in speaker diaphragm sample No. 1 produced in the examples. [Figure 6] 6 is a partially enlarged photograph of the fiber shown in FIG. 5. [Figure 7] 1 is a photograph showing a digital microscope image of another fiber used in a speaker diaphragm produced in an example. [Figure 8] 1 is a photograph showing a digital microscope image of another fiber used in a speaker diaphragm produced in an example. [Figure 9] 1 is a photograph showing an electron microscope image of fibers used in speaker diaphragm sample No. 10 produced in the examples. [Figure 10] 10 is a partially enlarged photograph of the fiber shown in FIG. 9. [Figure 11] 13 is a graph showing an example of evaluation of damping characteristics by a spectrogram for a speaker diaphragm of a comparative example. [Figure 12] 1 is a graph showing an example of evaluation of damping characteristics of a speaker diaphragm according to the present disclosure using a spectrogram. [Figure 13] FIG. 2 is a flow diagram showing a method for manufacturing a speaker diaphragm according to an embodiment of the present disclosure. [Figure 14] 1 is a schematic diagram of a speaker including a speaker diaphragm according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings used in the following description, characteristic parts may be enlarged and highlighted for convenience, and non-characteristic parts may be omitted for the same purpose.

[0012] Fig. 1 is a schematic front view showing speaker diaphragm 1 according to the first embodiment. Fig. 2 is a vertical cross-sectional view of speaker diaphragm 1. Fig. 3 is an enlarged schematic view of the structure of speaker diaphragm 1. Fig. 14 is a schematic view showing speaker S including speaker diaphragm 1 and housing H to which speaker diaphragm 1 is attached. The diaphragm 1 of this embodiment is made of a base material 1a having a resin matrix 2 mainly composed of a thermoplastic resin and fibers 3 dispersed in the resin matrix 2. For example, the fibers 3 are polyparaphenylene benzobisoxazole fibers, and the average length of the fibers 3 is 0.5 mm or more and 3.0 mm or less.

[0013] The fibers 3 dispersed in the resin matrix 2 are polyparaphenylene benzobisoxazole fibers. These fibers make it easy to sufficiently increase the rigidity of the diaphragm 1. In particular, since the average length of the polyparaphenylene benzobisoxazole fibers in the diaphragm 1 is within the above-mentioned range, the fibers 3 can be uniformly dispersed in the resin matrix 2. As a result, the rigidity of the diaphragm 1 can be uniformly increased over the entire area.

[0014] The shape of the diaphragm 1 is desirably a cone or dome shape. The base material 1a of the diaphragm 1 can have a pair of skin layers constituting the surface layers on the front and back sides thereof, and a core layer formed between the pair of skin layers.

[0015] One embodiment of the manufacturing method of the diaphragm 1 preferably includes a kneading step of uniformly mixing the thermoplastic resin and the fibers 3 at high temperature and high shear to generate a kneaded composition, a step of extruding the kneaded composition into a rod shape, a step of cutting the extruded body in the extrusion step into pellets, and a step of injection molding the pellets obtained in the cutting step. The fibers 3 are preferably polyparaphenylene benzobisoxazole fibers. The average length of the fibers 3 after the cutting step is preferably 0.5 mm or more and 3.0 mm or less.

[0016] According to the above-mentioned manufacturing method, the speaker diaphragm is injection molded using pellets cut from a rod-shaped extruded body containing a thermoplastic resin and polyparaphenylene benzobisoxazole fibers, so that a speaker diaphragm in which the polyparaphenylene benzobisoxazole fibers are sufficiently uniformly dispersed in the thermoplastic resin can be manufactured.

[0017] In particular, according to the manufacturing method of the diaphragm 1, since the average length of the polyparaphenylene benzobisoxazole fiber in the pellet is within the above-mentioned range, the fiber 3 can be uniformly dispersed in the thermoplastic resin without becoming entangled in the obtained speaker diaphragm. If the fibers 3 become tangled, clumps of the fibers 3 may occur, which may clog the flow path of the material in a manufacturing method such as injection molding. In addition, the clumps of the fibers 3 are not uniformly dispersed in the thermoplastic resin, so the rigidity of the speaker diaphragm 1 cannot be increased. On the other hand, according to the manufacturing method of the diaphragm 1, the fibers 3 are connected in a spun manner, so that the fibers 3 can be uniformly dispersed in the thermoplastic resin, thereby increasing the rigidity of the diaphragm 1. In other words, the manufacturing method of the diaphragm 1 can manufacture a speaker diaphragm having uniformly increased rigidity over the entire area.

[0018] In the present disclosure, the term "main component" refers to the component with the highest content in terms of mass. For example, the term "main component" refers to a component with a content of 50% by mass or more, preferably a content of 70% by mass or more, and more preferably a content of 90% by mass or more. The term "average fiber length" refers to the average length of any 10 fibers. The term "front side" refers to the sound emission direction side. The term "back side" refers to the side opposite to the sound emission direction side. The term "surface layer" refers to a region of the target object or layer that is 50 μm or less deep from the front and back sides. When the target object is as thin as 100 μm, the surface layer may be interpreted as being about 1 / 3 of the thickness of the target object.

[0019] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings as appropriate. [Speaker diaphragm] 1 to 3 is made of a base material 1a having a resin matrix 2 mainly composed of a thermoplastic resin and fibers 3 dispersed in the resin matrix 2. The diaphragm 1 is a single body of the base material 1a.

[0020] The diaphragm 1 can be configured to have a shape suited to the speaker to be used, and is cone-shaped or dome-shaped in Figs. 1 and 2. That is, the base material 1a is cone-shaped or dome-shaped. The strength of the diaphragm 1 is increased by making the diaphragm 1 cone-shaped or dome-shaped. The size of the diaphragm 1 can be set according to the speaker to be used. The diaphragm 1 may be used in a small speaker provided in, for example, headphones, earphones, portable electronic devices, etc.

[0021] <Base material> The diaphragm 1 is made of a base material 1a having a resin matrix 2 and fibers 3 dispersed in the resin matrix 2. The base material 1a can be formed by injection molding and press molding, which will be described later. The base material 1a may have a pair of skin layers constituting the surface layers on the front side and back side of the base material 1a, and a core layer formed between the pair of skin layers. That is, the core layer may be interposed between the pair of skin layers. The pair of skin layers are layers formed from the resin matrix 2 and fibers 3 of the surface layer portion that flowed in contact with the cavity of the mold during injection molding. The core layer is a layer formed from the resin matrix 2 and fibers 3 that cooled and solidified relatively slowly without contacting the cavity of the mold. In the diaphragm 1, the orientation direction of the fibers 3 in the skin layer may be different from the orientation direction of the fibers 3 in the core layer.

[0022] The substrate 1a of the speaker diaphragm 1 (the speaker diaphragm 1 itself in this embodiment) has a substantially uniform thickness. The lower limit of the average thickness T of the substrate 1a of the speaker diaphragm 1 is preferably 50 μm, more preferably 80 μm. The upper limit of the average thickness T of the substrate 1a of the speaker diaphragm 1 is preferably 800 μm, more preferably 650 μm. If the average thickness T is less than the lower limit, the rigidity of the speaker diaphragm 1 may be insufficient, or it may be difficult to form the speaker diaphragm 1 by injection molding. Conversely, if the average thickness T exceeds the upper limit, the speaker diaphragm 1 may become unnecessarily heavy. "Substantially uniform thickness" means that the ratio of the maximum thickness to the minimum thickness is 1 or more and 1.20 or less. "Average thickness" means the average value of thicknesses at any 10 points. The ratios given above with respect to "substantially uniform thickness" are for speaker diaphragms of substantially uniform thickness, and do not apply to speaker diaphragms which have intentional ribs or the like.

[0023] (Resin matrix) As described above, the main component of the resin matrix 2 is a thermoplastic resin. Examples of the thermoplastic resin include, for example, polyethylene, polypropylene, polystyrene, fluororesin, polycarbonate, polysulfone, polyethersulfone, polyethylene terephthalate, polybutylene terephthalate, polyamide, polyimide, and acrylonitrile-butadiene-styrene resin, and may be one of these resins alone or a mixture of two or more of these resins. In particular, polypropylene is preferable as the thermoplastic resin. By using polypropylene as the thermoplastic resin, the vibration damping rate (internal loss) of the speaker diaphragm 1 at an audible frequency can be increased. In addition, when the thermoplastic resin is polypropylene, it becomes easy to disperse the fibers 3 in a non-bonded state with the resin matrix 2 as described later. This further increases the vibration damping rate, and makes it easy to improve the reproducibility of the sound. At least a part of the fibers 3 may not be bonded to the resin matrix 2. The fibers 3 may not be bonded to the resin matrix 2 at all.

[0024] (fiber) The fiber 3 is a polyparaphenylene benzobisoxazole fiber having a plurality of loss regions 3a, which will be described in detail later. Since the fiber 3 is a polyparaphenylene benzobisoxazole fiber, the rigidity of the diaphragm 1 can be increased while suppressing a decrease in the vibration damping rate of the diaphragm 1.

[0025] The content of the fibers 3 in the base material 1a is preferably in the range of 3% by mass or more and 30% by mass or less. The lower limit of the content of the fibers 3 in the base material 1a (in other words, the content of the fibers 3 in the diaphragm 1) is preferably 3% by mass, more preferably 5% by mass. On the other hand, the upper limit of the content of the fibers 3 in the base material 1a is preferably 30% by mass, more preferably 22% by mass, and even more preferably 15% by mass. If the content of the fibers 3 is less than the lower limit, the rigidity of the diaphragm 1 may be insufficient. Conversely, if the content of the fibers 3 exceeds the upper limit, the fibers 3 may be entangled with each other in the resin matrix 2, and the uniform dispersion of the fibers 3 in the resin matrix 2 may be insufficient. In addition, if the content of the fibers 3 exceeds the upper limit, when a resin composition containing a resin and a thermoplastic resin is heated and passed through a nozzle or the like of an injection molding device, clogging may occur due to uneven distribution of the fibers 3, and manufacturing of the diaphragm 1 may become difficult.

[0026] The lower limit of the average length of the fibers 3 is 0.5 mm, preferably 1.0 mm. On the other hand, the upper limit of the average length of the fibers 3 is preferably 3.0 mm, more preferably 2.5 mm, and most preferably 1.5 mm. If the average length of the fibers 3 is less than the lower limit, the effect of improving the rigidity of the fibers 3 may be insufficient. Conversely, if the average length of the fibers 3 exceeds the upper limit, the fibers 3 may be easily entangled with each other, and the uniform dispersion of the fibers 3 in the resin matrix 2 may be insufficient. The length of each fiber 3 dispersed in the resin matrix 2 may be non-uniform as long as the average length is within the above-mentioned range.

[0027] The upper limit of the maximum length of the fibers 3 dispersed in the resin matrix 2 is preferably 5.0 mm, more preferably 4.0 mm, and further preferably 3.0 mm. By setting the maximum length of the fibers 3 to the above upper limit or less, it is easy to reliably prevent the fibers 3 from becoming entangled with each other.

[0028] The average aspect ratio of the fibers 3 is preferably in the range of 20-300. The lower limit of the average aspect ratio of the fibers 3 is preferably 20, more preferably 50. On the other hand, the upper limit of the average aspect ratio of the fibers 3 is preferably 300, more preferably 200. If the average aspect ratio is less than the lower limit, it may be difficult to control the orientation direction of the fibers 3. Conversely, if the average aspect ratio exceeds the upper limit, the fibers 3 may be easily entangled with each other. The "average aspect ratio of fibers" refers to the average value of the ratio of the length to the diameter (diameter) of 10 arbitrarily extracted fibers. The diameter of the fibers may be 10 μm or more and 50 μm or less. The average diameter of the fibers may be 10 μm or more and 50 μm or less.

[0029] This allows the speaker diaphragm 1 to have a large vibration damping rate. In the speaker diaphragm 1, from the viewpoint of increasing the rigidity by the fibers 3, it is preferable that there is no gap between the resin matrix 2 and the fibers 3. In the diaphragm 1, the fibers 3 and the thermoplastic resin are incompatible and are not chemically bonded to each other, so that the fibers 3 can be held in a non-bonded state with the resin matrix 2. Even if the fibers 3 and the thermoplastic resin are not chemically bonded to each other, the speaker diaphragm 1 allows the fibers 3 to be uniformly dispersed in the resin matrix 2 by controlling the content and average length of the fibers 3 within the above-mentioned ranges.

[0030] (loss area) 3, a plurality of kink- or lump-shaped loss regions 3a are intermittently formed along the length of the fiber 3. The loss regions 3a are generated by kneading and extruding the fibers under special conditions in a manufacturing method described later in detail, in which a strong shear force is applied to the fibers. The loss regions 3a are portions formed to bulge outwardly from the outer periphery of the fiber 3 like nodes at arbitrary intervals along the length of the fiber 3, as shown in Figures 5 and 6 described later in the Examples. The loss regions 3a can be explained as portions of the fiber 3 that have undergone plastic deformation such as bending, twisting, or crushing under high temperature and high shear conditions, and bulge outwardly in the radial direction of the fiber 3, or portions observed as buckling of the fiber. The buckled portions of the fiber can also be explained as loss regions called kink bands in which the fiber is locally bent and destroyed.

[0031] It is preferable that about 1 to 10 loss regions 3a are formed in a length 30 times the average diameter of the fibers 3. For example, when the average diameter of the fibers 3 is 10 μm, about 1 to 10 loss regions 3a are formed in a length of 300 μm. The loss region 3a is a portion formed by applying a strong shear force to the fibers. Therefore, the diameter of the loss region 3a is larger than the average diameter of the fibers 3. The diameter of the loss region 3a is 1.1 to 2 times the average diameter of the fibers 3. For example, when the average diameter of the fibers 3 is 10 μm, the diameter of the loss region 3a is 11 μm or more and 20 μm or less. The diameter of the loss region 3a may be 5% to 50% larger than the average diameter of the fibers 3. The average diameter of the loss region 3a may be 5% to 50% larger than the average diameter of the fibers 3. The diameter of the loss region 3a may be 12 μm or more and 80 μm or less. The average diameter of the loss region 3a may be 12 μm or more and 80 μm or less.

[0032] If the number of loss regions 3a is less than the lower limit, the damping effect in a specific band is insufficient, making it difficult to obtain a crisp reproduced sound in this band. In the example of Fig. 11 and Fig. 12, the damping effect is insufficient in the range of 2000 to 4200 Hz. If the number of loss regions 3a exceeds the upper limit, it becomes difficult to mass-produce the humps, resulting in a problem of high manufacturing costs.

[0033] (Other Ingredients) The base material 1a of the diaphragm 1 may contain other components in addition to the resin matrix 2 and the fibers 3, as long as the effects of the present disclosure are not impaired. These other components may include, for example, a colorant such as titanium oxide, an ultraviolet absorbing agent, a compatibilizer, and the like.

[0034] <Advantages> The diaphragm 1 has polyparaphenylene benzobisoxazole fibers as fibers 3 dispersed in the resin matrix 2 of the base material 1a, and the fibers have a plurality of loss regions 3a, so that the fibers 3 increase the rigidity and the loss regions 3a increase the loss. In particular, the average length of the polyparaphenylene benzobisoxazole fibers in the diaphragm 1 is within the above-mentioned range. Therefore, for example, by controlling the content of the fibers 3 within the above-mentioned range, the fibers 3 can be uniformly dispersed in the resin matrix 2. As a result, the speaker diaphragm 1 can have a uniform increase in rigidity over the entire region. It is believed that adding about 10% by mass of fibers increases the rigidity by about 20%, and is also estimated to have a large effect on the increase in loss. Furthermore, adding about 10% by mass of fibers also improves the loss modulus, which affects the loss characteristics.

[0035] The fibers 3 have a plurality of loss regions 3a. Therefore, by including the fibers 3 in the base material 1a at the above-mentioned mass %, the mechanism of friction loss increases, and the damping of the diaphragm 1 can be increased. For this reason, a speaker having the diaphragm 1 can produce a tight, sharp reproduced sound with large attenuation. For example, in the frequency band of 2000 to 4200 Hz, a sharp, clear reproduced sound can be produced.

[0036] [Manufacturing method for speaker diaphragms] Next, a method for manufacturing the diaphragm 1 shown in Fig. 1 will be described with reference to Fig. 4. The method for manufacturing the diaphragm 1 according to this embodiment includes a kneading step of uniformly mixing a thermoplastic resin and fibers 3 at high temperature and high shear to generate a kneaded composition, a step (kneading and extruding step) S1 of extruding the kneaded composition into a rod shape, a step (cutting step) S2 of cutting the extruded body extruded in the kneading and extruding step S1 into pellets, and a step (molding step) S3 of injection molding the pellets obtained in the cutting step S2. In molding thin objects such as tweeter (Tw) diaphragms and headphone diaphragms, it is preferable that the manufacturing method for diaphragm 1 includes a pressing process S4 for press-molding the pre-shaped product obtained by the injection molding, as described below (see Figure 13).

[0037] (Kneading and extrusion process S1) In the kneading and extrusion step S1, a resin composition containing a thermoplastic resin and fibers 3 is kneaded and extruded into a rod shape. The kneading and extrusion step S1 can be performed using an extrusion molding device. The extrusion molding device includes, for example, an extruder having a cylinder that guides the resin composition and a screw installed in the cylinder, kneading the resin composition, a T-die that flows out the resin composition kneaded by the extruder into a rod shape, and a cooling section that cools the resin composition extruded from the T-die. In the kneading and extrusion step S1, the resin composition is extruded into a rod shape and then cooled in a cooling section to solidify the resin composition in the shape it had when extruded, thereby obtaining a rod-shaped extruded body. The screw used for kneading is preferably a type capable of applying sufficient shear force to the fibers used in this embodiment. A typical screw is a type having a uniform spiral groove formed on the outer periphery of the shaft, but in this embodiment, a special screw of a type called a Dulmage screw is preferably used. The Dulmage screw is configured by arranging a plurality of kneading promotion parts in the center of the length direction of the screw shaft having a spiral groove, the kneading promotion parts having a small spiral groove with a different pitch from the spiral grooves in other parts. By providing these kneading promotion parts, the pellets can be mixed while being kneaded, and a large shear force can be applied to the fibers in the pellets.

[0038] The thermoplastic resin used in the kneading and extrusion step S1 may be the above-mentioned thermoplastic resin contained as the main component of the resin matrix 2 of the base material 1a of the diaphragm 1 shown in Fig. 1. In particular, polypropylene is preferable as this thermoplastic resin.

[0039] The fiber 3 used in the kneading and extrusion step S1 is a polyparaphenylene benzobisoxazole fiber. The length of the polyparaphenylene benzobisoxazole fiber is not particularly limited, but can be, for example, 1 mm or more and 10 mm or less, and preferably 1 mm or more and 3 mm or less. If the fiber is too long, it becomes difficult to knead it, and the fibers become entangled and difficult to enter the cylinder. If the fiber is too short, the sound quality will not be good. In particular, when making a thin diaphragm such as a tweeter (Tw), it is desirable to have short fibers, and if the fibers are long, they will form lumps and will not be able to be uniformly dispersed. In the manufacturing method of the speaker diaphragm, the length of the fibers 3 contained in the base material 1a of the obtained diaphragm 1 can be adjusted within the above-mentioned range by adjusting the length of the pellets in the cutting step S2 described below.

[0040] The lower limit of the content of the fibers 3 in the resin composition is preferably 3% by mass, more preferably 6% by mass. On the other hand, the upper limit of the content of the fibers 3 is preferably 30% by mass, more preferably 22% by mass, and even more preferably 15% by mass. If the content of the fibers 3 is less than the lower limit, the rigidity of the obtained speaker diaphragm 1 may be insufficient. On the other hand, if the content of the fibers 3 exceeds the upper limit, the uniform dispersion of the fibers 3 in the resin matrix 2 may be insufficient.

[0041] The resin composition may contain, as other components, a colorant such as titanium oxide, an ultraviolet absorbing agent, a compatibilizer for making the thermoplastic resin and the fibers 3 compatible, and the like.

[0042] (Cutting process S2) In the cutting step S2, the extruded body extruded in the kneading and extrusion step S1 is cut at equal intervals in the longitudinal direction to form a plurality of cylindrical pellets. The fibers 3 contained in the extruded body are easily oriented in the extrusion direction. Therefore, by cutting the extruded body at equal intervals, the average length of the fibers 3 can be kept equal to or less than the length of the pellets. In the cutting step S2, the polyparaphenylene benzobisoxazole fibers having a length within the above-mentioned range are cut into two or more in the longitudinal direction at the same time as the pellets are formed, so that the length of the fibers 3 contained in the base material 1a of the obtained speaker diaphragm 1 can be easily adjusted to be non-uniform. In the cutting step S2, for example, the extruded body is cut at intervals of 3 mm or less to form a plurality of cylindrical pellets having a length of 3 mm or less.

[0043] The lower limit of the average length of the fibers 3 after the cutting step is 0.5 mm, preferably 1.0 mm. On the other hand, the upper limit of the average length of the fibers 3 after the cutting step is 3.0 mm, preferably 2.5 mm, more preferably 1.5 mm. If the average length of the fibers 3 is less than the lower limit, the rigidity of the resulting diaphragm 1 may not be sufficiently increased. Conversely, if the average length of the fibers 3 exceeds the upper limit, the fibers 3 may be easily entangled with each other in the base material 1a of the resulting speaker diaphragm 1, and the uniform dispersion of the fibers 3 in the resin matrix 2 may be insufficient.

[0044] (Molding process S3) In the molding step S3, the base material 1a of the diaphragm 1 is formed by injection molding of the pellets obtained in the cutting step S2. The molding step S3 can be performed using an injection molding device. This injection molding device has, for example, a cylinder with a nozzle at the tip, a hopper connected to the cylinder and into which the pellets obtained in the cutting step are introduced, a screw installed in the cylinder, and a mold in which a cavity communicating with the opening of the nozzle is formed. The cavity has an inverted shape of the base material 1a of the diaphragm 1. The cavity has a portion corresponding to the bottom (the center in the axial view) of the base material 1a of the diaphragm 1 that communicates with the nozzle opening. In the molding step S3, the cavity is filled with a resin composition (melted pellets) radially from the portion corresponding to the bottom. Also, in the molding step S3, after filling with the resin composition, the cavity is cooled to harden the resin composition. The molded product in which the resin composition is hardened is configured as the base material 1a of the diaphragm 1.

[0045] The lower limit of the cavity temperature in the molding step S3 is preferably 30°C. Meanwhile, the upper limit of the cavity temperature is preferably 50°C. If the cavity temperature is below the lower limit, the fluidity of the resin in the cavity may be insufficient, making it difficult to control the orientation direction of the fibers 3. Conversely, if the cavity temperature exceeds the upper limit, it may be difficult to sufficiently cool the resin composition after filling the cavity, making it difficult to remove the base material 1a of the obtained diaphragm 1 from the cavity.

[0046] The lower limit of the injection speed of the resin composition in the molding step S3 is preferably 80 mm / s, more preferably 100 mm / s. On the other hand, the upper limit of the injection speed is preferably 1000 mm / s, more preferably 500 mm / s. If the injection speed is less than the lower limit, the fluidity of the resin composition in the cavity may be insufficient, making it difficult to control the orientation direction of the fibers 3 in the cavity. Conversely, if the injection speed exceeds the upper limit, the fluidity of the resin composition in the cavity may be too high, making it difficult to control the orientation direction of the fibers 3 in the cavity.

[0047] <Advantages> In the manufacturing method according to the present embodiment, a rod-shaped extruded body containing thermoplastic resin and polyparaphenylene benzobisoxazole fiber is cut into pellets, and the base material 1a of the diaphragm 1 is injection molded. Therefore, a speaker diaphragm can be manufactured in which polyparaphenylene benzobisoxazole fiber with a damping region is sufficiently uniformly dispersed in the thermoplastic resin. In particular, in the manufacturing method of the diaphragm, the average length of the polyparaphenylene benzobisoxazole fiber in the pellet is within the above-mentioned range. Therefore, for example, the content of the polyparaphenylene benzobisoxazole fiber with the damping region in the resin composition can be controlled within the above-mentioned range. Therefore, in the base material 1a of the obtained speaker diaphragm, the fibers can be uniformly dispersed in the thermoplastic resin without being entangled. As a result, the manufacturing method described above can manufacture a speaker diaphragm 1 with uniformly increased rigidity over the entire region.

[0048] (Press process S4) (Method of forming thin films for tweeters (TW) and headphone diaphragms) A vibration plate-shaped injection molded preform of 0.3 to 0.5 mm is clamped in a press mold with a cavity equivalent to the target thickness (about 100 um) that has been heated to (melting point to melting point + 50°C) and pressurized. The preform is held for about 10 to 30 seconds, then cooled to (melting point -50 to melting point -100°C) and demolded.

[0049] [Other embodiments] The above-described embodiments do not limit the configuration of the present disclosure. Therefore, in the embodiments, the components of each part of the embodiments can be omitted, replaced, or added based on the description in this specification and common technical knowledge, and all of them should be interpreted as belonging to the scope of the present disclosure. For example, the diaphragm does not necessarily have to be cone-shaped, but may be dome-shaped or flat, for example. EXAMPLES

[0050] [No.1] A resin composition containing polypropylene (manufactured by Japan Polypropylene Corporation) as a thermoplastic resin containing pigments and additives, and polyparaphenylene benzobisoxazole fiber ("Zylon" (registered trademark) manufactured by Toyobo Co., Ltd.) with a fiber length of 1 mm was kneaded and extruded into a rod shape using a single-screw extruder. The extruded resin composition was cooled and solidified in the shape at the time of extrusion (kneading and extrusion process). The polypropylene content in the resin composition was 95% by mass, and the polyparaphenylene benzobisoxazole fiber content was 5% by mass. The extrusion conditions were a discharge rate of 2 kg / h and an extrusion temperature of 165°C to 190°C.

[0051] The extruded body extruded in the kneading and extrusion process was cut into pellets with a length of 3 mm (cutting process). Furthermore, the cylindrical pellets obtained by cutting in the cutting process were injection molded in an injection molding machine to obtain No. 1 speaker diaphragm (single substrate). This injection molding apparatus has a cylinder with a nozzle at its tip, a hopper connected to the cylinder into which the pellets obtained in the cutting process are poured, a screw mounted within the cylinder, and a mold having a cavity formed therein that communicates with the opening of the nozzle. The screw used was a Dulmage screw manufactured by Nippon Oil Machinery Co., Ltd., which is configured with three kneading promoters in the shape of a bridge, each having small spiral grooves with different pitches formed in the center of the screw shaft in the longitudinal direction. The cavity had a cone-shaped internal space, and the nozzle opening was connected to the bottom of the internal space. The injection molding conditions were a cylinder temperature of 200°C to 220°C, a mold temperature of 45°C, an injection speed of 400mm / s, an injection pressure of 200MPa, and a back pressure of 8MPa.

[0052] [No.2] Speaker diaphragm No. 2 (single substrate) was manufactured under the same conditions as speaker diaphragm No. 1, except that Zylon (registered trademark, manufactured by Toyobo Co., Ltd.) with a fiber length of 3 mm was used as the polyparaphenylene benzobisoxazole fiber, the polypropylene content in the resin composition was 90 mass%, and the polyparaphenylene benzobisoxazole fiber content was 10 mass%.

[0053] [No.3] Speaker diaphragm No. 3 (substrate alone) was manufactured under the same conditions as speaker diaphragm No. 1, except that Zylon (registered trademark, manufactured by Toyobo Co., Ltd.) with a fiber length of 1 mm was used as the polyparaphenylene benzobisoxazole fiber, the polypropylene content in the resin composition was 85 mass%, and the polyparaphenylene benzobisoxazole fiber content was 15 mass%. [No.4] Speaker diaphragm No. 4 (substrate alone) was manufactured under the same conditions as speaker diaphragm No. 1, except that Zylon (registered trademark, manufactured by Toyobo Co., Ltd.) with a fiber length of 3 mm was used as the polyparaphenylene benzobisoxazole fiber, the polypropylene content in the resin composition was 78.6 mass%, and the polyparaphenylene benzobisoxazole fiber content was 21.4 mass%.

[0054] [No.5] The No. 5 diaphragm (single substrate) was manufactured under the same conditions as the No. 1 speaker diaphragm, except that Zylon (registered trademark, manufactured by Toyobo Co., Ltd.) with a fiber length of 1 mm was used as the polyparaphenylene benzobisoxazole fiber, the polypropylene content in the resin composition was 90 mass%, and the polyparaphenylene benzobisoxazole fiber content was 10 mass%.

[0055] [No.6] No. 6 diaphragm (single substrate) was manufactured under the same conditions as No. 1 speaker diaphragm, except that the polypropylene content in the resin composition was 90 mass % and the polyparaphenylene benzobisoxazole fiber content was 10 mass %.

[0056] [No.7] The No. 7 diaphragm (single substrate) was manufactured under the same conditions as the No. 1 speaker diaphragm, except that Zylon (registered trademark, manufactured by Toyobo Co., Ltd.) with a fiber length of 1 mm was used as the polyparaphenylene benzobisoxazole fiber, the polypropylene content in the resin composition was 80 mass%, and the polyparaphenylene benzobisoxazole fiber content was 20 mass%.

[0057] [No.8] The No. 8 diaphragm (single substrate) was manufactured under the same conditions as the No. 1 speaker diaphragm, except that Zylon (registered trademark, manufactured by Toyobo Co., Ltd.) with a fiber length of 1 mm was used as the polyparaphenylene benzobisoxazole fiber, the polypropylene content in the resin composition was 70 mass%, and the polyparaphenylene benzobisoxazole fiber content was 30 mass%. [No.9] A speaker diaphragm (single substrate) No. 9 was obtained by injection molding using 100% polypropylene (manufactured by Japan Polypropylene Corporation) that did not contain polyparaphenylene benzobisoxazole fiber, using the above-mentioned injection molding device. [No.10] A diaphragm No. 10 (single substrate) was manufactured under the same conditions as the speaker diaphragm No. 1, except that Twaron (Twaron (registered trademark) manufactured by Teijin Limited) with a fiber length of 6 mm was used as the para-aramid fiber, the polypropylene content in the resin composition was 90 mass%, and the para-aramid fiber content was 10 mass%.

[0058] For the base material of speaker diaphragm No. 1, the resin matrix was heated at 400°C and burned off, leaving only the fibers (residue left after the resin was decomposed and removed), and the results of this observation under an electron microscope are shown in the photograph in Figure 5. The results of an enlarged electron microscope observation of one of the loss areas formed in the fibers shown in Figure 5 are shown in the photograph in Figure 6. As shown in Fig. 5, multiple nodular loss regions were intermittently formed along the length of the fiber, and in one of these loss regions, as shown in Fig. 6, it was confirmed that the fiber had broken, causing a partial crack and forming a kink-like bump.

[0059] Using any of the manufacturing conditions described in Nos. 2 to 9, it was possible to manufacture a diaphragm substrate in the same manner as in Example No. 1. Figures 7 and 8 show the results of observing the fibers with a digital microscope after the resin matrix was burned off, leaving only the fibers.

[0060] For the base material of speaker diaphragm No. 10, the resin matrix was heated at 400°C and burned off, leaving only the fibers (residue left after the resin was decomposed and removed), and the results of this observation under an electron microscope are shown in the photograph in Figure 9. The results of an enlarged electron microscope observation of one of the loss areas formed in the fibers shown in Figure 9 are shown in the photograph in Figure 10. As shown in Fig. 9, multiple nodular loss regions were formed intermittently along the length of the fiber. In one of these loss regions, the fiber was broken and partially buckled, forming a kink band, as shown in Fig. 10.

[0061] The cumulative spectrum of the reproduced sounds obtained from the speaker diaphragms No. 1 and No. 9 was measured using the following procedure. 1. Mount the target speaker unit into the housing of the Yamaha HS7 monitor speaker. 2. Obtain the impulse response of this speaker 1m on axis in an anechoic chamber. 3. The (falling) cumulative spectrum is calculated from the obtained impulse response and expressed as a contour diagram.

[0062] The cumulative spectrum was obtained by referring to the literature "J. Audio Eng. Soc., vol. 25, p. 370 (1977)". The measurement results of diaphragm No. 9 are shown in FIG. 11, and the measurement results of diaphragm No. 1 are shown in FIG. As is clear from a comparison of the attenuation characteristics shown in FIG. 11 and FIG. 12, it was confirmed that the diaphragm containing the polyparaphenylene benzobisoxazole fiber having a plurality of attenuation regions had less reverberation of the reproduced sound in the range of 2000 to 4200 Hz. These results show that the diaphragm containing polyparaphenylene benzobisoxazole fiber with a damping region is able to reproduce crisp, clear sound. [Industrial Applicability]

[0063] As described above, the speaker diaphragm according to the present disclosure can be suitably used as a relatively inexpensive diaphragm that can uniformly increase rigidity by incorporating fibers and can obtain crisp, clear reproduced sound in a predetermined frequency band (e.g., a frequency band of 2000 to 4200 Hz). [Explanation of symbols]

[0064] 1...Speaker diaphragm 1a...Base material 2…Resin matrix 3. Fiber 3a...attenuation area

Claims

1. A substrate having a resin matrix containing a thermoplastic resin as a main component and fibers dispersed in the resin matrix, The fiber has a plurality of loss regions where the fiber is locally broken by bending, or a plurality of loss regions having a diameter 5% to 50% larger than the average diameter of the fiber. Speaker diaphragm.

2. The speaker diaphragm according to claim 1 , wherein the content of the fibers in the substrate is 3% by mass or more and 15% by mass or less.

3. 3. The speaker diaphragm according to claim 1, wherein the number of the plurality of lossy regions is one or more in a range along the length of the fibers that is 30 times the average diameter of the fibers.

4. 3. The speaker diaphragm according to claim 1, wherein the number of the plurality of loss regions is 1 or more and 10 or less in a range along the length direction of the fibers having a length 30 times the average diameter of the fibers.

5. 3. The speaker diaphragm according to claim 1, wherein the fibers are polyparaphenylene benzobisoxazole fibers.

6. 3. The speaker diaphragm according to claim 1, wherein the fibers have a diameter of 10 μm or more and 50 μm or less.

7. 3. The speaker diaphragm according to claim 1, wherein the diameter of the lossy region is 12 μm or more and 80 μm or less.

8. The speaker diaphragm according to claim 1 , wherein the plurality of loss regions in which the fibers are locally bent and broken are kink bands.

9. A speaker comprising the speaker diaphragm according to claim 1.

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