Speaker diaphragm

Abstract

To provide a diaphragm for a speaker capable of achieving sharp and clear sound quality.SOLUTION: A diaphragm for a speaker is provided with a base material 1a having a resin matrix 2 containing thermoplastic resin as a main component and fibers 3 dispersed in the resin matrix. The fibers have a plurality of loss areas 3a in which the fibers are locally bent and broken, or a plurality of loss areas having diameters 5% to 50% larger than an average diameter of the fibers.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a diaphragm for a speaker. This application claims priority based on Japanese Patent Application No. 2023-142350 filed on September 1, 2023, and incorporates all of its disclosures herein.

Background Art

[0002] A diaphragm for a speaker is desired to have high rigidity so as to efficiently generate sound. Also, a diaphragm for a speaker is required to have excellent environmental resistance, and high water resistance is also desired. From such a viewpoint, today, instead of a diaphragm for a speaker made of a paper pulp mat, various diaphragms for a speaker made of synthetic resin have been proposed.

[0003] As an example of a diaphragm for a speaker made of synthetic resin, a diaphragm obtained by injection molding a polyparaphenylene benzoxazole fiber having a high tensile modulus of elasticity and polypropylene into a cone shape is known (see Patent Document 1). Also, a diaphragm is known in which long fibers of 3 to 5 mm are contained in a resin and injection molded so that the long fibers are radially located from the center to the periphery of a conical diaphragm (see Patent Document 2). Furthermore, a diaphragm for a speaker made of a reinforced resin using polybenzazole fibers having a void diameter of 25 Å or less is known (see Patent Document 3). Furthermore, a diaphragm for a speaker is known that includes a base material 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

Patent Document 2

[0005] As described above, various diaphragms for speakers are provided. However, the diaphragms for speakers according to the prior art have a problem that it is unclear whether a user can experience a reproduced sound with high sound quality.

[0006] An object of the present invention is to provide a diaphragm for a speaker that can realize a crisp and clear sound quality. [Means for Solving the Problems]

[0007] (1) The diaphragm for a speaker according to the first aspect of the present disclosure includes a resin matrix containing a thermoplastic resin as a main component, and fibers dispersed in the resin matrix, and 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. [Effects of the Invention]

[0008] According to this embodiment, it is possible to provide a diaphragm for a speaker that can realize a crisp and clear sound quality. [Brief Description of the Drawings]

[0009]

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Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings used in the following description, parts that are characteristic may be enlarged and emphasized for convenience. Also, for the same purpose, parts that are not characteristic may be omitted from the illustration.

[0011] FIG. 1 is a schematic front view showing a diaphragm 1 for a speaker according to the first embodiment. FIG. 2 is a longitudinal sectional view of the diaphragm 1 for a speaker. FIG. 3 is a schematic enlarged view of the structure of the diaphragm 1 for a speaker. FIG. 14 is a schematic view showing a speaker S including the diaphragm 1 for a speaker and a housing H to which the diaphragm 1 for a speaker is attached. The diaphragm 1 of this embodiment is composed 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.

[0012] The fibers 3 dispersed in the resin matrix 2 are polyparaphenylene benzobisoxazole fibers. With these fibers, it is easy to sufficiently increase the rigidity of the diaphragm 1. In particular, in the diaphragm 1, since the average length of the polyparaphenylene benzobisoxazole fibers is within the above-mentioned range, the fibers 3 can be uniformly dispersed in the resin matrix 2. As a result, the diaphragm 1 can uniformly increase the rigidity over the entire region.

[0013] The shape of the diaphragm 1 is preferably conical or dome-shaped. The base material 1a of the diaphragm 1 can have a configuration including a pair of skin layers constituting the surface layer on the front surface side and the back surface side, and a core layer formed between the pair of skin layers.

[0014] One aspect of the manufacturing method of the diaphragm 1 preferably includes a kneading step of uniformly kneading a 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 extruded 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.

[0015] According to the above manufacturing method, since the diaphragm for a speaker is injection-molded using pellets obtained by cutting a rod-shaped extruded body containing a thermoplastic resin and polyparaphenylene benzobisoxazole fibers, a diaphragm for a speaker in which the polyparaphenylene benzobisoxazole fibers are dispersed in the thermoplastic resin sufficiently uniformly can be manufactured.

[0016] In particular, according to the manufacturing method of the diaphragm 1, since the average length of the polyparaphenylene benzobisoxazole fibers in the pellets is within the above range, the fibers 3 can be uniformly dispersed in the thermoplastic resin without being entangled in the obtained diaphragm for a speaker. If the fibers 3 are entangled, lumps of the fibers 3 are generated, and in a manufacturing method such as injection molding, there is a risk of clogging the flow path of the material. Further, since the lumps of the fibers 3 are not uniformly dispersed in the thermoplastic resin, the rigidity of the diaphragm 1 for a speaker cannot be increased. On the other hand, according to the manufacturing method of the diaphragm 1, since the fibers 3 are connected so as to be spun, the fibers 3 can be uniformly dispersed in the thermoplastic resin, so that the rigidity of the diaphragm 1 can be increased. That is, the manufacturing method of the diaphragm 1 can manufacture a diaphragm for a speaker in which the rigidity is uniformly increased over the entire region.

[0017] In the present disclosure, the "main component" means the component having the largest content in terms of mass conversion. For example, the "main component" means a component having 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 "average length of the fibers" means the average value of the lengths of any 10 fibers. The "front surface side" means the sound emission direction side. The "back surface side" means the side opposite to the sound emission direction side. The "surface layer" means a region having a depth of 50 μm or less from the front and back surfaces of the object or layer to be targeted. When the object is thin such as 100 μm, about 1 / 3 of the thickness of the object may be interpreted as the surface layer.

[0018] Hereinafter, embodiments of the present disclosure will be described with appropriate reference to the drawings. [Diaphragm for Speaker] The diaphragm 1 for a speaker shown in FIGS. 1 to 3 is composed 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 the base material 1a alone.

[0019] The diaphragm 1 can be configured in a shape suitable for the speaker to be used, and is conical or dome-shaped in FIGS. 1 and 2. That is, the base material 1a is conical or dome-shaped. By the diaphragm 1 being conical or dome-shaped, the strength of the diaphragm 1 is further increased. Also, the size of the diaphragm 1 can be set according to the speaker to be used. The diaphragm 1 may be used for a small speaker provided in, for example, a headphone, earphone, portable electronic device, etc.

[0020] <Base material> The diaphragm 1 is composed 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 described later. The base material 1a may have a pair of skin layers constituting the surface layer on the front surface side and the back surface side thereof, and a core layer formed between the pair of skin layers. That is, a 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 and the orientation direction of the fibers 3 in the core layer may be different.

[0021] The base material 1a of the diaphragm 1 for speakers (in this embodiment, the diaphragm 1 for speakers itself) has a substantially uniform thickness. The lower limit of the average thickness T of the base material 1a of the diaphragm 1 for speakers is preferably 50 μm, more preferably 80 μm. The upper limit of the average thickness T of the base material 1a of the diaphragm 1 for speakers is preferably 800 μm, more preferably 650 μm. If the average thickness T is less than the lower limit, the rigidity of the diaphragm 1 for speakers may be insufficient, or it may be difficult to form the diaphragm 1 for speakers by injection molding. Conversely, if the average thickness T exceeds the upper limit, the diaphragm 1 for speakers 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 the thicknesses at any 10 points. The ratio described regarding the above "substantially uniform thickness" is for the case of a diaphragm for speakers with a substantially uniform thickness, and this ratio is not applicable to a diaphragm for speakers intentionally provided with ribs or the like.

[0022] (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, acrylonitrile-butadiene-styrene resin, which may be used alone or in a mixture of two or more of these. In particular, as the thermoplastic resin, polypropylene is preferable. By using polypropylene as the thermoplastic resin, the vibration attenuation rate (internal loss) at audible frequencies of the diaphragm 1 for speakers can be increased. Also, when the thermoplastic resin is polypropylene, as described later, it becomes easy to disperse the fiber 3 in a non-bonded state with the resin matrix 2. Thereby, the vibration attenuation rate can be further increased, and it is easy to improve the sound reproducibility. At least a part of the fiber 3 may not be bonded to the resin matrix 2. The fiber 3 may not be bonded to the resin matrix 2 at all.

[0023] (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.

[0024] The content of the fiber 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 fiber 3 in the base material 1a (in other words, the content of the fiber 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 fiber 3 in the base material 1a is preferably 30% by mass, more preferably 22% by mass, and still more preferably 15% by mass. If the content of the fiber 3 is less than the lower limit, the rigidity of the diaphragm 1 may be insufficient. Conversely, if the content of the fiber 3 exceeds the upper limit, the fibers 3 may be entangled with each other in the resin matrix 2, and the uniform dispersibility of the fiber 3 in the resin matrix 2 may be insufficient. Further, if the content of the fiber 3 exceeds the upper limit, when the resin composition containing the resin and the thermoplastic resin is heated and passed through the nozzle or the like of the injection molding apparatus, it is likely to be clogged due to the uneven distribution of the fiber 3, and the production of the diaphragm 1 may be difficult.

[0025] The lower limit of the average length of the fiber 3 is 0.5 mm, preferably 1.0 mm. On the other hand, the upper limit of the average length of the fiber 3 is preferably 3.0 mm, more preferably 2.5 mm, and most preferably 1.5 mm. If the average length of the fiber 3 is less than the lower limit, the effect of improving the rigidity by the fiber 3 may be insufficient. Conversely, if the average length of the fiber 3 exceeds the upper limit, the fibers 3 are likely to be entangled with each other, and the uniform dispersibility of the fiber 3 in the resin matrix 2 may be insufficient. Note that the lengths of the respective fibers 3 dispersed in the resin matrix 2 may be non-uniform as long as the average length is within the above range.

[0026] 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 even more preferably 3.0 mm. Thus, by setting the maximum length of the fibers 3 to be equal to or less than the above upper limit, it is easier to reliably prevent the fibers 3 from getting entangled with each other.

[0027] The average aspect ratio of the fibers 3 is preferably in the range of 20 to 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 easily get entangled with each other. The "average aspect ratio of the fibers" means a value obtained by averaging the ratios of the lengths to the diameters (diameters) 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.

[0028] Thereby, the diaphragm 1 for a speaker can increase the vibration attenuation rate. In the diaphragm 1 for a speaker, 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, since the fibers 3 and the above-mentioned thermoplastic resin are incompatible and not chemically bonded to each other, the fibers 3 can be held in a non-bonded state with the resin matrix 2. Further, even when the fibers 3 and the thermoplastic resin are not chemically bonded, the diaphragm 1 for a speaker can uniformly disperse the fibers 3 in the resin matrix 2 by controlling the content and average length of the fibers 3 within the above-mentioned ranges.

[0029] (Loss region) As shown in FIG. 3, a plurality of loss regions 3a, which can be referred to as kink-shaped or knob-shaped, are intermittently formed along the length direction of the fiber 3. The loss region 3a is a portion generated by kneading and injecting so as to apply a strong shearing force to the fiber under special conditions in the manufacturing method to be described in detail later. As shown in FIGS. 5 and 6 to be described later in the examples, the loss region 3a is a portion formed so as to bulge out on the outer periphery of the fiber 3 like a node at arbitrary intervals along the length direction of the fiber 3. The loss region 3a can be explained as a portion where a part of the fiber 3 is broken, twisted, crushed, etc. under high temperature and high shear conditions to form a plastic deformation portion, bulge out radially outside the fiber 3, or is observed as buckling of the fiber. The buckled portion of the fiber can also be explained as a loss region called a kink band where the fiber is locally bent and broken.

[0030] Preferably, about 1 to 10 loss regions 3a are formed at a length 30 times the average diameter of the fiber 3. For example, when the average diameter of the fiber 3 is 10 μm, about 1 to 10 are formed at a length of 300 μm. The loss region 3a is a portion formed by applying a strong shearing force to the fiber. Therefore, the diameter of the loss region 3a is larger than the average diameter of the fiber 3. The diameter of the loss region 3a is 1.1 to 2 times the average diameter of the fiber 3. For example, when the average diameter of the fiber 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 have a diameter 5% to 50% larger than the average diameter of the fiber 3. The average diameter of the loss region 3a may have a diameter 5% to 50% larger than the average diameter of the fiber 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.

[0031] If the number of loss regions 3a is less than the aforementioned lower limit, the attenuation effect in a predetermined band is insufficient, and it becomes difficult to obtain a sharp reproduced sound in this band. In the examples of FIGS. 11 and 12, the attenuation effect at 2000 to 4200 Hz is insufficient. When the number of loss regions 3a exceeds the aforementioned upper limit, it becomes difficult to create a large number of bumps, resulting in a problem of high manufacturing cost.

[0032] (Other components) The base material 1a of the diaphragm 1 may contain other components other than the resin matrix 2 and the fiber 3 as long as the effects of the present disclosure are not impaired. These other components may include, for example, colorants such as titanium oxide, ultraviolet absorbers, compatibilizers, and the like.

[0033] <Advantages> Since the fiber 3 dispersed in the resin matrix 2 of the base material 1a of the diaphragm 1 is a polyparaphenylene benzobisoxazole fiber and the fiber has a plurality of loss regions 3a, the fiber 3 can increase the rigidity, and the loss regions 3a can easily increase the loss. In particular, for the diaphragm 1, the average length of the polyparaphenylene benzobisoxazole fiber is within the aforementioned range. Therefore, for example, by controlling the content of the fiber 3 within the aforementioned range, the fiber 3 can be uniformly dispersed in the resin matrix 2. As a result, the diaphragm 1 for a speaker can uniformly increase the rigidity over the entire region. When about 10% by mass of the fiber is added, it is considered that the rigidity increases by about 20%, and it is estimated that it greatly affects the increase in loss. Furthermore, when about 10% by mass of the fiber is added, the loss elastic modulus that affects the loss characteristics also improves.

[0034] The fiber 3 has a plurality of loss regions 3a. Therefore, when the fiber 3 is contained in the base material 1a in the aforementioned mass%, the mechanism of frictional loss increases, and the attenuation as the diaphragm 1 can be increased. Therefore, for a speaker having the diaphragm 1, it is possible to obtain a reproduced sound with a large attenuation and a sharp and good tone. For example, in the band of 2000 to 4200 Hz, a sharp and clear reproduced sound can be obtained.

[0035] [Method for manufacturing a diaphragm for a speaker] Next, with reference to FIG. 4, the method for manufacturing the diaphragm 1 shown in FIG. 1 will be described. The method for manufacturing the diaphragm 1 according to the present embodiment includes a kneading step of uniformly kneading a thermoplastic resin and the fiber 3 at a high temperature and high shear to generate a kneaded composition, a step (kneading and extrusion 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 extrusion step S1 into pellets, and a step (molding step) S3 of injection molding the pellets obtained in the cutting step S2. In the molding of thin products such as a diaphragm for a tweeter (Tw) and a headphone diaphragm, it is preferable that the method for manufacturing the diaphragm 1 includes a pressing step S4 of press-molding a preliminary shaped product obtained by the injection molding as described later (see FIG. 13).

[0036] (Kneading and extrusion step S1) In the kneading and extrusion step S1, while kneading a resin composition containing a thermoplastic resin and the fiber 3, it is extruded into a rod shape. The kneading and extrusion step S1 can be performed using an extrusion molding apparatus. The extrusion molding apparatus has, for example, a cylinder for guiding the resin composition and a screw mounted in the cylinder, an extruder for kneading the resin composition, a T-die for flowing out the resin composition kneaded by this extruder in a rod shape, and a cooling unit for cooling the resin composition extruded from this T-die. In the kneading and extrusion step S1, after the resin composition is extruded into a rod shape, it is cooled by the cooling unit to solidify the resin composition in the shape at the time of extrusion. Thereby, a rod-shaped extruded body is obtained. Note that, as the screw used for kneading, it is preferable to use a type that can apply sufficient shearing force to the fibers used in this embodiment. A general screw is a type in which uniform spiral grooves are formed on the outer periphery of the shaft, but in this embodiment, it is preferable to use a special screw called a damage screw. The damage screw has a configuration in which a plurality of die-shaped kneading promotion parts with small spiral grooves having a pitch different from that of the spiral grooves in other parts are arranged at the central part in the length direction of the screw shaft on which the spiral grooves are formed. By providing this kneading promotion part, it is possible to mix while kneading the pellets, and a large shearing force can be applied to the fibers in the pellets.

[0037] As the thermoplastic resin used in the kneading and extrusion step S1, the aforementioned 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 may be used. In particular, polypropylene is preferable as this thermoplastic resin.

[0038] 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 for example, it can be 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, kneading becomes difficult and the fibers get entangled and it becomes difficult to enter the cylinder. If the fiber is too short, the sound quality will not improve. In particular, when making a thin diaphragm such as a tweeter (Tw), it is desirable for the fiber to be short. If the fiber is long, it will form fiber lumps and cannot be uniformly dispersed. In the method for manufacturing a diaphragm for a speaker, by adjusting the length of the pellets in the cutting step S2 described later, the length of the fiber 3 contained in the base material 1a of the obtained diaphragm 1 can be adjusted within the aforementioned range.

[0039] The lower limit of 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 of 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 is less than the lower limit, the rigidity of the resulting diaphragm 1 for a speaker may be insufficient. Conversely, if the content of fiber 3 exceeds the upper limit, the uniform dispersibility of fiber 3 in the resin matrix 2 may be insufficient.

[0040] The resin composition may contain, as other components, a colorant such as titanium oxide, an ultraviolet absorber, a compatibilizer for compatibilizing the thermoplastic resin and fiber 3, and the like.

[0041] (Cutting step 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 columnar pellets. The fiber 3 contained in the extruded body is likely to be oriented in the extrusion direction. Therefore, by cutting this extruded body at equal intervals, the average length of fiber 3 can be suppressed to be less than or equal to the length of the pellet. In the cutting step S2, by simultaneously dividing the polyparaphenylene benzobisoxazole fiber having a length within the above-mentioned range into two or more in the longitudinal direction when forming the pellet, it is easy to unevenly adjust the length of the fiber 3 contained in the base material 1a of the resulting diaphragm 1 for a speaker. In the cutting step S2, for example, by cutting the extruded body at intervals of 3 mm or less, a plurality of columnar pellets having a length of 3 mm or less are formed.

[0042] The lower limit of the average length of fiber 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 fiber 3 after the cutting step is 3.0 mm, preferably 2.5 mm, and more preferably 1.5 mm. If the average length of fiber 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 fiber 3 exceeds the upper limit, the fibers 3 are likely to become entangled with each other in the base material 1a of the resulting diaphragm 1 for a speaker, and the uniform dispersibility of fiber 3 in the resin matrix 2 may be insufficient.

[0043] (Forming Step S3) In forming step S3, the base material 1a of the diaphragm 1 is formed by injection molding of the pellets obtained in cutting step S2. Forming step S3 can be carried out using an injection molding apparatus. This injection molding apparatus has, for example, a cylinder having a nozzle at its tip, a hopper connected to the cylinder into which the pellets obtained in the cutting step are introduced, a screw mounted in the cylinder, and a mold in which a cavity communicating with the opening of the nozzle is formed. The cavity has the inverted shape of the base material 1a of the diaphragm 1. A portion corresponding to the bottom (central portion in the axial direction view) of the base material 1a of the diaphragm 1 in the cavity communicates with the opening of the nozzle. In forming step S3, the resin composition (melt of the pellets) is radially filled into the cavity from the portion corresponding to this bottom. Also, in forming step S3, after the filling of the resin composition, the cavity is cooled and the resin composition is cured. The molded product in which this resin composition is cured is configured as the base material 1a of the diaphragm 1. The lower limit of the temperature inside the cavity in forming step S3 is preferably 30°C. On the other hand, the upper limit of the temperature inside the cavity is preferably 50°C. If the temperature inside the cavity is less than the lower limit, the fluidity of the resin in the cavity becomes insufficient, and it may become difficult to control the orientation direction of the fiber 3. Conversely, if the temperature inside the cavity exceeds the upper limit, it may become difficult to sufficiently cool the resin composition after filling into the cavity, and it may become difficult to take out the obtained base material 1a of the diaphragm 1 from the cavity.

[0044] The lower limit of the injection speed of the resin composition in forming 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 becomes insufficient, and it may become difficult to control the orientation direction of the fiber 3 in the cavity. Conversely, if the injection speed exceeds the upper limit, the fluidity of the resin composition in the cavity becomes too large, and it may become difficult to control the orientation direction of the fiber 3 in the cavity.

[0045] <Advantages> In the manufacturing method according to the present embodiment, the base material 1a of the diaphragm 1 is injection-molded using pellets obtained by cutting a rod-shaped extruded body containing a thermoplastic resin and poly(paraphenylene benzobisoxazole) fibers. Therefore, a diaphragm for a speaker in which poly(paraphenylene benzobisoxazole) fibers with a damping region are sufficiently and uniformly dispersed in a thermoplastic resin can be manufactured. In particular, in the method for manufacturing a diaphragm, the average length of the poly(paraphenylene benzobisoxazole) fibers in the pellets is within the above-mentioned range. Therefore, for example, the content of the poly(paraphenylene benzobisoxazole) fibers with a damping region in the resin composition can be controlled within the above-mentioned range. Therefore, in the base material 1a of the obtained diaphragm for a speaker, the fibers can be uniformly dispersed in the thermoplastic resin without being entangled. As a result, the diaphragm 1 for a speaker with uniformly enhanced rigidity over the entire region can be manufactured by the above-mentioned manufacturing method.

[0046] (Pressing step S4) (Method for forming a thin film for a tweeter (Tw) and a headphone diaphragm) For an injection-molded preformed product with a diaphragm shape and a thickness of 0.3 to 0.5 mm, it is sandwiched between a press mold having a cavity corresponding to the target thickness (about 100 μm) heated to (melting point to melting point + 50°C) and pressurized. After holding the preformed product for about 10 to 30 seconds, it is cooled to (melting point - 50 to melting point - 100°C) and demolded.

[0047] [Other embodiments] The embodiments described above do not limit the configuration of the present disclosure. Therefore, in the embodiments, based on the description in this specification and common technical knowledge, omission, substitution, or addition of the components of each part of the above embodiments is possible, and all of them should be construed as belonging to the scope of the present disclosure. For example, the diaphragm does not necessarily have to be cone-shaped, and it may be, for example, dome-shaped or flat-plate-shaped.

Example

[0048] [No.1] A resin composition containing polypropylene (manufactured by Nippon Polypropylene Corporation) as a thermoplastic resin containing a pigment and an additive, and polyparaphenylene benzobisoxazole fiber with a fiber length of 1 mm (Zylon (registered trademark) manufactured by Toyobo Co., Ltd.) was kneaded with a single-screw extruder and extruded into a rod shape. Further, the extruded resin composition was cooled and solidified in the shape at the time of extrusion (kneading and extrusion process). The content of polypropylene in this resin composition was 95% by mass, and the content of polyparaphenylene benzobisoxazole fiber was 5% by mass. Further, the extrusion conditions were a discharge rate of 2 kg / h and an extrusion temperature of 165°C to 190°C.

[0049] The extruded body extruded in the kneading and extrusion process was cut into pellets with a length of 3 mm (cutting process). Further, using the columnar pellets obtained by the cutting in the cutting process, injection molding was performed with an injection molding apparatus to obtain a diaphragm for a No. 1 speaker (a single substrate). This injection molding apparatus has a cylinder having a nozzle at the tip, a hopper connected to the cylinder into which the pellets obtained in the cutting process are charged, a screw mounted in the cylinder, and a mold in which a cavity communicating with the opening of the nozzle is formed. As this screw, a Daruma screw manufactured by Nippon Yusoki Co., Ltd. having a configuration in which three small kneading promotion parts with different pitches are provided at the central part in the length direction of the screw shaft was used. Further, 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 were a cylinder temperature of 200°C to 220°C, a mold temperature of 45°C, an injection speed of 400 mm / s, an injection pressure of 200 MPa, and a back pressure of 8 MPa.

[0050] [No.2] Using Zylon (registered trademark "Zylon" manufactured by Toyobo Co., Ltd.) with a fiber length of 3 mm as the polyparaphenylene benzobisoxazole fiber, except that the content of polypropylene in the resin composition was 90% by mass and the content of polyparaphenylene benzobisoxazole fiber was 10% by mass, a diaphragm for No. 2 speaker (single substrate) was manufactured under the same conditions as the diaphragm for No. 1 speaker.

[0051] [No.3] Using Zylon (registered trademark "Zylon" manufactured by Toyobo Co., Ltd.) with a fiber length of 1 mm as the polyparaphenylene benzobisoxazole fiber, except that the content of polypropylene in the resin composition was 85% by mass and the content of polyparaphenylene benzobisoxazole fiber was 15% by mass, a diaphragm for No. 3 speaker (single substrate) was manufactured under the same conditions as the diaphragm for No. 1 speaker. [No.4] Using Zylon (registered trademark "Zylon" manufactured by Toyobo Co., Ltd.) with a fiber length of 3 mm as the polyparaphenylene benzobisoxazole fiber, except that the content of polypropylene in the resin composition was 78.6% by mass and the content of polyparaphenylene benzobisoxazole fiber was 21.4% by mass, a diaphragm for No. 4 speaker (single substrate) was manufactured under the same conditions as the diaphragm for No. 1 speaker.

[0052] [No.5] Using Zylon (registered trademark "Zylon" manufactured by Toyobo Co., Ltd.) with a fiber length of 1 mm as the polyparaphenylene benzobisoxazole fiber, except that the content of polypropylene in the resin composition was 90% by mass and the content of polyparaphenylene benzobisoxazole fiber was 10% by mass, a diaphragm for No. 5 speaker (single substrate) was manufactured under the same conditions as the diaphragm for No. 1 speaker.

[0053] [No.6] Except that the content of polypropylene in the resin composition was 90% by mass and the content of polyparaphenylene benzobisoxazole fiber was 10% by mass, a diaphragm for No. 6 speaker (single substrate) was manufactured under the same conditions as the diaphragm for No. 1 speaker.

[0054] [No.7] Using Zylon (registered trademark "Zylon" manufactured by Toyobo Co., Ltd.) with a fiber length of 1 mm as the polyparaphenylene benzobisoxazole fiber, except that the content of polypropylene in the resin composition was 80% by mass and the content of polyparaphenylene benzobisoxazole fiber was 20% by mass, a diaphragm for No. 7 speaker (single substrate) was manufactured under the same conditions as the diaphragm for No. 1 speaker.

[0055] [No.8] Using Zylon (registered trademark "Zylon" manufactured by Toyobo Co., Ltd.) with a fiber length of 1 mm as the polyparaphenylene benzobisoxazole fiber, except that the content of polypropylene in the resin composition was 70% by mass and the content of polyparaphenylene benzobisoxazole fiber was 30% by mass, a diaphragm for No. 8 speaker (single substrate) was manufactured under the same conditions as the diaphragm for No. 1 speaker. [No.9] 100% polypropylene (manufactured by Nippon Polypropylene Co., Ltd.) containing no polyparaphenylene benzobisoxazole fiber was injection-molded using the aforementioned injection molding apparatus to obtain a diaphragm for No. 9 speaker (single substrate). [No.10] Using Twaron (registered trademark "Twaron" manufactured by Teijin Ltd.) with a fiber length of 6 mm as the para-aramid fiber, except that the content of polypropylene in the resin composition was 90% by mass and the content of para-aramid fiber was 10% by mass, a diaphragm for No. 10 speaker (single substrate) was manufactured under the same conditions as the diaphragm for No. 1 speaker.

[0056] Regarding the substrate of the diaphragm for No. 1 speaker, the resin matrix was heated at 400 °C and burned out to leave only the fibers (residue after decomposing and removing the resin), and the results of electron microscope observation are shown in the photograph of Fig. 5. The results of electron microscope observation of an enlarged view of one of the loss regions formed in the fibers shown in Fig. 5 are shown in the photograph of Fig. 6. As shown in Fig. 5, a plurality of intermittent nodular loss regions are formed along the length direction of the fiber. As shown in Fig. 6, it was confirmed that in one of the loss regions, the fiber was broken and partially cracked, forming a knob-like kink.

[0057] The substrate for the diaphragm could be manufactured in the same manner as in the example of No. 1 according to any of the manufacturing condition examples described in No. 2 to No. 9. Figs. 7 and 8 show the results of observing the fibers after burning out the resin matrix and leaving only the fibers using a digital microscope.

[0058] Regarding the substrate of the diaphragm for the speaker of No. 10, the resin matrix was heated at 400 °C to burn out, leaving only the fibers (the residue after decomposing and removing the resin), and the results of electron microscope observation are shown in the photograph of Fig. 9. The results of observing one of the loss regions formed in the fibers shown in Fig. 9 under an enlarged view using an electron microscope are shown in the photograph of Fig. 10. As shown in Fig. 9, a plurality of intermittent nodular loss regions are formed along the length direction of the fiber. As shown in Fig. 10, it was confirmed that in one of the loss regions, the fiber was broken and partially buckled, generating a kink band.

[0059] Regarding the reproduced sound obtained from the diaphragms of No. 1 and No. 9 speakers, the cumulative spectrum was measured according to the following procedure. 1. Mount the target speaker unit in the housing of the Yamaha monitor speaker HS7. 2. Obtain the impulse response at 1 m on the axis of this speaker in an anechoic chamber. 3. Calculate the (falling) cumulative spectrum from the obtained impulse response and express it as a contour plot.

[0060] The cumulative spectrum was obtained with reference to the literature "J. Audio Eng. Soc., vol. 25, p. 370 (1977)". The measurement results of the diaphragm of No. 9 are shown in Fig. 11, and the measurement results of the diaphragm of No. 1 are shown in Fig. 12.

[0061] As is clear from comparing the attenuation characteristics shown in FIGS. 11 and 12, it was confirmed that the diaphragm including polyparaphenylene benzobisoxazole fibers having a plurality of attenuation regions has less afterglow of the reproduced sound at 2000 to 4200 Hz. From this result, it can be seen that the diaphragm including polyparaphenylene benzobisoxazole fibers having an attenuation region can reproduce a sharp and clear sound.

Industrial Applicability

[0062] As described above, the diaphragm for a speaker according to the present disclosure can uniformly increase the rigidity with fibers and is preferably used as a relatively inexpensive diaphragm that can obtain a sharp and clear reproduced sound in a predetermined frequency band (for example, a frequency band of 2000 to 4200 Hz).

Explanation of Signs

[0063] 1…Diaphragm for speaker 1a…Base material 2…Resin matrix 3…Fiber 3a…Loss region

Claims

Claim 1 A base material having a resin matrix containing a thermoplastic resin as a main component and fibers dispersed in the resin matrix, wherein 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, a diaphragm for a speaker.

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