Acoustic device

Abstract

To provide an acoustic device including a diaphragm made of fiber-reinforced resin containing carbon fiber, in which the sound pressure is less likely to vary depending on the frequency of the emitted sound.SOLUTION: An acoustic device includes a diaphragm including a fiber-reinforced resin that includes a thermoplastic resin and carbon fiber, and an actuator disposed in contact with the diaphragm.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an audio device. [Background technology]

[0002] Conventionally, fiber-reinforced resins, which are resin compositions containing reinforcing fibers (such as carbon fibers), have been used in various applications because they can be used to mold lightweight, high-strength molded articles. For example, fiber-reinforced resins may be used for diaphragms included in acoustic devices such as speakers.

[0003] For example, Patent Document 1 discloses a flat speaker including a flat diaphragm, an actuator for vibrating the diaphragm in the thickness direction, and a connection plate disposed between the diaphragm and the actuator. Patent Document 1 states that the diaphragm may be made of a material that is a combination of resin and carbon fiber.

[0004] For example, Patent Document 2 discloses a smart speaker having a speaker diaphragm made of a thermoplastic resin-carbon fiber composite material, in which the proportion of carbon fibers having an average fiber length of 0.01 to 0.5 mm is 60% by weight or more of the total carbon fibers. According to Patent Document 2, the smart speaker is capable of emitting clear sound. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-038185 A [Patent Document 2] JP 2020-053925 A Summary of the Invention [Problem to be solved by the invention]

[0006] As disclosed in Patent Documents 1 and 2, acoustic devices having a diaphragm made of fiber-reinforced resin containing carbon fiber are known.

[0007] Incidentally, in an audio device, it is desirable for the sound pressure not to vary with the frequency of the emitted sound in order to prevent the occurrence of phenomena such as high and low sounds being heard differently. Therefore, there is a demand for the development of an audio device in which the sound pressure does not vary with the frequency of the emitted sound.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide an acoustic device that includes a diaphragm made of fiber-reinforced resin that contains carbon fiber, and in which the sound pressure is less likely to vary depending on the frequency of the sound emitted. [Means for solving the problem]

[0009] In order to solve the above problems, one aspect of the present invention relates to an acoustic device as set forth in the following items [1] to [5]. [1] A diaphragm including a fiber-reinforced resin including a thermoplastic resin and a carbon fiber; an actuator disposed in contact with the diaphragm; 2. An audio device comprising: [2] The weight average fiber length of the carbon fibers is 1.0 mm or more. [1] An acoustic device according to the present invention. [3] The acoustic device according to [1] or [2], wherein the thermoplastic resin is a polyolefin resin. [4] The acoustic device according to any one of [1] to [3], wherein the polyolefin resin is a polypropylene resin. [5] The content of the carbon fiber is 5% by mass or more and 75% by mass or less based on the total mass of the fiber reinforced resin. An acoustic device according to any one of [1] to [4]. Effect of the Invention

[0010] According to the present invention, it is possible to provide an acoustic device that includes a diaphragm made of fiber-reinforced resin that contains carbon fiber, and in which the sound pressure is less likely to vary depending on the frequency of the sound emitted. [Brief description of the drawings]

[0011] [Figure 1] Fig. 1A is a schematic diagram showing the external appearance of an audio device according to this embodiment, and Fig. 1B is a schematic diagram showing an exemplary embodiment of the audio device when in use. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing an exemplary configuration of the actuator. [Diagram 3] FIG. 3 is a schematic cross-sectional view showing an exemplary configuration of an audio device according to the first modification of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing the appearance of a molded product for evaluation produced in an example of the present invention. [Diagram 5] FIG. 5 is a schematic diagram showing an actuator attached to the wall surface of a molded article for evaluation in an embodiment of the present invention. [Figure 6] FIG. 6 is a schematic diagram showing how sound pressure variability is evaluated in an embodiment of the present invention. [Figure 7] FIG. 7 is a diagram showing the effect of frequency on sound pressure evaluated in an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described in detail. However, the present invention is not limited to the following embodiment.

[0013] 1. Sound equipment configuration Fig. 1A is a schematic diagram showing the appearance of an acoustic device 100 in this embodiment, and Fig. 1B is a schematic diagram showing an exemplary embodiment of the acoustic device 100 when in use. The acoustic device 100 in this embodiment includes a diaphragm 110 including a fiber-reinforced resin that includes a thermoplastic resin and carbon fiber, and an actuator 120 arranged in contact with the diaphragm 110. The acoustic device 100 is, for example, a speaker.

[0014] In the acoustic device 100, the diaphragm 110 including fiber-reinforced resin containing carbon fiber and the actuator 120 are arranged in contact with each other, and the vibration of the actuator 120 is transmitted to the diaphragm 110, and sound is generated from the diaphragm 110. The present inventors have found that by arranging the diaphragm 110 including fiber-reinforced resin containing carbon fiber and the actuator 120 in contact with each other, it is possible to reduce the difference in sound pressure for each frequency of the sound generated from the vibration of the diaphragm 110. The following reasons are considered for this.

[0015] The inclusion of carbon fiber in the fiber-reinforced resin can increase the elastic modulus of the diaphragm 110. Increasing the elastic modulus of the diaphragm 110 can increase the propagation speed of the elastic waves transmitted from the actuator 120 within the diaphragm 110. This makes it less susceptible to the effects of the resonance phenomenon, and can prevent the sound pressure from increasing significantly at a specific frequency.

[0016] Here, the acoustic waves are less likely to attenuate because the actuator 120 is disposed in contact with the diaphragm 110. This makes it possible to prevent a decrease in sound pressure at a particular frequency (particularly in the high frequency range where attenuation is likely to occur).

[0017] For these reasons, it is believed that the sound emitted from the acoustic device 100 has small differences in sound pressure for each frequency, and therefore the sound pressure is less likely to vary depending on the frequency.

[0018] Based on the above findings, the configuration of the audio device 100 will be described below.

[0019] 1-1.Diaphragm The diaphragm 110 includes a fiber-reinforced resin. In this specification, the term "diaphragm" refers to a member that is in contact with the actuator 120 and can vibrate and emit sound when vibration is transmitted from the actuator 120. The shape of the diaphragm 110 may be a flat plate or a three-dimensional shape composed of a wall portion having a certain thickness. For example, the shape of the diaphragm 110 may be a cone shape, a dome shape, a box shape, or the like. In this embodiment, the shape of the diaphragm 110 is a box shape as shown in FIG. 1. The planar shape of the diaphragm 110 is not particularly limited, and may be, for example, a rectangle, a circle, an ellipse, or the like.

[0020] In this embodiment, the box-shaped diaphragm 110 has an opening 110a formed at a position opposite the bottom surface and a plurality of wall portions 110b, and an actuator can be disposed on the wall portions 110b of the box-shaped diaphragm 110 from the opening 110a. Also, as shown in Fig. 1B, in this embodiment, the acoustic device 100 is used with the diaphragm 110 disposed so that the bottom surface becomes the upper surface. The shape of the opening 110a is not particularly limited, and may be, for example, a rectangle, a circle, an ellipse, or the like.

[0021] The thicknesses of the walls 110b (lengths of the arrows a and b in FIG. 1A) may be different from each other or may be the same. The thicknesses of the walls 110b are not particularly limited, but are preferably 0.2% to 3% of the length of the box-shaped diaphragm 110 in the thickness direction (for example, the length of the arrow A for the arrow a in FIG. 1A). In particular, the thickness of the wall 110b in contact with the actuator 120 (length of the arrow b in FIG. 1A) is more preferably 0.3% to 4% of the length of the box-shaped diaphragm 110 in the thickness direction (length of the arrow B in FIG. 1A). By having the thickness within the above range, the fluctuation of the sound pressure for each frequency can be further suppressed.

[0022] 1-1-1.Fiber reinforced resin The fiber reinforced resin includes a thermoplastic resin and carbon fibers.

[0023] (thermoplastic resin) The thermoplastic resin may be derived from a fossil fuel, may be derived from a biomass feedstock, or may be a mixture thereof.

[0024] Examples of the thermoplastic resin include polyolefin resin, polyamide resin, polyester resin, polystyrene resin, thermoplastic polyimide resin, polyamideimide resin, polycarbonate resin, polyphenylene ether resin, polyphenylene sulfide resin, polyacetal resin, acrylic resin, polyetherimide resin, polysulfone resin, polyether ketone resin, polyether ether ketone resin, polyarylate resin, polyether nitrile resin, vinyl chloride resin, ABS resin, and fluororesin, etc. Among these, polyolefin resin is preferred from the viewpoint of further suppressing the fluctuation in sound pressure for each frequency of the sound emitted from the acoustic device 100.

[0025] Examples of the polyolefin resin include polymers of α-olefins, cyclic olefins, non-conjugated dienes, and aromatic olefins. Of these, polymers mainly composed of α-olefins are preferred. The carbon number of the α-olefin is preferably 2 to 20, more preferably 2 to 10, and even more preferably 2 to 8. Examples of such α-olefins include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 3-methyl-1-butene, and 4-methyl-1-pentene. Of these, propylene is preferred from the viewpoint of further suppressing the fluctuation in sound pressure for each frequency of the sound emitted from the acoustic device 100. That is, the polyolefin resin is preferably a polypropylene resin. The polypropylene resin is preferably a propylene homopolymer.

[0026] The polyolefin resin may be a resin (modified polyolefin resin) obtained by modifying an unmodified polyolefin resin with an unsaturated carboxylic acid or a derivative thereof.The modified polyolefin resin is preferably a modified polypropylene resin.

[0027] Examples of the unsaturated carboxylic acid used for the modification include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, sorbic acid, and angelic acid, and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, tetrahydrophthalic acid, norbornene dicarboxylic acid, and bicyclo[2.2.1]hept-2-ene-5,6-dicarboxylic acid.

[0028] Examples of the unsaturated carboxylic acid derivatives used for the modification include acid anhydrides, acid halides, esters, amides, imides, and metal salts of the above-mentioned unsaturated carboxylic acids. Specific examples of the unsaturated carboxylic acid derivative include unsaturated dicarboxylic acid anhydrides such as maleic anhydride, itaconic anhydride, citraconic anhydride, tetrahydrophthalic anhydride, and bicyclo[2.2.1]hept-2-ene-5,6-dicarboxylic anhydride; unsaturated dicarboxylic acid halides such as malenyl chloride; acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate; methacrylic acid esters such as methyl methacrylate and glycidyl methacrylate; maleic acid esters such as monomethyl maleate, monoethyl maleate, dimethyl maleate, and diethyl maleate; other esters such as diethyl fumarate, dimethyl itaconate, diethyl citraconic acid, dimethyl tetrahydrophthalate, and dimethyl bicyclo[2.2.1]hept-2-ene-5,6-dicarboxylate; acrylamide, maleic acid amide, maleimide, sodium acrylate, and sodium methacrylate.

[0029] Among these, unsaturated dicarboxylic acids or derivatives thereof are preferred, and unsaturated dicarboxylic acids or its anhydride is more preferred, with maleic acid or maleic anhydride being even more preferred.

[0030] The thermoplastic resin may be a styrene-based thermoplastic elastomer such as styrene-butadiene-styrene copolymer (SBS), styrene-isoprene-styrene copolymer (SIS), styrene-ethylene / butylene-styrene copolymer (SEBS), and styrene-ethylene / propylene-styrene copolymer (SEPS).

[0031] In this embodiment, the fiber reinforced resin may contain only one type of thermoplastic resin, or may contain two or more types in combination. When the fiber reinforced resin contains two or more types of thermoplastic resin, the thermoplastic resin may be, for example, a mixture of a polyolefin resin (preferably a polypropylene resin), a modified polyolefin resin (preferably a modified polypropylene resin), and a polyamide resin, or a mixture of a polyolefin resin (preferably a modified polypropylene resin).

[0032] Examples of the polyamide resin include polyamide 6 / 10, polyamide 6 / 12, polyamide 6 / 14, polyamide 11, polyamide 12, polyamide 10 / 10, polyamide 10 / 12, polyamide 10 / T, and the like.

[0033] When the fiber reinforced resin contains two or more types of thermoplastic resin, from the viewpoint of further suppressing the fluctuation in sound pressure for each frequency of the sound emitted from the acoustic device 100, the content of polyolefin resin (including modified polyolefin resin) relative to the total mass of the thermoplastic resin is preferably 60 mass% or more and 95 mass% or less, and more preferably 60 mass% or more and 90 mass% or less.

[0034] The content of the modified polyolefin resin in the polyolefin resin is preferably 0.1% by mass to 20% by mass, more preferably 0.1% by mass to 15% by mass, based on the total mass of the thermoplastic resin. When the content of the modified polyolefin resin is within the above range, the impregnation of the resin component into the carbon fiber is improved, and cracking of the molded body due to the carbon fiber not impregnated with the resin component (dry fiber) can be suppressed.

[0035] The content of the polyamide resin relative to the total mass of the thermoplastic resin is preferably 0% by mass or more and 50% by mass or less, and more preferably 0% by mass or more and 30% by mass or less. When the content of the polyamide resin is 0% by mass or more, the mechanical properties of the molded body are easily improved and the tensile creep strain of the molded body is easily reduced. Furthermore, when the content of the polyamide resin is 50% by mass or less, the impregnation of the resin component into the carbon fiber is good, and cracking of the molded body due to carbon fiber (dry fiber) not impregnated with the resin component can be suppressed.

[0036] From the viewpoint of improving the impregnation ability of the thermoplastic resin into the carbon fiber, the melting point measured by a differential scanning calorimeter (DSC) at a heating rate of 10°C / min is preferably 130°C or higher and 180°C or lower, and more preferably 140°C or higher and 170°C or lower.

[0037] From the viewpoint of improving the impregnation ability of the thermoplastic resin into the carbon fiber, the melt flow rate (MFR) measured under a load of 2.16 kg in accordance with JIS K 7210 (2014) is preferably 0.01 g / 10 min or more and 300 g / 10 min or less, and more preferably 1 g / 10 min or more and 300 g / 10 min or less.

[0038] The content of the thermoplastic resin relative to the total mass of the fiber reinforced resin is preferably 50% by mass or more and 95% by mass or less, and more preferably 55% by mass or more and 95% by mass or less. When the content is 50% by mass or more, the moldability of the fiber reinforced resin is improved, and the diaphragm 110 can be easily molded into a desired shape. Furthermore, when the content is 95% by mass or less, it is easier to include more carbon fiber in the fiber reinforced resin, and the strength of the diaphragm 110 can be increased.

[0039] (Carbon Fiber) In this embodiment, the carbon fibers are randomly dispersed in the thermoplastic resin, which is the matrix resin.

[0040] The carbon fiber may be any of polyacrylonitrile, rayon, pitch, polyvinyl alcohol, regenerated cellulose, and pitch produced from mesophase pitch. The carbon fiber may be a general-purpose fiber or a high-strength fiber. The carbon fiber may also be a recycled fiber.

[0041] As described above, the carbon fiber makes it difficult for the sound pressure of the sound emitted from the audio device to vary depending on the frequency of the sound. Furthermore, the inclusion of carbon fiber in the fiber-reinforced resin can increase the mechanical strength (particularly the bending strength and bending modulus) of the diaphragm 110.

[0042] The weight average fiber length (Lw) of the carbon fiber is preferably 1.0 mm or more, more preferably 1.0 mm or more and 5 mm or less, and even more preferably 1.2 mm or more and 3 mm or less. When the weight average fiber length is 1.0 mm or more, the elastic modulus of the diaphragm 110 can be further increased. This increases the propagation speed of the elastic wave in the diaphragm 110, so that the sound pressure of the sound emitted from the acoustic device 100 is less likely to vary depending on the frequency. Here, the increase or decrease in the weight average fiber length is highly correlated with the increase or decrease in the elastic modulus of the diaphragm 110. Therefore, it is preferable to adopt the weight average fiber length as the fiber length of the carbon fiber in this embodiment.

[0043] The weight average fiber length can be calculated by the following formula (1). Lw = ΣNi Li 2 / (ΣNi Li) (1) Li: Fiber length [μm] Ni: Number of carbon fibers with fiber length Li [-]

[0044] The fiber length Li in formula (1) can be measured, for example, by cutting out a portion of the diaphragm 110, removing the resin composition contained in the test piece by thermal decomposition or dissolution in a solvent to prepare a test piece for observation, photographing the test piece with an optical microscope, and performing image analysis.

[0045] The average fiber diameter (Da) of the carbon fibers is preferably 0.1 μm or more and 50 μm or less, more preferably 1 μm or more and 30 μm or less, and even more preferably 1 μm or more and 20 μm or less. When the average fiber diameter is 0.1 μm or more, it is sufficient to bundle only a smaller amount of carbon fibers when bundling the carbon fibers, and therefore the productivity of the resin composition can be improved. When the average fiber diameter is 0.1 μm or more, the carbon fibers are less likely to break, and therefore the elastic modulus of the diaphragm 110 can be further increased. This can increase the propagation speed of the elastic waves in the diaphragm 110, and can make it more difficult for the sound pressure generated from the acoustic device 100 to fluctuate for each frequency. When the average fiber diameter is 50 μm or less, it is easier to increase the aspect ratio of the carbon fibers, and can suppress a decrease in the strength of the diaphragm 110.

[0046] The average fiber diameter can be measured, for example, by cutting out a portion of the diaphragm 110, removing the resin composition contained in the test piece by pyrolysis or dissolution in a solvent to prepare a test piece for observation, photographing the test piece with an optical microscope, and performing image analysis.

[0047] The carbon fibers may be bundled with a sizing agent. The sizing agent may be any of acrylic sizing agents, urethane sizing agents, acid copolymer sizing agents, etc. Among these, when the carbon is a long fiber having an average fiber length of 1.0 mm or more, the impregnation of the resin component is good, so that acrylic sizing agents and acid copolymer sizing agents are preferred, and acid copolymer sizing agents are more preferred.

[0048] The carbon fiber may be subjected to a surface treatment such as oxidation etching or coating. Examples of oxidation etching treatment include air oxidation treatment, oxygen treatment, treatment with an oxidizing gas, treatment with ozone, corona treatment, flame treatment, (atmospheric pressure) plasma treatment, and treatment with an oxidizing liquid (nitric acid, aqueous solution of alkali metal hypochlorite, potassium dichromate-sulfuric acid, and potassium permanganate-sulfuric acid). Examples of materials for coating the carbon fiber include carbon, silicon carbide, silicon dioxide, silicon, plasma monomer, ferrocene, and iron trichloride.

[0049] The carbon fiber content is preferably 5% by mass or more and 75% by mass or less, and more preferably 5% by mass or more and 70% by mass or less, based on the total mass of the fiber reinforced resin. When the content is 5% by mass or more, the elastic modulus of the diaphragm 110 can be increased, and the sound propagation speed within the diaphragm 110 can be increased. This makes it possible to make it more difficult for the sound pressure generated by the acoustic device 100 to vary for each frequency.

[0050] (Other Ingredients) The fiber reinforced resin may contain components other than the above-mentioned components. Examples of the other components include a flame retardant, a flame retardant assistant, a filler, a colorant, an antibacterial agent, and an antistatic agent. These components may be used alone or in combination of two or more.

[0051] Examples of the flame retardant include halogen-based flame retardants such as halogenated aromatic compounds, phosphorus-based flame retardants such as nitrogen-containing phosphate compounds and phosphoric acid esters, nitrogen-based flame retardants such as guanidine, triazine, melamine and derivatives thereof, inorganic flame retardants such as metal hydroxides, boron-based flame retardants, silicone-based flame retardants, sulfur-based flame retardants, and red phosphorus-based flame retardants.

[0052] Examples of the flame retardant synergist include antimony compounds, metal compounds containing zinc, metal compounds containing bismuth, magnesium hydroxide, and clay silicates.

[0053] Examples of fillers include glass components such as glass beads and glass flakes, silica, graphite, calcium silicate, aluminum silicate, kaolin, talc, clay, and other silicate compounds, metal oxides such as iron oxide, titanium oxide, zinc oxide, antimony oxide, and alumina, calcium, magnesium, and metal carbonates or sulfates.

[0054] Examples of colorants include pigments and dyes.

[0055] 1-1-2. How to make the diaphragm The diaphragm 110 can be produced by using the above-mentioned thermoplastic resin, carbon fiber, and fiber-reinforced resin containing other components, and employing a known molding method such as injection molding, extrusion molding, or press molding.

[0056] The fiber reinforced resin that is the material of the diaphragm can be produced by melting and kneading the above-mentioned components.

[0057] The method of melt-kneading is not particularly limited. For example, the above-mentioned components may be melt-kneaded with a melt kneader such as a roll mill, a Banbury mixer, or a kneader, or may be dry-blended with a kneader such as a tumbler blender, a Henschel mixer, or a ribbon mixer, and then melt-kneaded and extruded with an extruder such as a single-screw extruder or a twin-screw extruder. The melt-kneaded fiber-reinforced resin in a molten state may be directly injected into a molding machine and molded, or may be extruded and processed into a predetermined shape (e.g., pellets) to form a solid fiber-reinforced resin composition, and then molded.

[0058] When the diaphragm 110 is manufactured by injection molding, the fiber-reinforced resin used may be a pellet-shaped fiber-reinforced resin. In this case, the pellet-shaped fiber-reinforced resin may be a resin composition in which carbon fibers are oriented in one direction, or a resin composition in which carbon fibers are oriented randomly. The carbon fibers may be partially cut by making slits.

[0059] The resin composition in which the carbon fibers are oriented in one direction may be, for example, a pellet-shaped resin composition in which the weight average fiber length of the carbon fibers is 0.5 μm or more and 10 μm or less. In the resin composition, the weight average fiber length of the carbon fibers is more preferably 0.5 μm or more and 3 μm or less.

[0060] A resin composition in which carbon fibers are oriented in one direction can be produced by impregnating the unidirectionally oriented carbon fibers with a resin component and other components. For example, the unidirectionally oriented carbon fibers can be run through an impregnation roll or an impregnation die, and then brought into contact with the molten resin component and other components in the impregnation roll or the impregnation die, thereby impregnating the fibers with the resin component and other components. After impregnation, the resin component can be cooled and solidified, and then processed into pellets to produce a solid fiber-reinforced resin composition.

[0061] 1-2.Actuator The actuator 120 is a member for generating vibration. Fig. 2 is a schematic cross-sectional view showing an exemplary configuration of the actuator 120. As shown in Fig. 2, in this embodiment, the actuator 120 has a base part 121 and a vibration part 122. However, the configuration of the actuator 120 is not limited to this.

[0062] Base portion 121 accommodates a part of vibration portion 122 and supports vibration portion 122. The shape of base portion 121 is not particularly limited, but may be, for example, a rectangular column, a circular column, or an elliptical column. The material of base portion 121 is not particularly limited.

[0063] The vibration part 122 vibrates when power (voltage) corresponding to the acoustic signal is supplied. The shape of the vibration part 122 is not particularly limited, and may be, for example, a rectangular column, a circular cylinder, or an elliptical cylinder. The material of the vibration part 122 is, for example, a conductive material such as copper or aluminum. In this embodiment, a part of the vibration part 122 is housed in the base part 121, and the remaining part protrudes from the base part 121, and vibrates back and forth along the axial direction. The vibration part 122 may have an electrode (not shown) for supplying a voltage to the vibration part 122 through a wiring.

[0064] In the acoustic device 100 according to this embodiment, the vibrating portion 122 of the actuator 120 is disposed in contact with the diaphragm 110 .

[0065] In this specification, the actuator 120 is arranged "in contact with" the diaphragm 110, and includes not only a state in which these members are simply in separable contact, but also a state in which they are bonded or joined by an adhesive or other method. In this specification, "bonding" refers to a state in which the surfaces of two members are bonded by chemical interaction (chemical bonding), intermolecular force, or mechanical bonding. Also, in this specification, "bonding" refers to a state in which at least one of the two members (for example, the base part 121 of the actuator 120) is heated and the two members are fused together. Examples of the other methods include a method of bonding the actuator 120 and the diaphragm 110 by attaching them with tape, a method of bonding these members using a double-sided adhesive sheet, a method of directly fixing them with screws or the like, and a method of inserting the actuator and bonding them by injection molding or press molding.

[0066] That is, an adhesive layer derived from an adhesive, and an adhesive member such as a tape or a double-sided adhesive sheet may be included between the actuator 120 and the vibration part 122 of the vibration plate 110. However, no layers or members other than the adhesive layer and the adhesive member are included between the actuator 120 (vibration part 122) and the vibration plate 110. The actuator 120 (vibration part 122) and the vibration plate 110 are in direct contact with each other or in close contact with each other via an adhesive layer or adhesive member.

[0067] Examples of the adhesive include an epoxy adhesive containing an epoxy resin, a silicone adhesive containing a silicone resin, etc. The adhesive layer may contain a coupling agent such as a silane coupling agent.

[0068] From the viewpoint of further suppressing the fluctuation in sound pressure for each frequency of the sound emitted from the acoustic device 100, it is preferable that the actuator 120 and the diaphragm 110 are in direct contact with each other and adhered to each other without using an adhesive layer or the adhesive member. Also, it is preferable that the actuator 120 is in contact with a flat portion of the diaphragm 110.

[0069] The number of actuators 120 arranged in the acoustic device 100 is not particularly limited, but it is more preferable to arrange one actuator 120 for one diaphragm 110.

[0070] In addition, the number of actuators 120 per unit area (units / m2) on the same plane of the diaphragm 110 including the contact surface between the diaphragm 110 and the actuators 120 is 2 ) is preferably 1 or more and 5 or less, and more preferably 2 or more and 4 or less. 2 ) is 5 or less, interference and phase shifts of elastic waves are less likely to occur, and fluctuations in sound pressure for each frequency of the sound emitted from the acoustic device 100 are less likely to occur.

[0071] Furthermore, in this embodiment, actuator 120 (at least one actuator 120 when there are multiple actuators 120 for one diaphragm 110) may be disposed in contact with a flat surface of diaphragm 110, or in contact with an edge or end surface of diaphragm 110. From the viewpoint of improving acoustic characteristics, actuator 120 is preferably disposed in contact with a flat surface of diaphragm 110.

[0072] In this embodiment, the actuator 120 (at least one actuator 120 when there are multiple actuators 120 for one diaphragm 110) is preferably arranged in the center of the same plane of the diaphragm 110 including the contact surface between the diaphragm 110 and the actuator 120. This makes it more difficult for the sound pressure emitted from the acoustic device 100 to vary depending on the frequency. In this specification, "arranged in the center" means that the actuator 120 is arranged so that the center (center of gravity) of the diaphragm 110 (the above plane) is included in the contact surface between the actuator 120 (vibration section 122) and the diaphragm 110.

[0073] The ratio of the contact area between actuator 120 and diaphragm 110 (contact area per actuator) to the area of ​​the same plane of diaphragm 110 including the contact surface between diaphragm 110 and actuator 120 is preferably 0.2% to 5%, more preferably 0.3% to 3%. By having the ratio within the above range, it is possible to make it more difficult for the sound pressure generated by acoustic device 100 to vary for each frequency.

[0074] 1-3.Other materials Acoustic device 100 may have components other than diaphragm 110 and actuator 120. For example, acoustic device 100 may further have a housing for accommodating actuator 120, or may further have a substrate for mounting diaphragm 110 and actuator 120 thereon.

[0075] The acoustic device 100 can be manufactured by assembling the above-mentioned components and arranging them so that the diaphragm 110 and the actuator 120 are in contact with each other. Note that the acoustic device 100 consisting of only the diaphragm 110 and the actuator 120 may be configured to be portable.

[0076] 2. Variations (Variation 1) 3 is a schematic cross-sectional view showing an exemplary configuration of an acoustic device 100 according to Modification 1 of the present invention. In the acoustic device 100 according to Modification 1, the shape of the diaphragm 110 is flat. Therefore, the acoustic device 100 according to Modification 1 can be used as a planar speaker.

[0077] In the first modification, the thickness of diaphragm 110 is preferably 6% to 70% and more preferably 10% to 40% of the thickness of actuator 120. When the thickness is within the above range, the difference in sound pressure for each frequency emitted from acoustic device 100 can be further reduced.

[0078] 3.Other The acoustic device 100 may be a speaker having a shape other than those described above, such as a cone-type speaker, a dome-type speaker, a horn-type speaker, etc. The acoustic device 100 may also be a device other than the above-mentioned speakers, so long as it is a device that generates sound by the diaphragm 110 and the actuator 120. The acoustic device 100 may be used by being placed, for example, on a wall, a door, or inside a vehicle cabin. EXAMPLES

[0079] The present invention will now be described with reference to examples, which should not be construed as limiting the scope of the present invention.

[0080] 1. Preparation of materials The following materials were prepared:

[0081] 1-1.Thermoplastic resin Polypropylene resin (PP-1) Prime Polypro J13B manufactured by Prime Polymer Co., Ltd., MFR (JIS K7210 (2014) compliant, 230°C, 2.16 kg load): 220g / 10min Glass fiber composite polypropylene resin (PP-2) Mostron L-4070PL, manufactured by Prime Polymer Co., Ltd. Glass fiber content: 40% by mass Polypropylene resin (PP-3) Prime Polypro J137G manufactured by Prime Polymer Co., Ltd., MFR (JIS K7210 (2014) compliant, 230°C, 2.16 kg load): 30g / 10min Maleic acid modified polyolefin resin (PP-4) Polyamide resin (PA) Polyamide 12, UBE 3012U manufactured by UBE Corporation

[0082] The maleic acid modified polyolefin resin (PP-4) was prepared as follows.

[0083] 100 parts by mass of polypropylene resin (J106G manufactured by Prime Polymer Co., Ltd.) was premixed with 1 part by mass of dialkyl peroxide (Perhexa 25B manufactured by NOF Corp.) and 3 parts by mass of powdered maleic anhydride (CRYSTAL MAN manufactured by NOF Corp.). This mixture was fed to a twin-screw melt-kneading extruder (TEX30α manufactured by JSW, L / D=53, D=30mm) whose temperature was adjusted to 190°C, and melt-kneaded under the condition of 200 rpm. Then, the strand obtained by melt-kneading was cooled in a water tank to obtain a maleic anhydride-modified polypropylene. Thereafter, in order to remove the unmodified residual maleic anhydride, the obtained maleic anhydride-modified polypropylene resin was vacuum dried at 40°C for 2 hours. Through these operations, the maleic anhydride modified polypropylene resin obtained had a maleic acid content of 2.5% by mass and an MFR (based on JIS K7210 (2014), 230°C, 2.16 kg load) of 800 g / 10 min.

[0084] 1-2.Carbon fiber Carbon Fiber Toray Industries, Inc. continuous fiber (roving)

[0085] 2. Fabrication of Fiber-reinforced Resin (Fiber reinforced resin composition 1) Polypropylene resin (PP-1), maleic acid modified polyolefin resin (PP-4), and polyamide resin (PA) were charged in the amounts shown in Table 1 into the hopper of a screw extruder (TEX30α manufactured by JSW) whose temperature was adjusted to 250°C. The carbon fibers were expanded and spread at an adjusted speed so that the ratio of carbon fibers in the resulting fiber reinforced resin composition 1 was 9% by mass. The spread carbon fibers were then introduced into the die head of the extruder, stranded, cooled and solidified, and pelletized using a strand cutter to obtain pelletized fiber reinforced resin (pellet length: 9 mm) 1.

[0086] (Fiber reinforced resin composition 2) The long fiber composite polypropylene resin (PP-2) and the polypropylene resin (PP-3) were blended in the ratio shown in Table 1, and mixed so that the proportion of glass fiber in the resulting fiber reinforced resin composition 2 was 10 mass %, thereby obtaining fiber reinforced resin composition 2.

[0087] (Fiber reinforced resin composition 3) The long fiber composite polypropylene resin (PP-2) and the polypropylene resin (PP-3) were blended in the ratio shown in Table 1, and mixed so that the proportion of glass fiber in the resulting fiber reinforced resin composition 3 was 30 mass %, thereby obtaining fiber reinforced resin composition 3.

[0088] 3. Preparation of molded bodies for evaluation The fiber reinforced resin composition 1 was put into an injection molding machine with a clamping force of 1300 tons, and a box-shaped body (molded body for evaluation) 1 (box-shaped diaphragm) of 325 mm x 465 mm x 155 mm shown in FIG. 4 was injection molded while changing the conditions as appropriate, mainly under the following conditions. The above-mentioned evaluation molded body has an opening 110a inside one of two 325 mm x 465 mm faces, and the opening 110a is formed at a position 2 mm away from the outer edge of the face. In other words, the thickness of the wall of the molded body is 2 mm. In this embodiment, the face facing the opening 1a among the inner faces of the above-mentioned evaluation molded body is the inner bottom face, and the outer surface of the opening 110a is the bottom face. In addition, the four inner faces connecting the opening 110a and the bottom face are the inner faces. Barrel temperature: 250℃ Mold temperature: 60℃

[0089] Instead of the fiber reinforced resin composition 1, the fiber reinforced resin composition 2 and the fiber reinforced resin composition 3 were used to injection mold a box-shaped body (molded body for evaluation) 2 and a box-shaped body (molded body for evaluation) 3, respectively, in the same manner as described above. The dimensions of the molded body for evaluation 2 and the molded body for evaluation 3 are the same as those of the molded body for evaluation 1.

[0090] 4. Evaluation and Measurement (average fiber length) Test pieces 1 to 3 were prepared by cutting out a portion from each of the evaluation molded bodies 1 to 3. The test pieces were then placed in an electric furnace and left for 3 hours under the following temperature conditions to pyrolyze the polypropylene resin in the test pieces. Thereafter, only the carbon fibers or glass fibers were taken out of the electric furnace, and a microscopic image of the carbon fibers or glass fibers was obtained using an optical microscope. From the obtained microscopic images, 500 to 2000 carbon fibers or glass fibers were randomly selected, and the fiber lengths were measured. Using the measured fiber lengths, the weight average fiber length was calculated based on the following formula (1). Lw = ΣNi Li 2 / (ΣNi Li) (1) Li: Fiber length [μm] Ni: Number of carbon fibers with fiber length Li [-]

[0091] (Flexural modulus and flexural strength) A portion was cut out from each of the evaluation molded bodies 1 to 3 to prepare test pieces 1 to 3 in accordance with JIS K 7162 (1994). Test pieces 1 to 3 were subjected to a bending test at a bending speed of 2 mm / s in accordance with ISO 178 (2019), and the flexural modulus (GPa) and flexural strength (MPa) were determined based on the stress-strain curve.

[0092] (Specific gravity of molded body) The measurement was performed in accordance with JIS K 7112.

[0093] (Sound pressure variability) Fig. 5 is a schematic diagram showing the actuator attached with tape from above in a state where the actuator is in direct contact with the wall surface of the evaluation molded body, and Fig. 6 is a schematic diagram showing the state where the variability of sound pressure is evaluated. In a semi-anechoic chamber, the actuator 120 (Vibro Transducer Vp408, manufactured by Aquve Lab Co., Ltd.) was attached with tape from above in a state where the actuator was in direct contact with the center (position shown in Fig. 4) of one of the inner surfaces of the 461 mm x 153 mm inner surface of the evaluation molded body 1, and the evaluation molded body 1 was placed on polyurethane foam (Calmflex F2, manufactured by Inoac Corporation) laid on the floor.

[0094] After connecting the actuator 120 and the power amplifier 11 (Fostex AP20d, manufactured by Foster Electric Co., Ltd.), the evaluation molded body 1 was turned upside down so that the bottom surface (465 mm x 325 mm) was the upper surface, and the output level of the power amplifier was set to 50%. A 1V output level sine sweep signal was output by the generator function of the FFT analyzer 13 (PULSE, manufactured by Spectris Co., Ltd.), and the actuator was vibrated through the power amplifier. This caused the evaluation molded body 1 to vibrate, and the radiated sound from the evaluation molded body 1 was recorded using the microphone 12 at a position 50 mm away from the bottom surface of the evaluation molded body 1. Based on the recorded radiated sound, the change in sound pressure level [dB] for each frequency [Hz] was obtained using the FFT analyzer 13. The results are shown in FIG. 7. Based on the obtained results, the variability of the sound pressure was evaluated according to the following evaluation criteria. ○: Between frequencies of 3000Hz and 10000Hz, the difference between the maximum and minimum sound pressure levels is less than 20dB. ×: Between frequencies of 3000Hz and 10000Hz, the difference between the maximum and minimum sound pressure levels is 20dB or more.

[0095] The ingredients and evaluation results of each resin composition are shown in Table 1. The composition values ​​in Table 1 are given in parts by mass.

[0096] [Table 1]

[0097] As shown in Table 1 and Figure 7, it was found that by arranging the actuator in contact with a diaphragm containing fiber-reinforced resin, which contains thermoplastic resin and carbon fiber, the fluctuation in sound pressure at each frequency was suppressed. [Industrial Applicability]

[0098] INDUSTRIAL APPLICABILITY The acoustic device of the present invention is less susceptible to fluctuations in sound pressure for each frequency of the emitted sound, and is therefore useful, for example, in the field of acoustics. [Explanation of symbols]

[0099] 1. Evaluation Molding 11. Power Amplifier 12 Microphone 13. FFT Analyzer 100 Sound equipment 110 Diaphragm 110a opening 110b Wall section 120 Actuator 121 Base 122 Vibration part 130 Cap 140 Damper

Claims

1. A diaphragm including a fiber-reinforced resin including a thermoplastic resin and carbon fiber; an actuator disposed in contact with the diaphragm; 2. An audio device comprising:

2. The weight average fiber length of the carbon fibers is 1.0 mm or more.

2. An acoustic device according to claim 1.

3. The thermoplastic resin is a polyolefin resin.

3. An acoustic device according to claim 1 or 2.

4. The polyolefin resin is a polypropylene resin.

4. An acoustic device according to claim 3.

5. The content of the carbon fiber is 5% by mass or more and 75% by mass or less with respect to the total mass of the fiber reinforced resin.

3. An acoustic device according to claim 1 or 2.

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