Speaker diaphragm, speaker diaphragm manufacturing method, and speaker

Abstract

To obtain a diaphragm for a speaker with high sound pressure, and a speaker.SOLUTION: A diaphragm 1 for a speaker includes a reinforcing fiber layer 10 in which carbon fibers 11 are randomly oriented in a thermoplastic resin, and a thermoplastic resin layer 20 arranged so as to sandwich the reinforcing fiber layer 10. It is preferable that the basis weight of the diaphragm 1 for the speaker is 60 g / m2 or more and 120 g / m2 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a speaker diaphragm, a method for manufacturing a speaker diaphragm, and a speaker. [Background technology]

[0002] Speaker diaphragms are required to have functional characteristics such as a high modulus of elasticity, high rigidity, and large internal loss. Materials such as paper pulp sheets, metal sheets, and resin sheets have traditionally been used to provide these characteristics. However, conventional speaker diaphragms do not necessarily fully satisfy the required characteristics. For example, paper pulp sheets have a moderate internal loss, but their modulus of elasticity and rigidity are insufficient, making it impossible to achieve a sufficient sound velocity. Metal sheets have high rigidity, but are heavy and have small internal loss, making them prone to generating inherent sounds unique to metal. Furthermore, resin sheets are lighter than metal sheets and have large internal loss, but their rigidity is insufficient, making it impossible to achieve a sufficient sound velocity.

[0003] Patent Document 1 describes an invention relating to a resin speaker diaphragm formed by injection molding a thermoplastic resin. In this invention, it is said that by incorporating a mica-based material into a polymer consisting only of propylene as the thermoplastic resin material, a resin speaker diaphragm that is lightweight yet has excellent rigidity can be obtained. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-363882 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been a growing demand for lighter and smaller speakers to be installed in vehicles, given the need for improved fuel efficiency and design. In this regard, the increased sound pressure achieved by reducing the weight of speaker diaphragms allows for the speaker's drive source to be made smaller and lighter, contributing to improved vehicle fuel economy and ease of installation. Lowering the output of in-vehicle audio equipment also contributes to reduced vehicle power consumption. For these reasons, lightweight resin sheets are effective as materials for speaker diaphragms used in in-vehicle speakers.

[0006] However, when the thickness of the resin sheet is reduced in pursuit of weight reduction, it becomes difficult to ensure the rigidity required for the speaker diaphragm. Furthermore, with the speaker diaphragm manufactured by injection molding as described in Patent Document 1, it is difficult to further reduce the thickness, and there is also the problem that sufficient weight reduction cannot be achieved. Therefore, there is still room for improvement from the perspective of increasing sound pressure while maintaining rigidity.

[0007] The present invention has been made to solve these conventional problems, and an object of the present invention is to provide a speaker diaphragm with high sound pressure, a method for manufacturing a speaker diaphragm, and a speaker. [Means for solving the problem]

[0008] In order to solve the above problems, the speaker diaphragm of the present invention comprises a reinforced fiber layer in which carbon fibers are randomly oriented in a thermoplastic resin, and thermoplastic resin layers arranged so as to sandwich the reinforced fiber layer.

[0009] According to the above configuration, the use of a resin material allows for weight reduction, while the randomly oriented carbon fibers provide the necessary rigidity for the speaker diaphragm. This allows for a speaker diaphragm with high sound pressure. Furthermore, since the reinforced fiber layer is sandwiched between thermoplastic resin layers, water penetration into the reinforced fiber layer is suppressed. This allows for the watertightness required for applications such as in-car speakers to be achieved.

[0010] In order to solve the above problems, the method for manufacturing a speaker diaphragm of the present invention is a method for manufacturing the speaker diaphragm, and includes a lamination step of laminating a nonwoven fabric sheet containing carbon fiber and a thermoplastic resin sheet to form a laminate, and a press molding step of press-molding the laminate in a mold.

[0011] According to the above-mentioned configuration, a speaker diaphragm that is thin and lightweight, has high sound pressure, and is excellent in watertightness can be easily formed. In order to solve the above-mentioned problems, a speaker of the present invention includes the above-mentioned speaker diaphragm.

[0012] According to the above configuration, a lightweight speaker with high sound pressure can be obtained. [Effects of the Invention]

[0013] According to the present invention, a speaker diaphragm with high sound pressure and a speaker can be obtained. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 2 is a cross-sectional view of a vibration system to which the speaker diaphragm of the present embodiment is attached. [Figure 2] An enlarged cross-sectional view of a speaker diaphragm. [Figure 3] FIG. 10 is a diagram showing the acoustic characteristics of a laminated structure of a reinforcing fiber layer and a thermoplastic resin layer. [Figure 4] FIG. 10 is a diagram illustrating a frequency spectrum in a test example. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A speaker diaphragm (hereinafter referred to as a diaphragm) embodying the present invention will be described below. A diaphragm 1 of this embodiment is applied to an in-vehicle speaker that is installed in a vehicle.

[0016] As shown in Fig. 1, the diaphragm 1 of this embodiment has a cone shape. The outer periphery of the diaphragm 1 is supported by an edge 2, and the center of the diaphragm 1 is supported by a damper 4 fixed to a frame 3. A center cap 5 is attached to the center of the diaphragm 1, and a voice coil 6 for passing an acoustic signal current is bonded to it. These components constitute the vibration system of the speaker, and the outer periphery of the vibration system is supported by the frame 3.

[0017] Since the diaphragm 1 is a component that determines the acoustic characteristics, the selection of the material is important. As shown in FIG. 2, the diaphragm 1 of this embodiment has a laminated structure including a reinforcing fiber layer 10 in which carbon fibers 11 are oriented in a thermoplastic resin, and a thermoplastic resin layer 20 disposed so as to sandwich the reinforcing fiber layer 10. The reinforcing fiber layer 10 is formed by randomly oriented relatively short carbon fibers 11 in a thermoplastic resin. The length of the carbon fibers 11 is preferably approximately 3 to 13 mm, and more preferably 5 to 7 mm. When the length of the carbon fibers 11 is approximately 13 mm or less, the carbon fibers 11 are less likely to become biased in the thermoplastic resin, and the carbon fibers 11 are more appropriately dispersed, compared to when the carbon fibers 11 are longer. This results in a better dispersion of the carbon fibers 11 in the molded diaphragm 1. Furthermore, when the length of the carbon fibers 11 is approximately 3 mm or more, the rigidity of the diaphragm 1 is improved, compared to when the carbon fibers 11 are shorter. Diaphragm 1 has reinforcing fiber layer 10 in which carbon fibers 11 of this length are randomly oriented, which makes it possible to achieve both a reduction in weight of diaphragm 1 and an improvement in the rigidity required of diaphragm 1. This allows for a diaphragm 1 with excellent sound pressure.

[0018] There are no particular limitations on the material of the thermoplastic resin that constitutes the reinforcing fiber layer 10. Examples of such materials include polypropylene, polyethylene, polyamide, polyvinyl chloride, and polycarbonate.

[0019] The thermoplastic resin layers 20 are laminated on both sides of the reinforcing fiber layer 10 so as to sandwich the reinforcing fiber layer 10. Therefore, the carbon fibers 11 oriented in the reinforcing fiber layer 10 are not exposed on the surface of the diaphragm 1, which prevents moisture such as water or water vapor from penetrating into the interior of the diaphragm 1 and ensures the watertightness of the diaphragm 1. The type of thermoplastic resin that constitutes the thermoplastic resin layer 20 is not particularly limited. It is preferable that the thermoplastic resin that constitutes the reinforcing fiber layer 10 and the thermoplastic resin that constitutes the thermoplastic resin layer 20 are the same type.

[0020] The boundary between the reinforcing fiber layer 10 and the thermoplastic resin layer 20 may or may not be clearly distinguishable. This is because, in the manufacturing process described later, the thermoplastic resin constituting the reinforcing fiber layer 10 and the thermoplastic resin constituting the thermoplastic resin layer 20 may be thermally melted and integrated, making the boundary therebetween difficult to clearly recognize. For this reason, the outer surface side of the portion where the carbon fibers 11 are present is defined as the thermoplastic resin layer 20, and the portion where the carbon fibers 11 are present is defined as the reinforcing fiber layer 10.

[0021] 2, the presence of thermoplastic resin layer 20 prevents carbon fibers 11 in reinforcing fiber layer 10 from being exposed on the surface of diaphragm 1. The presence of thermoplastic resin layer 20 on the surface of diaphragm 1 ensures the watertightness of diaphragm 1.

[0022] The weight of the diaphragm 1 having the reinforcing fiber layer 10 and the thermoplastic resin layer 20 is 60 g / m 2 More than 100g / m 2 Preferably, it is 70 g / m or less. 2 More than 90g / m 2 It is more preferable that the weight is within this range. When compared to conventional diaphragms made of thermoplastic resin, the sound pressure in the mid-range is increased, resulting in a clearer sound. Furthermore, the necessary rigidity is imparted to the diaphragm 1, improving its physical strength, and the increase in sound pressure in the high-range becomes more pronounced.

[0023] The density of diaphragm 1 is 0.5 g / cm 3More than 1.0g / cm 3 It is preferable that the concentration is 0.6 g / cm or less. 3 More than 0.9g / cm 3 With a density in this range, sound pressure increases by approximately 3 dB or more in the midrange and by approximately 10 dB or more in the treble range compared to diaphragms made of conventional thermoplastic resin.

[0024] The thickness of diaphragm 1 is preferably 200 μm or less, and more preferably 100 μm or less. As will be explained later, diaphragm 1 can be formed by press molding to reduce the thickness, resulting in a diaphragm 1 that is lightweight yet has an appropriate basis weight and density and excellent rigidity.

[0025] Next, a method for manufacturing the diaphragm 1 will be described. The manufacturing process of diaphragm 1 includes a lamination step of laminating a nonwoven fabric sheet containing carbon fiber and a thermoplastic resin sheet to form a laminate, and a press molding step of press molding the laminate in a mold.

[0026] The nonwoven fabric sheet to be laminated in the lamination step is a nonwoven fabric sheet containing thermoplastic resin fibers and carbon fibers (hereinafter referred to as a carbon fiber nonwoven fabric sheet). The carbon fiber nonwoven fabric sheet may be formed by any of the conventionally known dry methods or wet methods, and contains thermoplastic resin fibers and carbon fibers intertwined therein.

[0027] The Vf (Fiber Volume Content (%)) of the carbon fiber nonwoven fabric sheet used in the lamination process is preferably 15% to 45%, and more preferably 25% to 35%. When Vf is within this range, the carbon fibers are adequately dispersed, preventing uneven distribution of the carbon fibers in the carbon fiber nonwoven fabric sheet. This ensures that the carbon fibers are well dispersed in the molded diaphragm 1.

[0028] In the lamination process, a carbon fiber nonwoven fabric sheet cut to the same shape and two thermoplastic resin sheets are prepared, and the thermoplastic resin sheets are laminated on both sides of the carbon fiber corroded sheet to form a laminate. At this time, pre-sheet molding may be performed if necessary. Pre-sheet molding is a process in which the laminate is pressed into a flat plate prior to press molding. By pre-sheet molding, the carbon fiber nonwoven fabric sheet and the thermoplastic resin sheet are temporarily bonded, preventing them from slipping apart.

[0029] Next, the laminate is placed in a mold in which a cavity in the shape of diaphragm 1 is formed, and press molding is performed. By press molding the laminate, the thermoplastic resin constituting the carbon fiber nonwoven fabric sheet and the thermoplastic resin constituting the thermoplastic resin sheet are thermally melted and integrated, and diaphragm 1 in which reinforcing fiber layer 10 and thermoplastic resin layer 20 are laminated is formed.

[0030] The temperature, pressure, pressing time, etc. during press molding can be set as appropriate. These can be adjusted according to the type of thermoplastic resin fiber that makes up the carbon fiber nonwoven fabric sheet and the type of thermoplastic resin that makes up the thermoplastic resin sheet. Furthermore, it is preferable to set the temperature, pressure, pressing time, etc. during press molding so that the thermoplastic resin that makes up the thermoplastic resin layer 20 and the thermoplastic resin that makes up the reinforcing fiber layer 10 do not completely integrate with each other. By setting the thermoplastic resin layer 20 to be present on the surface of the diaphragm 1, a diaphragm 1 that is guaranteed to be watertight can be obtained.

[0031] During press molding, portions of the carbon fiber nonwoven fabric sheet and the thermoplastic resin sheet are thermally melted and integrated near the boundary between these sheets, resulting in a mixture of the thermoplastic resin derived from the carbon fiber nonwoven fabric sheet and the thermoplastic resin derived from the thermoplastic resin sheet. As a result, in the diaphragm 1, the thermoplastic resin constituting the reinforcing fiber layer 10 and the thermoplastic resin constituting the thermoplastic resin layer 20 are thermally melted and integrated, making the boundary between them indistinguishable. Therefore, the reinforcing fiber layer 10 may be formed almost entirely from the carbon fiber nonwoven fabric sheet, or may be formed with the carbon fiber nonwoven fabric sheet and the thermoplastic resin derived from the thermoplastic resin sheet mixed together. Similarly, the thermoplastic resin layer 20 may be formed almost entirely from the thermoplastic resin sheet, or may be formed with the thermoplastic resin sheet and the thermoplastic resin derived from the carbon fiber nonwoven fabric sheet mixed together.

[0032] After press molding, the laminate is removed from the mold, and the excess peripheral portion is cut off, thereby obtaining the diaphragm 1. Next, the function of the diaphragm 1 of this embodiment will be described.

[0033] As shown in Figure 1, when an acoustic signal current is input to the voice coil 6 from outside the speaker, the voice coil 6 oscillates according to the value of the input current. The amplitude of the voice coil 6 also vibrates the diaphragm 1. The vibration of the diaphragm 1 vibrates the surrounding air, generating sound waves.

[0034] The diaphragm 1 of this embodiment includes a reinforcing fiber layer 10 in which carbon fibers 11 are oriented in random directions. This prevents the carbon fibers 11 from overlapping excessively, resulting in a thinner reinforcing fiber layer 10. This reduces the overall thickness of the diaphragm 1 and reduces its weight, resulting in high sound pressure. Furthermore, the inclusion of carbon fibers 11 imparts rigidity to the diaphragm 1, allowing for a sufficient sound velocity.

[0035] In this regard, known fiber-reinforced resin diaphragms include prepregs in which woven or knitted carbon fibers are impregnated with thermoplastic resin, and prepregs in which long carbon fibers are oriented in one direction. Diaphragms molded from such prepregs are prone to pinholes due to undulations caused by the carbon fibers. Suppressing pinholes requires a certain amount of resin, which tends to increase the thickness and thus the weight. While rigid, they do not produce high sound pressure. The diaphragm 1 of this embodiment has a laminated structure in which thermoplastic resin layers 20 sandwich the reinforcing fiber layer 10, covering pinholes in the reinforcing fiber layer 10. This suppresses leakage of air vibrations due to pinholes when the vibrations of the diaphragm 1 vibrate the surrounding air. This allows for a thin and lightweight diaphragm 1 with a reduced amount of resin to efficiently convert the vibrations of the diaphragm 1 into air vibrations, thereby increasing the sound pressure of the diaphragm 1.

[0036] Furthermore, in the diaphragm 1 of this embodiment, the carbon fibers 11 in the reinforcing fiber layer 10 are oriented in a well-dispersed state. Therefore, when the diaphragm 1 vibrates, effective internal friction occurs due to the carbon fibers 11 inside the diaphragm 1, resulting in excellent internal loss.

[0037] Next, the effects of the diaphragm 1 of this embodiment will be described. (1) The diaphragm 1 of this embodiment includes a reinforcing fiber layer 10 in which carbon fibers 11 are randomly oriented in a thermoplastic resin, and a thermoplastic resin layer 20 arranged to sandwich the reinforcing fiber layer 10. Therefore, the randomly oriented carbon fibers 11 can impart rigidity to the diaphragm 1 while achieving a reduction in weight. This allows the sound pressure of the diaphragm 1 to be increased.

[0038] (2) The reinforced fiber layer 10 is sandwiched between the thermoplastic resin layers 20, and the carbon fibers 11 in the reinforced fiber layer 10 are not exposed on the surface of the diaphragm 1. This prevents water from penetrating into the reinforced fiber layer 10, achieving the watertightness required for applications such as in-car speakers.

[0039] (3) The manufacturing method of the diaphragm 1 of this embodiment includes a lamination step of laminating a carbon fiber nonwoven fabric sheet containing carbon fiber 11 with a thermoplastic resin sheet to form a laminate, and a press molding step of press-molding the laminate in a mold. Therefore, it is possible to make the diaphragm thinner than diaphragms made by injection molding. A lightweight, watertight speaker diaphragm can be easily molded.

[0040] The above embodiment can be modified as follows: The above embodiment and the following modifications can be applied in combination with each other within the scope of technical compatibility. The diaphragm 1 may have a layer configuration other than the reinforcing fiber layer 10 and the thermoplastic resin layer 20. For example, a decorative layer may be provided on the surface of the thermoplastic resin layer 20, or a reinforcing layer, adhesive layer, etc. Even when these layers are provided, by adjusting the basis weight, density, thickness, etc. within predetermined ranges, the diaphragm 1 can be lightweight, have excellent rigidity, and produce high sound pressure.

[0041] The diaphragm 1 may be applied to devices other than car speakers. Next, the technical ideas that can be understood from the above-described embodiment and modified examples will be described below. (A) A reinforced fiber layer in which carbon fibers are randomly oriented in a thermoplastic resin, and a thermoplastic resin layer disposed so as to sandwich the reinforced fiber layer, and the density is 0.5 g / cm 3 More than 1.0g / cm 3 The following is a speaker diaphragm.

[0042] By having the density within the above range, not only can high sound pressure be achieved in the mid-range, but also sounds with good extension in the high-range can be achieved. (b) A speaker diaphragm having a thickness of 200 μm or less, comprising a reinforced fiber layer in which carbon fibers are randomly oriented in a thermoplastic resin and thermoplastic resin layers arranged so as to sandwich the reinforced fiber layer.

[0043] A thickness of 200 μm or less makes it possible to obtain a diaphragm that is lightweight and has high sound pressure. (c) A speaker diaphragm comprising a reinforcing fiber layer in which carbon fibers are randomly oriented in a thermoplastic resin, and thermoplastic resin layers arranged so as to sandwich the reinforcing fiber layer, the length of the carbon fibers being approximately 3 to 10 mm.

[0044] By including a reinforced fiber layer in which carbon fibers having lengths within the above range are randomly oriented, it is possible to achieve both a lighter diaphragm weight and improved rigidity required of the diaphragm, resulting in a diaphragm with excellent sound pressure. [Example]

[0045] <Selection of diaphragm material> First, taking into consideration that the sound pressure characteristics of a diaphragm are affected by its mass and thickness, we created the following sheet-like samples to select the diaphragm material and evaluated their performance.

[0046] (Sample 1) Sample 1 was prepared by laminating a polycarbonate (PC) thermoplastic resin sheet on both sides of a carbon fiber nonwoven fabric sheet in which carbon fibers were impregnated with polycarbonate and press-molding the sheet. The carbon fiber nonwoven fabric sheet was prepared by a wet method in a state in which carbon fibers with a length of approximately 6 mm and polycarbonate fibers were suspended. The basis weight of the carbon fiber nonwoven fabric sheet was 112 g / m. 2 , and Vf was 35%. The total thickness of Sample 1 was about 150 μm.

[0047] (Sample 2) Sample 2 was prepared by laminating polypropylene sheets as thermoplastic resin sheets on both sides of a carbon fiber nonwoven fabric sheet in which carbon fibers were impregnated with polypropylene (PP). The carbon fiber nonwoven fabric sheet was prepared by a wet method in a state in which carbon fibers with a length of approximately 6 mm and polypropylene fibers were suspended. The basis weight of the carbon fiber nonwoven fabric sheet was 70 g / m. 2 , and Vf is 25%. The total thickness of Sample 2 is approximately the same as that of Sample 1.

[0048] (Sample 3) A carbon fiber nonwoven fabric sheet in which carbon fibers were impregnated with polypropylene was laminated on both sides with polypropylene sheets as thermoplastic resin sheets and press-molded to be used as Sample 3. The carbon fiber nonwoven fabric sheet was prepared by a wet method, and the length of the carbon fibers in the carbon fiber nonwoven fabric sheet was approximately 6 mm, and the basis weight was 70 g / m. 2 , Vf30%. The total thickness of Sample 3 is approximately the same as that of Sample 1.

[0049] (Sample 4) A carbon fiber nonwoven fabric sheet in which carbon fibers were impregnated with polypropylene was laminated on both sides with polypropylene sheets as thermoplastic resin sheets and press-molded to be used as Sample 4. The carbon fiber nonwoven fabric sheet was prepared by a wet method, and the length of the carbon fibers in the carbon fiber nonwoven fabric sheet was approximately 6 mm, and the basis weight was 70 g / m. 2 The total thickness of Sample 4 was approximately the same as that of Sample 1.

[0050] (Sample 5) A carbon fiber reinforced resin sheet material with an epoxy resin matrix (Tenax (registered trademark) prepreg product number 112, manufactured by Teijin Limited) was press-molded to prepare Sample 5. The total thickness of Sample 5 was approximately the same as that of Sample 1.

[0051] (Sample 6) The polypropylene sheet was used as Sample 6. The total thickness of Sample 6 was approximately the same as that of Sample 1.

[0052] The density, modulus of elasticity, internal loss, and sound velocity of each sample were measured by the vibrating reed method to evaluate the acoustic properties as a diaphragm. The measurement results are shown in Table 1.

[0053] [Table 1] As can be seen from Table 1, Samples 1 to 4, which were formed by laminating and press-molding carbon fiber nonwoven fabric sheets and thermoplastic resin sheets, had lower densities and were lighter than carbon fiber reinforced resin sheet materials and polypropylene sheets. Among them, Samples 2 to 4, which were formed by laminating and press-molding carbon fiber nonwoven fabric sheets and polypropylene sheets, were 54.0%, 69.8%, and 71.7% lighter than Sample 5, which was a carbon fiber reinforced resin sheet material. These results demonstrate that when a diaphragm formed by laminating and press-molding a carbon fiber nonwoven fabric sheet and a thermoplastic resin sheet is used, it can produce higher sound pressure than a diaphragm made of so-called carbon fiber reinforced resin prepreg, in which the long carbon fibers are oriented in one direction, or a thermoplastic resin sheet.

[0054] The results of the internal loss and sound velocity for each sample are shown in Figure 3. Samples 1 to 4 had a larger internal loss than Sample 5, which used a carbon fiber reinforced resin sheet material with a high elastic modulus, and a larger sound velocity than Sample 6, which used a polypropylene sheet with a low elastic modulus. These results show that when Samples 1 to 4, which have a reinforced fiber layer with randomly oriented carbon fibers and thermoplastic resin layers laminated on both sides of the reinforced fiber layer, are used, a diaphragm with less resonance and better balanced acoustic characteristics can be obtained compared to when Sample 5 is used. Note that the basis weight is 112 g / m 2 In Sample 1, in which the carbon fiber nonwoven fabric sheet was laminated, the total weight was approximately 100 g / m 2 The weight of the diaphragm is 100g / m 2 It was found that the following would result in a diaphragm with good internal loss and sound velocity.In Figure 3, the ranges of acoustic characteristics of diaphragms made from conventionally used paper pulp, metal, and resin materials are shown enclosed by dotted lines, solid lines, and two-dot chain lines.

[0055] <Creating a diaphragm> Based on the knowledge gained from material selection, we actually created a diaphragm and evaluated its acoustic characteristics. (Test Example 1) Weight 60g / m 2A flat sheet, consisting of a 15 μm thick polypropylene sheet laminated on each side of a carbon fiber nonwoven fabric sheet with a Vf of 35%, was placed in a mold with a cavity shaped like a diaphragm. The sheet was heated while pressed at room temperature in the mold, and then press-molded at a temperature of 180°C and a pressure of 5 MPa for 5 minutes to obtain a diaphragm. The length of the carbon fibers in the carbon fiber nonwoven fabric sheet was approximately 6 mm. The total basis weight, total thickness, density, and mass of the obtained diaphragm were measured. The elastic modulus, internal loss, and sound velocity were also measured using the vibrating reed method. The results are shown in Table 2. The same applies below.

[0056] (Test Example 2) A diaphragm was obtained by laminating 10 μm thick polypropylene sheets on both sides of a carbon fiber nonwoven fabric sheet similar to that used in Test Example 1, and press-molding the resulting sheet under the same conditions as in Test Example 1. The measurement items for the obtained diaphragm were the same as those in Test Example 1.

[0057] (Test Example 3) Weight 60g / m 2 A diaphragm was obtained by laminating 10 μm thick polypropylene sheets on both sides of a carbon fiber nonwoven fabric sheet with a Vf of 25% and press-molding the resulting flat sheet under the same conditions as in Test Example 1. The length of the carbon fibers in the carbon fiber nonwoven fabric sheet was approximately 6 mm.

[0058] (Test Example 4) Weight 50g / m 2 A 5 μm thick polypropylene nonwoven fabric sheet was laminated on both sides of a carbon fiber nonwoven fabric sheet with a Vf of 35%, and the laminate was pressed into a flat plate (pre-sheet molding). A 10 μm thick polypropylene nonwoven fabric sheet was laminated on both sides of the pre-sheet molded sheet, and the sheet was placed in a mold having a cavity in the shape of a diaphragm. The sheet was press-molded under the same conditions as in Test Example 1 to obtain a diaphragm. The length of the carbon fibers in the carbon fiber nonwoven fabric sheet was approximately 6 mm.

[0059] (Test Example 5) The same procedure as in Test Example 4 was carried out except that the thickness of each of the polypropylene nonwoven fabric sheets laminated on both sides of the pre-formed sheet was 15 μm.

[0060] (Test Example 6) Weight 50g / m 2 A 5 μm thick polypropylene sheet was laminated on both sides of a carbon fiber nonwoven fabric sheet with a Vf of 35% to form a pre-sheet. The surface of the pre-sheet was heated for 10 seconds with an IR heater adjusted to 350°C, and then immediately press-molded at a pressure of 0.2 MPa for 5 seconds to obtain a diaphragm. The length of the carbon fibers in the carbon fiber nonwoven fabric sheet was approximately 6 mm.

[0061] (Test Example 7) Weight 50g / m 2 A 5 μm thick polypropylene sheet was laminated on both sides of a carbon fiber nonwoven fabric sheet with a Vf of 35%, and pre-molded. The diaphragm was then obtained by press molding under the same conditions as in Test Example 1. The length of the carbon fibers in the carbon fiber nonwoven fabric sheet was approximately 6 mm.

[0062] (Comparative Example 1) A diaphragm was obtained by laminating only the polypropylene sheet in a mold and press-molding under the same conditions as in Test Example 1. The total basis weight, total thickness, density, and mass of the diaphragm are as shown in Table 2.

[0063] (Comparative Example 2) The diaphragm for current in-car speakers was made by injection molding polypropylene in a mold (KFC-1696PS, manufactured by JVC Kenwood Corporation). The total basis weight, total thickness, density, and mass of the diaphragm are shown in Table 2.

[0064] [Table 2] (Measurement of sound pressure on each diaphragm) Sound pressure was measured for each diaphragm in Test Examples 1 to 7 and Comparative Examples 1 and 2. Sound pressure measurements were performed using the frequency response sine wave method specified in JEITA standard RC-8124C of the Japan Electronics and Information Technology Industries Association (JEITA), measuring sound pressure at 500 Hz, which is the mid-range, and sound pressure at 16 kHz, which is the treble range. Furthermore, using the obtained sound pressure measurement results, the average sound pressure was calculated within the frequency ranges of 450 to 560 Hz, which are the cutoff frequencies of 1 / 3 octave frequencies centered around 500 Hz in the mid-range, and 14 to 18 kHz, which are the cutoff frequencies of 1 / 3 octave frequencies centered around 16 kHz in the treble range.

[0065] [Table 3] The sound pressure characteristics of the diaphragms of Test Examples 1 to 7 were evaluated in comparison with the sound pressure characteristics of the current product, Comparative Example 2. The evaluation criteria were as follows.

[0066] ◎: Sound pressure is increased by more than 3dB in the mid-range and more than 10dB in the high-range compared to the current model. 〇: Sound pressure is increased by more than 3dB in the mid-range and more than 5dB in the high-range compared to the current model. △: Sound pressure is more than 1dB higher in the mid-range than the current model.

[0067] As can be seen from Tables 2 and 3, the diaphragms of Test Examples 1 to 7, which had a reinforced fiber layer with randomly oriented carbon fibers and thermoplastic resin layers laminated on both sides of the reinforced fiber layer, had higher sound pressure in the mid-range compared to Comparative Example 2, which is a current speaker diaphragm. In particular, Test Examples 1 to 5 had a 3 dB or more increase in sound pressure compared to Comparative Example 2, which means that the increase in sound pressure in the frequency band similar to that of a human voice was significant. These were highly evaluated as performance required for speaker diaphragms.

[0068] Compared with the diaphragm of Comparative Example 1, which was molded solely from a polypropylene sheet to have a similar thickness, the diaphragms of Test Examples 1 to 7 showed no change in sound pressure in the frequency range of 450 to 560 Hz shown in Table 3, but showed a significant increase in sound pressure in the frequency range of 300 to 450 Hz. FIG. 4 shows the frequency spectra of Test Example 3 and Comparative Examples 1 and 2. As a result, the diaphragm of Test Example 3 showed a maximum increase in sound pressure of about 5 dB in the frequency range of 300 to 450 Hz compared to the diaphragm of Comparative Example 1. The diaphragm of Comparative Example 1 lacked rigidity due to the absence of carbon fiber, resulting in insufficient strength and causing the diaphragm to vibrate in a bending manner. It is believed, however, that the inclusion of carbon fiber derived from the carbon fiber nonwoven fabric sheet ensured the necessary rigidity for the diaphragm.

[0069] In addition, from Tables 2 and 3, the weight of the diaphragm is 60 g / m 2 The diaphragms of Test Examples 1 to 5 described above showed a significant increase in sound pressure in the midrange of 3 dB or more compared to the diaphragm of Comparative Example 2, a current product. Furthermore, the sound pressure in the high-frequency range was increased by 5 dB or more compared to the current product. The sound pressure increased in the frequency range of 14 to 18 kHz, a phenomenon that is significantly different from diaphragms made of, for example, paper pulp. It is believed that the inclusion of carbon fibers derived from the nonwoven fabric sheet ensures the necessary rigidity for the diaphragm, and the improved physical strength contributes to the increase in sound pressure in the high-frequency range. As shown in Figure 4, the diaphragm of Test Example 3 showed a significant increase in sound pressure in the frequency range of 3 to 18 kHz compared to the diaphragms of Comparative Examples 1 and 2.

[0070] From Tables 2 and 3, the density is 0.6 g / cm 3 More than 0.9g / cm 3 In the diaphragms of the following test examples 1 to 3, the sound pressure in the midrange was increased by 3 dB or more, and the sound pressure in the treble range was increased by 10 dB or more, compared to the diaphragm of the current product, comparative example 2. With the density in this range, the increase in sound pressure in the treble range was remarkable.

[0071] Furthermore, in the diaphragms of Test Examples 2 and 3, which had a thickness of 100 μm or less, the sound pressure in the high frequency range was increased by approximately 15 dB compared to the diaphragm of Comparative Example 2. [Explanation of symbols]

[0072] 1... Diaphragm (speaker diaphragm)

Claims

1. a reinforcing fiber layer in which carbon fibers are randomly oriented in a thermoplastic resin; thermoplastic resin layers arranged so as to sandwich the reinforcing fiber layer; Equipped with At the boundary between the reinforcing fiber layer and the thermoplastic resin layer, a mixed resin region is formed in which the thermoplastic resin derived from the reinforcing fiber layer and the thermoplastic resin derived from the thermoplastic resin layer are mixed and integrated, A speaker diaphragm in which a resin region is formed in the reinforcing fiber layer that is not mixed with the thermoplastic resin derived from the thermoplastic resin layer, and a resin region is formed in the thermoplastic resin layer that is not mixed with the thermoplastic resin derived from the reinforcing fiber layer.

2. a lamination step of laminating a nonwoven fabric sheet containing thermoplastic resin fibers and carbon fibers and thermoplastic resin sheets on both sides of the nonwoven fabric sheet so as to sandwich the nonwoven fabric sheet to form a laminate; a press molding step of press-molding the laminate in a mold; Equipped with In the press molding process, at least one of the temperature, pressure, and pressing time during press molding is set so that a portion of the nonwoven fabric sheet and the thermoplastic resin sheet are thermally melted at the boundary between the nonwoven fabric sheet and the thermoplastic resin sheet to form a mixed resin region in which the thermoplastic resin derived from the nonwoven fabric sheet and the thermoplastic resin derived from the thermoplastic resin sheet are mixed, and a resin region in which the thermoplastic resin derived from the thermoplastic resin sheet is not mixed is formed in the nonwoven fabric sheet, and a resin region in which the thermoplastic resin derived from the nonwoven fabric sheet is not mixed is formed in the thermoplastic resin sheet.

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

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