JP7779646B2 - Speaker diaphragm, speaker diaphragm manufacturing method, and speaker - Google Patents

Description

The present invention relates to a speaker diaphragm, a method for manufacturing a speaker diaphragm, and a speaker.

Speaker diaphragms require functional properties 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 make speaker diaphragms with these characteristics. However, the reality is that conventional speaker diaphragms do not necessarily fully satisfy the required characteristics. For example, while paper pulp sheets have a moderate internal loss, their modulus of elasticity and rigidity are insufficient, making it impossible to achieve a sufficient sound speed. Metal sheets have high rigidity, but are heavy and have small internal loss, making them prone to generating metal-specific sounds. 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 speed.

Patent Document 1 describes an invention relating to a resin speaker diaphragm formed by injection molding a thermoplastic resin. It claims that by incorporating a mica-based material into a polymer consisting solely of propylene as the thermoplastic resin material, a lightweight resin speaker diaphragm with excellent rigidity can be obtained.

Japanese Patent Application Laid-Open No. 2004-363882

In recent years, there has been a growing demand for lighter and smaller speakers to be installed in vehicles, given their 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 easier installation. Lowering the output of in-car audio equipment also contributes to reduced vehicle power consumption. For these reasons, lightweight resin sheets are effective as a material for speaker diaphragms used in in-car speakers.

However, reducing the thickness of the resin sheet in pursuit of weight reduction presents the problem of making it difficult to ensure the rigidity required for a speaker diaphragm. Furthermore, with speaker diaphragms made by injection molding, such as those described in Patent Document 1, it is difficult to further reduce the thickness, making it difficult to achieve sufficient weight reduction. Therefore, there is still room for improvement in terms of increasing sound pressure while maintaining rigidity.

The present invention was made to solve these problems in the past, and its purpose is to provide a speaker diaphragm with high sound pressure, a method for manufacturing a speaker diaphragm, and a speaker.

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.

With the above configuration, the use of a resin material allows for weight reduction, while the randomly oriented carbon fibers provide the necessary rigidity for a speaker diaphragm. This allows for a speaker diaphragm with high sound pressure. Furthermore, because 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.

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

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.

The above configuration allows for a lightweight speaker with high sound pressure.

The present invention makes it possible to obtain a speaker diaphragm and speaker that produce high sound pressure.

FIG. 2 is a cross-sectional view of a vibration system to which the speaker diaphragm of the present embodiment is attached. An enlarged cross-sectional view of a speaker diaphragm. FIG. 10 is a diagram showing the acoustic characteristics of a laminated structure of a reinforcing fiber layer and a thermoplastic resin layer. FIG. 10 is a diagram illustrating a frequency spectrum in a test example.

The following describes a speaker diaphragm (hereinafter referred to as "diaphragm") that embodies the present invention. The diaphragm 1 of this embodiment is applied to an in-vehicle speaker that is installed in a vehicle.

As shown in Figure 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 carrying an acoustic signal current is adhered to it. These components form the vibration system of the speaker, and the outer periphery of the vibration system is supported by the frame 3.

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 reinforced fiber layer 10 in which carbon fibers 11 are oriented in a thermoplastic resin, and a thermoplastic resin layer 20 sandwiching the reinforced fiber layer 10. The reinforced 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 compared to when the carbon fibers 11 are longer than this length, and the carbon fibers 11 are more appropriately dispersed. 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 than this length. The diaphragm 1 has the reinforced fiber layer 10 in which the carbon fibers 11 of this length are randomly oriented, which makes it possible to achieve both a reduction in the weight of the diaphragm 1 and an improvement in the rigidity required of the diaphragm 1. This allows the diaphragm 1 to have excellent sound pressure.

The thermoplastic resin material that constitutes the reinforcing fiber layer 10 is not particularly limited. Examples of such materials include polypropylene, polyethylene, polyamide, polyvinyl chloride, and polycarbonate.

The thermoplastic resin layers 20 are laminated on both sides of the reinforced fiber layer 10, sandwiching the reinforced fiber layer 10. As a result, the carbon fibers 11 oriented in the reinforced fiber layer 10 are not exposed to 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. There are no particular restrictions on the type of thermoplastic resin that makes up the thermoplastic resin layer 20. It is preferable that the thermoplastic resin that makes up the reinforced fiber layer 10 and the thermoplastic resin that makes up the thermoplastic resin layer 20 are the same type.

The boundary between the reinforcing fiber layer 10 and the thermoplastic resin layer 20 may or may not be clearly distinguishable. This is because, during the manufacturing process described below, the thermoplastic resin that makes up the reinforcing fiber layer 10 and the thermoplastic resin that makes up the thermoplastic resin layer 20 may be thermally melted and integrated, making the boundary between them difficult to discern. For this reason, the area outer than the area where the carbon fibers 11 are present is defined as the thermoplastic resin layer 20, and the area where the carbon fibers 11 are present is defined as the reinforcing fiber layer 10.

As shown by the dotted line in Figure 2, the presence of the thermoplastic resin layer 20 prevents the carbon fibers 11 in the reinforcing fiber layer 10 from being exposed on the surface of the diaphragm 1. The presence of the thermoplastic resin layer 20 on the surface of the diaphragm 1 ensures the watertightness of the diaphragm 1.

The basis weight of the diaphragm 1 including the reinforcing fiber layer 10 and the thermoplastic resin layer 20 is preferably 60 g/ ^m² or more and 100 g/ ^m² or less, and more preferably 70 g/ ^m² or more and 90 g/ ^m² or less. When the basis weight is within this range, compared to conventional diaphragms made of thermoplastic resin, the sound pressure in the mid-range is increased, resulting in a clearer sound. In addition, the necessary rigidity of the diaphragm 1 is imparted, improving physical strength, and the increase in sound pressure in the high-frequency range is significant.

The density of diaphragm 1 is preferably 0.5 g/cm or ^more and 1.0 g/cm ^or less, and more preferably 0.6 g/cm or ^more and 0.9 g/cm or ^less . When the density is in this range, the sound pressure in the midrange increases by approximately 3 dB or more, and the sound pressure in the treble range increases by approximately 10 dB or more, compared to diaphragms made of conventional thermoplastic resin.

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

Next, a method for manufacturing the diaphragm 1 will be described.
The manufacturing process of the diaphragm 1 includes a lamination process in which a nonwoven fabric sheet containing carbon fiber and a thermoplastic resin sheet are laminated to form a laminate, and a press molding process in which the laminate is press molded in a mold.

The nonwoven fabric sheet to be laminated in the lamination process 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 either a conventional dry method or a wet method, and contains thermoplastic resin fibers and carbon fibers intertwined within it.

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%. A Vf within this range ensures adequate dispersion of the carbon fibers, preventing them from becoming unevenly distributed in the carbon fiber nonwoven fabric sheet. This ensures that the carbon fibers are well dispersed in the molded diaphragm 1.

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 stage, 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. Pre-sheet molding temporarily bonds the carbon fiber nonwoven fabric sheet and the thermoplastic resin sheet, preventing them from shifting from one another.

Next, the laminate is placed in a mold with a cavity in the shape of the diaphragm 1 and press-molded. By press-molding the laminate, the thermoplastic resin that makes up the carbon fiber nonwoven fabric sheet and the thermoplastic resin that makes up the thermoplastic resin sheet are thermally melted and integrated, forming the diaphragm 1 in which the reinforcing fiber layer 10 and the thermoplastic resin layer 20 are laminated.

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 fibers that make up the carbon fiber nonwoven fabric sheet and the type of thermoplastic resin that makes up the thermoplastic resin sheet. It is also 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 become completely integrated. By setting the thermoplastic resin layer 20 so that it is present on the surface of the diaphragm 1, a diaphragm 1 that is guaranteed to be watertight can be obtained.

During press molding, portions of the carbon fiber nonwoven fabric sheet and the thermoplastic resin sheet near their boundaries are thermally melted and integrated, 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 no longer clearly recognizable. Therefore, the reinforcing fiber layer 10 may be formed almost entirely from the portion derived from the carbon fiber nonwoven fabric sheet, or may be formed with the carbon fiber nonwoven fabric sheet mixed with the thermoplastic resin derived from the thermoplastic resin sheet. Similarly, the thermoplastic resin layer 20 may be formed almost entirely from the portion derived from the thermoplastic resin sheet, or may be formed with the thermoplastic resin sheet mixed with the thermoplastic resin derived from the carbon fiber nonwoven fabric sheet.

After the 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.

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. This amplitude of the voice coil 6 also causes the diaphragm 1 to vibrate. The vibration of the diaphragm 1 vibrates the surrounding air, generating sound waves.

The diaphragm 1 of this embodiment includes a reinforced fiber layer 10 in which carbon fibers 11 are oriented in random directions. This prevents excessive overlapping of the carbon fibers 11, resulting in a thinner reinforced 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.

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 undulations due to the carbon fibers, resulting in pinholes inside the diaphragm. Suppressing pinholes requires a certain amount of resin, which tends to increase the thickness and, consequently, weight. While rigid, these diaphragms do not achieve 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.

In addition, 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 is generated by the carbon fibers 11 inside the diaphragm 1, resulting in excellent internal loss.

Next, the effects of the diaphragm 1 of this embodiment will be described.
(1) The diaphragm 1 of this embodiment includes a reinforced 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 reinforced 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.

(2) The reinforced fiber layer 10 is sandwiched between 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.

(3) The manufacturing method for the diaphragm 1 of this embodiment includes a lamination process in which a carbon fiber nonwoven fabric sheet containing carbon fibers 11 is laminated with a thermoplastic resin sheet to form a laminate, and a press molding process in which the laminate is press-molded in a mold. This allows for a thinner wall compared to diaphragms made by injection molding. A lightweight, watertight speaker diaphragm can be easily molded.

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 a predetermined range, the diaphragm 1 can be lightweight, have excellent rigidity, and have high sound pressure.

The diaphragm 1 may be used in applications other than in-vehicle speakers.
Next, the technical ideas that can be understood from the above-described embodiment and modified examples will be described below.
(i) A speaker diaphragm having a density of 0.5 g/cm3 or more and 1.0 g/ ^cm3 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.

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.

By making the thickness 200 μm or less, a diaphragm that is lightweight and has high sound pressure can be obtained.
(c) A speaker diaphragm comprising a reinforced fiber layer in which carbon fibers are randomly oriented in a thermoplastic resin, and thermoplastic resin layers arranged to sandwich the reinforced fiber layer, wherein the length of the carbon fibers is approximately 3 to 10 mm.

By having a reinforced fiber layer in which carbon fibers with lengths within the above range are randomly oriented, it is possible to reduce the weight of the diaphragm while improving the rigidity required of the diaphragm. This results in a diaphragm with excellent sound pressure.

<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.

(Sample 1)
Sample 1 was prepared by laminating polycarbonate (PC) thermoplastic resin sheets 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 carbon fiber nonwoven fabric sheet had a basis weight of 112 g/ ^m2 and a Vf of 35%. The total thickness of Sample 1 was approximately 150 μm.

(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 carbon fiber nonwoven fabric sheet had a basis weight of 70 g/ ^m2 and a Vf of 25%. The total thickness of Sample 2 was approximately the same as that of Sample 1.

(Sample 3)
A carbon fiber nonwoven fabric sheet in which carbon fibers were impregnated with polypropylene was laminated on both sides of a polypropylene sheet as a thermoplastic resin sheet 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, the basis weight was 70 g/ ^m2 , and Vf was 30%. The total thickness of Sample 3 was approximately the same as that of Sample 1.

(Sample 4)
A carbon fiber nonwoven fabric sheet in which carbon fibers were impregnated with polypropylene was laminated on both sides of a polypropylene sheet as a thermoplastic resin sheet 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, the basis weight was 70 g/ ^m2 , and Vf was 36%. The total thickness of Sample 4 was approximately the same as that of Sample 1.

(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.

(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.

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

As can be seen from Table 1, Samples 1 to 4, which were formed by laminating and press-molding a carbon fiber nonwoven fabric sheet and a thermoplastic resin sheet, had lower densities and were lighter than carbon fiber reinforced resin sheet materials and polypropylene sheets. Among these, Samples 2 to 4, which were formed by laminating and press-molding a carbon fiber nonwoven fabric sheet and a polypropylene sheet, 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 achieve 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.

The internal loss and sound velocity results for each sample are shown in Figure 3. Samples 1 to 4 had higher internal loss than Sample 5, which used a carbon fiber reinforced resin sheet material with a high elastic modulus, and higher sound velocity than Sample 6, which used a polypropylene sheet with a low elastic modulus. These results indicate 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, diaphragms with less resonance and better balanced acoustic characteristics are obtained than when Sample 5 is used. Note that Sample 1, which is laminated with a carbon fiber nonwoven fabric sheet with a basis weight of 112 g/ ^m² , has a total basis weight of approximately 100 g/ ^m² . It was found that a diaphragm with a basis weight of 100 g/ ^m² or less provides a diaphragm with good internal loss and sound velocity. Note that in Figure 3, the ranges of acoustic characteristics of diaphragms made from conventionally used paper pulp materials, metal materials, and resin materials are indicated by dotted lines, solid lines, and two-dot chain lines.

<Creating a diaphragm>
Based on the knowledge gained from material selection, we actually created a diaphragm and evaluated its acoustic characteristics.
(Test Example 1)
A flat sheet was formed by laminating 15 μm thick polypropylene sheets on both sides of a carbon fiber nonwoven fabric sheet with a basis weight of 60 g/m ² and a Vf of 35%, and the resulting sheet was placed in a mold having 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 resulting 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.

(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.

(Test Example 3)
A diaphragm was obtained by laminating a 10 μm thick polypropylene sheet on each side of a carbon fiber nonwoven fabric sheet with a basis weight of 60 g/m ² and 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.

(Test Example 4)
A 5 μm-thick polypropylene nonwoven fabric sheet was laminated on both sides of a carbon fiber nonwoven fabric sheet with a basis weight of 50 g/m ² and a Vf of 35%, and 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 diaphragm-shaped cavity and press-molded under the same conditions as in Test Example 1 to obtain a diaphragm. The length of the carbon fiber in the carbon fiber nonwoven fabric sheet was approximately 6 mm.

(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.

(Test Example 6)
A 5 μm thick polypropylene sheet was laminated on both sides of a carbon fiber nonwoven fabric sheet with a basis weight of 50 g/m ² and 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 fiber in the carbon fiber nonwoven fabric sheet was approximately 6 mm.

(Test Example 7)
A pre-sheet was formed by laminating 5 μm thick polypropylene sheets on both sides of a carbon fiber nonwoven fabric sheet with a basis weight of 50 g/m ² and a Vf of 35%, followed by press molding 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.

(Comparative Example 1)
Only the polypropylene sheet was laminated in a mold and press-molded to obtain a diaphragm 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.

(Comparative Example 2)
The diaphragm for a current in-car speaker was made of polypropylene injection molded 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.

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

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:

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

Tables 2 and 3 show that the diaphragms of Test Examples 1 to 7, which have 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, a current speaker diaphragm. In particular, Test Examples 1 to 5 had an increase of more than 3 dB compared to Comparative Example 2, and it can be said that the increase in sound pressure in the frequency band corresponding to the human voice was significant. This was highly rated as the performance required for speaker diaphragms.

Compared to the diaphragm of Comparative Example 1, which was molded solely from a polypropylene sheet to achieve a similar thickness, the diaphragms of Test Examples 1 to 7 showed no observed change in sound pressure in the 450-560 Hz frequency range shown in Table 3, but showed a significant increase in sound pressure in the 300-450 Hz frequency range. Figure 4 shows the frequency spectra of Test Example 3 and Comparative Examples 1 and 2. This shows that the diaphragm of Test Example 3 showed a maximum increase in sound pressure of approximately 5 dB in the 300-450 Hz frequency range 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. However, it is believed that the inclusion of carbon fiber derived from the carbon fiber nonwoven fabric sheet ensures the necessary rigidity for the diaphragm.

Furthermore, Tables 2 and 3 show that the diaphragms of Test Examples 1 to ⁵ , which have a diaphragm weight of 60 g/m or more, exhibited a significant increase in sound pressure of 3 dB or more in the midrange compared to the diaphragm of Comparative Example 2, a current product. Furthermore, the sound pressure in the high-frequency range 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 formed from, 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 increased sound pressure in the high-frequency range. As shown in Figure 4, the diaphragm of Test Example 3 exhibited 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.

As can be seen from Tables 2 and 3, the diaphragms of Test Examples 1 to ³ , which had densities of 0.6 g/ ^cm3 or more and 0.9 g/cm3 or less, had a sound pressure increase of 3 dB or more in the midrange and a sound pressure increase of 10 dB or more in the treble range compared to the diaphragm of Comparative Example 2, which is the current product. With densities in this range, the increase in sound pressure in the treble range was remarkable.

Furthermore, the diaphragms of Test Examples 2 and 3, which had thicknesses of 100 μm or less, had a sound pressure increase of around 15 dB in the high-frequency range compared to the diaphragm of Comparative Example 2.

1... Diaphragm (speaker diaphragm)

Claims (3)

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