JP7383464B2 - Acoustic diaphragm and method for manufacturing the acoustic diaphragm - Google Patents

Description

The present invention relates to an acoustic diaphragm and a method for manufacturing an acoustic diaphragm.

2. Description of the Related Art As an acoustic diaphragm for use in audio equipment such as speakers and sonar sensors, a technique is known in which a laminate in which metal foil and thermoplastic resin film are laminated is used.
For example, Patent Document 1 discloses an acoustic diaphragm obtained by thermocompression-bonding a stack of aluminum metal foil and an unstretched thermoplastic resin film. As the unstretched thermoplastic resin film, a polyurethane thermoplastic resin film, a polyamide thermoplastic resin film, and a polyester thermoplastic resin film are used.

Patent No. 3911935

When manufacturing the acoustic diaphragm of Patent Document 1, an aluminum metal foil and an unstretched thermoplastic resin film are stacked together and heated to near the melting temperature of the unstretched thermoplastic resin film. A lamination process is performed in which the plastic resin film is pressure-bonded to the aluminum metal foil. Since the aluminum metal foil and the unstretched thermoplastic resin film that constitute the acoustic diaphragm have different coefficients of thermal expansion, large warpage occurs in the acoustic diaphragm obtained through the lamination process. Warpage of the acoustic diaphragm causes deterioration in workability when processing the acoustic diaphragm into a speaker shape or the like.

This invention was made in view of these circumstances, and its purpose is to provide an acoustic diaphragm that is less likely to warp.

An acoustic diaphragm that solves the above problems includes a metal foil and a thermoplastic resin film laminated on the metal foil, and the thermoplastic resin film has a linear expansion coefficient in the MD direction and a linear expansion coefficient in the TD direction. The ratio of the coefficient of linear expansion in the thickness direction to the coefficient of linear expansion of the smaller one is 3.0 or more and 10.0 or less, and the total basis weight of the metal foil and the thermoplastic resin film is 45 g/m or more and 150 g or ^more . / ^m2 or less.

The metal foil preferably has a specific gravity of 1.7 or more and 5.0 or less.
The difference between the smaller of the linear expansion coefficient in the MD direction and the linear expansion coefficient in the TD direction of the thermoplastic resin film and the linear expansion coefficient of the metal foil is 0 ppm/K or more and 15 ppm/K or less. It is preferable that there be.

It is preferable that the linear expansion coefficient of the metal foil is 5.0 ppm/K or more and 35 ppm/K or less.
It is preferable that the smaller of the linear expansion coefficient in the MD direction and the linear expansion coefficient in the TD direction of the thermoplastic resin film is 10 ppm/K or more and 50 ppm/K or less.

Preferably, at least one of the thermoplastic resin films adjacent to the metal foil is a polyimide film.
A method for manufacturing an acoustic diaphragm that solves the above problems includes a laminating step of thermocompression bonding the metal foil and the thermoplastic resin film.

According to the present invention, warpage occurring in the acoustic diaphragm can be suppressed.

FIG. 1 is a cross-sectional view of an acoustic diaphragm according to an embodiment. FIG. 3 is a cross-sectional view of a modified acoustic diaphragm. FIG. 3 is a cross-sectional view of a modified acoustic diaphragm.

An embodiment of the present invention will be described below.
As shown in FIG. 1, the acoustic diaphragm 10 is a laminate including a sheet-shaped metal foil 11 and a thermoplastic resin film 12 laminated on one main surface of the sheet-shaped metal foil 11. The acoustic diaphragm 10 is used as an acoustic vibration converting member in an audio device. Examples of audio equipment to which the acoustic diaphragm 10 is applied include speakers, sonar sensors, and microphones.

(metal foil)
Examples of the metal constituting the metal foil 11 include aluminum, titanium, magnesium, copper, and alloys thereof. Among these metals, metals whose specific gravity is preferably 1.7 or more and 5.0 or less, and more preferably 2.4 or more and 4.9 or less. In this case, sound quality is improved when the acoustic diaphragm 10 is applied to a speaker.

The linear expansion coefficient CTEM of the metal foil 11 is, for example, preferably 5.0 ppm/K or more and 35 ppm/K or less, more preferably 7.0 ppm/K or more and 30 ppm/K or less, and 8.0 ppm/K. More preferably, it is 28 ppm/K or less. By setting the linear expansion coefficient CTEM within the above range, the difference in linear expansion coefficient with the thermoplastic resin film 12 becomes smaller, and the effect of suppressing warping of the acoustic diaphragm 10 based on the difference in linear expansion coefficient is improved. do.

The thickness of the metal foil 11 is, for example, preferably 10 μm or more and 50 μm or less, more preferably 14 μm or more and 35 μm or less.
The basis weight of the metal foil 11 is, for example, preferably 27 g/m ² or more and 130 g/m ² or less, and more preferably 37 g/m ² or more and 90 g/m ² or less.

(thermoplastic resin film)
Specific examples of the thermoplastic resin film 12 include polyimide films such as multilayer aromatic polyimide films and single-layer polyimide films, polyetherimide films, polyester films (including liquid crystal films), polyamide films (including aramid films), Examples include vinyl ester film, fluorine thermoplastic resin film, polyetherketone film (including polyetheretherketone film), polyphenylsulfone film, and the like. A multilayer aromatic polyimide film is a non-pressure-adhesive aromatic polyimide film with a thermocompression-adhesive polyimide layer formed on both sides. Commercially available products can be used. Such a multilayer aromatic polyimide film is described, for example, in a patent document (Japanese Patent Laid-Open No. 2001-270033). Among these, it is particularly preferable that the thermoplastic resin film 12 is a polyimide film.

The thermoplastic resin film 12 may contain other components such as additives.
The thermoplastic resin film 12 may have voids inside a resin such as a foam.

The thermoplastic resin film 12 may have a structure in which it is combined with a non-thermoplastic resin film as long as it can be bonded to the metal foil 11 and does not impede the effects and acoustic properties of the invention. For example, it may have a multilayer structure in which the thermoplastic resin film 12 is adhered to one or both sides of a non-thermoplastic resin film, or the thermoplastic resin film 12 may be a sea component and the non-thermoplastic resin film may be an island component. It may also have a sea-island structure.

The thermoplastic resin film 12 has a ratio CTEZ/CTEX of the linear expansion coefficient CTEZ in the thickness direction to the linear expansion coefficient CTEX, which is the smaller of the linear expansion coefficient in the MD direction and the linear expansion coefficient in the TD direction, of 3.0 or more 10 .0 or less. Further, the ratio CTEZ/CTEX is preferably 4.0 or more and 9.5 or less, more preferably 5.0 or more and 9.0 or less.

When the ratio CTEZ/CTEX is 3.0 or more, it means that the thermoplastic resin film 12 is oriented in the plane direction to a level higher than a certain level, and thereby, warping that occurs in the acoustic diaphragm 10 can be suppressed. . Further, by setting the ratio CTEZ/CTEX to 10.0 or less, it is possible to suppress a decrease in durability of the thermoplastic resin film 12 against shearing in the plane direction, and to ensure extensibility in the plane direction. This improves the workability when processing the acoustic diaphragm 10. For example, the acoustic diaphragm 10 can be easily drawn into a predetermined shape such as a dome shape.

The linear expansion coefficient CTEX of the thermoplastic resin film 12 is, for example, preferably 10 ppm/K or more and 50 ppm/K or less, more preferably 12 ppm/K or more and 43 ppm/K or less, and 14 ppm/K or more and 35 ppm/K or less. It is more preferable that it is the following. By setting the linear expansion coefficient CTEX within the above range, stretchability in the plane direction is ensured, and workability when processing the acoustic diaphragm 10 is improved.

The thickness of the thermoplastic resin film 12 is, for example, preferably 12 μm or more and 90 μm or less, more preferably 16 μm or more and 75 μm or less.
The basis weight of the thermoplastic resin film 12 is, for example, preferably 18 g/m ² or more and 120 g/m ² or less, more preferably 22/m ² or more and 100 g/m ² or less.

(acoustic diaphragm)
In the acoustic diaphragm 10, it is preferable that the difference CTEX-M (absolute difference) between the linear expansion coefficient CTEX of the thermoplastic resin film 12 and the linear expansion coefficient CTEM of the metal foil 11 is 0 ppm/K or more and 15 ppm/K or less, More preferably, it is 0 ppm/K or more and 12 ppm/K or less. By setting the difference CTEX-M within the above range, the effect of suppressing warpage occurring in the acoustic diaphragm 10 is improved.

The thickness of the acoustic diaphragm 10 is, for example, preferably 22 μm or more and 100 μm or less, more preferably 25 μm or more and 85 μm or less.
The basis weight of the acoustic diaphragm 10, that is, the total basis weight of the metal foil 11 and the thermoplastic resin film 12, is 45 g/ ^m2 or more and 150 g/ ^m2 or less, and 45 g/ ^m2 or more and 130 g/ ^m2 or less. is preferred. By setting the basis weight of the acoustic diaphragm 10 within the above range, warpage occurring in the acoustic diaphragm 10 can be suppressed. Further, by setting the basis weight of the acoustic diaphragm 10 to 150 g/m ² or less, it is possible to suppress a decrease in sound pressure due to an increase in weight. By setting the basis weight of the acoustic diaphragm 10 to 45 g/m ² or more, the rigidity of the acoustic diaphragm 10 is improved, and self-supporting properties can be easily ensured even when used in audio equipment such as large speakers. Become.

In the acoustic diaphragm 10, the resin ratio, that is, the volume ratio of the thermoplastic resin film 12 to the metal foil 11 and the thermoplastic resin film 12 is preferably 60% or less, more preferably 40% or less. . By setting the resin ratio of the thermoplastic resin film 12 within the above range, warpage occurring in the acoustic diaphragm 10 can be effectively suppressed. Further, when the acoustic diaphragm 10 is applied to a speaker, it is possible to suppress warpage that occurs in the acoustic diaphragm 10 and improve sound quality at a high level. Note that the lower limit of the resin ratio of the thermoplastic resin film 12 is, for example, 10%.

It is preferable that the adhesive strength between the metal foil 11 and the thermoplastic resin film 12 in the acoustic diaphragm 10 is, for example, 0.4 N/mm or more. In this case, it is possible to suppress the occurrence of peeling when processing the acoustic diaphragm 10 into a predetermined shape.

The acoustic diaphragm 10 preferably has an internal loss tan δ of 0.02 or more and 0.08 or less. In this case, when the acoustic diaphragm 10 is applied to a speaker, the sound quality in the high frequency range and the sound quality in the low frequency range are improved.

The acoustic diaphragm 10 is processed into a predetermined shape, such as a flat plate shape or a dome shape, depending on its use, and is applied to an audio device.
The acoustic diaphragm 10 can be manufactured, for example, through a lamination process in which a metal foil 11 and a thermoplastic resin film 12 are stacked and bonded together under heat. The specific method of thermocompression bonding in the lamination step is not particularly limited, and for example, known methods such as a method using a roll type laminating device and a method using a double belt press device can be used.

Next, the effects of this embodiment will be described.
(1) The acoustic diaphragm 10 includes a metal foil 11 and a thermoplastic resin film 12 laminated on the metal foil 11. The ratio CTEZ/CTEX of the linear expansion coefficient CTEZ in the thickness direction to the linear expansion coefficient CTEX of the thermoplastic resin film 12 is 3.0 or more and 10.0 or less. The total basis weight of the metal foil 11 and the thermoplastic resin film 12 is 45 g/m ² or more and 150 g/m ² or less.

According to the above configuration, warpage occurring in the acoustic diaphragm 10 can be suppressed. This improves the workability when processing the acoustic diaphragm 10.
(2) The metal foil 11 has a specific gravity of 1.7 or more and 5.0 or less.

According to the above configuration, sound quality is improved when the acoustic diaphragm 10 is applied to a speaker.
(3) The difference CTEX-M between the linear expansion coefficient CTEX of the thermoplastic resin film 12 and the linear expansion coefficient CTEM of the metal foil 11 is 0 ppm/K or more and 15 ppm/K or less.

According to the above configuration, the effect of suppressing warpage occurring in the acoustic diaphragm 10 can be more significantly obtained.
(4) The linear expansion coefficient CTEM of the metal foil 11 is 5.0 ppm/K or more and 35 ppm/K or less.

According to the above configuration, it is easy to set the difference CTEX-M between the linear expansion coefficient CTEX of the thermoplastic resin film 12 and the linear expansion coefficient CTEM of the metal foil 11 within the above range.
(5) The linear expansion coefficient CTEX of the thermoplastic resin film 12 is 10 ppm/K or more and 50 ppm/K or less.

According to the above configuration, by ensuring stretchability in the plane direction, workability when processing the acoustic diaphragm 10 is improved.
(6) The resin ratio of the acoustic diaphragm 10 is 40% or less.

According to the above configuration, the effect of suppressing warpage occurring in the acoustic diaphragm 10 can be more significantly obtained. Furthermore, when the acoustic diaphragm 10 is applied to a speaker, the sound quality is further improved.
(7) The thermoplastic resin film 12 is a polyimide film.

According to the above configuration, the effect of suppressing warpage occurring in the acoustic diaphragm 10 can be more significantly obtained.
(8) The method for manufacturing the acoustic diaphragm 10 includes a lamination step in which the metal foil 11 and the thermoplastic resin film 12 are bonded together by thermocompression.

According to the above configuration, it is possible to manufacture the acoustic diaphragm 10 that is unlikely to warp.
Note that this embodiment can be implemented with the following modifications. This embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.

- The number of layers of metal foil 11 constituting acoustic diaphragm 10 is not limited to one layer, and acoustic diaphragm 10 may include two or more layers of metal foil 11.
For example, in the acoustic diaphragm 10 shown in FIG. 2, a first metal foil 11a, a thermoplastic resin film 12, and a second metal foil 11b are laminated in order from one side in the lamination direction. That is, the thermoplastic resin film 12 is laminated so as to be located between the first metal foil 11a and the second metal foil 11b. In this case, the effect of suppressing warpage occurring in the acoustic diaphragm 10 can be more significantly obtained.

In addition, when a plurality of metal foils 11 are provided, the acoustic diaphragm 10 may have a portion in which the metal foils 11 are successively laminated in the lamination direction. Note that the plurality of metal foils 11 may all be the same metal foil, or may be different metal foils.

- The number of layers of thermoplastic resin film 12 constituting acoustic diaphragm 10 is not limited to one layer, and acoustic diaphragm 10 may include two or more layers of thermoplastic resin film 12.

For example, in the acoustic diaphragm 10 shown in FIG. 3, a first thermoplastic resin film 12a, a metal foil 11, and a second thermoplastic resin film 12b are laminated in order from one side in the lamination direction. That is, the first thermoplastic resin film 12a and the second thermoplastic resin film 12b are laminated on both sides of the metal foil 11. In this case, the effect of suppressing warpage occurring in the acoustic diaphragm 10 can be more significantly obtained.

Moreover, when a plurality of thermoplastic resin films 12 are provided, the acoustic diaphragm 10 may have a portion in which the thermoplastic resin films 12 are laminated continuously in the lamination direction. Note that the plurality of thermoplastic resin films 12 may all be the same thermoplastic resin film, or may be different thermoplastic resin films.

Moreover, when a plurality of thermoplastic resin films 12 are provided, it is preferable that at least one thermoplastic resin film 12 in contact with the metal foil 11 is a polyimide film. In this case, the effect (7) above can be obtained.

- The acoustic diaphragm 10 may further include layers other than the metal foil 11 and the thermoplastic resin film 12, such as a protective layer.
Next, the technical idea that can be understood from the above embodiment and modification examples will be described below.

(a) The acoustic diaphragm, wherein the volume ratio of the thermoplastic resin film to the metal foil and the thermoplastic resin film is 40% or less.
(b) The acoustic diaphragm, in which the thermoplastic resin film is laminated on both sides of the metal foil or between the metal foils.

Next, the embodiments will be described in more detail with reference to Examples and Comparative Examples.
Hereinafter, the difference CTEX-M between the linear expansion coefficient CTEX of the thermoplastic resin film and the linear expansion coefficient CTEM of the metal foil in the acoustic diaphragm will be referred to as "CTE difference".

<Test 1>
(Example 1)
A 20 μm thick aluminum foil AL (material: 1N30) and a 25 μm thick polyimide film PI (Upilex VT manufactured by Ube Industries, Ltd.) were laminated and thermocompressed using a double belt press machine to produce the acoustic material of Example 1. I got a diaphragm. Table 1 shows the specific gravity and linear expansion coefficient CTEM of the metal foil used in the acoustic diaphragm of Example 1, and the linear expansion coefficient CTEX, CTEZ and basis weight of the thermoplastic resin film. Further, Table 2 shows the CTE difference, basis weight, and resin ratio of the acoustic diaphragm of Example 1.

In addition, the linear expansion coefficient CTEX and linear expansion coefficient CTEZ of the thermoplastic resin film, and the linear expansion coefficient CTEM of the metal foil were measured as follows.
(Measurement of linear expansion coefficient CTEX)
A sample cut out from a thermoplastic resin film was heat-treated at 300° C. for 30 minutes as a pretreatment. The heat-treated sample was set in a TMA (Thermal Mechanical Analysis) device (TMA-Q400 manufactured by TIA Instruments), and the amount of thermal expansion was measured from 50 ° C to 200 ° C while increasing the temperature at a heating rate of 10 ° C / min. The coefficient of linear expansion was determined. Note that samples were taken from two locations in the MD direction and TD direction of the thermoplastic resin film, and the smaller of the measured values of the two samples was taken as the linear expansion coefficient CTEX.
(Measurement of linear expansion coefficient CTEZ)
A sample cut from a thermoplastic resin film was set in a laser interference type thermal dilatometer (Laser thermal dilatometer L1X-1, manufactured by ULVAC Riko), heated to 300°C as a pretreatment, held for 5 minutes, and then heated to room temperature. Cooled. Thereafter, while increasing the temperature at a rate of 2° C./min, the amount of thermal expansion from 50° C. to 200° C. was measured, and the coefficient of linear expansion CTEZ was determined.

(Measurement of linear expansion coefficient CTEM)
A sample cut out from the metal foil was heat-treated at 300° C. for 30 minutes as a pretreatment. The heat-treated sample was set in a TMA (Thermal Mechanical Analysis) device (TMA-Q400 manufactured by TIA Instruments), and the amount of thermal expansion was measured from 50 ° C to 200 ° C while increasing the temperature at a heating rate of 10 ° C / min. The coefficient of linear expansion was determined. Note that the samples were taken from two locations in the MD direction and the TD direction of the metal foil, and the smaller of the measured values of the two samples was taken as the linear expansion coefficient CTEM.

(Example 2)
As the metal foil, aluminum foil AL (5052) with a thickness of 20 μm was used. Other points are the same as in Example 1.

(Example 3)
Titanium foil with a thickness of 20 μm was used as the metal foil. Moreover, a polyimide film PI having a thickness of 12.5 μm was used as the thermoplastic resin film. Other points are the same as in Example 1.

(Comparative example 1)
The acoustic diaphragm of Comparative Example 1 was made of aluminum foil AL (1N30) with a thickness of 30 μm.
(Comparative example 2)
An aluminum foil AL (5052) with a thickness of 30 μm was used as the acoustic diaphragm of Comparative Example 2.

(Comparative example 3)
A titanium foil with a thickness of 20 μm was used as the acoustic diaphragm of Comparative Example 3.
(Comparative example 4)
A titanium foil with a thickness of 25 μm was used as the acoustic diaphragm of Comparative Example 4.

(Comparative example 5)
A magnesium alloy foil (AZ31B) with a thickness of 44 μm was used as the acoustic diaphragm of Comparative Example 5.
(Comparative example 6)
A first polyimide film PI having a thickness of 25 μm (Upilex VT manufactured by Ube Industries, Ltd.) and a second polyimide film PI having a thickness of 50 μm (Upilex VT manufactured by Ube Industries, Ltd.) were pressed using a double belt press machine as described above. A thermoplastic resin film laminated and heat-pressed in the following order was used as an acoustic diaphragm of Comparative Example 6. Each numerical value shown in the thermoplastic resin film column of Table 1 is the numerical value of the thermoplastic resin film after thermocompression bonding. Note that the ratio CTEZ/CTEX of the linear expansion coefficient CTEZ of the first polyimide film PI is 5.3, and the ratio CTEZ/CTEX of the linear expansion coefficient CTEZ of the second polyimide film PI is 6.1.

(Comparative example 7 )
Aluminum foil AL (1N30) with a thickness of 20 μm, a first polyimide film PI with a thickness of 25 μm, and a second polyimide film PI with a thickness of 50 μm were laminated and heated in the above order using a double belt press machine. The pressure-bonded thermoplastic resin film was used as an acoustic diaphragm of Comparative Example 7 .

(Comparative example 8 )
As the metal foil, aluminum foil AL (1N30) with a thickness of 6 μm was used, and as the thermoplastic resin film, a polyimide film PI with a thickness of 12.5 μm was used. Other points are the same as in Example 1.
(Comparative Example 9)
A polyethylene terephthalate film PET with a thickness of 25 μm was used as the thermoplastic resin film. Other points are the same as in Example 1.

(Evaluation of warpage)
Warpage occurring in the acoustic diaphragms of each Example and each Comparative Example was evaluated.
A sample cut into a size of 10 cm long x 10 cm wide from the acoustic diaphragm of each example and each comparative example was left to stand in an environment of 23° C. and 65% RH for 24 hours or more, and then the concave surface in the warped shape was It was placed on a horizontal table with the top side facing up. The lifting height of the part of the sample that rose the most from the stand was measured, and the warpage of the acoustic diaphragm was evaluated based on the following criteria. The results are shown in Table 2.

A: The lifting height is less than 2 mm.
B: The rising height is 2 mm or more and less than 5 mm.
C: The rising height is 5 mm or more and less than 10 mm.

D: The floating height is 10 mm or more, or it is curled into a tubular shape.
(Evaluation of workability)
The workability of the acoustic diaphragms of each Example and each Comparative Example was evaluated.

The operation of processing a sheet-like acoustic diaphragm into a dome shape using a mold was performed 10 times using the acoustic diaphragms of each example and each comparative example. The number of times a machining defect occurred among the 10 machining operations was measured, and the workability of the acoustic diaphragm was evaluated based on the following criteria. The results are shown in Table 2.

A: The acoustic diaphragm could be easily set in the mold, and no processing defects occurred.
B: It was difficult to easily set the acoustic diaphragm in the mold, but no processing defects occurred.

C: Processing defects occurred one or more times.
D: Processing could not be performed.
(Sound quality evaluation)
A speaker was manufactured by bonding a voice coil to the back surface of the acoustic diaphragm of each example and each comparative example, which was processed into a dome shape with a diameter of 34 mm. Five panelists listened to the sound output from the manufactured speakers and evaluated the sound quality of the acoustic diaphragm based on the following criteria. The results are shown in Table 2. Note that sound quality evaluation was omitted for acoustic diaphragms that could not be processed.

A: Five panelists judged the sound quality to be desirable.
B: The number of panelists who judged the sound quality to be favorable was 4.
C: The number of panelists who judged the sound quality to be favorable was three.

D: The number of panelists who judged the sound quality to be favorable was two or less.
Furthermore, the internal loss tan δ of the acoustic diaphragms of each example and each comparative example at 25° C. and 100 Hz was measured using a dynamic viscoelasticity measuring device. The results are shown in Table 2.

(Evaluation of adhesion)
The adhesion of the acoustic diaphragms of each Example and Comparative Examples 7 to 9 was evaluated.
Strip samples with a width of 1 cm and a length of 20 cm were prepared from the acoustic diaphragms of each of Examples and Comparative Examples 7 to 9 in the MD direction and the TD direction, and the adhesion was evaluated using the 90° peeling method described in JIS C 6471. evaluated. Among the results of evaluation three times each in the MD direction and the TD direction, the minimum value was taken as the adhesion of the diaphragm.

(Evaluation of long-term reliability)
The long-term reliability of the acoustic diaphragms of each Example and Comparative Examples 7 to 9 was evaluated.
The acoustic diaphragms of each Example and Comparative Examples 7 to 9 were subjected to a heat cycle test under the following temperature cycle conditions, and the adhesion thereafter was evaluated by the same method as in the above evaluation of adhesion.

Heat cycle test conditions: Hold at -50°C for 10 minutes, then raise the temperature to 150°C over 2 hours, hold at 150°C for 10 minutes, and then lower the temperature to -50°C over 2 hours. With this cycle as 1, repeat 3000 cycles.

As shown in Tables 1 and 2, the acoustic diaphragms of Comparative Examples 1 to 6, which were made of only one of metal foil and thermoplastic resin film, did not warp; Significant warpage occurs in the acoustic diaphragms of Comparative Examples 7 to 9. When the acoustic diaphragms of Comparative Examples 7 to 9 were processed, the workability was poor or the processing itself was impossible.

On the other hand, even in the case of an acoustic diaphragm made by laminating metal foil and thermoplastic resin film, the linear expansion coefficient CTEZ ratio CTEZ/CTEX of the thermoplastic resin film is 3.0 or more and 10.0 or less, and the total basis weight is No major warpage occurred in the acoustic diaphragms of Examples 1 to 3 in which the diaphragm was 45 g/m ² or more and 150 g/m ² or less. The acoustic diaphragms of Examples 1 to 3 could be easily processed without causing processing defects.

From the results of sound quality evaluation, adhesion evaluation, and long-term reliability evaluation, it can be seen that the acoustic diaphragms of Examples 1 to 3 are applicable as acoustic diaphragms for speakers. Although the details are omitted, when the frequency characteristics of the acoustic diaphragms of Examples 1 to 3 were measured, they showed good sound pressure reproducibility over all frequencies.

<Test 2>
As shown in Table 3, acoustic diaphragms of Examples 4 to 8 were produced in which the thickness and arrangement of the metal foil and thermoplastic resin film were different, and various evaluations were performed in the same manner as in Test 1. The results are shown in Table 4.

(Example 4)
A polyimide film PI with a thickness of 12.5 μm was used as the thermoplastic resin film. Other points are the same as in Example 1.

(Example 5)
As the metal foil, aluminum foil AL (1N30) with a thickness of 12 μm was used, and as the thermoplastic resin film, a polyimide film PI with a thickness of 12.5 μm was used. Other points are the same as in Example 1.

(Example 6)
A polyimide film PI with a thickness of 50 μm was used as the thermoplastic resin film. Other points are the same as in Example 1.

(Example 7)
Using a double belt press device, the same polyimide film PI with a thickness of 12.5 μm was laminated and thermocompressed on both sides of an aluminum foil AL (1N30) with a thickness of 20 μm to obtain an acoustic diaphragm of Example 7.

(Example 8)
Using a double belt press device, the same aluminum foil AL (1N30) with a thickness of 12 μm was laminated and thermocompressed on both sides of a polyimide film PI with a thickness of 25 μm to obtain an acoustic diaphragm of Example 8.

As shown in Tables 3 and 4, the results of Examples 1, 4 to 6 show that as the resin ratio decreases, warpage is suppressed and the sound quality evaluation improves. In particular, when the resin ratio is 60% or less, the effect of suppressing warpage and the effect of improving sound quality are obtained. When the resin ratio is 40% or less, the sound quality is further improved.

Furthermore, from the results of Examples 7 and 8, it was found that warping can be suppressed by using an acoustic diaphragm with a laminated structure in which metal foil is sandwiched between thermoplastic resin films, or a laminated structure in which a thermoplastic resin film is sandwiched between metal foils. It can be seen that the results are more noticeable.

(Industrial applicability)
Since the present invention can be easily processed into a dome-shaped speaker using a mold, it can be suitably used as a diaphragm for an active speaker or a support for a voice coil. In addition, since it has good acoustic properties, it can be suitably used for flat speaker diaphragms, headphone diaphragms, earphone diaphragms, and the like.

DESCRIPTION OF SYMBOLS 10... Acoustic diaphragm, 11... Metal foil, 11a... First metal foil, 11b... Second metal foil, 12... Thermoplastic resin film, 12a... First thermoplastic resin film, 12b... First thermoplastic resin film.

Claims (7)

metal foil and
A thermoplastic resin film laminated on the metal foil,
The thermoplastic resin film has a ratio of the linear expansion coefficient in the thickness direction to the smaller of the linear expansion coefficient in the MD direction and the linear expansion coefficient in the TD direction, which is 3.0 or more and 10.0 or less. ,
An acoustic diaphragm, wherein the metal foil and the thermoplastic resin film have a total basis weight of 45 g/m ² or more and 150 g/m ² or less. The acoustic diaphragm according to claim 1, wherein the metal foil has a specific gravity of 1.7 or more and 5.0 or less. The difference between the smaller of the linear expansion coefficient in the MD direction and the linear expansion coefficient in the TD direction of the thermoplastic resin film and the linear expansion coefficient of the metal foil is 0 ppm/K or more and 15 ppm/K or less. The acoustic diaphragm according to claim 1 or 2. The acoustic diaphragm according to claim 3, wherein the metal foil has a linear expansion coefficient of 5.0 ppm/K or more and 35 ppm/K or less. According to any one of claims 1 to 4, the smaller of the linear expansion coefficient in the MD direction and the linear expansion coefficient in the TD direction of the thermoplastic resin film is 10 ppm/K or more and 50 ppm/K or less. Acoustic diaphragm described. The acoustic diaphragm according to any one of claims 1 to 5, wherein at least one of the thermoplastic resin films adjacent to the metal foil is a polyimide film. A method for manufacturing an acoustic diaphragm according to any one of claims 1 to 6, comprising:
A method for manufacturing an acoustic diaphragm, comprising a laminating step of thermocompression bonding the metal foil and the thermoplastic resin film.