JPH0423699A - Acoustic diaphragm - Google Patents

Abstract

PURPOSE:To obtain a characteristic more excellent than that of any conventional diaphragm and to process the diaphragm in an optional shape with a very simple method by forming the acoustic diaphragm through the use of a foaming state graphite film. CONSTITUTION:A foaming state graphite film is used for an acoustic diaphragm 1. The internal structure of the foaming state graphite film is regarded as a kind of honey-comb structure and the graphite layer with excellent acoustic characteristic is substantially consecutive in a planar direction on the surface as well as the inside. Thus, only the foaming state graphite film offers a same structure as the acoustic diaphragm in which the graphite film is adhered to the surface of the honey-comb material with an adhesives substantially. Since a space is provided in the inside, cracks hardly take place. An optional shape such as dome is formed by press forming. The acoustic characteristic is remarkably improved by the press forming.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an acoustic diaphragm used in audio equipment such as speakers and microphones.

BACKGROUND OF THE INVENTION In recent years, digitalization of audio equipment has progressed, and performance requirements for diaphragms such as speakers have become increasingly strict.

For example, it is required that there is little deformation due to external forces and that distortion of the sound is small, and that the reproduced sound range is wide and clear sound quality is produced.To achieve this, it is required that it is lightweight and has excellent elastic distortion and rigidity. . To summarize this as conditions for specific physical property values: ■ Young's modulus (E) is large; ■ Density (ρ) is small; ■ Speed of sound (sound wave propagation velocity V) is large; ■ Internal vibration. The loss (tan δ) is appropriate, the zero strength is large, and (1) it can be molded into any shape. However, there is a relationship of v-IT75 between V, E, and ρ. Of course, in addition to these conditions, it goes without saying that it is required to be easy to manufacture and to be stable against external conditions such as heat and humidity.

Conventionally, materials such as paper, plastic, aluminum, titanium, beryllium, poron, and silica have been used as materials for the diaphragm. These materials have been used alone or in composites with glass fibers, carbon fibers, etc., or in the form of metal alloys.

However, paper and plastics have low Young's modulus and density.
Characteristics such as sound velocity are not sufficient as a diaphragm, and the frequency characteristics in particular in high frequency bands are extremely poor, making it difficult to obtain clear sound quality as a diaphragm for tweeters, squawkers, etc. Aluminum, magnesium, titanium, etc. have a very high speed of sound, but
Because the internal loss of vibration is small, high frequency resonance occurs,
This also provided insufficient characteristics as a high frequency diaphragm. On the other hand, poron, aluminum, etc. have superior physical properties compared to the above materials, so
As a diaphragm, it can produce high quality sound. However, Poron Yabe IJ IJum is extremely expensive,
Moreover, it has the disadvantage of extremely poor workability.

Overcoming the drawbacks of conventional diaphragm materials as mentioned above, it has excellent high frequency characteristics and reproduces high quality tone.
Diaphragms using carbon materials are being developed. This takes advantage of the excellent physical properties of carbon (graphite) and uses it as a diaphragm. Methods for obtaining such a diaphragm material include the following.

(1) A method of compositely integrating graphite powder and polymer resin.

(2) A method in which graphite powder and polymer resin are integrated into a composite and then sintered to form a graphite/carbon composite type.

(3) A method of carbonizing a polymer by heat treatment.

Among these, a typical example obtained by method (1) is a diaphragm in which a vinyl chloride resin matrix is composited with graphite powder.

This is known as a diaphragm with excellent properties.

Method (2) includes a method in which graphite powder is mixed with the liquid crystal component of crude oil cracking pitch and heat treated and carbonized, and a method in which a binder is added to the graphite powder to bind it and heat treated and carbonized. In the latter case, when carbonizing the binder, a thermosetting resin monomer or initial polymer is heat-treated and carbonized together with a thermoplastic resin that has functional groups that decompose when heated and react with each other to crosslink and harden. etc. are known.

These methods were developed with the aim of increasing the yield of carbon as an organic material and preventing shrinkage and deformation during heat treatment, and it is possible to obtain a diaphragm with excellent characteristics.

However, the diaphragm produced by method (1) has poor humidity and temperature characteristics, and its vibration characteristics deteriorate significantly at temperatures above 30°C.

Method (2) all require complicated manufacturing processes;
Industrially, this was extremely disadvantageous in mass production. For example, in terms of the manufacturing process, there is a problem in that extremely complicated processes such as high-temperature heat treatment and solvent fractional extraction are required to industrially obtain crude oil cracked pitch and its liquid crystal component used as raw materials, and mass production is difficult. For the surface, the graphite powder and binder resin are sufficiently kneaded using a mixer with high shearing force, and the mechanochemical reaction causes the folded graphite crystals and the binder resin to have a strong affinity and disperse with each other, forming a graphite crystal surface. There was a problem in that a sophisticated technique was required to orient the material in the plane direction of the sheet. Moreover, although it is said that the diaphragms obtained by these methods have extremely excellent characteristics that have not been seen before, their characteristics are slightly inferior to those of the diaphragm that is currently said to have the best characteristics. This was far below the theoretical elastic modulus of graphite single crystal, which is 1020 GPa.

In method (3), since all conventional plastic films are non-graphitizable materials, properties as initially expected could not be obtained. Moreover, the carbon yield of the plastic material used is low, the dimensional shrinkage during heat treatment is large, and deformation, cracking, etc. often occur. That is, with this method, it is difficult to form a diaphragm into an arbitrary shape, withstand sufficient quality control, and to obtain a diaphragm with excellent characteristics.

Problems to be Solved by the Invention Therefore, in order to solve the drawbacks of method (3), the inventors obtained graphite by heat-treating a specific polymer in an inert gas, and then vibrated it. I proposed using it as a board.

However, the graphite obtained by this method is thin, and furthermore, the dimensional shrinkage during heat treatment is still large, causing deformation and cracking, making it impossible to mold it into arbitrary shapes. There were certain problems. As a result, this method has the disadvantage that only a flat diaphragm can be produced, and in terms of strength, it cannot be used alone as an acoustic diaphragm. To compensate for this drawback, honeycombs are created using materials such as mica epoxy and metal, and graphite films are attached to both sides using adhesives. However, with this structure, the characteristics of the speaker depend on the materials of the honeycomb and adhesive. Even in the manufacturing process, the graphite film is very thin, about 20 μm, and easily breaks, making it extremely difficult to handle when assembling speakers.

In view of these circumstances, this invention eliminates the drawbacks of the graphite diaphragm developed by the inventors, allows it to be processed into any shape with a very simple method, and is more durable than any conventional diaphragm. Another object of the present invention is to provide a carbonaceous (graphite) diaphragm having excellent characteristics.

Means for Solving the Problems In order to achieve the above object, an acoustic diaphragm according to the present invention uses a graphite film in a foamed state.

The expanded graphite film has a certain amount of internal space, which overcomes the fragility of the fully layered graphite film. This internal structure is a kind of honeycomb structure, and as shown in Figure 1, the graphite layer with excellent acoustic properties is substantially continuous in the surface direction, not only inside but also on the surface. This foamed graphite film alone has excellent vibration characteristics. Further, even when used as a core material of a honeycomb structure for a conventional graphite film, it does not have an adverse effect on acoustic properties like adhesives or conventional honeycomb materials.

On the other hand, even if the graphite film has spaces between its layers, if the layers become discontinuous as shown in FIG. 3, the acoustic properties will be greatly reduced and the graphite film cannot be used as an acoustic diaphragm.

Example Examples of the present invention will be described in detail below.

The acoustic diaphragm of the present invention uses a foamed graphite film.

The layered structure peculiar to graphite can be seen in Figure 4, and here, in the foamed state, the layer spacing of the layered structure of graphite is widened as shown in Figure 1, the layer spacing is disordered, and there is a large gap between the layers. Refers to the state in which space is created.

Such a foaming state can occur, for example, when certain polymer films described below are heat-treated at high temperatures, gas is generated internally.
This gas can be obtained by widening the layer spacing.

The internal structure of the foamed graphite film can be seen as a kind of honeycomb structure, and the graphite layer with excellent acoustic properties is substantially continuous in the surface direction, not only inside but also on the surface. Therefore, this foamed graphite film has a structure that is substantially the same as the acoustic diaphragm that has been used in flat speakers, which is made by pasting a graphite film on the surface of a honeycomb material with adhesive. It has become. Therefore, this foamed graphite film can be used alone as an acoustic diaphragm, and as shown in FIG. It is also possible to form a diaphragm 1 made only of graphite by adhering it to the back surface. In the figure, 2 is a voice coil.

Polymer films preferably used in this invention are polyphenylene oxadiazole, polyimide, polyamide, polybenzimidazole, and polyparaphenylene vinylene. However, any polymer that can be graphitized by heat treatment can be used without being limited to the above.

The above polyimide has the general formula %formula% It is a polymer represented by

here, 几1 is~ represents, R2 is represents.

He's talented. Above polyamide What is do? general formula It is a polymer represented by Here, R1 represents.

The thickness of these polymer films is 25 μm or more and 100 μm
m or less, a graphite film in a foamed state can be obtained by heat treatment in an inert gas at a temperature of 2400'C or higher. If the thickness exceeds 100 μm, too much gas is generated from within the film during heat treatment, so that a foamed film with continuous graphite structure layers cannot be obtained by treatment under normal pressure. However, as the inventors have already filed a patent application (Japanese Patent Application No. 1-123250), if the thickness is 400 μm or less, heat treatment of 2400'G or more in an inert gas and pressurized atmosphere is required. By doing so, a foamed state as shown in FIG. 1 can be achieved. For films with a thickness exceeding 400 μm, heat treatment under a pressurized atmosphere can result in the following properties as shown in Figure 3.
It becomes a graphite structure with discontinuous layers. On the other hand, 25 μm
For polymer films with a temperature of less than 2,400° C., heat treatment at 2,400° C. or higher results in a graphite film having an almost perfect layered structure as shown in FIG. 4, and does not become a foamed graphite film as shown in FIG. However, even such a thin polymer film can be made into a foamed state as shown in FIG. 1 by heat treatment at 24QO°C or higher if an inorganic filler is mixed in when the film is prepared. This is because the inorganic filler vaporizes at high temperatures during heat treatment.
This is to create a foaming state as shown in Figure 1 when the gas escapes from the film.

When the thickness of the polymer film is 5 μm or less, the thickness of the film after graphitization is 1 μm or less, and the escape route created by the gas created by vaporizing the inorganic filler becomes larger than the film thickness. Although a foamed state is obtained, it is not a continuous state as shown in FIG. 1, but a discontinuous state as shown in FIG. 3. This graphite film is extremely thin and difficult to handle when assembling speakers, making it impractical.

The foamed graphite film described above makes an excellent diaphragm as it is, but it can be stretched by more than 10% by rolling, so it can be formed into any shape such as the dome shape shown in Figure 2 by pressure forming. Can be formed into this is,
This is a major feature of this new graphite diaphragm, which compensates for the poor workability of conventional graphite diaphragms. The pressure required for pressurization is generally 2 ok/m or more. The upper limit of pressure is generally not regulated, but 2000 kg/cr
A pressure of /I or higher is not practically necessary. It is often effective to heat the material during pressurization. As shown in FIG. 2, the acoustic diaphragm obtained by this pressure molding method has a well-aligned graphite layer structure and has excellent vibration characteristics.

Examples of the present invention will be specifically described below.

Example 1 Polyphenylene oxadiazole film (Furukawa Electric ■
(60μm thick) in a nitrogen atmosphere at a heating rate of 20℃/
The temperature was raised to 1000° C. for 1 hour, and heat treatment was performed for 1 hour. The carbonaceous film thus obtained was heated in an ultra-high temperature furnace using a carbon heater (Shinsei Denko Seisakusho 46-6).
Heat treatment was performed at 3000'C for 1 hour at a heating rate of 20°C/min in an argon atmosphere at normal pressure.

A part of the foamed graphite film obtained in the above process was cut out, and its physical properties were measured using a Dynamic Mojira tester manufactured by Toyo Seiki Co., Ltd. The obtained value is
Sound speed 12.7 km/sec, internal loss 2.0X10
-2. A voice coil was attached to this diaphragm and the frequency characteristics were measured. As a result, the limit frequency is 34K
It turned out to be H2.

When compared with the limit frequency of mica material, which is about 30 KHz, it can be seen that the acoustic diaphragm according to the present invention is a diaphragm with excellent acoustic properties.

Example 2 A polyimide film (manufactured by Dapon Co., Ltd., trade name: Kapton H film, thickness 76 μm) was heat-treated to 3000° C. in the same manner as in Example 1. The physical properties of the obtained graphite film were measured in the same manner as in Example 1.

As a result, the sound velocity was 13,316 p/sec, and the internal loss was 1.
It was 8×1σ2. When a voice coil was attached to this diaphragm and the limit frequency was measured, it was approximately 4o KHz.
It was found that the diaphragm has excellent acoustic properties.

Example 3 Polyamide film (manufactured by Asahi Kasei ■, trade name MK film, thickness 60 μm) was coated with 30 μm in the same manner as in Example 1.
Heat treatment was performed up to 00°C. The physical properties of the obtained graphite film were as follows: velocity of sound 10.1/12+I/5ec1 internal loss 1.84×10−2. When a voice coil was attached to this diaphragm and the limit frequency was measured, it was found to be approximately 37 KHz, indicating that the diaphragm has excellent acoustic characteristics.

Example 4 A polybenzimidazole film (thickness: 50 μm) was heat-treated to 30°C in the same manner as in Example 1 (a foamed film was produced. The physical properties of this graphite film were as follows: the speed of sound was 11. 7 jan/sec
, the internal loss was 2.3×10. When a voice coil was attached to this diaphragm and the limit frequency was measured, it was found to be approximately ss, 5 KHz, indicating that the diaphragm had excellent acoustic characteristics.

Example 6 Polyimide in solution form (manufactured by Toshi ■, trade name: Trenice #3
000) was mixed with calcium phosphate powder (10% by weight).
). A silicone rubber frame was placed on a glass substrate, the mixed liquid was poured into the frame, the solvent was evaporated, and heat treatment was performed to obtain a thickness of 100 μm%, 200 μm, 300 μm, and 300 μm, respectively.
A polyimide film of 5'OOμm was prepared.

These were subjected to heat treatment at a temperature of 300° C. in the same manner as in Example 1, with an argon atmosphere pressure of 10 kg/−.

Table 1 shows the measurement results of each physical property value.

When the film thickness of the surface polymer was up to 300 μm, the foamed state as shown in FIG. 1 was obtained, and very good acoustic properties were obtained. However, when the thickness reached 500 μm, the internal loss could not be measured due to severe peeling of the surface. Other acoustic characteristics were also quite poor.

As described above, when the film thickness was 400 μm or less, a diaphragm with excellent acoustic characteristics was obtained by increasing the pressure of the inert gas atmosphere.

Example 6 The foamed graphite films produced by the methods of Examples 1 to 40 were molded into a dome shape at a pressure of 200 to 9/cd. Since it is not possible to directly measure the sound velocity and internal loss values of a molded body, a flat film sample was separately prepared and its sound velocity and internal loss characteristics were measured. The acoustic characteristics (limit frequency) were measured by attaching a voice coil to the dome-shaped molded body. The results obtained are shown in Table 2.

Table 2 Figures in parentheses indicate data for flat films.

As can be seen from the table, compared to the flat film, the molded body has improved sound velocity characteristics by approximately 10%, and conversely, internal loss has decreased by approximately 10%. The limit frequency has been greatly improved.

Effects of the Invention Since the acoustic diaphragm according to the present invention uses a foamed graphite film, it has good vibration characteristics even when used alone, and can also be used in combination with a conventional graphite film. And since it has space inside,
Hard to break. The dome-shaped cylinder can be formed into any shape by pressure molding. This pressure molding can significantly improve acoustic properties. Therefore, the acoustic diaphragm according to the present invention is most suitable for use in audio equipment such as speakers.

[Brief explanation of the drawing]

1 to 4 schematically show the cross-sectional state of a graphite film, FIG. 1 is a cross-sectional view of the graphite film of the present invention in a foamed state with continuous layers,
The figure is a cross-sectional view of a graphite film according to the present invention obtained by pressure-molding the graphite film of Figure 1 into a dome shape, and Figure 3 is a cross-sectional view of a graphite film in a foamed state with discontinuous layers. , FIG. 4 is a sectional view of a graphite film having an almost perfect layered structure, and FIG. 5 is a sectional view showing the acoustic diaphragm of the present invention attached to a voice coil. DESCRIPTION OF SYMBOLS 1... Acoustic diaphragm, 11... Conventional graphite film, 12... Graphite film of this invention,
2...Voice coil. Name of agent: Patent attorney Shigetaka Awano and one other name

Claims (5)

[Claims] (1) An acoustic diaphragm using a foamed graphite film. (2) The acoustic diaphragm according to claim 1, wherein the foamed graphite film is formed by pressure molding. (3) The foamed graphite film is made of at least one polymer film selected from polyphenylene oxadiazole, polyimide, polyamide, polybenzimidazole, and polyparaphenylene vinylene at a temperature of 2400°C or higher in an inert gas. 3. The acoustic diaphragm according to claim 1, wherein the acoustic diaphragm is obtained by heat-treating the acoustic diaphragm. (4) The acoustic diaphragm according to claim 3, wherein a polymer film having a thickness of 5 to 400 μm is used. (5) Claim 1 wherein a non-foamed graphite film is bonded to the front and back surfaces of a foamed graphite film.
5. The acoustic diaphragm according to any one of 4 to 4.