JPH03274999A - Manufacture of acoustic diaphragm - Google Patents

Abstract

PURPOSE:To realize a graphite diaphragm with an excellent acoustic characteristic by compression molding carbon powder at a high temperature obtained from a condensation high polymer chemical compound subject to heat treatment at a low temperature and pulverization. CONSTITUTION:A condensation high polymer chemical component being one of polyphenileneoxadiazole, polyimide, polyamide, polybenzimidazole, and polyparaphenylenevinylene is heat-treated at a temperature of 400-1000 deg.C and pulverized, the obtained powder is subject to press heat processing at a temperature of 2000 deg.C or over by using a molding jig and the result is graphite- processed. Thus, an acoustic diaphragm having an excellent characteristic of a graphite is realized.

Description

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

2. Description of the Related Art In recent years, the digitalization of audio equipment has progressed, and the performance requirements for diaphragms such as speakers have become increasingly strict. Such diaphragms are required to be less deformed by external forces, have less distortion of sound, and produce clear sound quality with a wide playback range.To achieve this, they must be lightweight and have excellent elasticity and rigidity properties. This is required. Specifically, the conditions for physical property values can be summarized as follows.

■ High Young's modulus (E) ■ Low density (ρ) ■ High speed of sound (velocity of sound propagation V) ■ Appropriate vibrational internal loss (tanδ) ■ Excellent strength However, ■ , E, and ρ have the relationship V=(E/p)''.

Of course, other factors include being manufactured in a container and being stable against external conditions such as heat and humidity.

Paper, plastic, aluminum, magnesium, titanium, beryllium, boron, silica, mica, etc. have conventionally been used as materials for such diaphragms. These materials have been used alone, in composites with glass fibers, carbon fibers, etc., and in metal alloys.

Paper and plastics do not have sufficient properties such as Young's modulus, density, and sound velocity, and their properties are particularly poor in high frequency bands.

Aluminum, magnesium, titanium, mica, etc. are quite superior in terms of sound speed, but their internal loss of vibration is too small, causing a high-frequency resonance phenomenon, so they do not have good characteristics in high-frequency bands.

Boron and beryllium have good properties such as superior sound quality compared to the above materials, but they are extremely expensive and have poor workability, so their use is extremely limited.

Therefore, in order to overcome the drawbacks of the conventional diaphragms, graphite-based diaphragms have been recently developed that have excellent high-frequency resonance and timbre reproducibility. Attempts are being made to use graphite, which has physical properties suitable for diaphragm materials. Specifically, there are the following.

(a) A composite type consisting of graphite powder and resin.

Specifically, graphite powder is composited with vinyl chloride resin as a matrix.

etc.) Polymer compound sheets are carbonized and graphitized individually.

Several types of polymer films (eg phenolic resin) have been investigated.

(C) A graphite/carbon composite type made by sintering a composite material consisting of graphite powder and resin.

Specifically, it is obtained by mixing graphite powder with the liquid crystal component of crude oil cracking pitch and then carbonizing it by heat treatment, or
Examples include those obtained by adding a binder to graphite powder and then carbonizing it by heat treatment. In the latter case,
As a raw material for the carbonized binder, there is a method of heat treatment carbonization using a thermosetting resin monomer or a thermoplastic resin having a functional group that decomposes an initial polymer upon heating and reacts with each other to crosslink and harden. These materials have a high carbonization yield as an organic material, have little shrinkage or deformation during heat treatment, and have good properties as a diaphragm.

Problems to be Solved by the Invention However, each of the excellent graphite-based diaphragms described above has the following problems.

In the case of (a), it has poor humidity and temperature characteristics and does not exhibit good vibration characteristics at temperatures above 30° C., so there is a problem that it is not practical.

In the case of (b), since the polymer (resin film) is a non-graphitizable material, there are problems such as low carbon yield and high dimensional shrinkage during heat treatment, which often causes deformation and cracking. . It has been difficult to obtain a diaphragm of high quality and good characteristics that can withstand practical use.

In the case of (C), what is the manufacturing process? For example, to obtain crude oil cracking pits and their liquid crystal components, extremely complicated processes such as high-temperature heat treatment and solvent fractional extraction are required. . moreover,
Graphite powder and binder are thoroughly kneaded using a mixer with high shearing force, and a mechanochemical reaction causes the graphite crystals and binder resin that are interlayered to have a strong affinity for and disperse each other, so that the crystal planes of graphite are aligned with the plane of the sheet. A technically difficult step of orienting the material in the same direction is required. Although this material has excellent properties, it is not as good as beryllium.
It is far below the theoretical elastic modulus of graphite single crystal, 1020 Gl'a.

In view of the above circumstances, it is an object of the present invention to provide a method by which a graphite-based diaphragm having excellent acoustic properties can be easily obtained.

Means for Solving the Problems In order to solve the problems, in the invention according to claim 1.2, a carbonaceous powder obtained by heat-treating a condensed polymer compound at a temperature of 400 to 1000°C and then pulverizing it, 2000
An acoustic diaphragm made of graphite is obtained by pressure molding at a temperature of ℃ or higher.

Function Condensation polymer compounds easily graphitize, so
The resulting diaphragm has been sufficiently graphitized and therefore has sufficient characteristics.

Since it is powdered once before being graphitized, it is less likely to be deformed or cracked than when it is graphitized in the form of a film, and moreover, it can be easily obtained into any shape.

Example The present invention will be explained in detail below.

The feature of the present invention is a manufacturing method for obtaining an acoustic diaphragm made of graphite by heat-treating a condensed polymer compound at a low temperature and then pulverizing it, which is then pressure-molded at a high temperature.

Examples of condensation polymer compounds include polyphenylene oxadiazole (hereinafter referred to as rPODJ), polyimide (hereinafter referred to as rPIJ), and polyamide (hereinafter referred to as rPIJ).
PAJ), polybenzimidazole (rP
BIJ), polyparaphenylene vinylene (hereinafter referred to as
rPPVJ), etc. These compounds may be used in combination.

Examples of PI (polyimide) include those represented by the following formula.

Here R1 is A substituent represented by any of Moreover, R2 is It is a substituent represented by either.

Examples of PA (polyamide) include those represented by the following formula.

It is a substituent.

The steps will be explained in more detail below.

First, usually, a film of the above condensed polymer compound is
There are some differences in processing temperature depending on the type of compound, but 4
Heat treatment at a temperature of 00 to 1000°C.

The processing time is usually about 15 minutes to 1 hour.

That is, the heat treatment is performed at a temperature higher than the temperature at which thermal decomposition occurs, but not higher than the temperature at which the graphite structure begins to develop. Through this heat treatment, the condensed polymer compound becomes carbonaceous.

Then, the heat-treated film is crushed. Since this film is not graphitized, it is easily powdered. Commonly used grinding methods can be used. The carbonaceous powder obtained by pulverization has a particle size of about 10 μm.

Next, the obtained powder is subjected to pressure and heat treatment using a forming jig to form graphite. In this case, in order to promote graphitization, the heat treatment is performed at a temperature of 2000"C or higher, more preferably at a temperature of 2500"C or higher.The treatment time is usually about 15 minutes to 3 hours.

The pressure applied during the heat treatment is preferably 4 kg/ci or more, and the pressure is started at a temperature below the heat treatment temperature before pulverization, or preferably at room temperature.

In this way, a diaphragm that fully exhibits the excellent characteristics of graphite can be easily obtained.

Since the shape of the diaphragm can be changed without any problem simply by changing the mold into which the powder is placed, it is virtually possible to set the shape of the diaphragm to any desired shape.

Diaphragms are used in audio equipment such as speakers and microphones, but are not limited thereto.

Next, embodiments of the invention will be described in more detail.

It goes without saying that this invention is not limited to the following embodiments.

- Example 1 - A POD film (manufactured by Furukawa Electric Co., Ltd., thickness 50 pm) was heat-treated at a temperature of 450° C. for 8 hours in a nitrogen atmosphere at a temperature increase rate of 20° C./min. After treatment, it was hard and brittle. Then, it was crushed using an attritor for 5 hours. This powder was placed in an R60 carbon spherical molding jig, and was heated in a hot press furnace (G15X manufactured by Chugai Roko Kogyo Co., Ltd.).
15 11T-B-GP-HP15), and was subjected to pressure heat treatment for 2 hours in an argon atmosphere. The heat treatment temperature is 28
The temperature was increased from room temperature to 00°C at a rate of 20°C/min. The pressure is 2
00 kg/cj at room temperature to obtain a dome-shaped diaphragm.

A voice coil was attached to the resulting diaphragm, and its frequency characteristics were investigated. As a result, the frequency limit was approximately 37 KHz. Considering that the limit frequency of mica material is about 30 KHz, it is clear that the diaphragm of the present invention has excellent acoustic properties.

In addition, a part of the diaphragm was cut out and the sound velocity and internal loss were examined using a dynamic modular star manufactured by Toyo Seiki. The sound velocity is 12.7 ka/sec, and the internal loss is 2.4X10-
"Met.

Example 2 A PI film (Kapton H film, manufactured by DuPont, thickness 75 μm) was heat-treated at a temperature of 500° C. for 12 hours in a nitrogen atmosphere. The temperature increase rate was 20°C/min.

Other than that, a dome-shaped diaphragm was obtained in the same manner as in Example 1.

The frequency limit of the obtained diaphragm was approximately 40 KHz, the sound velocity was 13.3 h/sec, and the internal loss was 1.8×10 −′.

Example 3 PA film (manufactured by Asahi Kasei MW film, thickness 50 μm)
m) was heat-treated at a temperature of 1000° C. for 8 hours in a nitrogen atmosphere. The temperature increase rate is 20°C/min.

In addition, the pressure during graphitization was 350 kg/
A dome-shaped diaphragm was obtained in the same manner as in Example 1, except that c1i was used.

The frequency limit of the obtained diaphragm was approximately 37 kHz.

Also, the speed of sound is 10.1 h/sec, and the internal loss is 2.0 x 10
It was 1.

Example 4 - FBI film (thickness 50 μm) was exposed to 10 μm in nitrogen atmosphere.
Heat treatment was performed at a temperature of 00°C for 8 hours. The temperature increase rate is 20℃
/ minute. Then, using an attritor, the powder was ground for 5 hours and placed in an R60 carbon spherical molding jig, and was subjected to pressure heat treatment in an argon atmosphere for 2 hours using the hot press furnace of Example 1. The temperature was 2800°C, which was raised from room temperature at a rate of 20°C/min. Pressure is 100kg/c
GL was added at room temperature to obtain a dome-shaped diaphragm.

The frequency limit of the obtained diaphragm is approximately 33.3kHz, the sound velocity is 11.7km/sec, and the internal loss is 2.0X10-
"Met.

Effects of the Invention As stated above, in this invention, since a condensation polymer compound is used as the material, a diaphragm with excellent acoustic properties that has been sufficiently graphitized can be obtained, and since it is once powdered, it can be easily deformed. It is possible to easily obtain a diaphragm of any shape without any cracks or cracks.

Claims (2)

[Claims] (1) Carbonaceous powder obtained by heat-treating a condensation polymer compound at a temperature of 400 to 1000°C and then pulverizing it is
A method for manufacturing an acoustic diaphragm, which obtains an acoustic diaphragm made of graphite by pressure molding at a temperature of 00°C or higher. (2) The method for producing an acoustic diaphragm according to claim 1, wherein the condensation polymer compound is at least one of polyphenylene oxadiazole, polyimide, polyamide, polybenzimidazole, and polyparaphenylene vinylene.