JPH0484599A - Manufacture of acoustic diaphragm - Google Patents

Abstract

PURPOSE:To easily obtain an excellent acoustic characteristic by applying heat treatment to a high polymer film compression molded to a dome or a cone shape at a specific temperature under an inert gas environment so as to attain graphite processing when a polyamide acid is converted into a polyamide by thermal polycondens. CONSTITUTION:The heat treatment processed under an inert gas environment is implemented so as to reach 2000 deg.C or over so that graphite processing is sufficiently progressed and a usual pressure of 0.1-200kg/cm<2> is exerted after the temperature reaches 2000 deg.C. Thus, since the compression molding to obtain a dome or a cone shape is implemented in the drawing enable state in the imide processing progressing stage in which imide processing is finished, a proper shape such as a done or cone is easily obtained. Thus, a graphite-made diaphragm with excellent acoustic characteristic is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method of manufacturing an acoustic diaphragm used for speakers, microphones, etc.

BACKGROUND OF THE INVENTION In recent years, digitalization of sound equipment has progressed, and the performance requirements for diaphragms such as subicars have become fairly strict.

For example, it is required that there is little deformation due to external force and that the distortion of the sound is small, and that the reproduced sound range is wide and clear sound quality can be produced.To achieve this, it is required that it is light and has excellent elastic modulus and rigidity. . To summarize this as conditions for specific physical property values, ■Young's modulus (E) is large, ■Density (ρ) is small, ■Sound velocity (sound wave propagation speed■) is large, and ■Internal vibration. The loss (tan δ) should be appropriate, the 0 intensity should be large, etc. However, between V, E, and ρ, V-(
There is a relationship of E/ρ)+7. Of course, in addition to these conditions, it is also required to be moldable, easy to manufacture, and stable against external conditions such as heat and humidity.

Conventionally, materials such as paper, plastic, aluminum, titanium, beryllium, boron, 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.
The characteristics such as sound velocity are not sufficient as a diaphragm, and the frequency characteristics especially in high frequency bands are extremely poor, making it difficult to obtain clear sound quality as a diaphragm for tweeters and the like. Furthermore, although materials such as aluminum, magnesium, and titanium have fairly high sound speeds, their internal loss of vibration is small, resulting in high-frequency resonance phenomena, which also provide insufficient characteristics for high-frequency diaphragms. . On the other hand, boron, beryllium, and the like have superior physical properties compared to the above-mentioned materials, and therefore can produce good sound quality as a diaphragm. However, boron and bryllium have the drawbacks of being extremely expensive and having extremely poor workability.

We aim to overcome the drawbacks of conventional diaphragm materials as mentioned above, have excellent high frequency characteristics, and reproduce high quality tone.
Diaphragms using carbon materials are being developed. This uses dirt as a diaphragm by taking advantage of the excellent physical properties of carbon (graphite l-). 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 film 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, making it possible to obtain a diaphragm with excellent characteristics.

In the case of method (3), several polymer films have been considered, but most polymer films are considered to be non-graphitizable materials that do not easily change to graphite I even when heat treated at high temperatures. The situation was that it was difficult to obtain an acoustic diaphragm that

Problems to be Solved by the Invention However, the acoustic 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;
Industrial G 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, graphite powder and binder resin are sufficiently kneaded using a kneading machine with a high shear force, and a mechanochemical reaction causes the folded graphite crystals and binder resin to have a strong affinity and disperse with each other, thereby creating a graphite crystal surface. The problem was that a sophisticated technique was required to orient the material in the direction of the surface of the material. 2.Although the diaphragms obtained by these methods have extremely superior properties that have not been seen before, their properties are slightly inferior to beryllium, which is currently said to have the best properties, and are superior to graphite. The theoretical elastic modulus of single crystal was less than 1020 GPa.

Method (3) is based on the recent finding that some condensation polymers are so-called graphitizable materials that graphitize by high-temperature heat treatment. just,
The diaphragm obtained by this method was limited to a flat one. This is because the polymer film used as the raw material is extremely difficult to mold. For example, a flat acoustic diaphragm has a disadvantage in that high-pitched sounds cannot be heard sufficiently when used in a large room because the sound pressure is inferior to that of a dome-shaped diaphragm.

In view of these circumstances, an object of the present invention is to provide a method by which a dome-shaped or cone-shaped acoustic diaphragm made of graphite having excellent acoustic properties can be easily obtained.

Means for Solving the Problems In order to achieve the above object, in the method for manufacturing an acoustic diaphragm according to the invention according to claims 1 to 3, when polyamic acid is converted into polyimide by thermal condensation polymerization, a dome-shaped or cone-shaped The polymer film that has been pressure-molded is subjected to heat treatment in an inert atmosphere at a temperature of 2000°C or higher to turn it into graphite.

When the shape formed in the molding process is a dome shape, it is not limited to a true spherical curved surface, but may be an oblate elliptical curved surface.

The imidization in this invention can be carried out, for example, by heating a film obtained by casting a solution containing polyamic acid and evaporating a part of the solvent at 70 to 400°C. conduct.

In the case of this invention, it is preferable that the fill 1 is pressurized in a temperature range of 2000° C. or higher.

Note that the resulting acoustic diaphragm does not need to be 100% graphite, and may have some residual graphite.

The polymer film pressure-molded into a dome or cone shape used in the present invention is made of polyimide, particularly preferably aromatic polyimide. Examples of aromatic polyimides include the following compounds.

Monoaromatic polyimide 11]1 Here, R, is the following substituent R2 is not the following substituent The above aromatic polyimide can be obtained, for example, as follows.

First, the following (formula 81, not pyromellitic anhydride) and the following (bJ, not diaminophenyl ether) are used.

(a) (b) ]111 Both are reacted to synthesize the following (C) soluble polyamic acid.

Next, a polyamic acid film is produced using the polyamic acid solution by the Cass I method or the like. For example, a polyamic acid solution is cast onto a substrate and then dried (heated) to remove a portion of the solvent to obtain a polyamic acid film. In this case, examples of the solvent include a mixed solution of N-methylpyrrolidone, dimethylacetamide, and an aromatic hydrocarbon. Next, although it varies depending on the type of polyamic acid, it is usually heat-dehydrated and imidized at a temperature in the range of 70 to 400°C (preferably 120 to 300°C) to form a polyimide film according to the following formula (d).

(d) In this invention, instead of molding a film that has already been imidized, for example, as in claim 2,
The film obtained by casting a solution containing polyamic acid and evaporating a part of the solvent is 70 to 4
Pressure molding is performed at a temperature of 00°C.

Usually, molding is carried out using a mold made of stainless steel or the like when imidization has progressed to some extent (in the middle of imidization), and after molding, further heat treatment is performed to complete imidization.

If molded polyimide film is heat-treated to graphite as it is, it tends to shrink in size and cause wrinkles to form on the surface or lose its shape. It is preferable to press.

The heat treatment carried out in an inert (gas) atmosphere is carried out at a temperature of 2000'C (more preferably 2500'C), which is sufficient for graphitization.
℃) or higher, and after reaching 2000°C or higher, a pressure of about 0.1 to 200 kg/cJ is usually applied. Pressures above 200 kg/ca are generally not required. This pressurization not only prevents wrinkles from occurring in the resulting acoustic diaphragm but also prevents defects from forming in the graphite crystals.

Function: In the method for manufacturing an acoustic diaphragm of the present invention, in order to perform pressure molding into a dome shape or a cone shape in a stretchable state at the imidization progress stage where imidization is completed, [゛-
It is possible to easily obtain a suitable shape such as a wedge shape or a cone shape. Furthermore, since the polymer film is made of aromatic polyimide, a material that can be easily converted into graphite, an excellent graphite diaphragm can be obtained.

EXAMPLES The present invention will be described in detail below. Of course, the present invention is not limited to Example G below.

Examples 1 to 3 Using a polyamic acid solution (manufactured by Toshi Co., Ltd., trade name: TRENICE), it was cast to a thickness of 250 μm on a glass substrate by the doctor blade method, heated to 120°C, and mixed with a solvent (N-methylpyrrolidone). Part of the mixture (mixture of dimethylacetamide and aromatic hydrocarbon) was evaporated to obtain a polyamic acid film.

The obtained film was peeled off from the glass substrate, set in a stretching device (Shibayama Kagaku Kikai Seisakusho, polymer stretching device), and
℃ temperature for 10 minutes to proceed with imidization.
0mm and R15mm dome-shaped stainless steel mold (Example 1), diameter 30mm 'T: R25rnm dome-shaped stainless steel mold (Example 2), diameter 30mm and R
After pressure molding using a 40 mm dome-shaped stainless steel mold (Example 3), the temperature was raised to 350°C.
After that, heat treatment was performed for 10 minutes to complete imidization.
A dome-shaped aromatic polyimide film was obtained.

Next, the obtained dome-shaped polyimide film was heated in a hot press furnace (G15X15HTB-Gl manufactured by Chugai Roko Kogyo Co., Ltd.
l ・III'15) in an argon atmosphere for 20
The temperature was raised to 2800°C at a heating rate of °C/min, and at that temperature, a dome-shaped carbon shape-retaining mold with a diameter of 30mm and R1.5mm (Example 1), a diameter of 30mm and R25+m
n dome-shaped carbon shape-retaining mold (Example 2),
Using a dome-shaped carbon shape retaining mold (Example 3) with a diameter of 30 mm and radius of 40 mm, a pressure of 50 kg/c+Il was applied and held for 2 hours to obtain a dome-shaped acoustic diaphragm.

Example 4 Using a polyamic acid solution (manufactured by Toshi Co., Ltd., trade name: TRENICE), it was cast onto a glass substrate with a thickness of 250 II Ill by the doctor blade method.
C. to partially evaporate the solvent (mixture of N-methylpyrrolidone, dimethylacetamide, and aromatic hydrocarbon) to obtain a polyamic acid film.

The obtained film was peeled off from the glass substrate and placed in a stretching device (Shibayama Kagaku Kikai Seisakusho Polymer Stretching Equipment).
When the temperature reached 20°C, 10% stretching was applied in two axial directions.1. Pressure molded from below using a dome-shaped stainless steel mold with a diameter of 30 mm and a radius of 100 mm, and then
The temperature was raised to 350° C. and heat treatment was carried out for 1 minute to complete imidization, yielding a dome-shaped aromatic polyimide film.

Then, the obtained dome-shaped polyimide film was heated in a hot press furnace (Chugai Furnace) by Nigyo G], 5 X], 5
II Tn-cp-npl, 5) in an argon atmosphere at a heating rate of 20°C/min to 280 (1'), and at that temperature, F'?100 at a diameter of 30 + nm.
50 mm using a dome-shaped carbon shape-retaining mold.
A pressure of kg/c% was applied and maintained for 2 hours to obtain a dome-shaped acoustic diaphragm.

Physical properties (sound velocity, internal loss) of the acoustic diaphragms of Examples 1 to 4 were measured using a Dynamic Modulus Star manufactured by Toyo Seiki. Furthermore, a voice coil was attached and the (reproduction) limit frequency was measured. The measurement results are shown in Table 1.

Note that when a part of the acoustic diaphragm of Examples 1 to 3 was cut out and the cross section was observed using a scanning electron microscope (Model T-300 manufactured by JEOL Ltd.), a layered structure peculiar to graphite was observed.

(The following is a blank space) Table 1 As shown in Table 1, the acoustic diaphragm of the example has excellent acoustic characteristics.

Effects of the Invention As described above, in the method for manufacturing an acoustic diaphragm according to the present invention, the shape is suitable for pressure molding in a stretchable state before imidization, and the polymer film J Since , is a polyimide that can be easily converted into graphite, a graphite diaphragm with good acoustic properties can be obtained.

Name of agent: Patent attorney Shigetaka Awano Haka1 G

Claims (3)

[Claims] (1) When polyamic acid is converted into polyimide by thermal condensation polymerization, a polymer film that is pressure-molded into a dome or cone shape is subjected to heat treatment in an inert atmosphere at a temperature range of 2000°C or higher to form graphite. A method for manufacturing an acoustic diaphragm. (2) A film obtained by casting a solution containing polyamic acid and evaporating a part of the solvent.
The method for manufacturing an acoustic diaphragm according to claim 1, wherein the acoustic diaphragm is press-molded at a temperature of 0 to 400°C. (3) The method for manufacturing an acoustic diaphragm according to claim 1 or 2, wherein the film is pressurized in a temperature range of 2000° C. or higher.