JPH11205893A - Diaphragm for electric acoustic converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain characteristics which hardly cause dividing vibration and is flat in the range of sound by using a diaphragm large in specific modulus and inner loss by impregnating a thermosetting resin into a woven fabric, consisting of polyparaphenylene benzobisoxazole fiber having specified tensile strength and initial tensional modulus, forming it into a prescribed shape and coating its one side with emulsion resin. SOLUTION: In this diaphragm 1, tensile strength is defined as being equal to or layer then 4.0 GPa and the initial tension modulus is defined as being equal to or longer than 140 GPa. A woven fabric consisting of polyparaphenylene benzobisoxazole fiber the void diameter of which is <=25 Åis impregnated with phenol resin, to which the prescribed quantity of diluent solvent and release agent are added to form a sheet the resin quantity of which becomes 10% by drying mass. The metallic mold having a prescribed shape is used and the sheet is pressurized/heated/dried for 10 seconds at 700 kg at 230 deg.C, for example, and the prescribed shape is obtained. One side of a formed body is coated with acrylic emulsion resin 2, dried and punched into the prescribed shape to obtain the objective diaphragm 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diaphragm for an electroacoustic transducer such as a speaker or a microphone, which is a kind of acoustic equipment.

[0002]

2. Description of the Related Art The physical properties required of a diaphragm for this type of electroacoustic transducer include a large specific elastic modulus, an appropriate internal loss, low mechanical fatigue, and excellent weather resistance. Points. To meet such demands, various metals, ceramics, synthetic resins, synthetic fibers, vegetable cellulose (wood, non-wood pulp), carbon fibers,
Materials such as aramid fibers have been proposed and processed and used using various processing methods.

[0003]

Among them, metals and ceramics have a high elastic modulus but a high density and a small internal loss, so they can be used for high-frequency reproduction. It is unsuitable for the sound range and all bands.
In the case of using synthetic resin, a sheet of synthetic resin alone, a mixture of base resin with filler, or an alloy with other resin, etc. Vacuum molding), pellets, and injection molding with an injection molding machine. These resin diaphragms have a high specific elastic modulus, an appropriate internal loss, and small variations in mass production. Therefore, it has relatively excellent properties, but is disadvantageous in that it is susceptible to heat and its thickness is not easily controlled, so that the degree of freedom in design is small.

On the other hand, a paper diaphragm obtained by papermaking using cellulose fibers of various plants has a high degree of freedom in design and has an appropriate internal loss, but the specific elastic modulus is not so large. In order to improve the specific elastic modulus, a mixture of various synthetic fibers, particularly aramid fibers, carbon fibers, and ceramic fibers, has been proposed and put into practical use.

There is also a diaphragm made of a woven fabric using only aramid fibers, or a woven fabric using only carbon fibers, instead of being mixed with vegetable cellulose fibers, and then resin-impregnated and formed. These diaphragms have high strength and a high specific modulus. In particular, a carbon fiber woven fabric has a higher specific modulus than aramid fiber.

[0006] However, carbon fibers have a high specific modulus, but have the disadvantage that the internal loss is not so large. In addition, the conductivity of carbon necessitates insulation treatment during speaker production, which is an obstacle in terms of cost.

Although aramid fibers have an appropriate internal loss, they do not have the same specific modulus as carbon fibers. Furthermore, since the specific gravity of both aramid fiber woven fabric and carbon fiber woven fabric is larger than that of the diaphragm using vegetable cellulose fiber, the resin covers the front and back of the woven fabric during molding, In the case of a molding method using a prepreg of the type performed simultaneously, the mass of the diaphragm increases,
There is a disadvantage that the efficiency of the speaker is easily reduced.

[0008] The present invention has been made in view of such a point,
The purpose is to compensate for the above-mentioned drawbacks of the prior art, to have an elastic modulus substantially equal to that of carbon fiber (about twice that of aramid fiber), a large internal loss, high strength and high heat resistance. Based on a woven fabric using polyparaphenylene benzobisoxazole (PBO) fiber, which is an organic fiber,
It is an object of the present invention to provide a diaphragm for an electroacoustic transducer which has a large specific elastic modulus, a large internal loss, can obtain good sound quality, and can reduce the weight and cost.

[0009]

A diaphragm according to the present invention impregnates a woven fabric made of polyparaphenylene-benzobisoxazole fiber having a tensile strength of 4.0 GPa or more and an initial tensile modulus of 140 GPa or more with a thermosetting resin. The above-mentioned object is achieved by forming a predetermined shape and coating one side with an emulsion resin.

[0010] In this case, the impregnation amount of the thermosetting resin is 3% or more and 20% or less in terms of dry mass% based on the mass of the woven fabric.

A phenol resin or a melamine resin is used as the thermosetting resin.

As the emulsion resin for one-sided coating, an acrylic emulsion, a vinyl acetate emulsion, and a styrene / butadiene emulsion are used.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a tensile strength of 4.0 GP
a, a woven fabric composed of polyparaphenylene-benzobisoxazole (PBO) fiber having an initial tensile modulus of 140 GPa or more is obtained by dry weight% and solid content of 3% to 20%.
% Or less, preferably 10% or less, by impregnating with a thermosetting resin and molding into a predetermined shape, so that a diaphragm made of a conventional woven fabric of aramid fibers and a diaphragm made of a woven fabric of carbon fibers are good. Specific elastic modulus (sound velocity)
The diaphragm having large initial loss and large internal loss and having initial physical properties closer to ideal is obtained.

In this case, compared to the prepreg of the type in which the resin covers the front and back surfaces of the woven fabric at the time of molding and performs sealing simultaneously, at the time of molding, only the shape is maintained with a small amount of resin, and the sealing is performed by the emulsion resin. , The amount of resin can be reduced, and a lighter diaphragm can be obtained.

The reason why the solid content of the thermosetting resin is set to 3% or more and 20% or less as described above is that if the solid content is less than 3%, the shape cannot be maintained. This is because the difference in mass from a type such as an epoxy prepreg that is performed up to stopping is reduced, and the effect of weight reduction is reduced.

[0016]

Next, examples of the present invention will be described. That is, in the present invention, as described above, a woven fabric using the polyparaphenylene-benzobisoxazole (PBO) fiber having the above-described physical properties was impregnated with a resin, molded, and coated on one side to produce a diaphragm. The specific manufacturing procedure is as follows.

1. A woven fabric composed of PBO fibers having a void diameter of 25 ° or less was impregnated with a phenol resin to which a diluting solvent and a release agent were added in predetermined amounts, to prepare a sheet having a resin amount of 10% by dry mass. Other melamine resins may be used as the thermosetting resin.

2. The sheet obtained above was dried by applying pressure and heat using a mold having a predetermined shape (a cone shape in this example) to obtain a predetermined shape. The pressure heating drying conditions here are:
700 kg, 230 ° C., 10 seconds.

3. An acrylic emulsion resin was coated on one surface (the back surface in this example) of the molded product obtained in the above 2, dried, and then punched into a predetermined shape to obtain a diaphragm main body. In addition, as the resin to be coated,
A vinyl acetate emulsion or a styrene / butadiene emulsion resin may be used.

4. An edge made of synthetic rubber was attached to the outer periphery of the diaphragm main body obtained in the above 3 to obtain the diaphragm 1 of FIG. In FIG. 1, 2 is an emulsion resin, and 3 is an edge.

In this example, a cone-shaped diaphragm is manufactured, but a center cap, a dome-shaped diaphragm, and the like can also be manufactured.

FIG. 2 shows the sound pressure characteristic with respect to the frequency of the present invention, wherein A is the present invention and B is the conventional example, and the present invention is flat from the low frequency range to the high frequency range and has a high high frequency reproduction limit. It has become something.

[0023]

As described above, according to the present invention, a woven fabric composed of polyparaphenylene / benzobisoxazole fibers is used, impregnated with a thermosetting resin, molded into a predetermined shape, and then coated on one side with an emulsion resin. According to this diaphragm, since the specific elastic modulus is large and the internal loss is relatively large, split vibration is unlikely to occur, it is flat from the low frequency range to the high frequency range, and the high frequency range is limited. High characteristics can be obtained.

Also, by reducing the amount of resin used, the weight of the diaphragm can be reduced, and the sound pressure level of the speaker can be improved. Further, since there is no conductivity, no insulation treatment is required at the time of manufacturing the speaker, and the manufacturing cost is reduced accordingly.

[Brief description of the drawings]

FIG. 1 shows an example of a diaphragm shape manufactured according to the present invention.

FIG. 2 shows sound pressure characteristics with respect to frequency according to the present invention.

[Explanation of symbols]

 1 diaphragm 2 emulsion resin 3 edge

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ryuji Ichiyanagi 2-2-2 Dojimahama, Kita-ku, Osaka Toyobo Co., Ltd.

Claims (4)

[Claims] 1. A woven fabric composed of polyparaphenylene-benzobisoxazole fiber having a tensile strength of 4.0 GPa or more and an initial tensile modulus of 140 GPa or more is impregnated with a thermosetting resin, formed into a predetermined shape, and then formed on one surface. A diaphragm for an electro-acoustic transducer, characterized in that an emulsion resin is coated on the diaphragm. 2. The diaphragm for an electroacoustic transducer according to claim 1, wherein the impregnation amount of the thermosetting resin is 3% or more and 20% or less in terms of dry weight based on the weight of the fabric. 3. The diaphragm for an electroacoustic transducer according to claim 1, wherein the thermosetting resin is a phenol resin or a melamine resin. 4. The diaphragm for an electroacoustic transducer according to claim 1, wherein the emulsion resin for one-side coating is an acrylic emulsion, a vinyl acetate emulsion, or a styrene-butadiene emulsion.