JPH09284884A - Diaphragm for electroacoustic transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diaphragm using fibers with high elastic rate, high strength, high internal loss, high stiffness and without any conductivity. SOLUTION: Polyparaphenylenebenzbisoxal(PBO) fibers of 20wt.% whose fiber length is cut to be 3mm and having tensile modulus of 250GPa and polypropylene of 80wt.% are molten and blended at 230 deg.C by using a monoaxial extruder to produce pellets. The pellets are injection-molded into a diaphragm/ having a prescribed cone shape is injected at a resin temperature of 240 deg.C, under an injection pressure of 100MPa, for an injection time of 1sec at a metallic die temperature of 60 deg.C and for a cooling time of 10sec. An edge 2 is attached to the obtained diaphragm, machine.

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 used in an electroacoustic transducer, and more specifically, it has a large specific elastic modulus, a proper internal loss, and weather resistance. An excellent diaphragm for an electroacoustic transducer.

[0002]

2. Description of the Related Art Physical properties required for a diaphragm for an electroacoustic transducer used in a speaker, a microphone, etc. have a large specific elastic modulus, an appropriate internal loss, little mechanical fatigue, and excellent weather resistance. There are points such as that. In order to meet such demands, various materials such as metals, ceramics, synthetic resins, synthetic fibers, plant cellulose (wood and non-wood pulp), microbial cellulose fibers, etc. have been proposed and processed using various processing methods. Has been used.

Among them, although metals and ceramics have a large elastic modulus, they are relatively excellent for high frequency reproduction because of their high density and small internal loss, but they are relatively excellent for high frequency reproduction. Not suitable for bandwidth.

Further, a paper diaphragm mainly composed of various cellulose fibers has an appropriate internal loss, but its specific elastic modulus is not so large, and it is weak against water and humidity. There is a problem for outdoor use, which requires a lot of water, and for on-vehicle use, which requires water during cleaning.

On the other hand, a diaphragm made of synthetic fibers is made of a synthetic resin alone or a base resin with a filler.
There are a mixture of the above, a resin alloyed with other resin, etc., which is formed into a sheet, which is molded (mainly vacuum molding), and pelletized by injection molding with an injection molding machine. These resin diaphragms also have a high specific elastic modulus,
It also has an appropriate internal loss, is resistant to water and humidity, and has little variation during mass production, so it can be said to be a diaphragm having relatively excellent performance.

Among them, the one obtained by mixing a fibrous filler with a synthetic resin based on a polyolefin polymer (mainly polypropylene) has a particularly excellent performance by utilizing the fiber orientation in injection molding. I got a vibrating plate.
Further, since its performance (mainly elastic modulus) depends on the performance of the filler to be added, the one using carbon fiber is now a relatively excellent diaphragm.

[0007]

However, in the case of using the carbon fiber, although the conductivity of carbon is not fatal in itself due to the structure of the speaker, the insulation treatment during the manufacture of the speaker is an obstacle in terms of cost. ing. Furthermore, many high-elasticity type carbon fibers have insufficient strength, and the fibers are often broken during mixing with a resin and injection molding, which causes a problem of variation in products.

The present invention has been made in view of the above circumstances, and has a diaphragm for an electroacoustic transducer, which has high elasticity, high strength, high internal loss, high toughness, and has no conductivity. The purpose is to provide.

[0009]

[Means for Solving the Problems] Polyparaphenylene benzbisthiazole (PBT), which is an organic fiber having an elastic modulus substantially equal to that of carbon fiber (about twice that of aramid fiber) and high strength, high internal loss, and high toughness ) Or polyparaphenylenebenzbisoxazole (PBO) or other polybenzazole (PBZ) fiber is mixed with a polyolefin-based polymer,
A diaphragm for an electroacoustic transducer is molded using an injection molding method.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The diaphragm for an electroacoustic transducer according to the present invention is characterized in that 5% by weight or more of polybenzazole fiber is mixed with a polyolefin polymer and the mixture is molded by an injection molding method.

In the diaphragm for an electroacoustic transducer according to the present invention, the polyolefin polymer is polypropylene,
It is characterized in that it is a polymer of an aliphatic olefin such as poly (4-methylpentene-1) or polyethylene, or an alloy thereof, and a copolymer containing the constituent monomer of the polymer as a main component. .

Further, in the diaphragm for an electroacoustic transducer according to the present invention, the polybenzazole fiber has a tensile strength of 4.0 G.
It is characterized by having an initial tensile elastic modulus of 140 GPa or more at Pa or more.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a front view of a one-sided cross section of a diaphragm according to the present invention. Reference numeral 1 is a diaphragm, and 2 is an edge. 1. 250GP tensile elastic modulus cut into a fiber length of 3mm
a of polyparaphenylene benzbisoxazole (PB
O) 20% by weight of fiber and polypropylene (Mitsubishi Polypro B
80% by weight of C2A) was melt mixed at 230 ° C. using a single screw extruder to prepare pellets. 2. The pellet obtained in the above 1 has a resin temperature of 240 ° C., an injection pressure of 100 MPa, an injection time of 1 second, a mold temperature of 60 ° C.,
It was injection-molded into a predetermined shape (this time, the cone shape in FIG. 1) with a cooling time of 10 seconds. 3. The edge 2 was attached to the diaphragm 1 obtained in the above 2.

The sound velocity (square root of specific elastic modulus) and internal loss (tan δ) of the three types of pellets (20% by weight of PBO fiber, 20% by weight of carbon fiber, 100% polypropylene) produced at the time of producing the above diaphragm were measured. It was measured. Table 1 shows the values. This time, we made a cone-shaped diaphragm, but it is also possible to make a dome-shaped diaphragm, a flat plate diaphragm, and a center cap. The measuring method is a vibration lead method.

FIG. 2 is a frequency characteristic diagram of the sound pressure of the speaker using the diaphragm according to the present invention and the sound pressure of the speaker using the diaphragm of 100% polypropylene. The solid line A in the figure is according to the present invention, which is composed of 20% by weight of polyparaphenylenebenzbisoxazole (PBO) fiber having a tensile elastic modulus of 250 GPa cut into a fiber length of 3 mm and 80% by weight of polypropylene (Mitsubishi Polypro BC2A) described above. Sound pressure of a 13 cm aperture speaker using a diaphragm-
It is a frequency characteristic. The broken line B is polypropylene (Mitsubishi Polypro BC2A) 1 with no filler.
Aperture 1 using a diaphragm of the same shape made using 100%
It is a sound pressure-frequency characteristic of a 3 cm speaker. Since the solid line A has a larger specific elastic modulus than the broken line B, the reproduction limit in the high range is extended.

FIG. 3 shows the sound pressure of a speaker using the diaphragm according to the present invention, carbon fiber 20%, polypropylene 8
It is a frequency characteristic figure of the sound pressure of the speaker which uses a 0% diaphragm. The solid line A in the figure indicates the fiber length of 3 m described above.
Diameter of 13 cm using a diaphragm according to the present invention composed of 20% by weight of polyparaphenylenebenzbisoxazole (PBO) fiber having a tensile elastic modulus of 250 GPa cut into m and 80% by weight of polypropylene (Mitsubishi Polypro BC2A).
Is a sound pressure-frequency characteristic of the speaker. Also, the broken line C
Uses a carbon fiber (Mitsubishi Dialead K223, tensile elastic modulus 220 GPa) instead of PBO fiber, and uses a diaphragm of the same shape manufactured in the same process.
Is a sound pressure-frequency characteristic of the speaker. There is almost no difference in the specific elastic modulus of the two, so the reproduction limit in the high range is almost the same,
Since the solid line A has a larger internal loss, a flatter response is obtained.

[0017]

As described above, the diaphragm for an electroacoustic transducer according to the present invention is formed by injection molding method by mixing 5% by weight or more of polybenzazole fiber with a polyolefin-based polymer. In the diaphragm for an electroacoustic transducer according to the invention, the polyolefin-based polymer is a polymer of an aliphatic olefin such as polypropylene, poly (4-methylpentene-1), or polyethylene, or an alloy thereof, and further, a constituent monomer of the polymer. In addition, since the electro-acoustic transducer diaphragm according to the present invention has a tensile strength of 4.0 GPa or more and an initial tensile elastic modulus of 140 GPa or more, Since the elastic modulus is large and the internal loss is relatively large, split vibration is unlikely to occur, it is flat from the low range to the high range, There can be obtained a speaker, also because there is no conductive, insulated at the time of speaker manufacturing is not required, manufacturing cost is inexpensive. Further, in the production of the diaphragm, since the bending unlike carbon fiber does not occur, it is possible to obtain a stable diaphragm with little variation in physical properties.

[Brief description of drawings]

FIG. 1 is a front view of a one-sided cross section of a diaphragm according to the present invention.

FIG. 2 is a frequency characteristic diagram of a sound pressure of a speaker using a diaphragm according to the present invention and a sound pressure of a speaker using a diaphragm of 100% polypropylene.

FIG. 3 is a frequency characteristic diagram of the sound pressure of the speaker using the diaphragm according to the present invention and the sound pressure of the speaker using the diaphragm of 20% carbon fiber and 80% polypropylene.

[Explanation of symbols]

 1 Vibration plate 2 Edge

Claims (3)

[Claims] 1. A diaphragm for an electroacoustic transducer, which is obtained by mixing 5% by weight or more of polybenzazole fiber with a polyolefin polymer and molding the mixture by an injection molding method. 2. The polyolefin-based polymer is mainly composed of a polymer of an aliphatic olefin such as polypropylene, poly (4-methylpentene-1) or polyethylene, or an alloy thereof, and a constituent monomer of the polymer. It is a copolymer, The diaphragm for electroacoustic transducers of Claim 1 characterized by the above-mentioned. 3. The diaphragm for an electroacoustic transducer according to claim 1, wherein the polybenzazole fiber has a tensile strength of 4.0 GPa or more and an initial tensile elastic modulus of 140 GPa or more.