JPH0431639B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to electro-acoustic transducers such as electrodynamic speakers and microphones, and more particularly to an acoustic transducer equipped with a diaphragm made from a fiber-based material.

[Conventional technology]

The acoustic characteristics of acoustic transducers, such as electrodynamic speakers, are mainly influenced by the physical characteristics of the vibration system, and the diaphragm plays the most important element in terms of performance in the vibration system. The material of this diaphragm is mainly made of natural fibers. For example, (A) sulfate valve (KP), sulfite pulp (SP), seed wool fiber, cotton pulp, kapok bast fiber, mitsumata, ramie, or inorganic fiber are blended and formed into a conical shape, This is mixed with a resin or the like, formed into a conical shape, and then impregnated with a solvent such as a resin. There is also a diaphragm (B) made of a film such as polypropylene or polyethylene, which is formed into a predetermined shape using compressed air or vacuum. Furthermore, (C) light metal materials such as aluminum, titanium, beryllium, etc., which are pressure-molded into conical shapes, and materials that have been in the spotlight in recent years, such as fine powders of metal oxides, nitrides, and borides, are also available. It has a sintered ceramic diaphragm. Various types of diaphragms are used in this way, but
The physical properties required for a diaphragm material are a low density ρ to improve efficiency, a high specific elastic modulus E/ρ to widen the reproduction band, and a high specific elastic modulus E/ρ to damp resonance and reduce sound pressure. -Having appropriate internal loss in order to flatten the frequency characteristics, etc.

[Problems to be solved by the invention]

The diaphragm obtained by papermaking as described above does not completely satisfy the above physical conditions;
It was not possible to obtain the desired sound pressure frequency characteristics. Furthermore, since the diaphragm obtained by the molding method is made of a plastic film such as polypropylene, it has a relatively high density and efficiency is reduced, making it impossible to obtain the expected characteristics. Furthermore, the diaphragm obtained by the pressure molding method is a light metal material, and in particular, the beryllium diaphragm has a very large √(E: elastic modulus, ρ: density) (about 12.3 Km/sec). Although extremely good sound pressure frequency characteristics can be obtained, the price is extremely high and it is difficult to put it into practical use. In addition, when other light metal materials are used, the density is large and √ is 5.24Km/
sec or less, and even if the structure of a diaphragm made of this type of material is improved, it cannot be expected to improve the sound pressure frequency characteristics over the current diaphragm. Regarding ceramic materials, as well as when using beryllium materials,
Although products with high properties can be obtained, they are susceptible to thermal deformation due to the influence of heat during the manufacturing process.Although products with high dimensional precision can be obtained, they also have the drawback of high costs. Table 1 shows the physical properties of a diaphragm using the above-mentioned diaphragm material.

【table】

[Means to solve the problem]

Therefore, the purpose of this invention is to provide an electroacoustic transducer equipped with a low-density diaphragm while maintaining appropriate internal loss and rigidity. The device is characterized in that it includes a diaphragm obtained by mixing inorganic fibers, typified by carbon fibers, into a suspension and forming the mixture into paper.

【Example】

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, the manufacturing process of a diaphragm for an electroacoustic transducer will be explained. Using a wet spinning machine, a high viscosity solution consisting of a water-soluble alkali alginate salt or a mixture of this and a water-soluble polymer material is used as a coagulant, and metal ions and/or acids having the ability to form a salt insoluble in alginic acid are used. Continuous fibers are formed by spinning into a coagulation bath consisting of an aqueous solution containing as a main component, and then the continuous fibers are cut into short fibers. Thereafter, the short fibers are dispersed and disintegrated without damaging the fiber form, foreign matter and bound fibers are removed using a screen or cleaner, and inorganic fibers are mixed and paper is made to obtain a diaphragm. Incidentally, alginic acid is a polysaccharide contained in brown algae, and is a copolymer of D-mannuronic acid and L-glucuronic acid, mainly composed of β-1,4 bonds. When this alginic acid is made into an aqueous solution as an alkali salt such as sodium, a highly viscous alginate alkaline solution can be obtained. Here, the water-soluble alkali alginate is
Alginate lithium, sodium, potassium,
Salts such as ammonium. Metal ions that have the ability to form insoluble salts for alginate are b in the periodic table.
, b, and transition metal ions, specifically Ca(), Sr(), Ba(), Al
(), Sn(), Pb(), Mn(), Cr(), Fe(),
Examples include Co(), Ni(), Cu(), Zn(), Ag(), etc. Further, as the acid, for example, salts, inorganic acids such as nitric acid and phosphoric acid, and organic acids such as formic acid and acetic acid are used. The fibers cut from the continuous fibers have an aspect ratio (ratio of fiber diameter (wet) to fiber length) of 150 or less in order to promote self-adhesion among fibers and to obtain a good diaphragm texture. Further, as the inorganic fibers, metal fibers, carbon fibers, glass fibers, etc. are used. First, alginate fibers are formed by the following spinning process. A sodium alginate solution is prepared, and the solution is injected into a calcium chloride spinning solution through a small nozzle with a diameter of 0.05 mm to 1 mm for spinning. Further, a small amount of hydrochloric acid and a cationic surfactant may be included in the spinning solution. When sodium alginate is brought into contact with the spinning solution, ion exchange occurs and can be converted into long fibers of calcium alginate. Here, the alginate alkali metal salt is water-soluble, but if it is a salt of a divalent or higher metal, fibers can be obtained without dissolving in water. Moreover, this alginic acid fiber has flame retardancy. The spinning conditions for forming alginate-based fibers in the examples were as follows: A 5% aqueous solution of sodium alginate with a degree of polymerization of 3.8 x 10 ⁵ Daltons was spun using a humidity spinning machine at a discharge rate of 3.5 ml/min.
55% from a 1000 hole nozzle consisting of 0.10mm
It was spun into a CaCl ₂ solution, the temperature was room temperature, the winding speed was about 2.1 to 28 rpm, and the stretching ratio was 1.3. After washing the alginic acid fibers produced under the above spinning conditions with water, staples having a fiber length of approximately 3 mm are prepared. In this way, alginic acid fibers, which are raw materials for diaphragms for electroacoustic transducers, are obtained. First, as shown in the flowchart of the manufacturing method according to this embodiment in FIG. 1, in the defibration step, 4 kg of alginate fibers of 80% were put into a predetermined defibrator, and the paper stock concentration was about 2.5%. The alginic acid fibers are defibrated so as not to damage their fiber morphology, and then defibrated and dispersed to a predetermined degree of beating using a beating degree measuring machine. Carbon fiber chop fiber with fiber cross section = perfect circle, diameter = 7.5μ, specific gravity = 1.7-1.8, strength = 290Kg/mm ² , elongation 1.0-1.2%, elastic modulus 23t/mm ² in dispersed alginic acid, Input 20% and 1 kg of a 5 mm cut length, disintegrate for 60 minutes at a paper stock concentration of 3.1% to disperse carbon fibers, and dye using 5% of a specified basic dye. Furthermore, in order to improve the infiltration strength as a sizing, urea resin was added at 3% (absolute dry ratio) to the paper stock, and sulfuric acid was added to improve the pH value of the paper stock liquid.
Adjust to 5.0-5.5. Next, the adjusted stock is adjusted to a suspension 2 having a stock concentration of 0.3% in a raw material tank 1 of a paper machine shown as a schematic cross-sectional view in FIG. This suspension 2 is sent to a paper stock tank 4 of a predetermined paper stock machine by a transfer pump 3 via a communication pipe, and in the paper stock tank 4, a paper stock tool 5 equipped in a predetermined shape is used to form paper. Make it. In this figure, numeral 6 is a suction pump. The paper-shaped diaphragm is taken out from the paper stock tank 4 and dried in a dryer 7 with hot air at about 100°C. Here, reference numeral 8 is a jig of a predetermined shape, and 9
is a vacuum suction pump. A composite diaphragm made of alginate fibers and carbon fibers can be obtained by cutting the dried diaphragm into inner and outer diameter portions of predetermined dimensions. Table 2 shows the dynamic property values of the diaphragm obtained by mixing the alginate fibers and carbon fibers thus obtained.

[Table] As is clear from Table 2, diaphragms made of composite materials made of alginate fibers and carbon fibers have a lower density than diaphragms made of conventional wood pulp fibers.
In addition, the propagation velocity, that is, the sound velocity, is high, the internal loss value is relatively large, the harmonic distortion is slight, the sound pressure frequency characteristics are flat over a wide band, and the propagation velocity is also compared to metal materials. However, the resonance is excellent and well-balanced. Furthermore, in the above embodiments, by changing the blending ratio of alginic acid fibers and carbon fibers, various characteristics of the diaphragm can be improved and manufacturing adjustments can be easily made to obtain desired characteristics.

【Effect of the invention】

As is clear from the above description, this invention provides a diaphragm by making a suspension of alginic acid fibers and inorganic fibers. , an acoustic transducer with significantly improved propagation speed can be obtained, and since the conventional papermaking process can be used as is, new manufacturing equipment is not required and a product with stable quality can be obtained.

[Brief explanation of drawings]

Figure 1 is a flowchart showing the manufacturing process of the diaphragm, Figure 2 is a paper stock machine for manufacturing the diaphragm,
And, it is a schematic explanatory view of a dryer.

Claims (1)

[Claims] 1. An electroacoustic transducer comprising a diaphragm made from a suspension containing alginic acid fibers and inorganic fibers. 2. The electroacoustic transducer according to claim 1, characterized in that carbon fiber is used as the inorganic fiber.