JPH0573119B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to improvements in diaphragms for electroacoustic transducers such as diaphragms for speakers, dust caps or center dome radiators, and diaphragms for microphones. [Prior Art] In recent years, the use of carbon fiber as a component of the diaphragm material for electroacoustic transducer diaphragms, such as speaker diaphragms, has been considered and put into practical use primarily for the purpose of increasing rigidity. There is. Examples of this type of diaphragm are: (1) A diaphragm made by mixing carbon fiber and pulp fiber and then shaping it using phenol resin, etc. (2) A sheet made by mixing carbon fiber with a thermoplastic resin such as polypropylene resin. A diaphragm that is molded and vacuum-formed, or a diaphragm that is injection-molded by mixing the above materials (3) Carbon fiber woven or non-woven fabric is impregnated with a thermosetting resin to make a prepreg, which is then press-molded. diaphragm. (4) A composite material obtained by mixing a layered mineral such as montmorillonite with a hardening agent or hardening accelerator adsorbed between the layers, a thermosetting resin, and carbon fiber is heated and pressed. A molded electroacoustic transducer diaphragm has been proposed by the applicant. [Problems to be Solved by the Invention] However, the conventional diaphragm described above has various drawbacks. For example, in (1), the high elasticity characteristic of carbon fiber is not fully utilized.
Even when the amount of carbon fiber mixed is 50 wt%, the Young's modulus is at most 5×10 _U10 dyn/cm ² . This is because a peak value occurs in Young's modulus with respect to the mixing ratio of carbon fiber and pulp fiber, and there is a limit to the mixing ratio of carbon fiber. In addition, in (2), fluidity during sheet molding,
The amount of carbon fiber mixed in is limited by the dimensions of the blowing nozzle. For example, in a sheet with a thickness of 0.3 to 0.5 mm, the amount of carbon fiber mixed is at most 20 wt%. Further, the above mixing amount is also limited by the vacuum forming process. On the other hand, in injection molding, the above mixing amount is at most
It is 15wt%. Therefore, the rigidity of the diaphragm cannot be increased sufficiently. In (3), a diaphragm with higher rigidity can be obtained compared to the above two examples, but in order to form a flat cloth into a cone or dome shape once organized as a woven cloth, the expansion and contraction of the carbon fiber itself is required. Since it is necessary to use the weave misalignment to shape the product, the manufacturing cost is extremely high because the shape can be formed through a number of steps such as preforming. It was difficult to mold a diaphragm with a complicated shape, such as one-piece molding of sion ribs. Furthermore, compared to the former, the diaphragm plate (4) has a density of 1.5 to 1.6 g/cm ³ and a Young's modulus of 1.5 × 10 ¹¹ to 1.8 ×
It has the advantage that E/ρ at 10 ¹¹ dyn/cm ² is significantly larger than the above three examples, it has excellent acoustic properties as a diaphragm plate, and it has good moldability, but
It has the disadvantages of low brittleness and low impact resistance. In general, filler-reinforced resins exhibit this tendency, and as a means to solve this problem, it is possible to treat the surface of the filler to improve its adhesion with the resin, or to use a resin with high impact resistance. However, this resulted in problems such as increased costs and deterioration of the acoustic characteristics of the diaphragm. [Means for Solving the Problems] The present invention is made by heat-pressing molding a composite material mainly composed of montmorillonite with a curing agent or curing accelerator adsorbed between layers, a thermosetting resin monomer, and carbon fiber. A diaphragm for an electroacoustic transducer in which the obtained layer and a fibrous layer are laminated, and a method for manufacturing the diaphragm, which includes forming a fibrous layer into a diaphragm shape and drying it into a mold. A powder composite material mainly composed of montmorillonite with a curing agent or curing accelerator adsorbed between the layers, a thermosetting resin monomer, and carbon fiber is placed on the fiber layer and molded under heat and pressure. In this method, the diaphragm for an electroacoustic transducer is manufactured by laminating and molding layers obtained by fluidizing the resin and heating and press-molding the fiber layer and the composite material using the resin. [Example] Montmorillonite (Al ₂ O ₃ · 4SiO ₂ · nH ₂ O, also known as bentonite), which is a type of hydrous aluminum silicate, was immersed in a solvent in which a curing agent or curing accelerator was dissolved in an appropriate solvent (at 60°C). , several hours). As a result, the curing agent or curing accelerator is adsorbed between the silicate layers of montmorillonite. After solution washing, this is dried to obtain a composite with a curing agent or curing accelerator. Next, a composite (adsorbing diaminodiphenylmethane as a hardening agent) is added to an 11-part epoxy resin monomer (trade name: Araldite).
6071) 40 parts hardening agent (diaminodiphenylsulfone) 4.5 parts mold release agent (zinc stearate) 1 part carbon fiber (average fiber length 0.1 mm)
43.5 parts The above mixture was stirred under heating (85°C) to mix uniformly, then cooled and pulverized to obtain a powdered composite material. On the other hand, the weight ratio of NUKP and dissolving pulp is 8:
2, and the mixture is freeness 550.
Beat until ~600. Next, the beaten pulp fibers are formed into a diaphragm-shaped paper and dried by air drying to obtain a diaphragm-shaped fiber layer. The fiber layer is placed in a concave mold having a concave portion having substantially the same shape as the diaphragm shape, and a certain amount of the powder composite is placed onto the fiber layer so that the deposited thickness thereof is substantially constant. Then, the convex mold that engages with the concave mold is lowered, and hot press molding is performed at a temperature of 150° C. and a press pressure of 100 kg/cm ² for about 5 minutes. Thus, a diaphragm having a predetermined shape was obtained in which a layer obtained by heat-pressing the composite material and the fiber layer were laminated. [Effects of the Invention] A diaphragm obtained by the above manufacturing method and the powdered composite were placed in the mold, and a diaphragm hot press-molded under substantially the same conditions was used as a comparative example, and the physical characteristics of both was measured and obtained the following results.

[Table] In the above table, E is Young's modulus, and t is thickness, which is the thickness that each diaphragm can have when molded into a diaphragm of the same weight. In addition, in order to compare the impact resistance of the example diaphragm and the comparative example diaphragm, a 16.5g steel ball was dropped and the falling distance at which the diaphragm was destroyed was measured; in the example, it was 126 cm. In comparison, it was 60 cm in the comparative example. As described above, according to the present invention, the bending rigidity and internal loss are significantly increased, and as is clear from the falling ball test, the brittleness which was a drawback of the conventional product has been improved, and the impact resistance has been improved. The first reason for the remarkable increase in the bending rigidity of the diaphragm of the present invention is that the layer obtained by thermoforming the composite resin has a high Young's modulus as described above, and this is because the layer is made of carbon fiber. The montmorillonite-epoxy composite is dispersed so as to fill the space between the montmorillonite layers, and a blended polymer is formed in which the epoxy polymer and montmorillonite intercalated between the montmorillonite layers are firmly bonded, and the blended polymer entangles the carbon fibers. This is thought to be because the particles are organized into a three-dimensional network structure. By laminating the high Young's modulus layer and the fiber layer, the shortcomings of the high Young's modulus layer, such as low brittleness and low impact resistance, are solved, and the high Young's modulus layer is composed only of the high Young's modulus layer. Compared to other diaphragms, the decrease in density is greater than the decrease in Young's modulus, so when compared with diaphragms of the same weight, a greater bending stiffness value can be obtained.Furthermore, due to the laminated structure with fiber layers, It has the advantage of being able to obtain a large internal loss. Further, according to the manufacturing method of the present invention, the epoxy resin in the composite material melts once in the press mold, becomes low in viscosity, and flows, but at a constant temperature (15
℃), the curing agent adsorbed between the layers of montmorillonite does not leach out, so it maintains a low viscosity fluid state, making it possible to fill every nook and cranny of a mold with a complex shape and improve shape and dimensional accuracy. At the same time, the thermosetting resin flowing in the mold infiltrates the surface of the fiber layer, making it possible to laminate both layers without the need for any other adhesive, and the bonded portion is made of pulp fibers. Since the thermosetting resin and carbon fiber are bonded together, the bonding force is extremely high. The amount of carbon fiber mixed in the composite material can be selected depending on the purpose, but it should be 30 to 60 wt, considering the degree of reinforcement and fluidity of the resin.
% is desirable. In addition, since the pulp fiber layer makes it easy for thermosetting resin to penetrate during hot-pressure molding, it is preferable that the pulp fiber layer is only dried after papermaking so that the fibers are less entangled and the porosity is increased.

Claims (1)

[Scope of Claims] 1. A layer obtained by heating and press-molding a composite material mainly composed of montmorillonite, a thermosetting resin monomer, and carbon fiber with a curing agent or curing accelerator adsorbed between the layers, and fibers. A diaphragm for an electroacoustic transducer, characterized in that the diaphragm is formed by laminating layers. 2. Claim No. 2, characterized in that the fiber layer and the layer obtained by heating and pressing the composite material are laminated using thermosetting resin that flowed out during heating and pressing the composite material. The diaphragm for an electroacoustic transducer according to item 1. 3 Powder whose main materials are montmorillonite, a thermosetting resin monomer, and carbon fiber, in which a fiber layer formed into a diaphragm shape and dried is placed in a mold, and a curing agent or curing accelerator is adsorbed between the layers. A shaped composite material is placed on the fiber layer and molded under heat and pressure to cause the resin to flow, and the layers obtained by heating and pressing the fiber layer and the composite material with the resin are laminated and molded. A method of manufacturing a diaphragm for an electroacoustic transducer, characterized by: