JPH0548678B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in a diaphragm for an electroacoustic transducer, and particularly to a diaphragm made of a material that has high rigidity and is extremely easy to mold. In recent years, diaphragms for electroacoustic transducers using carbon fiber as a component of the diaphragm have been considered and put into practical use primarily for the purpose of increasing rigidity. Examples of this type of diaphragm are: (1) A diaphragm made by mixing carbon fiber and valve 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. Vibration plates and the like have been put into practical use. However, the conventional diaphragm described above has various drawbacks. For example, in (1), the high elasticity characteristic of carbon fiber is not fully utilized, and even if the amount of carbon fiber mixed is 50 wt%, the Young's modulus is at most 5 ×
10 ¹⁰ dyn/cm. This is because a peak value occurs in Young's modulus with respect to the mixing ratio of carbon fibers and pulp fibers, and there is a limit to the mixing ratio of carbon fibers. In addition, in (2), the amount of carbon fiber mixed is limited by the fluidity of the mixture during sheet forming and the dimensions of the discharge 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. Furthermore, 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 carbon fiber itself must be formed. Since expansion and contraction cannot be expected, it is necessary to take advantage of the weave misalignment to form the product, so the manufacturing cost is extremely high as it is possible to form the product through a number of processes such as preforming. It has been difficult to mold diaphragms with complex shapes such as integrated molding of gagement ribs. Therefore, in this invention, a composite material whose main materials are montmorillonite, a thermosetting resin monomer, and carbon fiber with a hardening agent or hardening accelerator adsorbed between the layers, and an inorganic scale-like substance such as graphite fine powder, mica fine powder, etc. By heating and molding the mixture, a diaphragm with excellent physical properties can be provided and the molding can be facilitated.Examples will be described in detail below. For the purpose of this invention, montmorillonite (Al ₂ O ₃ .4Si ₂ O.nH ₂ O, also known as bentonite), which is a type of hydrous aluminum silicate in which a curing agent or a curing accelerator is adsorbed between layers, is important. The montmorillonite is immersed (60° C., several hours) in a solution containing a hardening agent or hardening accelerator in a suitable solvent. 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, add 10 parts of the composite (adsorbing diaminodiphenylmethane as a curing agent) to an epoxy resin monomer (trade name: Araldite).
6071) 35 parts hardening agent (diaminodiphenylsulfone) 4.4 parts mold release agent (zinc stearate) 1 part carbon fiber (polyacnylonitrile carbon fiber average length 0.35 mm) 50 parts The above mixture was heated ( The mixture was mixed uniformly by stirring at 85° C.), then cooled and pulverized to obtain a powdered composite material. 10 parts of graphite fine powder (all 325 mesh) was uniformly mixed into the composite material and molded using a mold of a predetermined shape at a temperature of 160℃, a press pressure of 85Kg/cm ² , and a molding time of 10 minutes.
A cone-shaped diaphragm (sample 1) with an opening diameter of 85 mm, a top diameter of 30 mm, and a total height of 19 mm was obtained by press molding in minutes. The above diaphragm (sample 1) and 50wt of kraft pulp
%, carbon fiber 35wt%, phenolic resin
The physical properties (density ρ,
Table 1 shows the results of measuring the Young's modulus (E).

[Table] However, density: g/cm ³ , Young's modulus: ×10 ¹⁰ dyn/cm ²
As is clear from the table, the diaphragm of the present invention has an extremely high E/ρ. Next, in the present invention, the effect of mixing an inorganic scale-like substance will be described. The mixing ratio of carbon fiber is a major factor in properly molding a diaphragm made of such a composite material. For example, when a resin with good fluidity and carbon fiber with a large average fiber length are kneaded and molded, the flow of the carbon fiber is less than that of the resin.
Particularly in the peripheral areas of the diaphragm (the areas where it is attached to the edges and the voice coil), a phenomenon occurs where the resin and carbon fiber separate.
This causes local variations in the characteristics of the diaphragm and deformations such as pinholes and warping. To solve this problem, it is necessary to heat the resin to crosslink and thicken it, or to reduce the fiber length of the carbon fiber, but in the former case, it is necessary to increase the molding pressure, which requires new molding equipment. In the latter case, as the fiber length becomes smaller, the Young's modulus of the molded diaphragm decreases, which is not favorable in terms of physical properties. On the other hand, in the present invention, since the graphato fine powder flows with the flow of the resin and has the effect of pushing away the carbon fibers, separation of the resin and the filler during molding is suppressed, and as a result, it can be inferred that the above-mentioned drawbacks can be solved. Therefore, in order to confirm the above effect, as an example without mixing graphite fine powder, only the above composite material was placed in a mold of the same shape at a temperature of 160°C and a press pressure of 85 kg/cm ² .
A diaphragm (sample 4) of the same shape was obtained by press molding in a molding time of 10 minutes. 100 pieces each of the diaphragm of the present invention (sample 1) and the diaphragm described above (sample 4) were molded, and the presence or absence of pinholes and deformation was examined, and Table 2 was obtained.

[Table] As is clear from Table 2, the diaphragm of the present invention (Sample 1) had extremely few pinholes or deformations during molding, and was excellent in mass production. By the way, when we investigated the pressing conditions in which pinholes would not occur in both of the diaphragms mentioned above, we found that the diaphragm according to the present invention (sample 1) does not require a preheating process and a press pressure of about 60 kg/cm ² is sufficient. The diaphragm (sample 4) required a preheating time of 60 seconds and a pressing pressure of about 100 kg/cm ² . From this consideration, it can be seen whether the diaphragm of this invention is suitable for mass production. Next, the physical properties of the diaphragm (Sample 4) were measured and compared with the diaphragm of the present invention (Sample 1).
Obtained the results in the table.

[Table] However, bending elastic modulus: Kg/cm ² , internal loss: tan δ
It is. As is clear from the above table, the diaphragm of this invention example (Sample 1) had increased Young's modulus, internal loss, and flexural modulus, and was found to have excellent physical properties. The reason why the Young's modulus of the diaphragm of this invention increases significantly is that montmorillonite fills the spaces between carbon fibers and graphite fine powder.
A blended polymer is formed in which the epoxy composite is dispersed and the epoxy polymer and montmorillonite are firmly bonded between the layers of montmorillonite, and the blended polymer entangles carbon fibers and graphite fine powder in a three-dimensional manner. This seems to be because it is organized into a network structure. In addition, in the diaphragm of the present invention, the epoxy resin once melts in the press mold and becomes low in viscosity and flows, but up to a certain temperature (150°C), the curing agent or curing accelerator adsorbed between the layers of montmorillonite is As a result of no leaching, it maintains a low viscosity fluid state.
Even if the mold has a complex shape, it is filled to every corner, and the fine graphite powder flows with the flow of the resin and has the effect of pushing away the carbon fibers, suppressing separation of the resin and filler during molding. As a result, each part of the diaphragm is uniform, and a diaphragm with high dimensional and shape accuracy can be obtained with few pinholes or deformations. Further, as a curing accelerator to be adsorbed to montmolinite, for example, ethylmethylimidazole can be used in combination with phthalic anhydride (hardening agent). As explained above, the present invention is based on a composite material mainly composed of montmorillonite, a thermosetting resin monomer, and carbon fiber in which a curing agent or curing accelerator is adsorbed between layers, and an inorganic scale-like substance such as graphite fine powder. , a diaphragm for an electroacoustic transducer characterized by being formed by heating and molding a mixture of fine mica powder, etc., which allows the diaphragm to be made highly rigid or lightweight, so that it can be used as a speaker with good frequency characteristics. can be provided. Furthermore, it is possible to prevent the occurrence of pinholes and deformation during molding, and it is possible to easily manufacture large quantities of diaphragms with high dimensional accuracy, making it possible to provide diaphragms with good characteristics at a low cost, which was not previously possible. It has excellent effects that have never been possible before. Although the present invention has been described as being applied to a cone-shaped diaphragm, it can of course be applied to a dome-shaped diaphragm and even a center dome radiator.

Claims (1)

[Scope of Claims] 1. A mixture of a composite material whose main materials are montmorillonite with a curing agent or curing accelerator adsorbed between the layers, a thermosetting resin monomer, and carbon fiber, and an inorganic scale-like substance, and formed by heating. A diaphragm for electroacoustic transducers featuring: 2. The diaphragm for an electroacoustic transducer according to claim 1, wherein the thermosetting resin monomer is an epoxy resin.