JPS6220757B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to Mg or Mg-based alloys (hereinafter referred to as Mg-based alloys).
This invention aims to improve the rust prevention and rigidity of a diaphragm based on Mg alloy. Conventionally, Al and Ti have been widely used as diaphragm materials for horn drivers and direct-radiation dome speakers, but these metals have relatively high densities and low tanδ, which causes internal loss, resulting in a decrease in conversion efficiency. It had various drawbacks such as harmful resonance and other problems. For this reason, a diaphragm made of Mg or Mg alloy, which has a relatively low density and a relatively large tan δ, has been devised and put into practical use. In fact, these diaphragms have shown better results than conventional metal diaphragms. However, since Mg or Mg alloy is an extremely active metal, it is easily oxidized in the air. The surface of Mg or Mg alloy is damaged by moisture in the air.
Hydroxides such as Mg ⁺⁺ +2(OH) ^- →Mg(OH) ₂ are generated. Also, due to sulfur dioxide gas, carbon dioxide gas, etc. in the air.
Compounds such as MgSO ₄ and MgCO ₃ are generated, and in some cases this can serve as a protective film, but under indoor conditions where it is normally used as a speaker diaphragm, it corrodes due to the presence of salts and acids that destroy this film, making it useless for practical use. I couldn't do it. In order to prevent corrosion of Mg, it is possible to alloy it by adding, for example, Zn, but this is not sufficient in practice, and alloying impairs the inherent advantages of Mg. Generally, to prevent corrosion of metals, plating with metals with excellent corrosion resistance is carried out.
Since the standard electrode potential of Mg is -2.363V, which is extremely electrically active, electrolytic corrosion occurs at the interface with the plated metal, which is undesirable. In addition, it has been considered that an oxide film is formed on the surface of Mg or Mg alloy by anodizing, etc. to give it an anticorrosion effect, but it is also possible to form it into a dome or cone shape by anodizing. Mg
Alternatively, when forming an oxide film on a Mg alloy diaphragm substrate, charges are concentrated on the protruding parts of the shape, making it difficult to obtain a uniform current density, making it difficult to form a film with a uniform thickness, and causing damage to each part of the diaphragm. The Takagi reproduction limit frequency varies due to non-uniformity of physical properties. In particular, variations in f ₀ occur due to variations in the flange portion, which is an edge portion integrally formed on the outer periphery of the dome-shaped vibrating portion. Furthermore, the cost of this device is high and the processing time is long, which causes an increase in manufacturing costs. In addition, methods of forming magnesium oxide on the surface of Mg or Mg alloy by vacuum evaporation or chemical vapor deposition do not produce a fine film, and the adhesion to Mg or Mg alloy is insufficient. Mg(OH) ₂ is generated at the interface between the two by (OH) ^- ions in the air that have passed through the fine pores of the magnesium, causing corrosion and flaking, making it unusable for practical use. Furthermore, diaphragms with corrosion-resistant metal bonded to the surface of Mg or Mg alloys are also being considered;
In order to prevent corrosion of the Mg alloy, the choice of adhesive is limited to hot melt adhesives that do not contain acids or salts. Furthermore, when gluing metal parts in the shape of a diaphragm, the adhesive tends to have non-stick parts, making the physical properties of each part of the diaphragm non-uniform, causing abnormal noise and other negative effects. Therefore, the present invention is characterized in that a chemical conversion film is formed by chemical conversion treatment on the surface of Mg or Mg alloy, and then a synthetic resin layer is further formed on top of the chemical conversion film.Examples will be described in detail below. explain. Example 1 A diaphragm substrate (weight 0.075 g) having a dome-shaped part with a diameter of 25 mmφ and a depth of 7.5 mm and a flange with a width of 3 mm on its outer periphery was obtained by press-molding a Mg-Al-Zn alloy with a thickness of 44 μm. . NaOH with this diaphragm substrate maintained at 50° to 60°C
It was immersed in a solution (100g/) for about 2 minutes to remove impurities on the surface, and then washed with water. Next, it was momentarily immersed in a 2% concentration NHO ₃ solution to neutralize it, and then washed with water. Next, a chromate treatment solution (Na ₂ Cr ₂ O ₇・2H ₂ O: 180 g/liquid and 70% HNO ₃
The diaphragm substrate is immersed in a mixture of 180ml/diluent solution for 0.5 to 2 minutes with air agitation, immediately washed with water, and dried with hot air at 50° to 80°C to complete the chromate treatment. . Next, 0.05 wt% of mercaptan was mixed as a polymerization catalyst into the diaphragm substrate subjected to the chromate treatment and methyl methacrylate from which hydroquinone, etc. mixed as a polymerization inhibitor had been removed by a vacuum method. Place the solution in a vacuum evaporator and
A methyl methacrylate film of about 1.5 μm was formed on the chromate-treated film under a vacuum of 10 ⁻³ to 3×10 ⁻⁴ mmHg. Thereafter, the diaphragm substrate taken out from the vapor deposition apparatus was heated at about 60° C. for 2 hours to perform the first stage polymerization of methyl methacrylate, and further heated at 40° C. for 15 hours to completely polymerize the resin. Example 2 A diaphragm substrate treated with chromate in the same manner as in Example 1 was immersed in a 25 wt% acrylic resin solution, pulled up, dried to the touch at room temperature for about 10 to 15 minutes, and then heated to an angle of about 70°. Drying was carried out at ~80°C for about 20 minutes. The thickness of the acrylic resin layer obtained by this process is 16
It was μm. As shown in Fig. 1, the diaphragm thus obtained has a base 1 made of Mg alloy, and a chromium compound 2 (Cr ₂ O ₃ .
It has a structure _in which a layer of CrO ₃ . Then, when the surface portion of the diaphragm is minutely observed, the chromium compound layer 2 formed on the surface portion including the defect holes 1a and recesses of the Mg alloy substrate 1 and a part of the surface of the Mg alloy substrate 1, and the chromium compound layer 2 formed inside the surface of the Mg alloy substrate Methyl methacrylate 3 or acrylic resin is layered on the surface of the chromium compound 2, including cracks and recesses. In this diaphragm, as a first step, the surface of the Mg alloy acts to block the outside air due to the chromium compound, and as a second step, the synthetic resin layer is protected against acids, salts, or sludge that attack the chromium compound. As a result of protecting the chromium compound layer from scratches etc., it has an extremely excellent anti-corrosion effect. In order to confirm the effectiveness of the diaphragm of this invention, it was left in a humidified atmosphere together with an untreated Mg alloy, an acrylic resin-layered Mg alloy, and a chromate-treated Mg alloy, and Table 1 shows the results. .

[Table] As is clear from Table 1, the diaphragm of the present invention, as shown in Examples 1 and 2, was able to obtain a practically sufficient rust prevention effect for use as a diaphragm for speakers. In particular, in the diaphragm according to Example 1, the methyl methacrylate resin is layered by vacuum deposition, so there are no pinholes in the film, and the resin layer is layered even on the minute defects of the chromium compound, so the effect is high. Most notable. In addition, in order to investigate the effects of the above treatments on the weight and Young's modulus of the diaphragm, the weight of the diaphragm subjected to each treatment was measured, and the Young's modulus of each diaphragm was measured by the vibration lead method. The results were obtained.

[Table] As is clear from this table, chromium-hydrochloric acid treatment not only improves rust prevention properties, but also increases the rigidity of the diaphragm, which makes it possible to reproduce even higher frequencies and expand the reproduction frequency band. Ru. Furthermore, although there is a significant weight increase due to the chromium compound and synthetic resin layer, this is not a practical problem, and particularly in Example 1, the increase is only about 5%. This is due to the fact that the methyl methacrylate resin layer can be formed extremely thinly as described above, and it can be said that this is the best example in combination with the above-mentioned rust prevention effect. In other embodiments of the present invention, as the chemical conversion treatment, for example, a film of a compound such as manganese, calcium, tin, selenium, etc. can be employed, and as the synthetic resin, almost any other synthetic resin can be employed. As explained above, this invention provides Mg or Mg
A diaphragm having an alloy as a base 1, which is characterized by having a chemical conversion film 2 formed by chemical conversion treatment on the base, and a synthetic resin film 3 further layered on top of the chemical conversion film 2. This has the effect of not only providing corrosion resistance that can be used as a diaphragm for personal use but also further increasing the rigidity of the Mg or Mg alloy diaphragm.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the diaphragm of the present invention.

Claims (1)

[Scope of Claims] 1. A diaphragm for an electroacoustic transducer comprising a substrate 1 made of Mg or an Mg alloy, a chemical conversion coating 2 formed on the surface thereof, and a synthetic resin coating 3 formed on the surface of the chemical conversion coating. 2 Chemical conversion coating 2 is a chromium compound and synthetic resin coating 3
The diaphragm for an electroacoustic transducer according to claim 1, wherein the diaphragm is a methyl methacrylate resin layered by vacuum deposition. 3. The diaphragm according to claim 1, wherein the chemical conversion film 2 is a chromium compound, and the synthetic resin film 3 is an acrylic resin.