JPH058637B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a center cap for an acoustic diaphragm. BACKGROUND TECHNOLOGY Generally, center caps used for acoustic diaphragms are lightweight, have high rigidity, have a moderate internal loss, and have a ratio of Young's modulus E to density ρ√
A great deal is needed. Conventional materials used include paper, phenolic resin-impregnated woven fabric, polyethylene terephthalate film, and metal plates. The center cap for an acoustic diaphragm has a large effect on the frequency characteristics of the diaphragm itself, especially in high frequency bands, so it is required to have the same physical properties as the diaphragm, such as high specific modulus, low density, and high internal loss. However, while paper has a large internal loss and can provide flat characteristics, its low rigidity causes split damping from low frequency bands, which not only deteriorates transient characteristics and distortion characteristics, but also causes changes in sound quality because it easily absorbs moisture. The sound quality is also likely to deteriorate due to slight age changes.
In addition, in the case of paper, paper is made one sheet at a time and requires a dry pressing process, which results in uneven thickness and density depending on the material and shape of the production process.The physical properties are unstable, and it takes a long time to obtain stable properties. This requires considerable skill and experience. Although polyethylene terephthalate film is thermoformable and has excellent water resistance, it has the drawbacks of low internal loss and low specific modulus. Also, 100℃
There is a problem that deformation easily occurs in a high temperature atmosphere. Although metal plates have high rigidity, they have low internal loss, making it difficult to damp high-frequency resonance, and the material is extremely hard and brittle, making them difficult to work with. Although the phenolic resin-impregnated woven fabric has a low density, it has a disadvantage of low efficiency due to its air permeability. As is clear from the above, paper, woven fabric impregnated with phenol resin, polyethylene terephthalate film, and metal plates are not necessarily satisfactory as center cap materials for acoustic diaphragms. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to provide a center cap for an acoustic diaphragm with high internal loss and low density. The center cap for an acoustic diaphragm of the present invention includes a polymeric thermoplastic resin such as polypropylene, a copolymer mainly composed of polypropylene, or a mixture thereof, titanium fibers or potassium titanate fibers, graphite and/or mica, etc. It is characterized by being formed from a material in which the scales are mixed with a filler. Example Hereinafter, an example of the present invention will be described based on tables and figures. To form a film from a material in which polypropylene, a copolymer mainly composed of polypropylene, or a mixture thereof, titanium fiber or potassium titanate fiber, and graphite and/or mica flake-like filler are mixed as raw materials. First,
A pelletized material is prepared by mixing raw materials at a vol% ratio (volume mixing ratio) as shown in Table 1. After that, the pellet material is extruded into a molding machine.
A film of any desired thickness is obtained by forming the film while heating it to a sheeting temperature of 230 to 260°C and passing it through several stages of cooling rolls. Then 150℃
The film is heated and softened using a hot plate of about 100 mL, and then molded into a sheet at a temperature of 230°C to 260°C in a vacuum or pressure atmosphere using a heated mold of a predetermined shape to obtain a desired center cap. The characteristics of the obtained center cap are shown in Table 2. As a comparative example, center caps were manufactured from a mixture of polypropylene and potassium titanate fibers and a mixture of polypropylene and mica powder by the manufacturing method of the present invention, and Table 1 shows their mixing ratios. Furthermore, in Table 2, the characteristics of a conventional center cap having a shape similar to that of this embodiment are also listed as a conventional example.

【table】

【table】

[Table] As is clear from Table 2, the center cap of this example has higher characteristic values than the conventional example, and the Young's modulus of the center cap containing 30 vol% of the total of potassium titanate fibers and graphite. paper cone,
About 3 times as much as 100% polypropylene, internal loss more than paper cone,

[Formula] yields a value that is more than 1.5 times that of 100% polypropylene. However, although there is no significant difference in physical properties compared to Comparative Example 1, in which only potassium titanate fibers were mixed with polypropylene,
In the case of Comparative Example 1, since the filler is only potassium titanate fibers, the filler exhibits vertical and horizontal directionality, which tends to cause split resonance and cause distortion in frequency characteristics. In the present invention, since a filler consisting only of titanium fibers or potassium titanate fibers exhibits directionality, flaky graphite mica or a mixture thereof is further added in order to improve the directionality. By adding fillers such as graphite and mica, there was no significant difference in physical properties, but flat frequency characteristics with less distortion were obtained. The graphite used in this example had a particle size of 1 to
The potassium titanate fiber is preferably 15 μm (average particle size 5 μm), and the potassium titanate fiber is Teismo (trademark) manufactured by Otsuka Chemical Co., Ltd.
and the average fiber length is 20 to 30 μm and the average fiber diameter is
It is 0.1 to 0.3 μm. Furthermore, when the sound pressure frequency characteristics of the center cap of the present invention and the conventional one are compared under the same measurement conditions, the results are as shown in FIG. The characteristics shown in A are those of the center cap of the present invention, and the characteristics shown in B are those of the conventional one. It can be seen that the center cap of the present invention has flat frequency characteristics in the high frequency range. Furthermore, the center cap of the present invention has almost no moisture absorption and excellent heat resistance, and can be mass-produced. Effects of the Invention As described above, according to the present invention, it is formed by mixing titanium fibers or potassium titanate fibers with a flaky filler in a synthetic resin such as polypropylene, so it has low density and high specific elasticity. A center cap for an acoustic diaphragm that satisfies the physical properties required for a center cap such as low frequency and high internal loss, prevents split resonance, and has high efficiency, a wide band, and a flat frequency response in the high frequency range. It will be done. In addition, the center cap has almost no hygroscopicity and has a high softening temperature, so it has little deterioration over time and is excellent in reliability. Furthermore, because the polymeric thermoplastic resin contains fine titanate fibers, the molding surface is smooth and faithful to minute changes in the molding pinion mold during the manufacturing process, and the resin The internal filling effect is uniform, and unreinforced parts are less likely to occur even in small details, reducing sink marks and warpage during molding.

[Brief explanation of drawings]

The figure is a graph of sound pressure frequency characteristics comparing the center cap of the present invention with a conventional one.

Claims (1)

[Scope of Claims] 1. An acoustic diaphragm made of a synthetic resin made of polypropylene, a copolymer mainly composed of polypropylene, or a mixture thereof, mixed with titanium fibers or potassium titanate fibers and a flaky filler. center cap. 2. The center cap according to claim 1, wherein the scale-like filler is a filler made of graphite, mica, or a mixture thereof. 3. The center cap according to claim 2, wherein the volume mixing ratio of the synthetic resin, the titanium fiber or the potassium titanate fiber, and the scale-like filler is 70:30. .