JPH0336360B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in diaphragms used in electroacoustic transducers such as speakers. To explain the conventional diaphragm of this type of converter in terms of a speaker, diaphragms made of paper or metal foil have been frequently used in the past. On the other hand, the physical properties required for a speaker diaphragm include light weight, high rigidity,
It is said to have good vibration energy absorption properties. In other words, it must be lightweight in order to improve conversion efficiency, it must be highly rigid in order to expand the piston vibration frequency range and reproduce the frequency range, it must be highly rigid in order to suppress steep resonance in the divided vibration range, and the input signal waveform. Good vibration energy absorption is required in order to output a sound waveform close to . Therefore, at least the basic physical properties required for a speaker diaphragm material are low density (light weight), high Young's modulus (high rigidity), and high internal loss (high vibration energy absorption). If we consider conventional diaphragm materials from this perspective, paper is characterized by its low density, but on the other hand, it has low internal loss, which causes peaks and dips in the frequency characteristics and flat frequency characteristics. It is difficult to obtain speakers with Furthermore, metal is characterized by a high Young's modulus, but has a high density and extremely low internal loss, which reduces conversion efficiency and makes it difficult to obtain a speaker with flat frequency characteristics. Furthermore, in the manufacturing process of diaphragms, paper diaphragms require processes such as beating, papermaking, and press molding, and the control of various conditions in each process is extremely complicated. It has the disadvantage that it is difficult to obtain a uniform diaphragm because the characteristics of the diaphragm vary. Furthermore, metal diaphragms also have the drawback that equipment costs such as press machines are high and the diaphragm cost is relatively high. Another major drawback of paper diaphragms is their hygroscopicity, which causes deterioration of various characteristics of the diaphragm. Therefore, in recent years, diaphragms formed by molding thermoplastic resin sheets such as polypropylene have been proposed and put into practical use. Such thermoplastics have a relatively low density (ρ:
1.0) and high internal loss, as well as manufacturing advantages such as the ability to easily provide uniform products through vacuum forming, etc., and the advantage of low hygroscopicity. Due to the low Young's modulus, the rigidity of the diaphragm was insufficient and the reproduction frequency band was limited. It is also possible to increase the rigidity by incorporating a filler into this type of material, but this has the drawback of significantly lowering the internal loss compared to the reinforcing effect of the filler. In this way, in conventional diaphragm materials, low density and high Young's modulus, and high Young's modulus and high internal loss are contradictory physical properties, so it is difficult to fully satisfy all of the above requirements. In actual design, the specific modulus of elasticity (E/ρ), which is the ratio of density (ρ) and Young's modulus (E), is used as a guideline, or one of the physical properties is characterized depending on the design purpose. was being carried out. Therefore, in this invention, by mixing a filler, the Young's modulus of the thermoplastic resin is increased, and
This is a diaphragm molded from a composite sheet that not only suppresses a decrease in internal loss due to its laminated structure with a resin that has high internal loss, but also has improved specific elastic modulus and internal loss compared to conventional materials.Examples will be explained in detail below. do. [Example 1] 20wt% scaly mica powder (average particle size 325 mesh, hereinafter referred to as mica flakes) subjected to polypropylene and epoxy silane coupling treatment and 5wt% subjected to titanate coupling treatment
scaly graphite powder (average particle size 250 mesh,
(hereinafter referred to as graphite flakes) were kneaded and extruded to obtain a first film having a thickness of 220 μm. On the other hand, styrene-isoprene-styrene block copolymer (isoprene content 27wt%), petroleum resin
25wt% and atactic polypropylene 5wt%
The mixed resin was sliced into a thickness of approximately 150 μm to obtain a second film. Then, the first film was placed on both sides of the second film, and the pressing temperature was 130°C and the pressing pressure was 24°C.
The second film was melted and adhered to the first film by pressing at Kg/cm ² . As a result, a composite sheet having a thickness of approximately 500 μm was obtained, which had an outer layer formed by the first film on both sides of an intermediate layer having a thickness of approximately 60 μm formed by the second film. [Example 2] Polypropylene and 25 wt % graphite flakes (average particle size: 250 mesh) subjected to titanate coupling treatment were kneaded and extruded to obtain a first film with a thickness of 230 μm. Then, the first film was placed on both sides of the second film having a thickness of about 150 μm obtained in the same manner as in Example 1, and pressed at a pressing temperature of 130°C and a pressing pressure of 24 kg/cm ² to melt the second film. and adhered to the first film. As a result, a composite sheet having a thickness of approximately 540 μm was obtained, which had an outer layer formed by the first film on both sides of an intermediate layer having a thickness of approximately 80 μm formed by the second film. [Example 3] 30wt% mica flakes (average particle size
325 mesh) and extrusion molding to obtain a first film having a thickness of approximately 180 μm. Hereinafter, in the same manner as in Example 2, an intermediate layer having a thickness of approximately 80 μm was formed from a second film, and an outer layer formed from the first film was formed on both sides of the intermediate layer having a thickness of approximately 80 μm.
A composite sheet of 440 μm was obtained. [Example 4] The mixed resin dissolved and dispersed in a mixed solvent of toluene and vinyl acetate (1:1) was coated on one side of the first film in Example 1 using a coater, and immediately after drying, a similar first film was applied. The first film was placed on the coating surface and passed through a heating roller (roller temperature: 130°C, roller pressure: 24 kg/cm ² ) to melt the mixed resin and adhere it to the first film. This results in a thickness of approx.
A composite sheet having a thickness of approximately 460 μm was obtained, having an outer layer formed from the first film on both sides of a 20 μm intermediate layer. Each of the composite sheets obtained in Examples 1 to 4 above was cut into 1.5 cm x 4 cm pieces, and the density, Young's modulus, and internal loss (tan δ) were measured using the vibration reed method at room temperature (20°C). The following table lists the diaphragm materials.

[Table] As is clear from this table, the composite sheet used in the diaphragm of the present invention has a specific elastic modulus 1.7 to 2.5 times higher than that of polypropylene, and also has an increased internal loss. There are also examples in which the specific modulus is slightly reduced compared to paper, but the internal loss is three times or more. Furthermore, the composite sheet used in the diaphragm of the present invention not only has a high internal loss but also has the following advantages. In general, the internal loss of synthetic resins changes with changes in temperature, and the temperature range within which high internal loss can be maintained is extremely narrow. For example, the dotted line shown in FIG. 1 is a curve showing the change in internal loss of polypropylene with temperature, but it has the disadvantage that it reaches its maximum value (0.089) near 15° C., and the internal loss decreases significantly around that point. However, as shown by the solid line, the composite sheet obtained in Example 1 reached a maximum value (0.098) near 20°C and was able to maintain a value close to the maximum value up to about 35°C. Therefore, the composite sheet used in the diaphragm of the present invention not only has a high internal loss, but also has the advantage that the internal loss changes little with temperature changes. Next, the composite sheet obtained in Example 1 was formed into a cone shape by vacuum forming, and a speaker with an effective vibration radius of 12.5 cm was manufactured by incorporating the composite sheet, and its frequency characteristics were measured. In FIG. 2, a is the above speaker equipped with the diaphragm of the present invention, b is a speaker with the same effective vibration radius equipped with a paper diaphragm, and c is a speaker with the same effective vibration radius equipped with a polypropylene diaphragm. are the respective frequency characteristics of As is clear from the figure, the peak and dip of characteristic a are significantly suppressed and flattened compared to characteristic b, and when compared with characteristic c, the frequency characteristic is further flattened and the reproduction limit frequency is lowered. The playback bandwidth is becoming wider. This shows that the diaphragm of the present invention has higher rigidity and significantly improved vibration energy absorbability compared to conventional diaphragms. In this way, the present invention not only makes it possible to provide a speaker with good frequency characteristics, but also enables large quantities of diaphragms with good dimensional accuracy and uniform quality because they can be obtained by vacuum or pressure forming a composite sheet. Furthermore, it is possible to provide a diaphragm that is easy to provide and is hardly affected by temperature and humidity. As explained above, the present invention is a diaphragm formed by molding a laminated composite sheet consisting of a layer mainly composed of a styrene-isoprene-styrene block copolymer and a thermoplastic resin layer mixed with an inorganic scale filler. Therefore, it is possible to provide a diaphragm which has high rigidity due to its high specific modulus of elasticity and high internal loss, and has good vibration energy absorption properties, and whose absorption properties hardly change under operating temperature conditions. This has the advantage that it is possible to provide a speaker with flat frequency characteristics and a wide reproduction bandwidth. In addition, although the case where polypropylene was used as the thermoplastic resin was described in the examples, other thermoplastic resins such as polyethylene, polyethylene terephthalate, and vinyl chloride may be used. Molybdenum sulfide ( _MOS2 ) is applicable. Furthermore, in the examples, a layer structure having a layer mainly composed of a styrene-isoprene-styrene block copolymer was described between two thermoplastic resin layers, but the above-mentioned polymer was coated on one side of one thermoplastic resin The present invention also applies to a two-layer structure in which a layer consisting mainly of the copolymer is formed, a laminate structure of three or more layers in which these layers are superimposed, or a three-layer structure in which a layer consisting mainly of the above-mentioned copolymer is formed on both sides of a thermoplastic resin. This can achieve the purpose and falls within the scope of the present invention. Furthermore, the present invention can be applied not only to cone-shaped diaphragms but also to dome-shaped diaphragms, center dome radiators, dustproof caps, and the like.

[Brief explanation of drawings]

FIG. 1 is a temperature characteristic diagram of internal loss of the diaphragm of the present invention and a polypropylene diaphragm, and FIG. 2 is a frequency characteristic diagram of a speaker equipped with the diaphragm of the present invention and a conventional diaphragm.

Claims (1)

[Scope of Claims] 1. A material mainly composed of a styrene-isoprene-styrene block copolymer, and a thermoplastic resin mixed with an inorganic scale filler layered on at least one surface of the material. Diaphragm for electroacoustic transducers. 2. The diaphragm for an electroacoustic transducer according to claim 1, wherein the thermoplastic resin is polypropylene, and the inorganic filler is mica, graphite, or a mixture thereof.