JPS6123718B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a diaphragm for audio equipment such as speakers and microphones that has both high elastic modulus and high internal loss. Conventionally, materials for highly elastic and lightweight diaphragms for audio equipment such as speakers include metals such as aluminum, titanium, and beryllium, CFRP, and composite materials made by mixing resin with flaky graphite. The internal loss is small, and the sound pressure near the high-frequency resonant frequency increases significantly in the reproduction characteristics of the speaker, and the fall characteristics are also poor. On the other hand, materials with high internal loss include paper, plastic, and composite materials thereof, but they have low elastic modulus, making it difficult to reproduce high frequencies, and cannot be used over a wide band. The present invention has been made in view of the above-mentioned points, and its purpose is to create a multilayer film by laminating a highly elastic film on a film made of a mixture of thermoplastic resin and graphite powder, the glass transition point of which is lower than room temperature. The object of the present invention is to provide a diaphragm for speakers, microphones, etc., which is lightweight and has characteristics of high elasticity and high internal loss. Hereinafter, the details of the present invention will be explained along with the manufacturing method according to the drawings. In FIG. 1, 1 is a diaphragm for a speaker, microphone, etc., and 2 and 3 are two-layered films constituting the diaphragm. Among these, the film 2 is a kneaded material film exhibiting physical properties of high internal loss, and is made by kneading a thermoplastic resin 2a whose glass transition point is lower than room temperature, such as polyvinylidene, and flaky graphite powder 2b, and rolling it. The graphite powder 2b was formed into a sheet shape by orienting the graphite powder 2b along the surface. In general, polymeric materials have the property that when the temperature reaches the glass transition point and rises above it, the elastic modulus decreases and the internal loss rapidly increases. Therefore, a film whose main component is a thermoplastic resin such as polyvinylidene chloride (PVDC) whose glass transition point is lower than room temperature can have a high internal loss at room temperature. Also, by kneading this film material and graphite powder,
Orienting the graphite powder along the surface significantly improves the elastic modulus of the film. As the thermoplastic resin 2a whose glass transition point is lower than room temperature, the above polyvinylidene chloride (PVDC) is mainly used,
PVDC alone, a copolymer of PVDC and polyvinyl chloride (PVC), and a copolymer of PVDC and polyacrylonitrile are preferred, and if necessary, a necessary plasticizer (BPBG) and stabilizer (lead stearate) are used. added. The graphite powder 2b preferably has an average particle size of about 20 μm or less, particularly 5 μm or less.
Furthermore, if the blending ratio of the thermoplastic resin 2a and the graphite powder 2b is in the range of 10 to 90 wt% of the graphite powder and 90 to 10 wt% of the resin, it is expected that the graphite powder will improve the elastic modulus and the moldability of the kneaded material. Graphite powder 50
~75 wt%, and when the resin content is 50 to 25 wt%, the properties of the molded product are significantly improved. The film 3 exhibiting high elasticity is made of lightweight and highly elastic metal materials such as aluminum, beryllium, titanium, etc.
As shown in FIGS. 1 and 2, a kneaded material of a thermoplastic resin 3a whose glass transition point is higher than room temperature and graphite powder 3b, in which the graphite powder 3b is oriented along the surface, is used. Thermoplastic resins 3a whose glass transition point is higher than room temperature include polyvinyl chloride (PVC) alone, copolymers of PVC and polyacrylonitrile, copolymers of PVC and polyvinyl acetate, etc., mainly PVC. A resin material is used. The graphite powder 3b used has the same size as the film 2, and the blending ratio of the resin 3a and the graphite powder 3b is also about the same as that of the film 2. The resin film is formed by kneading with a kneader or rolls, and then rolling with rolls to form a film in which graphite powder is oriented. In manufacturing the above-mentioned diaphragm, first, films 2 and 3 are formed, and then both films 2 and 3 are laminated as shown in Fig. 2, and then formed into a diaphragm shape such as a dome or a cone. . When the film 3 is made of a metal material, the film 2 and the film 3 are laminated by interposing an adhesive between the film 2 and the film 2, and when the film 3 is made of resin, the film 2 is laminated with the upper and lower surfaces of the film 2. Either the film 3 is stacked on any one or both sides and placed on a hot plate, or the hot plate is pressed from above and below to heat the hot plate to a sufficient melting temperature of the resin. In addition, to form the laminated film shown in FIG. 2, when both films 2 and 3 are made of resin, a vacuum forming method or a pressure forming method can be used in addition to the pressure forming method, and when the film 3 is made of a metal material, a vacuum forming method or a pressure forming method can be used. Use pressure molding method.
Further, when the film 3 is made of a metal material, a method may also be used in which the film 2 is formed into the shape of the diaphragm in advance in order to manufacture the diaphragm, and the film 3 is laminated by vapor-depositing the metal material onto the film 2. I can do it. As described above, the present invention has a structure in which a highly elastic film is laminated on a film whose main component is a thermoplastic resin whose glass transition point is lower than room temperature.
The overall internal loss can be improved by using a resin film with a low glass transition point, and since graphite powder is kneaded and oriented into the resin film with a low glass transition point, the elastic modulus of the film itself is also increased. It is possible to achieve high elasticity as a whole, and since the film is made of lightweight materials of resin and graphite powder, it can also achieve low density, and has high elasticity, low density and high internal Excellent properties such as loss and so on can be achieved. Next, the present invention will be specifically explained using examples. Composition example of film 2 Flake graphite powder 200 weight ratio PVDC/polyacrylonitrile copolymer
100 weight ratio Lead stearate (stabilizer) 2 〃 BPBG (plasticizer) 10 〃 Composition example of film 3 Flake graphite powder 200 weight ratio PVC 100 〃 Lead stearate 2 〃 BPBG 10 〃 Compositions of both films 2 and 3 The materials were heated and kneaded using rolls, and then rolled into films to obtain films 2 and 3. The films 2 and 3 thus obtained were laminated by thermocompression bonding into two layers as shown in FIG. The physical properties of Film 2, Film 3, and the laminate are as shown in the following table. Next, this laminate is held in a mold and vacuum formed while heating.
A cone-shaped diaphragm as shown in the figure was obtained. The frequency characteristics of this diaphragm are shown in FIG. First, as is clear from the table, in the laminated diaphragm of the present invention, the specific elastic modulus √, which is the ratio between the elastic modulus E and the density ρ, is comparable to metal aluminum and titanium, and far exceeds paper. It has an excellent internal loss comparable to paper and superior to metal materials by nearly two orders of magnitude. Further, in the characteristic diagram of FIG. 3, the frequency characteristics of a conventional diaphragm made of the same composition as the film 3 are shown by a broken line, and the frequency characteristics of the diaphragm of the laminated structure of the present invention are shown by a solid line. As is clear from the above, the diaphragm of the present invention has a characteristic that the resonance peak in the high frequency range is low and flat. 【table】

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an embodiment of the present invention, Fig. 2 is a cross-sectional view of a two-layer laminated film used in the above, and Fig. 3 is a cross-sectional view of an embodiment of the present invention and a conventional example. It is a frequency characteristic diagram. 1...Vibration plate, 2...Film, 3...Film.

Claims (1)

[Scope of Claims] 1. A highly elastic film is laminated on a kneaded material film mainly composed of a thermoplastic resin whose glass transition point is lower than room temperature and graphite powder, and in which the graphite powder is oriented along the surface. A multilayer structure diaphragm for audio equipment. 2. The acoustic device according to claim 1, wherein the thermoplastic resin having a low glass transition temperature is a copolymer of polyvinylidene warmed or polyvinylidene chloride and another thermoplastic resin. Diaphragm for equipment. 3. A patent claim characterized in that the above-mentioned high elasticity film is a kneaded material film mainly composed of a thermoplastic resin having a glass transition point higher than room temperature and graphite powder, and in which the graphite powder is oriented along the surface. A diaphragm for audio equipment according to item 1 or 2.