JP2007312286A - Speaker diaphragm - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an environmentally-enhancing, lightweight speaker diaphragm with good design. <P>SOLUTION: This speaker diaphragm consists mainly of blending materials of biodegradable plastics, polypropylene and cellulose fibers. The weight percents of biodegradable plastics, polypropylene and cellulose fibers are 45% or more but 55% or less, 20% or more but 30% or less and 20% or more but 30% or less respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a speaker diaphragm which is a sound wave generation unit of a speaker used in an acoustic device or the like.

  The speaker diaphragm is manufactured from a material that takes into consideration the functionality such as density, sound speed, elastic modulus, and internal loss, economy, workability, and design. Typical materials for the speaker diaphragm include industrial plastics such as polypropylene or polystyrene, and biodegradable plastics such as polylactic acid or aliphatic polyester (for example, Patent Document 1). A speaker diaphragm made of biodegradable plastic and pulp is also known (for example, Patent Document 2).

JP 2003-159243 A (Claims) JP 2005-260546 A (Claims)

  Among industrial plastics, polypropylene is a resin material that is lightweight, easy to mold, and excellent in high temperature and high humidity resistance. On the other hand, polypropylene is difficult to recycle. For this reason, the speaker diaphragm made of polypropylene is often buried in the ground after use. The polypropylene speaker diaphragm buried in the ground is not decomposed by microorganisms in the ground and remains in the ground for a long period of time. Therefore, the environmental resistance evaluation of the speaker diaphragm made of polypropylene is low.

  On the other hand, loudspeaker diaphragms made of biodegradable plastics such as polylactic acid are decomposed by underground microorganisms even if they are disposed of in the ground, and thus their environmental evaluation is high. However, the speaker diaphragm made of biodegradable plastic increases in weight because the density of the resin is higher than that of the industrial plastic. As a result, the sound pressure of the sound wave from the speaker is lowered.

  In addition, a speaker diaphragm made of biodegradable plastic and pulp is excellent in environmental friendliness and design, but there is a demand for a speaker diaphragm that is lighter and has high design. There is a limit to increasing the pulp blending ratio for such demands, particularly weight reduction.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a speaker diaphragm that is excellent in environmental friendliness, is lightweight, and has excellent design.

  In order to solve the above problems, the speaker diaphragm of the present invention is mainly composed of a mixture of biodegradable plastic, polypropylene and pulp, and the weight ratio of biodegradable plastic, polypropylene and pulp in the mixture is 45. % To 55%, 20% to 30%, and 20% to 30%.

  In another invention, in addition to the above-described invention, the biodegradable plastic is a polylactic acid resin.

  Further, in another invention, in addition to each of the above-described inventions, the pulp is a cellulosic fiber.

  According to the present invention, it is possible to obtain a speaker diaphragm that is excellent in environmental resistance, is lightweight, and has excellent design.

  Hereinafter, a speaker diaphragm according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a speaker 12 having a speaker diaphragm 10 according to an embodiment of the present invention. In addition to the speaker diaphragm 10, the speaker 12 includes a magnetic circuit 14, a voice coil 16, a damper 18, and a frame 20.

  The magnetic circuit 14 includes a first plate 22, a magnet 24, and a second plate 26. The first plate 22 has a shape in which a donut disk is joined to the outside of one open end of the cylinder.

  The magnet 24 is a ring-shaped magnetic body that surrounds the center pole 28 that is the cylindrical portion of the first plate 22 in a non-contact manner. The magnet 24 is supported by being bonded and fixed to the upper surface of the donut-shaped disk of the first plate 22.

  The second plate 26 has a ring shape that surrounds the center pole 28 of the first plate 22 in a non-contact manner, and is adhesively fixed to the surface of the magnet 24 opposite to the contact surface with the donut-shaped disk. .

  The voice coil 16 is a coil formed by winding a conductive wire, and is disposed in a gap between the outer wall of the center pole 28 of the first plate 22 and the inner wall of the second plate 26 in a non-contact manner.

  The damper 18 has a donut shape having concentric uneven surfaces on the surface. Further, the damper 18 supports the voice coil 16 at the inner periphery so that the voice coil 16 can swing in the central axis direction of the voice coil 16. The outer periphery of the damper 18 is connected to the inner wall of the frame 20.

  The speaker diaphragm 10 has a cylindrical shape such as a megaphone that has a small circular opening at one end and a large circular opening at the other end. The speaker diaphragm 10 is connected to the voice coil 16 at a small circular opening end. The large circular opening end of the speaker diaphragm 10 is bent outward toward the small circular opening end and fixed to the front panel 29.

  The frame 20 includes a cup-shaped first frame 30 on the rear side of the speaker 12 and a megaphone-shaped second frame 32 on the front side of the speaker 12. The first frame 30 functions as a housing that surrounds the first plate 22, the magnet 24, and the second plate 26.

  The second frame 32 has one end fixed to the second plate 26 and the other end fixed to the front panel 29. The second frame 32 functions as a housing that covers the damper 18 and the speaker diaphragm 10.

  Next, the operation of the speaker 12 will be described.

  An acoustic signal current is input to the voice coil 16 from the outside of the speaker 12. The voice coil 16 swings in the direction of the central axis of the voice coil 16 according to the current value input to the voice coil 16. With the amplitude of the voice coil 16, the speaker diaphragm 10 also vibrates. The vibration of the speaker diaphragm 10 generates sound waves by vibrating the surrounding air.

  Thus, since the speaker diaphragm 10 is a member that affects the acoustic characteristics, the selection of the material is important. Further, the material of the speaker diaphragm 10 must be selected in consideration of not only the acoustic characteristics, but also the design properties, weight, and recently the environmental load.

  The speaker diaphragm 10 according to the embodiment of the present invention is made of each material of biodegradable plastic, polypropylene, and pulp, and is manufactured by molding a mixture of these materials. The mixing ratio of cellulose fibers as biodegradable plastic, polypropylene and pulp is preferably in the range of 45% to 55%, 20% to 30% and 20% to 30% in terms of weight ratio ( The weight ratio of each material is determined so that the total weight of the biodegradable plastic, polypropylene, and cellulosic fiber is 100% by weight). In particular, the weight ratio of biodegradable plastic, polypropylene, and cellulosic fibers is more preferably 50%, 25%, and 25%. The speaker diaphragm 10 according to the present embodiment is made of a mixture of biodegradable plastic, polypropylene, and cellulosic fibers. However, in addition to these materials, the fourth substance may be confused. good.

  The speaker diaphragm 10 contains both biodegradable plastic and cellulosic fibers. Biodegradable plastics and cellulosic fibers are decomposed into water and carbon dioxide by microorganisms even when discarded in the ground. Therefore, the environmental resistance evaluation of the speaker diaphragm 10 made of these materials becomes extremely high.

  When the speaker diaphragm 10 is manufactured only from the biodegradable plastic, the sound pressure of the sound wave generated from the speaker diaphragm 10 is reduced because the density of the biodegradable plastic is large. If the sound pressure is low, the sound volume at the sound wave source is attenuated before reaching the listener.

  On the other hand, polypropylene and cellulosic fibers are lighter than biodegradable plastics. Therefore, the speaker diaphragm 10 can be reduced in weight by blending the biodegradable plastic with polypropylene and cellulosic fibers. Thereby, it can prevent that the sound pressure of the sound wave which generate | occur | produces from the speaker diaphragm 10 becomes small.

  Polypropylene has the advantages of being excellent in design and being lightweight, but has the disadvantage of not being decomposed by underground microorganisms and remaining in the ground for a long period of time. Therefore, by adding polypropylene to the speaker diaphragm 10, the design of the speaker diaphragm 10 can be improved and the weight can be reduced, but the evaluation of environmental performance is lowered.

  Therefore, the speaker diaphragm 10 is manufactured from a mixture having a blending ratio of 45 to 55% by weight of biodegradable plastic, 20 to 30% by weight of polypropylene, and 20 to 30% by weight of cellulosic fibers. It is possible to obtain the speaker diaphragm 10 that is balanced in both weight reduction. The total weight of the biodegradable plastic and the cellulosic fiber is preferably 70 to 80% by weight. When the total weight is 70% by weight or more, the environmental evaluation is improved, and when it is 80% by weight or less, the weight is light and the design is high. Further, when the cellulosic fiber is 20% by weight or more, polypropylene can be reduced, the environmental evaluation can be improved, and the weight can be reduced. On the other hand, when the cellulosic fiber is 30% by weight or less, easy moldability is enhanced.

  Further, depending on the surface shape of the speaker diaphragm 10, the surface of the speaker diaphragm 10 can be a high gloss surface, a semi-matt surface, or a matte surface (matt surface). The speaker diaphragm 10 may be manufactured by other than molding, for example, by placing a molten material thinly on a base, peeling it off after curing, and cutting it into the shape of the speaker diaphragm 10.

  Examples of the biodegradable plastic used as the material of the speaker diaphragm 10 include (1) polylactic acid (PLA), polycaprolactone (PCL), polybutylene succinate (PBS), polybutylene succinate adipate, polybutylene succinate carbonate or Chemically synthesized aliphatic polyesters such as polybutylene succinate terephthalate and copolymers thereof, (2) biopolyesters such as polyhydroxybutyrate produced by microorganisms, biocellulose, polysaccharides or polyamino acids, (3) microorganisms The produced modified starch or natural polymer can be used. Of these, polylactic acid is inexpensive, readily available, excellent in moldability by mold, has material strength, is transparent, and can be easily adjusted in color by coloring. Therefore, it is more preferable to use polylactic acid as a biodegradable plastic as a material of the speaker diaphragm 10.

  The pulp blended in the biodegradable plastic includes cellulosic fibers made of rayon, cotton, hemp, cupra, lyocell, etc., but is not limited to these cellulosic fibers, and obtained from wood. Unbleached kraft pulp (NUKP), bleached kraft pulp (NBKP), pulp obtained by beating newspaper as a recycled material, and the like can be used.

  Moreover, it is preferable that the thickness of the speaker diaphragm 10 is 0.2 mm or more and 0.4 mm or less.

  Next, a method for manufacturing the speaker diaphragm 10 according to the embodiment of the present invention will be described.

  First, biodegradable plastic, polypropylene and cellulosic fibers are uniformly mixed and processed into pellets. The pellets of the biodegradable plastic, polypropylene and cellulosic fiber mixture are then heated to melt. Next, a molten biodegradable plastic, polypropylene and cellulosic fiber mixture is filled into an injection device. Next, high-pressure injection of a melted mixture of biodegradable plastic, polypropylene, and cellulosic fibers into the mold of the speaker diaphragm 10 is performed from an injection device.

  In addition, as a type | mold, the resin type | mold etc. which have melting | fusing point higher than the melting temperature of a metal mold | die, a ceramic type | mold, or a biodegradable plastic, the mixture of a polypropylene and a cellulose fiber can be used. Among these, it is preferable to use a mold in consideration of the cost of the material, the workability of the material, the durability of the mold, the ease of extraction of the molded body from the mold, and the like.

  Next, the mixture of biodegradable plastic, polypropylene and cellulosic fibers injected into the mold is cooled and cured. And the speaker diaphragm 10 can be obtained by taking out the mixture of the hardened biodegradable plastic, a polypropylene, and a cellulosic fiber from a type | mold.

  In this manufacturing method, by changing the surface shape of the mold, the surface of the speaker diaphragm 10 can be made a high gloss surface, a semi-matt surface or a matte surface (matt surface). In addition, in this manufacturing method, the speaker diaphragm can be easily and in a desired color tone by adding a colorant in the process of uniformly mixing biodegradable plastic, polypropylene and cellulosic fibers and processing them into pellets. 10 can be colored. As the colorant, pigments or dyes can be used.

  The acoustic characteristics of the speaker diaphragm 10 can be evaluated by measuring density, sound speed, elastic modulus, internal loss, and the like.

  Examples of the present invention will be described below. First, polylactic acid (“Lacia” manufactured by Mitsui Chemicals, Inc.), a biodegradable plastic, and a resin (“XY” manufactured by Showa Marutsu Co., Ltd.) comprising 50% by weight of polypropylene and 50% by weight of cellulosic fibers. Were mixed at a weight ratio of 1: 1 and mixed uniformly to form mixed resin pellets. Thereby, the weight ratio of the mixed resin pellets was 50% by weight of polylactic acid, 25% by weight of polypropylene, and 25% by weight of cellulosic fibers.

  Next, this mixed resin pellet was dried and then heated and melted. Next, the molten mixed resin was filled into an injection apparatus. Next, the molten mixed resin was injected from the injection device into a heated speaker diaphragm mold at a high pressure.

  Next, the mold was cooled to cure the mixed resin in the mold, and then the cured mixed resin was taken out of the mold. Thus, a speaker diaphragm having a diameter of 13 cm and a thickness of 0.3 mm, comprising 50% by weight of polylactic acid, 25% by weight of polypropylene and 25% by weight of cellulosic fibers, was obtained.

  As Comparative Example 1, a speaker diaphragm was manufactured by molding only polylactic acid (“Lacia” manufactured by Mitsui Chemicals, Inc.). Further, as Comparative Example 2, a speaker diaphragm was manufactured by mixing and molding 85% by weight of polypropylene and 15% by weight of mica.

  The speaker diaphragms obtained in Examples, Comparative Example 1 and Comparative Example 2 were processed into strips, and the density, sound velocity, elastic modulus and internal loss, which are indicators of acoustic characteristics, were measured by the vibration lead method. The measurement results are shown in Table 1.

The density (1.215 g / cm ³ ) of the speaker diaphragm of the example was about 11% smaller than the density (1.346 g / cm ³ ) of the speaker diaphragm of Comparative Example 1. Therefore, the sound pressure of the sound wave generated from the speaker diaphragm of the embodiment is larger than that generated from the speaker diaphragm of Comparative Example 1. Further, regarding the internal loss, the speaker diaphragm of the example (tan δ = 0.0597) was about 36% larger than the speaker diaphragm of the comparative example 1 (tan δ = 0.0440). Therefore, the sound generated from the speaker diaphragm of the example has good acoustic characteristics that are less likely to resonate than the sound generated from the speaker diaphragm of Comparative Example 1. Note that the speaker diaphragm of the example had a sound velocity and a modulus of elasticity of about 8% and about 47% smaller than those of the speaker diaphragm of Comparative Example 1, respectively.

Further, the density (1.215 g / cm ³ ) of the speaker diaphragm of the example was about 16% larger than the density (1.048 g / cm ³ ) of the speaker diaphragm of Comparative Example 2. Further, the internal loss (tan δ = 0.0597) of the speaker diaphragm of the example was equal to or greater than the internal loss (tan δ = 0.0580) of the speaker diaphragm of Comparative Example 2. The loudspeaker diaphragm of the example had a sound velocity and an elastic modulus that were about 24% and about 33% smaller than the loudspeaker diaphragm of Comparative Example 2, respectively. Thus, the speaker diaphragm of the example is slightly inferior in acoustic characteristics as compared with the speaker diaphragm of Comparative Example 2. However, the speaker diaphragm of the example has a total of 75% by weight of the total weight of polylactic acid 50% by weight and cellulosic fiber 25% by weight compared to Comparative Example 2 in which industrial plastic is the main component. Because it is decomposed into water and carbon dioxide, it has excellent environmental resistance.

  FIG. 2 is a diagram for explaining the performance and environmental resistance of the speaker diaphragm with respect to the blending ratio of polylactic acid and a resin composed of 50% by weight of polypropylene and 50% by weight of cellulose fiber. Here, the horizontal axis represents the density of the speaker diaphragm, and the vertical axis represents the blending ratio of polylactic acid and a resin composed of 50% by weight of polypropylene and 50% by weight of cellulosic fibers. In addition, the arrow shown with a continuous line represents the compounding quantity of polylactic acid, and the arrow shown with a broken line represents the compounding quantity of resin which consists of 50 weight% of polypropylenes, and 50 weight% of cellulosic fibers. . FIG. 3 is a diagram illustrating frequency characteristics when the speaker diaphragms of the example and the comparative example 1 are used in a speaker having a diameter of 13 cm. Here, the horizontal axis represents the magnitude of the frequency, and the vertical axis represents the magnitude of the sound pressure.

  In the speaker diaphragm of the example, polylactic acid and a resin composed of 50% by weight of polypropylene and 50% by weight of cellulosic fibers are blended in a ratio of 1: 1 by weight. That is, the form of the speaker diaphragm of the embodiment is in a portion A surrounded by a solid line in FIG. The loudspeaker diaphragm of the example is excellent in environmental resistance because 75% by weight of the total weight of polylactic acid 50% by weight and cellulose fiber 25% by weight is decomposed into water and carbon dioxide in the ground. Have When comparing the speaker diaphragm of the example and the speaker diaphragm of Comparative Example 1 made of only polylactic acid (in the portion B surrounded by the solid line in FIG. 2), the speaker diaphragm of the Example is the same as that of Comparative Example 1. Although it is somewhat inferior to the environment as compared with the speaker diaphragm, it is superior in that it can be reduced in weight. Further, comparing the speaker diaphragm of the example with the speaker diaphragm of Comparative Example 2 (inside portion C surrounded by a solid line in FIG. 2) consisting of 85% by weight of polypropylene and 15% by weight of mica, the speaker of the example The diaphragm is inferior to the speaker diaphragm of Comparative Example 2 in terms of weight reduction, but is superior in terms of environmental resistance. As described above, the speaker diaphragm of the example is a speaker diaphragm balanced in both environmental evaluation and weight reduction, and has excellent performance efficiency in terms of internal loss and frequency characteristics.

  In addition, the frequency characteristics of each of the speaker diaphragms of the example and the comparative example 1 were examined using a speaker having a diameter of 13 cm. As shown in FIG. 3, the frequency characteristic of the speaker using the speaker diaphragm of the example is about 1.5 dB overall as compared with the frequency characteristic of the speaker using the speaker diaphragm of Comparative Example 1. It has improved. Therefore, it is considered that the frequency characteristics of the speaker diaphragm of the example are superior to the frequency characteristics of the speaker diaphragm of Comparative Example 1.

  INDUSTRIAL APPLICABILITY The present invention can be used for a speaker diaphragm that is a sound wave generator of a speaker used for an acoustic device or the like.

It is sectional drawing of the speaker which has the speaker diaphragm which concerns on embodiment of this invention. It is a figure for demonstrating the performance and environmental property of a speaker diaphragm with respect to the compounding ratio of polylactic acid and the resin which consists of 50 weight% of polypropylenes, and 50 weight% of cellulose fibers. It is a figure which shows each frequency characteristic at the time of using each speaker diaphragm of an Example and the comparative example 1 for the speaker for aperture diameter 13cm.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Speaker diaphragm 12 ... Speaker 14 ... Magnetic circuit 16 ... Voice coil 18 ... Damper 20 ... Frame 22 ... 1st plate 24 ... Magnet 26 ... 2nd plate 28 ... Center pole 29 ... Front panel

Claims (3)

  Mainly composed of a mixture of biodegradable plastic, polypropylene and pulp, and the weight ratio of biodegradable plastic, polypropylene and pulp in the mixture is 45% to 55%, 20% to 30%, 20% or more A speaker diaphragm, characterized by being in a range of 30% or less.   The speaker diaphragm according to claim 1, wherein the biodegradable plastic is a polylactic acid resin.   The speaker diaphragm according to claim 1, wherein the pulp is a cellulosic fiber.

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