JP2011077998A - Acoustic diaphragm of carbonaceous material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acoustic diaphragm of carbonaceous material with sufficient rigidity while having low density. <P>SOLUTION: On a surface of the acoustic diaphragm of carbonaceous material, irregularities 20 are provided in two directions, vertically and horizontally. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a carbonaceous acoustic diaphragm.

  Speaker diaphragms used in various audio devices, video devices, mobile devices such as mobile phones, and the like are required to be able to faithfully reproduce clear sound in a wide frequency band, particularly in a high sound range. For this reason, the material of the diaphragm is required to have seemingly contradictory properties such that the elastic modulus is high to give the diaphragm sufficient rigidity and the density is low to reduce the weight of the diaphragm. In particular, diaphragms for digital speakers, which have been attracting attention in recent years, are strongly demanded for these properties due to the demand for vibration response.

Patent Documents 1 and 2 listed below describe a diaphragm made of a material in which carbon nanofibers (vapor-grown carbon fibers) and graphite are uniformly dispersed in amorphous carbon. However, since this material has a high density of 1.0 g / cm ³ or more, in order to obtain desired acoustic characteristics, it is necessary to add a large amount of expensive carbon nanofibers and graphite to increase the elastic modulus. It is necessary to make the wall thickness thinner. Therefore, there is a problem of damage due to handling or the like, and a problem remains in productivity.

In Patent Document 3, the resin powder before being fired (carbonized) to become glassy carbon (amorphous carbon) is heated and point-fused to form a porous body, and then carbonized to form low-density amorphous carbon. It is described that a porous body is used. However, with this method, it is difficult to obtain a porous body having a high porosity of 40% or more, and it is not possible to obtain a porous body having a density of 1.0 g / cm ³ or less.

  Patent Document 4 describes an acoustic carbon diaphragm in which vapor-phase pyrolytic carbon is deposited on a carbonized nonwoven fabric or woven fabric impregnated with a resin. Even in this method, it is difficult to obtain a porous body having a high porosity of 40% or more.

  Patent Document 5 describes an acoustic diaphragm in which the surface of a foamed graphite film is etched and impregnated with plastic. This expanded graphite refers to a state where gas generated inside when carbonizing a polymer at a high temperature disturbs a layered structure peculiar to graphite, and it is difficult to design and control pores. For this purpose, the resin is impregnated with foamed graphite to reinforce the defective portions of the graphite that are partially thinned, thereby flattening the reproduction frequency. The resin is used to reinforce the defects in the graphite. That is the main point. Further, since the resin is impregnated by etching, the process is long and the management tends to be complicated.

JP 2004-32425 A (Patent No. 3630669) JP 2002-171593 A Japanese Patent Laid-Open No. 01-185098 Japanese Patent Laid-Open No. 62-163494 JP 05-22790 A

  Accordingly, an object of the present invention is to provide a carbonaceous acoustic diaphragm that is low in density and lightweight, has sufficient rigidity, exhibits good acoustic characteristics, and can be manufactured industrially at low cost.

According to the present invention, there is provided a carbonaceous acoustic diaphragm including amorphous carbon and having at least one surface provided with irregularities.
The unevenness is desirably periodic, and more desirably periodic in two directions intersecting each other.

  The carbonaceous acoustic diaphragm includes amorphous carbon and a carbon powder uniformly dispersed in the amorphous carbon, and includes a low-density layer made of a porous body having a porosity of 40% or more, amorphous carbon, It is preferable that two high density layers sandwiching the density layer therebetween, and the unevenness is provided on at least one outer surface of the high density layer.

Here, the porosity is a percentage of the volume of the pores with respect to the entire volume of the porous body including the pores, and is calculated from the volume and mass of the entire porous body, assuming that the density of the amorphous carbon serving as the skeleton is 1.5 g / cm ^3. It is defined as porosity.

  The surface irregularities as described above are formed on, for example, PTFE (tetrafluoride tetrafluoride) on one or both sides of a resin molded into a sheet before baking and carbonizing, for example, on a glass cloth knitted into a sheet. It can be formed by pressing what is impregnated with an ethylene resin and fired (hereinafter referred to as PTFE-impregnated cloth). A mold having a similar surface shape may be used.

  By providing unevenness on the surface, the weight can be reduced without impairing the rigidity, and good acoustic characteristics can be obtained.

It is a conceptual sectional view of an acoustic diaphragm obtained in an example. It is a graph of the measurement result of the surface roughness of a PTFE impregnation cloth.

(Example 1) Compounding 35% by mass of vinyl chloride resin as an amorphous carbon source, 1.4% by mass of carbon nanofibers having an average particle size of 0.1 μm and a length of 5 μm, and PMMA as a drilling material for pore formation After adding a diallyl phthalate monomer as a plasticizer to the composition and dispersing it using a Henschel mixer, the composition is sufficiently kneaded using a pressure kneader to obtain a composition, which is pelletized by a pelletizer for molding A composition was obtained. The molding composition pellets were formed into a sheet-like molded product having a thickness of 400 μm by extrusion molding. Further, furan resin was coated on both sides, and then PTFE impregnated cloth 970-4UL (manufactured by Nitto Denko Corporation) was pressed on both sides. After curing, the PTFE-impregnated cloth was peeled off to obtain a multilayer sheet. This multilayer sheet was treated in an air oven at 200 ° C. for 5 hours to obtain a precursor (carbon precursor). Thereafter, the temperature was increased in nitrogen gas at a temperature increase rate of 20 ° C./h, and the temperature was maintained at 1000 ° C. for 3 hours. After natural cooling, after holding in vacuum at 1400 ° C. for 3 hours, natural cooling was performed to complete firing. Thereby, as conceptually shown in FIG. 1, the low density of the porous body having the spherical pores 14 remaining after the carbon nanofiber powder 12 is uniformly dispersed in the amorphous carbon 10 and the PMMA particles disappear. An acoustic diaphragm having a layer 16 and a high-density layer 18 made of amorphous carbon covering both surfaces and having periodic irregularities 20 on the outer surface was obtained.

The porosity of the low density layer 16 of the acoustic diaphragm thus obtained was 70%, and the number average pore diameter was 60 μm. FIG. 2A shows a graph of the measurement results of the surface roughness of the PTFE-impregnated cloth used for forming periodic irregularities on the surface. Table 1 shows the measurement results of the thickness, bending elasticity, density, and surface roughness according to JIS B0601: 2001 of the entire diaphragm.
(Example 2) As a PTFE-impregnated cloth, a smooth type 9700UL was used instead of the product number 970-4UL, and an acoustic diaphragm was obtained in the same process as in Example 1 except that. The graph of the measurement result of the surface roughness of the used PTFE-impregnated cloth is shown in FIG. Table 1 shows the measurement results of the thickness, bending elasticity, density, and surface roughness according to JIS B0601: 2001 of the entire diaphragm.
(Comparative Example) An acoustic diaphragm was obtained by the same process as in Example 1 except that a PET film was used instead of the PTFE-impregnated cloth. Table 1 shows the measurement results of the thickness, bending elasticity, density, and surface roughness according to JIS B0601: 2001 of the entire diaphragm.

  As is clear from the results of Table 1, by providing periodic irregularities on the surface, the bending elasticity is improved and the density is lowered. Regarding the surface roughness parameters, the arithmetic average roughness Ra is preferably 0.5 μm or more, the maximum height Rz is preferably 3.1 μm or more, Ra is preferably 1 μm or more, and Rz is more preferably 5 μm or more. I understand.

  FIG. 2 shows the measurement results of the surface roughness of the PTFE-impregnated cloth used for forming periodic irregularities on the surface. The PTFE-impregnated cloth has periodic irregularities with a period of 30 μm or more, that is, a period of 50 μm or less, in two directions, the vertical direction and the horizontal direction, and these are transferred to both surfaces of the multilayer sheet. The

  As can be seen from FIG. 2, in the PTFE-impregnated cloth, the line defining the lower concave portion is bent more sharply than the line defining the upper convex portion in the figure. That is, the curvature of the surface defining the convex portion of the PTFE-impregnated cloth is smaller than the curvature of the surface defining the concave portion. On the contrary, in the multilayer sheet to which this is transferred, the curvature of the surface defining the concave portion is smaller than the curvature of the surface defining the convex portion. Such a shape is considered to maintain the structural rigidity.

Claims (8)

  A carbonaceous acoustic diaphragm comprising amorphous carbon and having at least one surface provided with irregularities.   The carbonaceous acoustic diaphragm according to claim 1, wherein the unevenness is periodic.   The carbonaceous acoustic diaphragm according to claim 2, wherein the unevenness is periodic in two directions intersecting each other.   The surface roughness of the surface provided with the unevenness has an arithmetic average roughness Ra measured according to JIS B0601: 2001 of 0.5 μm or more and a maximum height Rz of 3.1 μm or more. The carbonaceous acoustic diaphragm according to claim 1.   The carbonaceous acoustic diaphragm according to claim 4, wherein the arithmetic average roughness Ra is 1 μm or more and the maximum height Rz is 5 μm or more.   The carbonaceous acoustic diaphragm according to any one of claims 1 to 5, wherein a curvature of a surface defining a concave portion in the unevenness is smaller than a curvature of a surface defining a convex portion. A low density layer comprising amorphous carbon and a carbon powder uniformly dispersed in the amorphous carbon, and comprising a porous body having a porosity of 40% or more;
Comprising two layers of high density layers comprising amorphous carbon and sandwiching the low density layer therebetween,
The carbonaceous acoustic diaphragm according to claim 1, wherein the unevenness is provided on at least one outer surface of the high-density layer.   The carbonaceous acoustic diaphragm according to any one of claims 1 to 7, wherein a period of the unevenness is 50 µm or less.

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