FR2640843A1 - DIAPHRAGM FOR ACOUSTICAL APPARATUS - Google Patents

Abstract

The invention relates to a diaphragm for a hearing device. It has a hardened surface layer, consisting of an SiC film formed on the surface of a substrate comprising a fully carbon film. The diaphragm therefore has superior acoustic characteristics through the use of the superior physical characteristics of carbon. Area of application: speakers, microphones, etc.

Description

The invention relates to a diaphragm for a

  acoustic device. The invention relates more particularly to

  a diaphragm for an acoustic device with superior acoustic characteristics, such as a speaker and microphone diaphragm, because of its greater hardness, strength,

  comparison with conventional materials for diaphragms.

  In general, it is desirable that a diaphragm for loudspeakers and the like satisfy the following conditions: (1) low density; (2) a weak Young's modulus; (3) a high rate of propagation of long-wave waves; (4) an appropriately high value of its

loss by internal vibration.

  In addition, the formula V = (E / p) 1/2 (where V is the speed of sound, E is the Young's modulus, p is the density) requires a low density material and Young's modulus

  high to increase the speed of sound.

  Conventionally, it is well known, as acoustic diaphragms having a high Young's modulus, the

  diaphragms using light metals such as aluminum

  nium, titanium, magnesium, beryllium, boron, etc. However, acoustic diaphragms using aluminum, titanium, magnesium, etc. born

  not have a specific Young's modulus E / I satisfies

  making, and acoustic diaphragms using beryllium, boron, etc. have a very high specific Young's modulus, but these materials are very expensive and extremely difficult to implement at the industrial level, which results in a very high cost in comparison with that of the diaphragms using other materials. The object of the invention is to propose a

  diaphragm having superior acoustic characteristics

  from the use of the higher physical characteristics of carbon, taking into account the

  the classic materials of diaphragms.

  As is well known, carbon has, in its crystalline form such as diamond, graphite, etc. has its non-crystalline form such as carbon black, charcoal, etc., characteristics

  very extensive physical and chemical

  The present Applicant has carried out a thorough study aimed at obtaining the various desired functional characteristics by designing and combining these materials in accordance with the functions required. She already has

  invented a method of manufacturing an entire diaphragm

  carbon fiber, obtained by pre-forming a mixture of a thermosetting resin and a carbon powder as a starting material, to form a film, molding the film into a diaphragm shape and sintering it in an inert atmosphere, which was the subject of a patent application (Publication N, unexamined, Sho 60-121895). She also invented a method of manufacturing a vitreous carbon-based diaphragm using only a thermosetting resin as a starting material, and this was the subject of a patent application (Publication N, unexamined Sho 61-65596). Although the diaphragms according to these inventions can be industrially manufactured inexpensively and have superior physical characteristics, the present Applicant has conducted a thorough study to improve the physical characteristics of these diaphragms and has resulted in the development of a diaphragm having acoustic characteristics superior to those of the diaphragms having only an entirely carbonized film, by evaporation of an SiC film from a gaseous phase, on the surface of the diaphragm material comprising an entirely carbon-based film, this resulting the finding that SiC has a very high propagation speed of 11 000 m / s. Well known synthetic processes for evaporating an SiC film from a gaseous phase include the thermal vapor deposition method, the chemical vapor deposition method, the chemical vapor deposition method to plasma, etc., and any of these methods can be used in the present invention. The coefficient of thermal expansion of an SiC film is advantageously equal to or similar to that of an entirely carbon-based film. The coefficient of thermal expansion of SiC is 3.5-5.5x10-6 / -C, whereas that of vitreous carbon is 2- 3.5x10-6 / C, and that of composite carbon / carbon, composed of carbon powders, can be of the order of 3 - 5 x 10-6, depending on the content of the carbon powder added. According to the method used to synthesize SiC, there are certain cases in which the coefficient of thermal expansion of a carbon substrate has to be adjusted by a selection of the proportion of the SiC.

  Mix carbon powders, optionally, if necessary.

  The invention will be described in more detail with regard to exemplary embodiments to which it is not

limited.

Example 1

  As a hardener, 4% is added to

  weight of a 50% methanol solution of p-toluene acid

  sulfonic acid 100% by weight of an initial furfuryl alcohol / furfural resin condensate (product "UF-302" manufactured by HITACHI KASEI CO., LTD). After sufficient stirring by means of a high speed kneader, the mixture is applied to a carrier sheet by means of a coating apparatus having a scraping blade, and is then hardened to obtain a preformed B-phase sheet. After removing the carrier sheet, the preformed sheet is molded into a dome shape by means of a heat-cured, vacuum-molded apparatus and removed from the mold so that the a diaphragm molding is obtained. A postcuring treatment is applied to this molding for 5 hours in an air oven at 150 ° C. Then the sintering of the molding is completed by heating it in a nitrogen atmosphere oven, at a temperature rise rate of 15C / hour up to 500 C and C / hour between 500 and 1000 C, the molding being maintained for 3 additional hours at 1000-C before being able to cool naturally. The glassy carbon diaphragm thus obtained, having a diameter of 25 mm and a film thickness of 25 μm, was used as the substrate on which was deposited, by a well known method of chemical deposition.

vapor phase, a SiC film.

  In the SiC film synthesis, the flow rates of hydrogen, methane and silicon tetrachloride should be 1 liter / min, 3 ml / min and 3 ml / min, respectively, and their mixture is introduced into a vacuum bell under the pressure of 133.3 Pa. Furthermore, the substrate was maintained at a temperature of 500 ° C., plasma was induced by microwaves of 2.45 GHz and evaporation was carried out. during 2 hours. The film

SiC was 5 gm thick.

Example 2

  80% by weight of an initial furfural alcohol / furfural resin condensate (product "UF 302" manufactured by HITACHI KASEI CO., LTD) and 20% by weight were homogeneously mixed and dispersed in a Warner kneader. of natural graphite in flakes (average grain size of 1 μm), and this mixture was then strongly dispersed by the use of 3 ink kneading rollers to obtain a dough composition constituting the starting material . We added, as a hardener,

  4% by weight of a 50% methanol solution of p-acid

  toluenesulphonic to 100% by weight of the dough composition constituting the starting material, and the same operations as in Example 1 were repeated to obtain a completely carbonized diaphragm having a diameter of 25 mm and a film thickness of 40 μm. . This fully carbonized diaphragm was used as a substrate on which was deposited by evaporation, using a well known method of

  chemical vapor deposition, a SiC film.

  In the SiC film synthesis, the flow rates of hydrogen, methane and silicon tetrachloride must be 1 liter / min, 1 ml / min and 3 ml / min, respectively, and their mixture is introduced into a vacuum bell under the pressure of 4000 Pa.

  completely carbonaceous substrate was maintained at a

  1500 ° C. by a high-frequency induction heating, and the evaporation was carried out for 40 hours.

  minutes. The SiC film obtained had a thickness of 5 Nm.

  The characteristics of the diaphragm obtained according to the invention are compared with those of

  conventional diaphragms in the following table.

  Young's Module Speed, Mass Volume

  Material, km / s GPa mic, g / cm3 Aluminum 5.1 70.0 2.70 Titanium 4.9 110, 0 4.50 Beryllium 12.2 270.0 1.80 Example 1 (substrate) 7.5 78.0 1.40 Example 2 (substrate) 9.0 115.0 1.43

Example 1

  (after evaporation) 8.4 110.0 1.55

Example 2

  (after evaporation) 9.7 163.0 1.73 As is clearly shown in the table, the physical characteristics of the substrate, in both Examples 1 and 2, were improved by about 40% for the Young's modulus and about 10% for the speed of sound, compared with those presented by the substrate before evaporation. Moreover, the effects of the invention

  are not limited to examples and it is possible to improve

  still improve physical characteristics by increasing

the thickness of the film evaporates.

  Because of these superior characteristics, the diaphragm according to the invention can be effectively used as a diaphragm for reproductive apparatus

  digital sound, now widespread.

  It goes without saying that many modifications can be made to the diaphragm described and shown

  without departing from the scope of the invention.

Claims (1)

CLAIM   Diaphragm for acoustic device,   characterized in that a surface hardened layer of SiC film is formed on the surface of the diaphragm substrate comprising an all carbon film.