DE3840705A1 - DIAPHRAGMA FOR AN ACOUSTIC DEVICE - Google Patents

Abstract

A diaphragm for acoustic equipment wherein a surface-hardened layer of SiC film is formed, eg by vapour deposition, on the surface of a diaphragm substrate comprising a full or glassy carbonaceous layer. The diaphragm has superior acoustic characteristics by utilising the superior physical characteristics of carbon and can be used effectively as a diaphragm for digital-audio equipment.

Description

The present invention relates to a diaphragm for a acoustic device. It particularly affects a diaphragm for an acoustic device with superior acoustic Properties, e.g. a diaphragm for speakers and Microphones because of its greater hardness, greater strength, higher elasticity and the very light weight compared to the usual diaphragm Materials are more suitable for these purposes.

In general, a diaphragm for loudspeakers (Speaker diaphragm) and the like following Requirements met:

• 1. it should have a low density;
• 2. the Young's module is small;
• 3. the reproductive rate for longitudinal Waves is high;
• 4. The internal vibration loss is sufficiently large.

The formula

V = ( E / rho) ^1/2

(where V is the speed of sound, E is the Young's module and rho the density), requires a material with a low density and a high Young's module to increase the speed of sound.

So far you have acoustic diaphragms with high young's Module applied those where light metals like Aluminum, titanium, magnesium, beryllium, boron etc. are used were.

Acoustic diaphragms using aluminum, titanium, magnesium etc. are unsatisfactory with regard to the specific Young's module E / rho and acoustic diaphragms using beryllium, boron etc. have a large specific Young’s Module, but these materials are extremely expensive and very difficult to machine technically and therefore the costs are very high compared to the use of other materials.

The present invention relates to a diaphragm superior acoustic properties, in which the superior physical properties achieved by that one carbon in view of the disadvantages of usual diaphragm materials used.

It is known that carbon in crystalline form like for diamonds or in graphite and in one  non-crystalline form such as occurs in soot, charcoal, etc. and very broad physical and chemical properties having.

The inventor has therefore made great efforts to achieve various functional characteristics and to combine these materials according to the desired functions. The inventor has already invented a method for producing a diaphragm made entirely of carbon, in which a mixture of thermosetting resin and carbon powder as a raw material is molded into a film, and then the film is brought into diaphragm form and sintered in an inert atmosphere. This is described in JP-OS 6 01 21 895. Furthermore, the inventor invented a method for manufacturing a glass carbon diaphragm using only a thermosetting resin as a raw material. This is described in JP-OS 61 65 596. Although diaphragms can be easily manufactured technically using the aforementioned inventions and already have superior physical properties, the present invention is based on still improving the physical properties of these diaphragms. It has now been possible to produce a diaphragm with superior properties compared to those using only a film made entirely of carbon by applying a SiC film from a gas phase onto the surface of a diaphragm material which is made completely is built up from carbon-containing film, evaporates. SiC has a very high reproductive speed of 11,000 m / sec. on. The known synthetic methods for evaporating an SiC film from a gas phase include the thermal CVD method, the laser CVD method, the plasma CVD method, etc., all of which can be used in the present invention. The coefficient of thermal expansion of an SiC film is preferably the same as or similar to that of a film made entirely of carbon. The thermal expansion coefficient made of SiC is 3.5 to 5.5 × 10 ^-6 / ° C, while that of glassy carbon is 2 to 3.5 × 10 ^-6 / ° C, and for a carbon / carbon composite made of carbon powder, it can be in the range from 3 to 5 × 10 ^-6 depending on the amount of carbon powder added. In the method for producing SiC, there are some cases where the coefficient of thermal expansion of a carbon-containing substrate has to be adjusted by optimally selecting the mixing ratio of carbon powder.

The invention is illustrated below using the examples explained, these examples are not limiting are to be interpreted.

Example 1:

4% by weight of a 50% liquid p-toluenesulfonic acid in Methanol was 100% by weight of a hardener Initial condensates made of furyl alcohol / furfural resin (UF-302 manufactured by HITACHI KASEI CO. LTD.). To stir thoroughly with a high speed mixer was the mixture with a doctor blade on a sheet applied and pre-hardened to obtain a molded Leaf in the B stage.  

After removing the sheet on the back was the preformed sheet in one Vacuum forming device shaped like a dome by heating hardened and out of shape to obtain a diaphragm shape away. A post-curing treatment was carried out in 5 hours an air oven at 150 ° C. Then the Molded by heating in an oven in one Nitrogen gas atmosphere with a heating rate of 15 ° C / h up to 500 ° C and from 50 ° C / h between 500 and 1000 ° C completed, taking the temperature another 3 hours held at 1000 ° C and then naturally cool the molding let. The resulting glassy carbonaceous Diaphragm had a diameter of 25 mm and one Film thickness of 25 microns and was used as a substrate. An SiC film according to the known method was applied to this substrate CVD method evaporated.

In the synthesis of the SiC film, the flow rate of the Hydrogen, methane and silicon tetrachloride at 1 l / min., 3 ml / min. or 3 ml / min. amount and the Mixture is placed under a pressure of 1 torr Bell jar introduced. The substrate is at a Temperature kept at 500 ° C and the plasma was by means of Microwaves of 2.45 GHz introduced and the evaporation was carried out for 2 hours. The Sic film obtained has a thickness of 5 µm.

Example 2:

80% by weight of an initial condensate Furfuryl alcohol / furfural resin (UF 302 manufactured by HITACHI KASEI CO., LTD.) And 20% by weight of a natural  flaky graphite (average grain size 1 µm) were mixed and homogeneous in a Warner mixer dispersed and then followed Fine dispersion using 3 Ink kneading rollers, using a raw material paste received. 4% by weight of 50% liquid p-toluenesulfonic acid 100% by weight of the Given raw material paste composition and the process of Example 1 was repeated using a diaphragm, that was made entirely of carbon, with one Diameter of 25 mm and a film thickness of 40 µm received. This is made entirely of carbon Diaphragm was used as a substrate and was placed on it an SiC film is deposited by the known CVD method.

For the synthesis of the SiC film, the flow rates of Hydrogen, methane and silicon tetrachloride to 1 l / min, 1 ml / min. or 3 ml / min. set. The mixture was in a glass bell under a pressure of 30 torr introduced. The completely built on carbon Substrate was passed through at a temperature of 1500 ° C High frequency induction heating kept and the evaporation was carried out for 40 minutes. The SiC film obtained had a thickness of 5 µm.

The properties of diaphragms according to the invention are with those of common diaphragms in the following Compared table.

This table shows that both in the example 1 So in Example 2 the physical properties of the substrate with respect to the Young's module by about 40% and in terms of the speed of sound by about 10% have been improved compared to the substrate before Evaporation.

The effect achieved according to the invention is not on the in limited to the examples shown. Rather, you can further improve physical properties by the thickness of the vapor-deposited film is increased.

Because of the excellent properties you can Diaphragms according to the invention are particularly effective as Diaphragms for digital audio devices, as they are currently are very popular use.

Claims (1)

Diaphragm for an acoustic device with one on the Surface of a diaphragm substrate made entirely of carbon film is built up surface-hardened layer of an SiC film.