JPS5821995B2 - Multilayer diaphragm for acoustic transducer and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multilayer diaphragm for an acoustic transducer used for a speaker, a diaphragm for a microphone, a cantilever of a pickup cartridge for reproducing records, and a method for manufacturing the same.

In general, the physical properties required of the acoustic transducer diaphragm include (1) being lightweight, (2) having high rigidity and high elasticity, and (2) not exhibiting sharp resonance.

In particular, diaphragms for high-pitched speakers are required to exhibit smooth frequency characteristics up to high frequencies.

In order to satisfy these required characteristics, the material constituting the diaphragm must have a large Young's modulus E, a small specific gravity ρ, that is, a large E/ρ, and a large internal friction. Developing a material that satisfies all of these properties is extremely difficult.

However, even if sharp resonance cannot be avoided, if E/ρ is set sufficiently large, smooth frequency characteristics can be obtained up to a fairly high frequency range, so we believe that materials with high E/ρ should be used instead. It will be done.

Therefore, considering E/ρ to be an important characteristic, research has been increasingly conducted in recent years with the aim of developing diaphragm materials with high E/ρ characteristics.

On the other hand, metal materials such as aluminum or titanium are usually used as diaphragm materials for metal speakers, but these materials all have a relatively low E/ρ, and therefore, as mentioned above, have a low rigidity. There is a need for a diaphragm material that is a large metal-based material and has a much larger E/ρ than the metal-based materials.

Recently, a vibration plate with an extremely large E/ρ has been developed and is beginning to be used, but as is well known, this material is extremely toxic and difficult to handle, and requires equipment to prevent pollution. Because of this, it has to be expensive.

Therefore, for these reasons, there is currently a strong demand for the development of a diaphragm material that is not toxic like beryllium and has a large E/ρ.

The present inventors have made the above-mentioned slow-acting light weight, high rigidity and high elasticity, that is, a high E/ρ value,
Moreover, in order to obtain a low-cost diaphragm, we focused on boron carbide, which has the highest E/ρ of all materials, and conducted research to manufacture a diaphragm using this boron carbide. (1) Carbonized Boron alone is brittle and lacks strength, so
Although it is difficult to use it as a diaphragm for a loudspeaker for large inputs, the lack of strength of boron carbide can be overcome by using titanium or a titanium alloy with high toughness.

(2) However, adhesion between titanium or titanium alloys and boron carbide is relatively low, and with such low adhesion, sufficient strength improvement cannot be expected. On the other hand, if one of group 5a and 6a metals of the periodic table, which have good adhesion, and hafnium are interposed as an intermediate layer, the adhesion between the titanium or titanium alloy and boron carbide can be significantly improved. thing.

(3) If the intermediate layer is coated with the boron carbide layer by chemical vapor deposition (CVD), its adhesion will be extremely high.

The findings shown in items (1) to (3) above were obtained.

This invention was made based on the above findings, and
The main process is to first coat the surface of a base metal substrate with a predetermined surface shape with a lower layer of titanium or titanium alloy as a first layer with a layer thickness of 5 to 20 μm using a conventional method, and then to coat the surface of a base metal substrate with a predetermined surface shape with a layer thickness of 5 to 20 μm. Metals from groups 5a and 6a of the periodic table as the second layer by the method, as well as one of the hafnium
The intermediate layer consisting of seeds is coated with a layer thickness of 0.1 to 2 μm, and the base metal substrate thus coated with the lower layer and the intermediate layer is charged into a pyrolysis reactor, and into the pyrolysis reactor, A decomposition reaction is caused by introducing either a mixed gas containing boron halide vapor, hydrocarbon, and hydrogen as main components, or a mixed gas containing carboneline and an inert gas as main components. The upper layer consisting of three layers of boron carbide is 5 to 30 μm thick.
a first layer made of titanium or a titanium alloy with a layer thickness of 5 to 20 μm; 1-2 μm metal of group 5i or group 6a of the periodic table,
The present invention is also characterized in that it manufactures a multilayer diaphragm for an acoustic transducer, which is composed of a second layer as an intermediate layer made of one type of hafnium lining, and a third layer made of boron carbide with a layer thickness of 5 to 30 μm. It is something.

In this invention, the reason why titanium or a titanium alloy is used as the first layer (hereinafter referred to as the lower layer) is that these metals are strong and low density, and can withstand the temperature rise when boron carbide is deposited by the CVD method. The reason why the thickness of the lower layer is limited to a range of 5 to 20 μm is because
If the thickness is less than 5 μm, the necessary toughness cannot be obtained;
This is because if the value exceeds the value, the Young's modulus of the entire laminated diaphragm decreases.

In addition, in order to improve the Young's modulus of the entire diaphragm, it is better to make the thickness of the boron carbide coated on the third layer (hereinafter referred to as the upper layer) as thick as possible, but it is limited to 30 μm due to the constraint that it must be lightweight. On the other hand, if it is less than 5 μm, a sufficiently high E/ρ cannot be obtained as a diaphragm, so the range is set to 5 to 30 μm.

By the way, in addition to the vacuum evaporation method and the sputtering method, the coating of the lower layer and the second layer (hereinafter referred to as the intermediate layer) on, for example, a mild steel block as the base metal substrate may be carried out by an ion blasting method, and these methods may be used. In addition to the so-called physical vapor deposition method (PVD method), a chemical vapor deposition method (CVD method) may also be used.

The reason why refractory metals such as group 53 and 6a metals of the periodic table and hafnium are interposed between the lower and upper layers as the intermediate layer is that titanium or titanium alloy forming the lower layer reacts directly with boron carbide of the upper layer. This is to suppress the formation of a thick reaction zone.

However, if the thermal expansion coefficient of the intermediate layer is significantly different from that of boron carbide, this is not preferable because cracks may occur near the interface or boron carbide may peel off.

For these reasons, the intermediate layer should be a refractory material made of group 5a, group 6a, or hafnium, which has a thermal expansion coefficient relatively close to that of boron carbide and has a high melting point, which can act as a barrier to diffusion reactions. Metal is suitable.

The reason why the thickness of the intermediate layer is limited to 0.1 to 2 μm is that if it is less than 0.1 μm, it will not function as an intermediate layer, and if it exceeds 2 μm, the overall weight of the diaphragm will increase. be.

The thicknesses of the upper layer, middle layer, and lower layer are automatically determined depending on the value of E/ρ of the diaphragm to be manufactured and the weight of the entire diaphragm in grams. It is something.

On the other hand, a known method can be used for coating boron carbide as the upper layer using the CVD method.

That is, a halide of boron such as boron trichloride or a carbolein such as B4C2H6 is evaporated, and then introduced into a heating reactor together with a mixed gas of hydrocarbon and hydrogen or an inert gas, respectively, to form boron carbide through a decomposition reaction. .

At this time, the vapor deposition temperature varies depending on what kind of boron compound salt is used as a starting material, but for example, when using carborein, the vapor deposition temperature is 400 to 1000°C.
can be relatively low.

The manner in which boron carbide constituting the upper layer is coated will be specifically described below, particularly in the case where boron trichloride is used as the raw material.

The reaction formula at this time is BCl3+CH4+H2→B, C+H (J').

Here, the source of carbon involved in the carbonization reaction.

Although methane is used as a representative hydrocarbon, it is not limited to this, and any of saturated and unsaturated fatty acids, aromatics, and alicyclics may be used, and the number of carbon atoms, amount used, etc. may be adjusted as necessary. You can decide the choice.

The deposition rate of boron carbide is influenced by the temperature of the underlying metal/substrate, the deposition temperature, the gas flow rate, etc., but the influence of the above-mentioned temperature is the greatest.

The deposition conditions include a total gas flow rate of 300 to 500C.
The molar fraction of BCl3 was selected to be 0.45, and the temperature of the underlying metal substrate was selected to be 700 to 1300°C.

Here, if the molar fraction of methane gas (hydrocarbon) is too high, the carbon concentration in the boron carbide layer will increase, and as a result, free carbon will coexist in addition to boron carbide, resulting in Young's modulus. This is undesirable because it causes a decrease in

Therefore, the carbonization concentration is preferably between 0.075 and 0.13 mol.

Furthermore, if the temperature of the underlying metal substrate is too high, the reaction between the boron carbide layer and the intermediate layer will proceed excessively, which is also undesirable, so the upper limit of the temperature of the underlying metal substrate covering the lower layer and intermediate layer is , 1200℃ preferably 1100℃
It should be ℃.

Note that if the temperature of the base metal base is too low, the crystallization of the vapor-deposited boron carbide will be hindered, resulting in a decrease in properties, so the lower limit of the temperature of the base metal base is 800°C.
Preferably, the temperature is 900°C.

Next, the present invention will be explained using examples.

A mild steel block with a diameter of 401nrILφ was prepared as a base metal base, the surface of this mild steel block was processed to match the shape of the speaker diaphragm to be manufactured, and the respective materials shown in Table 1 were applied to the surface of the mild steel block. Multilayer diaphragms 1 to 5 of the present invention were manufactured by forming a multilayer consisting of an upper layer, an intermediate layer, and a lower layer having the components and layer thicknesses shown, and then melting and removing the mild steel block.

Note that the lower layer coating on the mild steel block is performed by ion blating method, and the intermediate layer coating on the lower layer is as follows:
The sputtering method was used, and the coating of the upper layer onto the intermediate layer was performed using the CVD method.

In this case, it is desirable to mask the parts other than the surface parts that need to be coated with boron carbide, so that it will be convenient to melt the mild steel block with acid later.

For the purpose of comparison, a comparative diaphragm 1.2 was manufactured with the components (titanium and titanium alloy) and layer thickness shown in Table 1.

The characteristics of the thus obtained coated diaphragms 1 to 5 of the present invention and comparative diaphragm 1.2 were measured, and the measurement results are shown in Table 1.

As shown in Table 1, it is clear that the multilayer diaphragm of the present invention has a lower density and a significantly higher Young's modulus, and therefore a significantly higher E/ρ value, than the comparative diaphragm.

As described above, the present invention provides a diaphragm for an acoustic transducer that is lightweight, has high rigidity and high elasticity, and exhibits smooth frequency characteristics up to a high frequency range, at a low cost. It can be manufactured.

Claims (1)

[Scope of Claims] 1. A first layer made of titanium or a titanium alloy with a layer thickness of 5 to 20 μm, and a layer made of one of the group 5a and 6a metals of the periodic table and hafnium with a layer thickness of 0.1 to 2 μm. A multilayer diaphragm for an acoustic transducer, comprising: a second layer as an intermediate layer; and a third layer made of boron carbide with a layer thickness of 5 to 30 μm. 2. A lower layer of titanium or titanium alloy as a first layer is coated on the surface of a base metal substrate having a predetermined surface shape by a conventional method to a layer thickness of 5 to 20 μm, and then a lower layer of titanium or a titanium alloy is coated with a layer thickness of 5 to 20 μm by a conventional method. Metals of groups 5a and 6a of the periodic table as a second layer, and one of hafnium
The intermediate layer consisting of seeds is coated with a layer thickness of 0.1 to 2 μm, and the base metal substrate thus coated with the lower layer and the intermediate layer is charged into a pyrolysis reactor, and the base metal substrate is charged into a pyrolysis reactor. , by introducing either a mixed gas containing boron halide vapor, hydrocarbon, and hydrogen as main components, or a mixed gas containing carbonate and an inert gas as main components to cause a decomposition reaction. The upper layer made of boron carbide as the third layer is 5 to 30 μm thick.
1. A method for manufacturing a multilayer diaphragm for an acoustic transducer, characterized in that the main steps include coating the intermediate layer with a layer thickness of 100 mL, and then dissolving and removing the underlying metal substrate.