JPS5821996B2 - 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 pick amplifier cart for playing records, etc., and a method for manufacturing the same.

In general, physical properties required of the diaphragm for an acoustic transducer include: (1) being lightweight; (5) 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 should have a large Young's modulus E and a small specific gravity ρ.
That is, it must have a large E/ρ and a large internal friction, but it is extremely difficult to develop a material that satisfies all of these properties.

However, even if 5 sharp resonances cannot be avoided, E/ρ
If E/ρ is made sufficiently large, smooth frequency characteristics can be obtained up to a fairly high frequency range, so it is considered that a material with a high E/ρ should be used.

Therefore, considering E/ρ as an important characteristic, research has been increasingly conducted in recent years with the aim of developing materials for diaphragms having a high E/ρ characteristic of 0.

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 relatively low E/ρ5, and therefore, as mentioned above, have 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. Therefore, for these reasons, there is a strong demand for the development of a diaphragm material that is not as toxic as beryllium and has a large E/ρ. is the current situation.

From the above-mentioned viewpoints, the present inventors have made it lightweight, has high rigidity and high elasticity, that is, has 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 a titanium polide layer and a boron layer with good adhesion are interposed as intermediate layers, the adhesion between the titanium or titanium alloy and boron carbide can be significantly improved.

(3) If the intermediate layer is coated with the boron carbide layer by chemical vapor deposition (OVD), 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 made of titanium or titanium alloy as a first layer with a layer thickness of 5 to 20 μm by a normal method, and then coat the lower layer with a layer thickness of 5 to 20 μm. The coated base metal substrate is charged into a pyrolysis reactor, and a mixed gas containing boron halide vapor and hydrogen as main components is introduced into the pyrolysis reactor to cause a decomposition reaction. , an intermediate layer consisting of a titanium polide layer and a boron layer as the second layer.
A layer thickness of ~5 μm is coated on the lower layer, and then a mixed gas containing boron halide vapor, hydrocarbon, and hydrogen as main components, or carboline and an inert gas is added to the pyrolysis reactor. A mixed gas containing as a main component is introduced to cause a decomposition reaction, whereby an upper layer of boron carbide as a third layer is coated on the intermediate layer with a layer thickness of 5 to 30 μm, and then Thereafter, by dissolving and removing the base metal substrate, a first layer made of titanium or titanium alloy with a layer thickness of 5 to 20 μm, and an intermediate layer made of a titanium polide layer and a boron layer with a layer thickness of 1 to 5 μm are formed. The present invention is characterized in that it manufactures a multilayer diaphragm for an acoustic transducer, which is comprised of a second layer made of boron carbide and a third layer made of boron carbide with a layer thickness of 5 to 30 μm.

In this invention, titanium or a titanium alloy is used as the first layer (hereinafter referred to as the lower layer) because these metals are strong and have low density, and because they are difficult to deposit when boron carbide is deposited using the OVD method. The reason why the thickness of the lower layer is limited to a range of 5 to 20 μm is because it can withstand temperature rise.
This is because when the thickness exceeds μm, the Young's modulus of the entire laminated diaphragm becomes low.

In addition, the titanium polide layer and the boron layer are interposed between the first layer and the third layer (hereinafter referred to as the upper layer) in the second layer (hereinafter referred to as the intermediate layer) because of the titanium or titanium alloy that constitutes the lower layer. This is to prevent the upper layer of boron carbide from reacting directly and forming a thick reaction zone.

Hereinafter, a method of coating the lower layer of the intermediate layer will be explained.

First, a mild steel block, which is a base metal substrate coated with a lower layer, is charged into a pyrolysis reactor, and a mixed gas containing boron trichloride and hydrogen as main components is introduced into the pyrolysis reactor to undergo a decomposition reaction.

At this time, the base metal temperature was set to 700 to 1300°C, the overall gas flow rate was set to 300 to 500 CC/min, and H2
/BCl3 molar fraction ratio was changed from 1.5 to 50, and the base metal temperature was 900 to 1.
It was found that 25 to 30 is the optimum condition for 100°C H2/BC1!3.

Under these conditions, the boron deposited in the underlying layer reacts with the underlying metal to form a thin titanium polide intermediate compound layer.

The titanium polide layer has a coefficient of thermal expansion of 5.5X10-
'/°C is close to the thermal expansion coefficient of boron carbide or boron, and also has good adhesion to the underlying titanium or titanium alloy, and has desirable properties as an intermediate layer.

The thickness of the titanium polide layer is preferably 1/10 or less of the thickness of the boron layer.

The boron layer has the effect of improving adhesion to the boron carbide and making the boron carbide denser when the boron carbide is coated on the boron layer as an upper layer.

A maximum thickness of 5 μm is sufficient for the thickness of the intermediate layer.

However, if the thickness is less than 1 μm, it will not function adequately as an intermediate layer, so the thickness of the intermediate layer must be within a certain range.

A thickness of 1 to 5 μm is desirable.

Furthermore, 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 intermediate layer as an upper layer as thick as possible, but it cannot exceed 30 μm due to the constraint that it must be lightweight. unfavorable, 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, coating the lower layer on, for example, a mild steel block as a base metal substrate may be performed by an ion blasting method in addition to a vacuum evaporation method or a sputtering method. Alternatively, a chemical vapor deposition method (OVD method) may be used.

The thicknesses of the upper layer, intermediate 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 that

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

That is, boron decogenide such as boron trichloride,
Or evaporate carbolein such as B2O, 2H6,
This is introduced into a heating reactor together with a mixed gas of hydrocarbon and hydrogen or an inert gas, respectively, and boron carbide is formed by 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 BCl30CH4+H2→B, 010HO/.

Here, methane is used as a representative hydrocarbon that is a source of carbon involved in the carbonization reaction, but it is not limited to this. The number of carbon atoms, the amount used, etc. can be selected and determined as necessary.

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

The vapor deposition conditions include a total gas flow rate of 300 to 500
QC/min, the mole fraction of BCl2 is 0.45,
The temperature of the underlying metal substrate was selected to be 700 to 1300°C.

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. This is not preferable because it causes a decrease in Young's modulus.

Therefore, the carbon concentration is preferably between 0.075 and 0.13 moles.

In addition, 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. The upper limit is 1200℃, preferably 110℃
It should be at 0°C.

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 4011 g 1φ is prepared as a base metal base, the surface of this mild steel block is processed to match the shape of the speaker diaphragm to be manufactured, and the surfaces of the mild steel blocks shown in Table 1 are applied to the surface of the mild steel block, respectively. The multilayer diaphragms 1 and 2 of the present invention were manufactured by forming a multilayer consisting of an upper layer, an intermediate layer, and a lower layer in terms of composition and layer thickness, and then melting and removing the mild steel block.

The lower layer was coated on the mild steel book by vacuum evaporation, the intermediate layer was coated on the lower layer by sputtering, and the upper layer was coated on the intermediate layer by CVD.

In this case, surfaces other than those that needed to be coated with boron carbide were masked to make it easier to later dissolve the mild steel block with acid.

In addition, for the purpose of comparison, a comparative diaphragm 12 having the components (tiin and titanium alloy) and layer thicknesses shown in Table 1 was manufactured.

The characteristics of the coated diaphragm 1゜2 of the present invention thus obtained and the comparison diaphragms 1 and 2 were measured, and the measurement results were used as the first
Shown in the table.

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 than the comparative diaphragm, and thus a significantly higher E/ρ value. .

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 high frequencies, 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, a second layer as an intermediate layer made of a titanium poride layer and a boron layer with a layer thickness of 1 to 5 μm, and a layer thickness of 5 to 5 μm. A multilayer diaphragm for an acoustic transducer, comprising a third layer made of boron carbide with a thickness of 30 μm. 2. On the surface of a base metal substrate having a predetermined surface shape, first coat a lower layer made of titanium or a titanium alloy as a first layer with a layer thickness of 5 to 20 μm by a normal method, and then coat the base metal with the lower layer. The substrate is placed in a pyrolysis reactor, and a mixed gas containing boron halide vapor and hydrogen as main components is introduced into the pyrolysis reactor to cause a decomposition reaction. An intermediate layer consisting of a titanium polide layer and a boron layer as
A layer thickness of 51 kn was coated on the above layer, and then a mixed gas containing boron halide vapor, hydrocarbon, and hydrogen as main components, or carboline and an inert gas was introduced into the pyrolysis reactor. By introducing any of the mixed gases contained as main components to cause a decomposition reaction, an upper layer made of boron carbide as a third layer is coated on the intermediate layer with a layer thickness of 5 to 30 μm, and then A method for manufacturing a multi-layer diaphragm for an acoustic transducer, characterized in that the main step consists of (5) dissolving and removing the base metal substrate.