JP3919173B2 - Diaphragm for electroacoustic transducer - Google Patents

Description

【００２８】
したがって、カーボンナノチューブを強化材として使用した振動板は、高弾性率炭素繊維強化振動板と比較すると、高い剛性と内部損失を有し、音響特性と寸法安定性に優れた軽量の電気音響変換器用振動板を得ることができる。
【００２９】
カーボンナノチューブと共に用いられる合成樹脂（マトリックス）としては、一般に入手できる熱可塑性樹脂、熱硬化性樹脂等が使用可能である。
【００３０】
なお、カーボンナノチューブは表面が滑らかなので、合成樹脂から抜けやすく、そのため、合成樹脂が割れやすいので、カーボンナノチューブに種々の分子を化合させる化学的修飾や金属コーティング等の処理は有効である。
【００３１】
また、カーボンナノチューブと合成樹脂との接着力を向上させるため、合成樹脂に相溶性があり、かつカーボンナノチューブとの接着性が良好な樹脂の選択が必要であり、混合法には乾式混合法と湿式混合法の使用が可能である。
【００３２】
種々の検討結果から基本的には、カーボンナノチューブに対する接着性は、高弾性率炭素繊維と類似していることが確認された。
【００３３】
また、検討結果から、ポリアミド系樹脂、エポキシ系樹脂も有効であったが、特にポリスチレン系飽和型熱可塑性エラストマー〔スチレン・エチレン・ブチレン・スチレンブロックコーポリマー（ＳＥＢＳ）、官能基付与ＳＥＢＳ、スチレン・エチレン・プロピレン・スチレンブロックコーポリマー、ランダムタイプの水素添加型スチレン・ブタジエンポリマー等〕、エチレン系変性α−オレフィン共重合体、変性ポリオレフィン等が接着性の面で有効であった。
【００３４】
合成樹脂としてポリプロピレンを使用する場合は、樹脂中に強化材としてのカーボンナノチューブを一様に分散させるために、二軸混練機で十分に混練して成形材料とする。
【００３５】
カーボンナノチューブに接着性の良い樹脂としてエチレン系変性α−オレフィン共重合体を用いる場合は、初めに接着性の良い樹脂にカーボンナノチューブを二軸混練機で一様に分散させたペレットを作製後、ポリプロピレンに所定量添加し、一様に分散して成形材料とする。また、ポリプロピレンとエチレン系変性α−オレフィン共重合体を二軸混練機等で混練後、カーボンナノチューブを添加して一様に分散して成形材料としてもよい。
【００３６】
このようにして得られたペレットを一般的に用いられる射出成形法、押出成形法等によって本発明の振動板を成形することができる。
【００３７】
高剛性で高内部損失の振動板を得る場合は、ポリプロピレン、ポリアミド、液晶ポリマー等の内部損失の大きな合成樹脂を用いれば良い。
【００３８】
マイクロホン用の振動板のように大きな内部損失を必要としない場合は、その目的に適合した合成樹脂を選択すれば良い。
【００３９】
また、高剛性で耐熱性を必要とする振動板に対しては、エポキシ樹脂、フェノール樹脂等の熱硬化性樹脂からなる合成樹脂を用いれば良い。
【００４０】
このように、目的、用途等に応じて適切な合成樹脂を適宜選択すれば良い。
【００４１】
また、本発明においてはマトリックス組成物に対して、本発明の効果を著しく損わない範囲で、難燃剤、酸化防止剤、紫外線防止剤、分散剤、可塑剤、有機あるいは無機系顔料、フィラー、核剤等の公知の添加剤を加えることができる。
【００４２】
【実施礼】
本発明では、使用する合成樹脂としては、ポリスチレン系飽和型熱可塑性エラストマー、エチレン系変性α−オレフィン共重合体、変性ポリオレフィンを単体または混合体として添加したものを用いている。
【００４３】
このうち、実施例では次の合成樹脂、カーボンナノチューブを用いて振動板を作製した。
【００４４】
ポリプロピレン：商品名 Ｊ１０８Ｍ，（株）グランドポリマー製
密度 ：９１０ｋｇ／ｍ^３（ＡＳＴＭ Ｄ１５０６）
ＭＦＲ：５０ｇ／１０ｍｉｎ（ＪＩＳ Ｋ６７５８）
【００４５】
エチレン系変性α−オレフィン共重合体：商品名 タフマー，三井化学（株）製
密度 ：８８５ｋｇ／ｍ^３（ＡＳＴＭ Ｄ１５０６）
表面硬度：ショアーＡ ８５（ＪＩＳ Ｋ６２５３）
【００４６】
カーボンナノチューブ：商品名 ＭＷＮＴ Ｇｒｏｕｎｄ Ｃｏｒｅ，本荘ケミカル（株）製
密度 ：１３３０〜１４００ｋｇ／ｍ^３
直径 ：３〜３０ｎｍ
長さ ：１〜１０μｍ
引張強度：５０ＧＰａ以上
弾性率 ；１８００ＧＰａ
弾性限界：大きな角度で曲げても損傷せず復元する
（復元力）
耐熱性 ：空気中で７５０℃まで安定
本実施例で使用したナノチューブはアーク放電法により作製した。使用したナノチューブ粉末には不純物として、粒状グラファイト、非晶質カーボンが含まれている。
【００４７】
比較例として、次のものを用いて振動板を作製した。
ＰＡＮ系炭素繊維：商品名 トレカ Ｍ６０Ｊ（東レ（株）製）
密度 ：１９４０ｋｇ／ｍ^３
直径 ：６．５μｍ
引張強度：３．９ＧＰａ
弾性率 ：５８８ＧＰａ
伸び率 ：０．７％
【００４８】
上記成分を表２に示す割合で配合し、樹脂組成物を調整した。
【００４９】
製造にあたっては、まず、直径０．４〜５００ｎｍ、長さ０．０６〜２００μｍのカーボンナノチューブと上記合成樹脂とを周知構造の二軸混練機を介して十分に混練して成形材料を作製する。カーボンナノチューブは電子線照射によって所望の長さに切断することができる。なお、必要に応じ、カーボンナノチューブには、予め化学的修飾や金属コーティング等の表面処理が施される。
【００５０】
カーボンナノチューブの直径を０．４ｎｍ以上としたのは、それより小さなカーボンナノチューブを製造することは難しいためである。また、５００ｎｍ以下としたのは、これより大とすると振動板としての所望の物性値から外れるためである。また、長さ０．０６μｍ以下では製造することが難しいためである。また、２００μｍ以下としたのは、それ以上だと振動板としての所望の物性値から外れるためである。
【００５１】
次に、図１（ａ）に示すように、可動側金型１と固定側金型２とからなる金型３のキャビティ内に、射出成形機のノズル４を当て、（ｂ）に示すように、成形材料５を内部に充填して射出成形し、所定時間経過後、型開きをして作製された振動板を取り出せば良い。
【００５２】
図２は成形されたコーン状振動板６の一例を示す。
【００５３】
この振動板６と、ＰＡＮ系炭素繊維を用いて作製した振動板とを振動リード法で測定した物性値は表２の通りである。また、その他の比較例として、チタンや、ポリプロピレン（Ｊ１０８Ｍ）単体の物性値も示す。
【００５４】
表２

【００５５】
表２に示した値より明らかなように、ポリプロピレンとカーボンナノチューブとからなる本発明品と高弾性率炭素繊維を強化材としたものとを比較すると、本発明品の方が密度が低く、軽量で高弾性率のものが得られる。
【００５６】
一方、内部損失は、重量比で２０％添加しても、内部損失の大きさは、ポリプロピレンとは大きな差はない。また、音速は金属チタンと同程度の値が得られた。
【００５７】
以上のように、本発明品にかかる電気音響変換器用振動板は、従来から使用されている炭素繊維強化振動板、グラファイト強化振動板等と比較して軽量で高剛性、高内部損失、高音速の物性が得られる。
【００５８】
その理由は、カーボンナノチューブがケージ物質（かご構造)でグラファイトのネットワークを基本としているためである。しかしながら、カーボンナノチューブはグラファイトとは相違し、縦波１つ、横波２つ、ねじれ１つの音響モードが存在し、これらの４つの音響モードの音速がｓｐ^２の結合を反映して通常の材料よりも著しく音速を速くしているためである。
【００５９】
なお、本発明は上記実施例に限定されるものでなく、本発明の精神を逸脱しない範囲で種々の変更が可能である。例えば上記実施例では合成樹脂としてはポリプロピレン、エチレン系変性α−オレフィン共重合体を用いた例について示したが、それら以外でも良く、また、射出成形により振動板を作製する例について説明したが、押出成形によっても作製することは可能である。さらに、振動板形状としてはコーン状のみならず、平板状、その他の形状のものであっても良いことは勿論である。
【００６０】
【発明の効果】
カーボンナノチューブで合成樹脂を強化した複合材料を成形してなる本発明の振動板によれば、優れた物性を有するため、成形性、寸法安定性、耐熱性、耐久性等が向上した電気音響変換器用振動板を得ることができ、この振動板を用いたスピーカによれば、周波数特性の広帯域化、平均化を図ることができ、音質の向上を期待することができる。
【図面の簡単な説明】
【図１】 （ａ）、（ｂ）は射出成形機による振動板の製造工程の説明図である。
【図２】 作製された振動板の一例を示す。
【符号の説明】
１ 可動側金型
２ 固定側金型
３ 金型
４ 射出成形機のノズル
５ 成形材料
６ 振動板[0001]
BACKGROUND OF THE INVENTION
The present invention uses carbon nanotubes as a reinforcing material for a synthetic resin, is lightweight, highly rigid, has high internal loss, and has excellent moldability, dimensional stability, heat resistance, etc. The present invention relates to a transducer diaphragm.
[0002]
[Prior art]
Conventionally, as a molding material for diaphragms for electroacoustic transducers, various synthetic resins or various synthetic resins are used as a matrix, and as a reinforcing material, high elastic modulus such as glass fiber and carbon fiber, and high elastic modulus such as Kevlar Organic fiber is used.
[0003]
In addition to the fiber reinforcement, flake graphite powder, flake mica and the like have been proposed and used.
[0004]
Among these, as a prior art using carbon fiber and flaky mica or flaky graphite powder, for example, there are the following.
[0005]
In Japanese Patent Publication No. 56-29437, a method for producing an acoustic diaphragm in which high-performance carbon fiber and flake-like mica are made into layers using a thermoplastic resin or thermosetting resin as a binder and cured by pressure and heating. Has been proposed.
[0006]
Japanese Patent Publication No. 6-39552 proposes a mixture of polypropylene and polyamide resin using carbon fibers and flake graphite powder as reinforcing materials.
[0007]
Further, as disclosed in JP-A-6-178385, a diaphragm in which a glass balloon, carbon fiber, and carbon graphite are added to a polypropylene polymer and a maleic anhydride-modified propylene copolymer has been proposed.
[0008]
Moreover, as disclosed in JP-A-9-284885, a speaker diaphragm in which mica as a reinforcing material is blended and blended in a polyolefin-based matrix resin improves acoustic characteristics and has a vivid color exhibiting pearly luster. A loudspeaker diaphragm that has been imparted and improved in design is also used.
[0009]
Further, as disclosed in Japanese Patent Application Laid-Open No. 59-28795, it has been proposed that a high elastic modulus carbon fiber is combined with a polypropylene polymer to obtain a better diaphragm than a paper diaphragm.
[0010]
[Problems to be solved by the invention]
The diaphragm described in Japanese Patent Publication No. 56-29437 is effective when it has a high elastic modulus, but has a drawback that the manufacturing process becomes complicated because it uses papermaking technology.
[0011]
The diaphragms in Japanese Patent Publication No. 6-39552 and Japanese Patent Laid-Open No. 6-178385 have the disadvantages that many kinds of composite materials are used, the manufacturing is complicated, and the cost is increased.
[0012]
In the diaphragm disclosed in Japanese Patent Laid-Open No. 9-284885, the mica can reduce the filling speed compared to other fillers compared to other fillers such as polypropylene resin and can be filled more than 30%, but the mica is elastic. Since the ratio is small, the density is relatively low (200 to 800 kg / m ³ ), and the physical properties of the paper diaphragm having sufficient elastic modulus and high internal loss (0.02 to 0.1 tan δ) for general performance are improved. It is difficult to do.
[0013]
In addition to ordinary carbon fibers, carbon graphite is used, but the elastic modulus of carbon graphite is about 70 GPa, which is not good for improving the physical properties as compared with 450 GPa of PAN-based high modulus carbon fiber.
[0014]
As in JP-A-59-28795, in a diaphragm using a high elastic modulus carbon fiber having a higher elastic modulus than carbon graphite, the fiber diameter of the high elastic modulus carbon fiber is as large as 6.5 to 10 μm, and When bending stress is applied, it breaks when it exceeds the elastic limit, so that there are problems that the processing conditions are limited and it is difficult to obtain a highly rigid diaphragm with good dimensional stability.
[0015]
The present invention has been proposed in view of the above, and the object is to use carbon nanotubes having a structure different from that of high elastic modulus carbon fibers, carbon whiskers, and carbon graphite as reinforcing materials for synthetic resins. Another object of the present invention is to provide a diaphragm for an electroacoustic transducer having high rigidity, high internal loss, and excellent dimensional stability, heat resistance, durability, and the like.
[0016]
[Means for Solving the Problems]
The present invention achieves the above object by molding the diaphragm with a composite material in which a synthetic resin is reinforced with carbon nanotubes.
[0017]
In this case, as the synthetic resin, polystyrene-based saturated thermoplastic elastomer, et styrene-modified α- olefin copolymer, characterized by using a material obtained by adding a modified polyolefin alone or as mixtures.
[0018]
Further, carbon nanotubes having a diameter of 0.4 to 500 nm and a length of 0.06 to 200 μm are used.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is characterized in that carbon nanotubes are used as the reinforcing material of the synthetic resin instead of the high elastic modulus carbon fiber.
[0020]
In other words, as a structural factor that improves the mechanical properties of fiber-reinforced composite materials,
(1) Content, length and aspect ratio of fiber reinforcement (length / diameter)
(2) Degree of fiber orientation (3) Interfacial adhesion (4) Matrix morphology, etc. For filler-based composite materials, filler particle size, morphology, interfacial adhesion, filler dispersibility, etc.
[0021]
As described above, powders such as high elastic modulus carbon fiber and mica are used for the reinforcing material of the conventional synthetic resin diaphragm. However, since these sizes are in units of μm, a sufficient composite effect can be obtained. Absent.
[0022]
On the other hand, the carbon nanotubes used in the present invention are in nm units, and the contact area with the matrix is remarkably increased as compared with the conventional product, so that the dispersibility and the interfacial adhesive force are increased. Further, the aspect ratio is remarkably increased, and a sufficient composite effect can be obtained.
[0023]
In other words, the diaphragm of the present invention uses carbon nanotubes that are lightweight and have a high elastic modulus, a high-rigidity diameter of 0.4 to 500 nm, and a length of 0.06 to 200 μm for reinforcing the synthetic resin. It is possible to improve physical properties and improve dimensional stability, etc., with respect to a diaphragm using high modulus carbon fiber as a material.
[0024]
This carbon nanotube can be manufactured by arc discharge method, laser ablation method, plasma synthesis method, hydrocarbon catalytic decomposition method, spinning method, etc., making a seamless coaxial cylinder of hexagonal mesh surface sheet of carbon atoms, Nanometer size and excellent mechanical strength.
[0025]
Carbon nanotubes are regarded as a kind of whiskers because of their unique structure, but when subjected to strong processing, they cause plastic deformation in a unique manner with buckling. It is different from fiber.
[0026]
Table 1 shows physical property values of the carbon nanotube and the highly elastic carbon fiber.
[0027]
Table 1

[0028]
Therefore, a diaphragm using carbon nanotubes as a reinforcing material has high rigidity and internal loss compared to a high modulus carbon fiber reinforced diaphragm, and is used for lightweight electroacoustic transducers with excellent acoustic characteristics and dimensional stability. A diaphragm can be obtained.
[0029]
As the synthetic resin (matrix) used together with the carbon nanotubes, generally available thermoplastic resins, thermosetting resins and the like can be used.
[0030]
In addition, since the carbon nanotube has a smooth surface, it is easy to come off from the synthetic resin, and therefore, the synthetic resin is easily broken. Therefore, treatments such as chemical modification for combining various molecules with the carbon nanotube and metal coating are effective.
[0031]
In addition, in order to improve the adhesion between the carbon nanotube and the synthetic resin, it is necessary to select a resin that is compatible with the synthetic resin and has good adhesion with the carbon nanotube. Wet mixing methods can be used.
[0032]
From various examination results, it was confirmed that the adhesion to carbon nanotubes was basically similar to that of high modulus carbon fibers.
[0033]
From the examination results, polyamide-based resins and epoxy-based resins were also effective. In particular, polystyrene-based saturated thermoplastic elastomers [styrene / ethylene / butylene / styrene block copolymer (SEBS), functional group-added SEBS, styrene / ethylene-propylene-styrene block copolymer, a random type of hydrogenated styrene-butadiene polymers, etc.], et styrene-modified α- olefin copolymer, modified polyolefin or the like was effective in terms of adhesion.
[0034]
When polypropylene is used as the synthetic resin, in order to uniformly disperse the carbon nanotubes as the reinforcing material in the resin, it is sufficiently kneaded with a biaxial kneader to obtain a molding material.
[0035]
When using an ethylene-based modified α-olefin copolymer as a resin having good adhesion to carbon nanotubes, after preparing pellets in which carbon nanotubes are uniformly dispersed in a resin having good adhesion with a biaxial kneader first, A predetermined amount is added to polypropylene and uniformly dispersed to obtain a molding material. Alternatively, polypropylene and an ethylene-modified α-olefin copolymer may be kneaded with a biaxial kneader or the like, and then carbon nanotubes may be added and dispersed uniformly to form a molding material.
[0036]
Thus, the diaphragm of this invention can be shape | molded by the injection molding method, extrusion molding method, etc. which are generally used for the obtained pellet.
[0037]
When obtaining a diaphragm having high rigidity and high internal loss, a synthetic resin having a large internal loss such as polypropylene, polyamide, or liquid crystal polymer may be used.
[0038]
When a large internal loss is not required unlike a diaphragm for a microphone, a synthetic resin suitable for the purpose may be selected.
[0039]
In addition, for a diaphragm that has high rigidity and requires heat resistance, a synthetic resin made of a thermosetting resin such as an epoxy resin or a phenol resin may be used.
[0040]
Thus, an appropriate synthetic resin may be appropriately selected according to the purpose, application, and the like.
[0041]
Further, in the present invention, flame retardants, antioxidants, UV inhibitors, dispersants, plasticizers, organic or inorganic pigments, fillers, in a range that does not significantly impair the effects of the present invention with respect to the matrix composition. Known additives such as a nucleating agent can be added.
[0042]
[Training]
In the present invention, the synthetic resin used is used as the added polystyrene-based saturated thermoplastic elastomer, et styrene-modified α- olefin copolymer, a modified polyolefin alone or as mixtures.
[0043]
Among these, the diaphragm was produced in the Example using the following synthetic resins and carbon nanotubes.
[0044]
Polypropylene: Trade name J108M, Grand polymer density: 910 kg / m ³ (ASTM D1506)
MFR: 50g / 10min (JIS K6758)
[0045]
Ethylene-based modified α-olefin copolymer: Trade name Toughmer, manufactured by Mitsui Chemicals, Inc. Density: 885 kg / m ³ (ASTM D1506)
Surface hardness: Shore A 85 (JIS K6253)
[0046]
Carbon nanotube: Product name MWNT Ground Core, Honjo Chemical Co., Ltd. Density: 1330-1400 kg / m ³
Diameter: 3-30nm
Length: 1-10μm
Tensile strength: 50 GPa or more Elastic modulus: 1800 GPa
Elastic limit: Restoration without damage even if bent at a large angle (restoring force)
Heat resistance: stable in air up to 750 ° C. The nanotubes used in this example were produced by the arc discharge method. The nanotube powder used contains granular graphite and amorphous carbon as impurities.
[0047]
As a comparative example, a diaphragm was manufactured using the following.
PAN-based carbon fiber: Trade name Torayca M60J (manufactured by Toray Industries, Inc.)
Density: 1940 kg / m ³
Diameter: 6.5 μm
Tensile strength: 3.9 GPa
Elastic modulus: 588 GPa
Elongation rate: 0.7%
[0048]
The said component was mix | blended in the ratio shown in Table 2, and the resin composition was adjusted.
[0049]
In production, first, a carbon nanotube having a diameter of 0.4 to 500 nm and a length of 0.06 to 200 μm and the synthetic resin are sufficiently kneaded through a biaxial kneader having a known structure to produce a molding material. The carbon nanotube can be cut into a desired length by electron beam irradiation. If necessary, the carbon nanotubes are subjected to surface treatment such as chemical modification and metal coating in advance.
[0050]
The reason why the diameter of the carbon nanotube is 0.4 nm or more is that it is difficult to produce a carbon nanotube smaller than that. Further, the reason why the thickness is set to 500 nm or less is that if it is larger than this, it will be out of the desired physical property value of the diaphragm. Moreover, it is because it is difficult to manufacture if the length is 0.06 μm or less. The reason why the thickness is 200 μm or less is that if it is more than that, the desired physical property value of the diaphragm is not satisfied.
[0051]
Next, as shown in FIG. 1A, the nozzle 4 of the injection molding machine is applied into the cavity of the mold 3 composed of the movable mold 1 and the fixed mold 2 as shown in FIG. In addition, the molding material 5 is filled inside and injection-molded, and after a predetermined time has elapsed, the mold is opened to take out the diaphragm.
[0052]
FIG. 2 shows an example of the shaped cone-shaped diaphragm 6.
[0053]
Table 2 shows the physical property values of the diaphragm 6 and the diaphragm manufactured using the PAN-based carbon fiber measured by the vibration lead method. In addition, as other comparative examples, physical property values of titanium and polypropylene (J108M) alone are also shown.
[0054]
Table 2

[0055]
As is clear from the values shown in Table 2, when the product of the present invention comprising polypropylene and carbon nanotubes is compared with the material using high modulus carbon fiber as a reinforcing material, the product of the present invention has a lower density and is lighter. A high elastic modulus can be obtained.
[0056]
On the other hand, even when the internal loss is added by 20% by weight, the magnitude of the internal loss is not significantly different from that of polypropylene. Moreover, the sound speed was similar to that of metallic titanium.
[0057]
As described above, the diaphragm for an electroacoustic transducer according to the present invention is lighter in weight and has higher rigidity, higher internal loss, higher sound speed than conventional carbon fiber reinforced diaphragm and graphite reinforced diaphragm. The physical properties of can be obtained.
[0058]
This is because carbon nanotubes are cage materials (cage structures) and are based on a graphite network. However, carbon nanotubes are different from graphite, and there are one longitudinal wave, two transverse waves, and one torsional acoustic mode, and the sound speed of these four acoustic modes reflects the coupling of sp ² than ordinary materials. This is because the speed of sound is remarkably increased.
[0059]
In addition, this invention is not limited to the said Example, A various change is possible in the range which does not deviate from the mind of this invention. For example, in the above examples, polypropylene and an ethylene-modified α-olefin copolymer were used as the synthetic resin. However, other examples may be used, and an example of producing a diaphragm by injection molding has been described. It can also be produced by extrusion. Furthermore, the diaphragm shape is not limited to a cone shape, but may be a flat plate shape or other shapes.
[0060]
【The invention's effect】
According to the diaphragm of the present invention formed by molding a composite material in which a synthetic resin is reinforced with carbon nanotubes, the electroacoustic conversion has excellent physical properties and improved formability, dimensional stability, heat resistance, durability, and the like. A ceramic diaphragm can be obtained, and according to a speaker using this diaphragm, the frequency characteristics can be widened and averaged, and an improvement in sound quality can be expected.
[Brief description of the drawings]
FIGS. 1A and 1B are explanatory views of a manufacturing process of a diaphragm by an injection molding machine.
FIG. 2 shows an example of a manufactured diaphragm.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Movable mold 2 Fixed mold 3 Mold 4 Injection molding machine nozzle 5 Molding material 6 Diaphragm

Claims (1)

Molded by a composite material in which a synthetic resin is reinforced with carbon nanotubes, the carbon nanotube having a diameter of 0.4 to 500 nm and a length of 0.06 to 200 μm, and a polystyrene-based saturated thermoplastic elastomer for the synthetic resin , et styrene-modified α- olefin copolymer, electroacoustic transducer diaphragm that characterized using a material obtained by adding a modified polyolefin alone or as mixtures.

Images