【発明の詳細な説明】[Detailed description of the invention]
産業上の利用分野
本発明は周波数特性が平坦でかつ低歪、広再生
周波数帯域の耐水性に優れた熱成形可能なスピー
カ用振動板に関するものである。
従来例の構成とその問題点
従来からスピーカ用振動板材料として紙コーン
が多く使用されてきたが、これは紙が低密度で適
度の弾性率、内部損失を有し、曲げ剛性も大きい
ためである。これらの物性は音響特性において能
率、再生帯域、周波数特性の平坦性、耐入力に大
きく関係している。しかし、紙コーンの場合は熱
成形ができないため一枚ずつコーン形状に抄造す
る必要があるなど加工工程が複雑となり、その為
に製造時での品質が安定しない欠点を持ち、又、
耐水性、耐湿性にも劣つている。紙に代わる材料
としてアルミニウム、ベリリウム等の金属材料や
ポリプロピレン、ポリエチレン等の高分子材料を
振動板とする試みがなされているが、金属材料の
場合は比弾性率が高い反面、内部損失は極端に低
い欠点を持ち周波数特性上では高域に鋭いピーク
を生じる。そのため主にツイータに使用されてい
るにすぎない。一方、高分子材料の場合は内部損
失が高く成形性、耐水、耐湿性にも優れている反
面、比弾性率、曲げ剛性が低い欠点をもつてい
た。
発明の目的
本発明の目的は、高分子材料よりなる振動板の
欠点である比弾性率、低剛性を改善し、広帯域
化、高耐入力化を図ることができるスピーカ用振
動板を提供することにある。
発明の構成
本発明のスピーカ用振動板は、ポリプロピレン
等の熱可塑性樹脂を基材とし、マイカ、鱗片状黒
鉛を強化材に用いることにより内部損失を低下さ
せることなく、高比弾性率、高剛性化を達成した
ものである。強化材としてマイカ単独を混入した
場合はマイカの比重が2.7と大きいため曲げ剛性
の点で不利となり、又、繰り返し疲労に弱い欠点
をもつ。一方、鱗片状黒鉛単独を混入した場合は
弾性率があまり高くならず、又、含有率を上げる
と導電性となり、間接リードタイプの振動板に用
いられない欠点をもつ。しかし、鱗片状黒鉛に少
量のマイカを混入する事により弾性率が大幅に向
上され、曲げ剛性も大きくなる。これは鱗片状黒
鉛の硬度がほぼ１であるのに対しマイカの硬度が
３と大きいため、混練中にマイカが鱗片状黒鉛の
ヘキ開を促進するためと考えられる。鱗片状物を
強化材にもつ場合の弾性率に関しては、すでに
Halpin−Tsaiやnielserらによつて詳しく研究さ
れ、複合物の弾性率は次式によつて表わされるこ
とが良く知られている。
Ｅ／E1＝１＋ABV2／１−RV2
Ａ＝2W／ｔ
Ｂ＝E2／E1−１／E2／E1＋Ａ
添字１、２は各々基材、強化材を表わし、Ｅは
弾性率、Ｖは体積分率、Ｗは鱗片物の直径、ｔは
厚みをそれぞれ示したものである。ヘキ開が進む
につれてｔは小さくなりＡが大きくなる。第１図
にＡの値とＥの関係を示すが、Ａの値が大きくな
るにつれてＥも大きくなることがわかる。
一方、内部損失は高分子樹脂自体の寄与と鱗片
状物の層間での損失の寄与の二つが効いており、
ヘキ開の進んだ状態においてもその低下は認めら
れなかつた。表１に各種シートの物性値を示す
が、オレフイン系樹脂を基材とする鱗片状黒鉛と
マイカの複合系においては、弾性率、比弾性率、
曲げ剛性がかなり大きくなつており、基材として
はオレフイン系樹脂が密度、内部損失の面で有効
であることがわかる。
実施例の説明
実施例 １
ポリプロピレン（宇部興産(株)製）75Wt％を基
材とし、これに鱗片状黒鉛（平均直径10μｍ）
22Wt％、マイカ（平均直径40μｍ）3Wt％を強化
材として添加し、二軸スクリユー押出機を用いて
良く混練してマスターペレツトを作り、次にこの
ペレツトを10時間、110℃で予備乾燥した後、一
軸スクリユー押出機を用いてＴダイより厚さ
160μｍの複合シートをひいた。次にこのシート
を遠赤外線で約７〜８秒加熱し、軟化した時点で
真空成形を行つた。シートの物性は表１に示す
が、黒鉛、マイカ単独を複合したものより弾性
率、比弾性率、曲げ剛性の点ですぐれていた。こ
れらのシートを用いた12cmスピーカ用振動板の周
波数特性を第２図に示すが、黒鉛、マイカ単独の
ものに比べ歪が小さく、再生帯域も広がるのが観
測された。尚、第２図中A1，A2，A3は本実施
例、マイカ単独、黒鉛単独の場合の音圧周波数特
性、B1，B2，B3は同じく歪特性を示している。
実施例 ２
４−メチルペンテンポリマ（三井石油化学(株)製
TPX）80wt％を基材とし、これに鱗片状黒鉛
（平均直径10μｍ）16Wt％、マイカ（平均直径40μ
ｍ）4Wt％を強化材として添加して実施例１と同
様の方法で厚さ150μｍのシートを作つた。第３
図に強化材の黒鉛とマイカの混合比を変えた時の
弾性率の変化を示すが、マイカの配合比としては
鱗片状黒鉛に対して10〜30Wt％が効果的である
ことがわかる。
又、基材としてはオレフイン系樹脂が内部損失
および密度、曲げ剛性の点で他の樹脂に比べて有
利であり、周波数特性上では高能率、低歪化が達
成できることがわかる。
INDUSTRIAL APPLICATION FIELD The present invention relates to a thermoformable speaker diaphragm that has flat frequency characteristics, low distortion, and excellent water resistance over a wide reproduction frequency band. Conventional structure and its problems Paper cones have traditionally been used as a material for speaker diaphragms, but this is because paper has a low density, moderate elastic modulus, internal loss, and high bending rigidity. be. These physical properties are closely related to acoustic characteristics such as efficiency, reproduction band, frequency characteristic flatness, and input resistance. However, since paper cones cannot be thermoformed, the processing process is complicated, as it is necessary to make each sheet into a cone shape, and as a result, the quality of the paper cone is not stable during manufacturing.
It also has poor water resistance and moisture resistance. Attempts have been made to use metal materials such as aluminum and beryllium, and polymer materials such as polypropylene and polyethylene as diaphragms to replace paper, but while metal materials have a high specific modulus of elasticity, their internal loss is extremely high. It has a low drawback and produces a sharp peak in the high range in frequency characteristics. Therefore, it is mainly used for tweeters. On the other hand, in the case of polymeric materials, although they have high internal loss and are excellent in formability, water resistance, and moisture resistance, they have the drawbacks of low specific modulus of elasticity and low bending rigidity. OBJECT OF THE INVENTION An object of the present invention is to provide a speaker diaphragm that can improve specific elastic modulus and low rigidity, which are disadvantages of diaphragms made of polymer materials, and can achieve a wide band and high input resistance. It is in. Structure of the Invention The speaker diaphragm of the present invention has a thermoplastic resin such as polypropylene as a base material, and uses mica and flaky graphite as reinforcing materials, thereby achieving high specific modulus and high rigidity without reducing internal loss. This is what we achieved. When mica alone is mixed as a reinforcing material, the specific gravity of mica is as high as 2.7, which is disadvantageous in terms of bending rigidity, and it also has the disadvantage of being weak against repeated fatigue. On the other hand, when flaky graphite is mixed alone, the elastic modulus is not very high, and when the content is increased, it becomes conductive, which has the disadvantage that it cannot be used in indirect lead type diaphragms. However, by mixing a small amount of mica into flaky graphite, the elastic modulus is greatly improved and the bending rigidity is also increased. This is thought to be because mica promotes cleavage of flaky graphite during kneading because the hardness of mica is as high as 3 while the hardness of flaky graphite is approximately 1. Regarding the elastic modulus when using scale-like materials as reinforcement, we have already
It is well known that the elastic modulus of a composite is expressed by the following equation, which was studied in detail by Halpin-Tsai and Nielser et al. E/E 1 =1+ABV 2 /1-RV 2 A=2W/t B=E 2 /E 1 -1/E 2 /E 1 +A Subscripts 1 and 2 represent the base material and reinforcing material, respectively, and E is the elasticity. V is the volume fraction, W is the diameter of the scales, and t is the thickness. As the opening progresses, t becomes smaller and A becomes larger. FIG. 1 shows the relationship between the value of A and E, and it can be seen that as the value of A increases, E also increases. On the other hand, the internal loss is due to two factors: the contribution of the polymer resin itself and the contribution of loss between the layers of the scale-like material.
No decrease was observed even in the state of advanced hexalysis. Table 1 shows the physical property values of various sheets, but in the composite system of flaky graphite and mica based on olefin resin, the elastic modulus, specific elastic modulus,
The bending rigidity is considerably increased, and it can be seen that olefin resin is effective as a base material in terms of density and internal loss. Description of Examples Example 1 Polypropylene (manufactured by Ube Industries, Ltd.) 75Wt% is used as a base material, and flaky graphite (average diameter 10 μm) is added to this.
22 Wt% and 3 Wt% of mica (average diameter 40 μm) were added as reinforcing agents and thoroughly kneaded using a twin-screw extruder to make master pellets, which were then pre-dried at 110°C for 10 hours. After that, use a single screw extruder to reduce the thickness from the T die.
A 160 μm composite sheet was drawn. Next, this sheet was heated with far infrared rays for about 7 to 8 seconds, and when it softened, vacuum forming was performed. The physical properties of the sheet are shown in Table 1, and it was superior to a composite of graphite and mica alone in terms of elastic modulus, specific elastic modulus, and bending rigidity. Figure 2 shows the frequency characteristics of a 12cm speaker diaphragm using these sheets, and it was observed that the distortion was smaller and the reproduction band was wider than when graphite or mica were used alone. In FIG. 2, A 1 , A 2 , and A 3 represent the sound pressure frequency characteristics of this example, mica alone, and graphite alone, and B 1 , B 2 , and B 3 similarly represent the distortion characteristics. Example 2 4-methylpentene polymer (manufactured by Mitsui Petrochemical Co., Ltd.)
TPX) 80wt% as a base material, to which flaky graphite (average diameter 10μm) 16Wt%, mica (average diameter 40μm)
m) A sheet with a thickness of 150 μm was prepared in the same manner as in Example 1 with the addition of 4 Wt% as a reinforcing material. Third
The figure shows the change in elastic modulus when the mixing ratio of reinforcing graphite and mica is changed, and it can be seen that a mixing ratio of mica of 10 to 30 Wt% relative to flaky graphite is effective. Furthermore, it can be seen that as a base material, olefin resin is more advantageous than other resins in terms of internal loss, density, and bending rigidity, and high efficiency and low distortion can be achieved in terms of frequency characteristics.
【表】【table】
【表】
第４図に本実施例とポリエステル（80Wt％）
を基材とし鱗片状黒鉛16Wt％、マイカ4Wt％を
強化材とするシートより作つた10cmスピーカ用振
動板の周波数特性を比較するが、本実施例の方が
広帯域、低歪となつており、基材としてオレフイ
ン系樹脂が有効であることがわかる。尚、第４図
中C1，C2は本実施例、従来の場合音圧周波数特
性、D1，D2は同じく歪特性を示している。
発明の効果
以上、詳述したように本発明によれば、熱可塑
性樹脂（特にオレフイン系）を基材としてマイ
カ、鱗片状黒鉛を強化材に持つシートからなるス
ピーカ用振動板であるため、周波数特性が平坦で
かつ広周波数帯域、低歪で耐水性に優れており、
又、真空成形や冷間プレス等の熱成形も可能で量
産性、品質面でも優れた利点を有する。[Table] Figure 4 shows this example and polyester (80Wt%)
The frequency characteristics of a 10cm speaker diaphragm made from a sheet made of 16Wt% flaky graphite and 4Wt% mica as reinforcement materials are compared, and this example has a wider band and lower distortion. It can be seen that olefin resin is effective as a base material. In FIG. 4, C 1 and C 2 indicate sound pressure frequency characteristics in this embodiment and in the conventional case, and D 1 and D 2 indicate distortion characteristics. Effects of the Invention As detailed above, according to the present invention, the speaker diaphragm is made of a sheet made of a thermoplastic resin (especially olefin type) as a base material and reinforced with mica and flaky graphite. It has flat characteristics, wide frequency band, low distortion, and excellent water resistance.
In addition, thermoforming such as vacuum forming and cold pressing is also possible, which has excellent advantages in terms of mass production and quality.
【図面の簡単な説明】[Brief explanation of drawings]
第１図は強化材としての鱗片状物の体積分率と
弾性率の関係を示す特性図、第２図は本発明の一
実施例を示すスピーカ用振動板と従来のスピーカ
用振動板の周波数特性の比較特性図、第３図は本
発明の他の実施例を示すスピーカ用振動板におけ
るマイカ、鱗片状黒鉛の含有率の関係を示す特性
図、第４図は同振動板と従来のスピーカ用振動板
の周波数特性の比較特性図である。
Figure 1 is a characteristic diagram showing the relationship between the volume fraction of a scale-like material as a reinforcing material and the elastic modulus, and Figure 2 is a frequency diagram of a speaker diaphragm showing an embodiment of the present invention and a conventional speaker diaphragm. Comparison of characteristics. Figure 3 is a characteristic diagram showing the relationship between mica and flaky graphite content in a speaker diaphragm according to another embodiment of the present invention. Figure 4 is a comparison diagram of the same diaphragm and a conventional speaker. FIG. 3 is a comparative characteristic diagram of the frequency characteristics of the diaphragm for use.