JPS6162074A - Discharging device - Google Patents

Abstract

PURPOSE:To attain uniform and stable discharging by specifying the product of the specific dielectric constant of a dielectric material and alpha defined by the shown formula at least in an area opposed to the inductive electrode width of the dielectric substance. CONSTITUTION:When an AC voltage is impressed between the inductive electrode 4 and a discharging electrode 5, discharge is generated near the discharging electrode 5 and positive and negative ions are generated. The discharge is creeping discharge expanding discharge along the surface of the dielectric material on the discharging electrode side. In this case, the product of the specific dielectric constant of the dielectric material and unevenness in thickness alphadefined by the shown formula (t = thickness distribution of the dielectric substance 3, t0 = the average thickness of dielectric substance 3) is set up 60 or less. Consequently, uniform discharge can be generated and a small-sized discharging device discharging at a low AC voltage can be obtained.

Description

【発明の詳細な説明】 失亙豆１ 本発明は静電記録、電子写真法等において帯′　　電除
電を行なう放電装置に関する。DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a discharge device for removing static electricity in electrostatic recording, electrophotography, etc.

背」１技−術 従来、静電記録、電子写真法においては線径０．１ｍｍ
程度のワイヤーに高電圧を印加する事によりコロナ放電
を行なうコロナ放電法が広く用いられている。1 technology Conventionally, in electrostatic recording and electrophotography, the wire diameter is 0.1 mm.
The corona discharge method, in which corona discharge is performed by applying a high voltage to a wire of approximately

しかしながら、このようなコロナ放電法では、ワイヤー
が細いため破損し易く、さらにはワイヤーの汚れにより
放電ムラが生じるため被帯電体への帯電が不均一となる
という欠点があった。However, such a corona discharge method has disadvantages in that the wire is thin and easily damaged, and furthermore, dirt on the wire causes uneven discharge, resulting in non-uniform charging of the charged object.

また、コロナ放電を安定して行なうのに必要なワイヤー
への印加電圧は約５〜７ＫＶと非常に高いため、空気中
の絶縁破壊の問題からワイヤーとこれを包囲している導
電性シールド部材との距離をある程度以上に離す必要が
あり、コロナ放電装置の小型化にも限界があった。In addition, the voltage applied to the wire required to stably perform corona discharge is extremely high, approximately 5 to 7 KV, so due to the problem of insulation breakdown in the air, the voltage applied to the wire and the conductive shielding material surrounding it is extremely high. There was a limit to the miniaturization of the corona discharge device.

また、他の放電方法として誘電体をはさむ２電極間に交
流電圧を印加し、これにより一方の電極（放電電極）の
周辺に正・負イオンを発生させる放電方法が特開昭５４
−５３５３７号公報により知られている。In addition, as another discharge method, an AC voltage is applied between two electrodes sandwiching a dielectric material, and thereby positive and negative ions are generated around one electrode (discharge electrode).
It is known from the publication No.-53537.

この方法によれば電極間に誘電体を用いたことにより比
較的低い交流電圧で放電を開始するが、この放電開始状
態付近で均一な放電を得ることは困難であるばかりでな
く、放電電圧を上昇させても充分均一な放電を得る事は
難しく、結果として放電ムラを生じるという欠点を有し
ていた。According to this method, a dielectric material is used between the electrodes to start the discharge at a relatively low AC voltage, but it is not only difficult to obtain a uniform discharge near this discharge starting state, but also to reduce the discharge voltage. Even if the temperature is increased, it is difficult to obtain a sufficiently uniform discharge, resulting in uneven discharge.

この原因として、放電電極近傍の材料特性に起因する要
素、さらに放電電極近傍の環境、特に湿度に対して大き
く依存し、湿度の上昇に伴なって放電が抑制される事が
考えられる。The reason for this is thought to be that it is highly dependent on factors originating from material properties near the discharge electrode, as well as the environment near the discharge electrode, especially humidity, and that discharge is suppressed as the humidity increases.

そこで、湿度の影響による放電の抑制を防止する為に、
誘電体材料、もしくは放電電極近傍を加熱することが米
国特許公報４４０８２１４号明細書により提案されてい
るが、均一な放電を得るにはいまだ不充分であった。Therefore, in order to prevent the suppression of discharge due to the influence of humidity,
US Pat. No. 4,408,214 proposes heating the dielectric material or the vicinity of the discharge electrode, but this is still insufficient to obtain a uniform discharge.

完」ＬＤ」Ｌ偵 本発明の目的は、均一で安定した放電を発生させる為の
放電装置を提供することにある。SUMMARY OF THE INVENTION An object of the present invention is to provide a discharge device for generating uniform and stable discharge.

本発明の他の目的は、比較的低い交流電圧で均一な放電
を発生させ、かつ、小型化の可能な放電装置を提供する
ことにある。Another object of the present invention is to provide a discharge device that can generate uniform discharge at a relatively low alternating current voltage and can be miniaturized.

先肚立１遣 本発明によれば、誘電体と、該誘電体を挾んで延びる誘
導電極および放電電極と、該誘導電極と放電電極との間
に交互電圧を印加して放電電極の近傍にイオンを発生さ
せる交互電圧印加手段とを有し、少なくとも該誘電体の
誘導電極巾に対向する領域において、誘電体材ネ１の比
誘電率をε、前記誘導電極と放電電極に挾まれた誘電体
材料の厚みをＴ、平均厚みをｔｏとした時、 で定義するαに対して、εα≦６０を満たす放電装置が
提供されるので均一で安定した放電が可能となる。According to the present invention, a dielectric body, an induction electrode and a discharge electrode that extend between the dielectric body, and a voltage applied alternately between the induction electrode and the discharge electrode in the vicinity of the discharge electrode. and an alternating voltage applying means for generating ions, and at least in a region facing the width of the induction electrode of the dielectric, the dielectric constant of the dielectric material 1 is set to ε, and the dielectric material sandwiched between the induction electrode and the discharge electrode is When the thickness of the body material is T and the average thickness is to, a discharge device that satisfies εα≦60 is provided for α defined as follows, so that uniform and stable discharge is possible.

実１例 以下、本発明の実施例について被帯電体を帯電する場合
を例として図面を用いて詳述する。EMBODIMENT OF THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, taking as an example a case in which a body to be charged is charged.

第１図は、本発明の実施例に用いられる放電装置を示す
。放電装置は放電部材ｌを有し、該放電部材１は被帯電
体２に対向して配置されている。放電部材ｌはセラミッ
ク、雲母、ガラス、テフロンエポキシ樹脂、ポリエチレ
ン等の誘電体３、該誘電体を挾んで配置された誘導電極
４および放電電極５を有する。誘導電極４と放電電極５
の間には交互電圧印加手段としての交流電源６により交
流電圧が印加される。尚、この交流電圧は正弦波形のも
のに限らず、パルス波形のものであってよい。FIG. 1 shows a discharge device used in an embodiment of the present invention. The discharge device has a discharge member 1, and the discharge member 1 is arranged to face a charged object 2. The discharge member 1 has a dielectric material 3 made of ceramic, mica, glass, Teflon epoxy resin, polyethylene, etc., and an induction electrode 4 and a discharge electrode 5 arranged to sandwich the dielectric material. Induction electrode 4 and discharge electrode 5
During this period, an alternating current voltage is applied by an alternating current power supply 6 serving as an alternating voltage applying means. Note that this AC voltage is not limited to a sinusoidal waveform, but may be a pulse waveform.

一方、被帯電体２は導電体基体２ａ上に絶縁体若しくは
、光導電体２ｂを有しており、導電体基体２ａと放電電
極５との間にはバイアス電源７によりバイアス電圧が印
加されている。このバイアス電圧は直流に限らず、特定
イオンが抽出できるように偏倚された交流であってもよ
い。また、このバイアス電圧は導電体基体２ａと誘導電
極４との間に印加してもよい。On the other hand, the charged object 2 has an insulator or a photoconductor 2b on a conductor base 2a, and a bias voltage is applied between the conductor base 2a and the discharge electrode 5 by a bias power supply 7. There is. This bias voltage is not limited to direct current, but may be biased alternating current so that specific ions can be extracted. Further, this bias voltage may be applied between the conductor base 2a and the induction electrode 4.

この構成で、誘導電極４と放電電極５との間に交流電圧
を印加すると、放電電極５近傍で放電が起り、正・負イ
オンが発生する。この正あるいは負イオンは、放電電極
５と導電体基体２ａ間のバイアス電圧の印加により、い
ずれかの極性分が選択的に抽出されて被帯電体２の絶縁
体もしくは光導電体２ｂ表面を特定極性に、かつ所望の
値に帯電させる。With this configuration, when an alternating current voltage is applied between the induction electrode 4 and the discharge electrode 5, a discharge occurs near the discharge electrode 5, and positive and negative ions are generated. By applying a bias voltage between the discharge electrode 5 and the conductive substrate 2a, either polarity of these positive or negative ions is selectively extracted and specifies the insulator of the charged object 2 or the surface of the photoconductor 2b. Charge to polarity and desired value.

このときの放電電極５からの放電は、放電電極側の誘電
体材料の表面に沿って放電がのびる沿面放電であり、ワ
イヤーに高電圧を印加するコロナ放電とは異質なもので
ある。このとき放電電極５からの電界は、最大のとき誘
導電極の巾方向両端まで達する。The discharge from the discharge electrode 5 at this time is a creeping discharge in which the discharge extends along the surface of the dielectric material on the discharge electrode side, and is different from a corona discharge in which a high voltage is applied to a wire. At this time, the electric field from the discharge electrode 5 reaches both widthwise ends of the induction electrode at its maximum.

第２図は、第１図に示した放電装置における実際の放電
状態を観察したものである。中央の白い部分が放電電極
５であり、その両側の黒い部分が沿面放電領域である。FIG. 2 shows an observation of an actual discharge state in the discharge device shown in FIG. The white part in the center is the discharge electrode 5, and the black parts on both sides are creeping discharge areas.

このときの交流印加電圧はビーク・ビーク値Ｖｐ−ｐ＝
３ＫＶ、周波数ｆ＝１０ＫＨｚであり、誘電体材料とし
て、９２％ＡＪ２０３　（平均厚み２００　ＩＬｍ、比
誘電率：９）を用い、誘導電極４及び放電電極５はタン
グステン電極をメタライズ法（Ａｚ２ｏｓのグリーンシ
ート上にスクリーン印刷によって電極を形成し、その後
シートと電極とを同時焼成し電極を形成する）によって
作製した。第２図の放電領域（黒色部）から判るように
放電に顕著なムラが認められた。このムラは交流印加電
圧を上昇させても消滅しないことが確認された。本発明
の放電装置を不図示の電子写真装置の放電器として使用
したところ、この放電ムラに対応して、画像濃度ムラが
認められた。The AC applied voltage at this time is the peak-to-peak value Vp-p=
3 KV, frequency f = 10 KHz, 92% AJ203 (average thickness 200 ILm, relative dielectric constant: 9) was used as the dielectric material, and the induction electrode 4 and discharge electrode 5 were made by metallizing tungsten electrodes (Az2os green sheet). An electrode was formed on the sheet by screen printing, and then the sheet and the electrode were co-fired to form the electrode). As can be seen from the discharge area (black area) in FIG. 2, remarkable unevenness was observed in the discharge. It was confirmed that this unevenness did not disappear even if the AC applied voltage was increased. When the discharge device of the present invention was used as a discharge device for an electrophotographic device (not shown), image density unevenness was observed corresponding to this discharge unevenness.

第２図の放電部材をａ−ｅ部で切断し、その厚さを測定
したところ１８０ＩＬｍ〜２２０　ｐｍ迄のムラが観測
された。ここで、放電部材の厚さとは誘導電極４と放電
電極５に挾まれた誘電体３の厚さのことを意味し、誘導
電極４に覆われた領域の厚さである。When the discharge member shown in FIG. 2 was cut at section ae and its thickness was measured, unevenness of 180 ILm to 220 pm was observed. Here, the thickness of the discharge member means the thickness of the dielectric 3 sandwiched between the induction electrode 4 and the discharge electrode 5, and is the thickness of the region covered by the induction electrode 4.

一方、誘電体材料として、エポキシ樹脂（平均厚さ２０
０　ｐ、　ｍ、比誘電率中３）を用い、誘導電極４及び
放電電極５は前記エポキシ樹脂上に銅箔をラミネートし
、その後エツチングを行う方法により形成した。このよ
うに形成した放電部材について、第２図と同様な方法で
放電状態を観察したところ、均一な放電が発生している
ことが確認された。この均一性は、交流印加電圧を変化
させても維持された。そこで前述と同様に放電部材を切
断しその厚さを測定したところｌ　８０　ＩＬｍ〜２２
０　ｇｍのムラが観測され、前記９２％ＡＪ２０３材料
を用いたものと同様の厚さのムラであった。したがって
、本例では同様の厚さムラの存在にもかかわらず、放電
ムラが無い。On the other hand, as a dielectric material, epoxy resin (average thickness 20
The induction electrode 4 and the discharge electrode 5 were formed by laminating a copper foil on the epoxy resin and then etching it. When the discharge state of the discharge member thus formed was observed in the same manner as shown in FIG. 2, it was confirmed that uniform discharge occurred. This uniformity was maintained even when the AC applied voltage was changed. Therefore, when the discharge member was cut in the same manner as described above and its thickness was measured, it was found that 180 ILm~22
An unevenness of 0 gm was observed, which was the same thickness unevenness as that using the 92% AJ203 material. Therefore, in this example, there is no discharge unevenness despite the presence of similar thickness unevenness.

本放電装置による放電は沿面放電であり、そのメカニズ
ムは複雑であるため、前記現象の解明は困難であるが、
本件発明者は、誘電体材料の比誘電率（と厚みムラαと
の積を６０以下にすることによって放電ムラを生じない
ようにできることを見出した。ここで、厚みムラαは ｔ　ｏ　−−ｔ　ｏ≦ｔ≦ｔ　ｏ　＋　−ｔ　。The discharge caused by this discharge device is a creeping discharge, and its mechanism is complicated, so it is difficult to elucidate the phenomenon.
The inventor of the present invention has discovered that discharge unevenness can be prevented by making the product of the dielectric constant (and the thickness unevenness α) of the dielectric material 60 or less.Here, the thickness unevenness α is t o −− t o≦t≦t o + −t.

１００　　　　　　　　　Ｚｏ。100 Zo.

で定義されるものである（Ｅ：誘電体の厚さ分布ｔＯ：
誘電体の平均厚さ）。(E: Thickness distribution of dielectric material tO:
average thickness of dielectric).

表１は種々の誘電体材料の放電部材を電子写真装置の放
電器として用いて、画像形成を行なったときの画質を示
す０画質が良好なものを０で、不良なものを×で示す。Table 1 shows the image quality when images are formed using discharge members made of various dielectric materials as discharge vessels of electrophotographic devices. Good image quality is indicated by 0, and poor image quality is indicated by x.

ここで画質が不良とは、画像濃度に有意なムラが認めら
れたことである。Here, "poor image quality" means that significant unevenness in image density was observed.

表−１ この表から、誘電体材料の比誘電率εと厚さムラαとの
積を６０以下にすることによって放電ムラが有効に避け
られることが理解される。Table 1 From this table, it is understood that discharge unevenness can be effectively avoided by setting the product of the dielectric constant ε of the dielectric material and the thickness unevenness α to 60 or less.

前述のごとく、沿面放電はそのメカニズムは複雑である
ため、この点の解明は困難であるが、大略はつぎのよう
に考えられる。As mentioned above, the mechanism of creeping discharge is complicated, so it is difficult to elucidate this point, but the general idea is as follows.

第３図及び第４図は、比誘電率の異なった２つの放電部
材の断面図である。第３図の誘電体の比誘電率をε！、
誘電体の厚みをｔｌ、第４図の誘電体の比誘電率をε２
誘電体の厚みをｔ２とし、ε１〉ε２とする。誘導電極
４と放電電極５の間に印加する交流電圧を一定として、
第３図および４図の放電電極５からの放電により発生す
る正・負イオン量は近似的にｔ２＝（ε２／ε１）・Ｌ
ｌが満たされた時、等しくなる。この理由は、誘導電極
４と放電電極５間の静電容量を等しくする場合、放電電
極側の誘電体材料表面に等しい電荷が分布するからであ
る。ここで、近似的と述べたのは、誘電体材料の誘電損
失による発熱の差、放電電極端面の形状による電界分布
の不均一性によって、発生する正・負イオン量が若干変
化するからである。3 and 4 are cross-sectional views of two discharge members having different dielectric constants. The relative permittivity of the dielectric in Figure 3 is ε! ,
The thickness of the dielectric is tl, and the relative permittivity of the dielectric in Figure 4 is ε2.
Let the thickness of the dielectric be t2, and let ε1>ε2. Assuming that the AC voltage applied between the induction electrode 4 and the discharge electrode 5 is constant,
The amount of positive and negative ions generated by the discharge from the discharge electrode 5 in FIGS. 3 and 4 is approximately t2=(ε2/ε1)・L
When l is satisfied, they become equal. The reason for this is that when the capacitance between the induction electrode 4 and the discharge electrode 5 is made equal, equal charges are distributed on the surface of the dielectric material on the discharge electrode side. The reason why I say "approximate" here is that the amount of positive and negative ions generated changes slightly due to differences in heat generation due to dielectric loss of the dielectric material and non-uniformity of electric field distribution due to the shape of the end face of the discharge electrode. .

第５図および第６図は、比誘電率の異なった誘電体材料
を同一の厚みにした時の誘電体材料の厚さムラに対する
電荷分布を模式化したものである。第５図の誘電体３の
比誘電率をＬｌ、第６図の誘電体３の比誘電率をε２と
し、ε１〉ε２とする。両図において、同じ大きさの厚
みムラが存在する時誘導電極４と放電電極５間に印加さ
れる交流電圧の半周期において、即ちＴ≦１７２ｆ（Ｔ
：観察時間（秒）、ｆ：交流電圧の周波数（Ｈ２））に
おける時間において、誘電体材料の表面に発生する電荷
分布は誘電体の比誘電率が大きい程、厚さムラに対する
電荷分布は大きくなる。この理由は電荷分布を電荷密度
σで表わすと、σ父εＥ（Ｅ：誘導電極４と放電電極５
との間の電界）であり厚さムラによる電界Ｅの変動に対
して、比誘電率が大きい程、電荷密度σの変動が大きく
なると考えられる。FIG. 5 and FIG. 6 schematically show the charge distribution with respect to the thickness unevenness of the dielectric materials when dielectric materials having different dielectric constants are made to have the same thickness. The relative permittivity of the dielectric 3 in FIG. 5 is Ll, the relative permittivity of the dielectric 3 in FIG. 6 is ε2, and ε1>ε2. In both figures, when thickness unevenness of the same size exists, T≦172f (T
: Observation time (seconds), f: Frequency of AC voltage (H2)), the charge distribution generated on the surface of the dielectric material is such that the larger the dielectric constant, the larger the charge distribution with respect to thickness unevenness. Become. The reason for this is that when the charge distribution is expressed by the charge density σ, σ father εE (E: induction electrode 4 and discharge electrode 5
It is considered that the larger the relative dielectric constant, the larger the variation in the charge density σ with respect to the variation in the electric field E due to thickness unevenness.

誘電体の誘電損失による発熱は、比誘電率εと誘電損失
ｔａｎδとの積（・ｔａｎδに比例し、この値があまり
大きくなると放電電極５近傍の発熱が顕著になり、放電
分布にムラが生じ易くなる事が認められた。Heat generation due to dielectric loss of the dielectric is proportional to the product of relative permittivity ε and dielectric loss tan δ (・tan δ; if this value becomes too large, heat generation near the discharge electrode 5 becomes noticeable, causing uneven discharge distribution. It was found that it became easier.

表１に示した方法で、ε・ｔａｎδの値と画質を調べた
ところ、ε・ｔａｎδの値が０．５より小さい事が望ま
しいものであった。When the value of ε and tan δ and the image quality were investigated using the method shown in Table 1, it was found that it is desirable that the value of ε and tan δ is smaller than 0.5.

因に、表１における誘電体材料のε・ｔａｎδの値は０
．１以下の値であった。Incidentally, the value of ε・tanδ of the dielectric material in Table 1 is 0.
．． The value was 1 or less.

第７図は本発明の他の実施例による放電装置に用いられ
る放電部材の斜視図であり、第９図は同底面図である。FIG. 7 is a perspective view of a discharge member used in a discharge device according to another embodiment of the present invention, and FIG. 9 is a bottom view thereof.

本実施例においては、放電電極が一本の例を用いたが、
図８に示すような放電電極を２本あるいは多数本用いて
も、前述の条件が満たされれば所期の均一性が得られる
。In this example, an example with one discharge electrode was used, but
Even if two or a large number of discharge electrodes as shown in FIG. 8 are used, the desired uniformity can be obtained if the above-mentioned conditions are satisfied.

以上の説明は、被帯電体を帯電する場合について行った
が、本放電装置は部材を除電する場合にも適用可能で、
この場合は放電部材を被除電体に近づけ、バイアス電圧
を印加せずに作動させる。The above explanation has been made for the case of charging a charged object, but the present discharging device can also be applied to the case of removing static electricity from a member.
In this case, the discharge member is brought close to the object to be neutralized and operated without applying a bias voltage.

光ｍ釆 以上説明したように、本発明によれば誘電体の材料の比
誘電率をε、誘導電極と放電電極に挾まれた誘電体材料
の厚み分布をＴ、誘電体材料の平均厚みをｔｏとした時
ｔｏ−（α／１００）・ｔｏ≦ｔ≦ｔｏ＋（α／１ＯＯ
）・ｔｏで表わされるαに対して、αε≦６０を満足さ
せて放電させる事によって、均一な放電を発生させる事
が可能になり、放電ムラを生じない、低い交流電圧で放
電する小型の放電装置を得る事が可能になった。As explained above, according to the present invention, the relative dielectric constant of the dielectric material is ε, the thickness distribution of the dielectric material sandwiched between the induction electrode and the discharge electrode is T, and the average thickness of the dielectric material is When set to, to-(α/100)・to≦t≦to+(α/1OO
)・By discharging while satisfying αε≦60 for α expressed as It was possible to obtain the device.

【図面の簡単な説明】[Brief explanation of the drawing]

第１図は本発明の実施例による放電装置の斜視図、 第２図は本発明を用いない場合の放電状態を　　　゛示
し、 第３図および第４図は、同一放電電流を得る場合の比誘
電率と厚さの関係を示す断面図、第５図および第６図は
誘電体材料表面の厚さムラと電圧密度分布を示す断面図
、 第７図は他の実施例に用いる放電部材の斜視図、 第８図は第７図の、放電装置の底面図である。 付合の説明 １、放電部材、２．被帯電体、２ａ、導電体基体、２ｂ
、光導電体、３．誘電体、４．誘導電極、５．放電電極
、６．交流電源、７．バイアス電源Fig. 1 is a perspective view of a discharge device according to an embodiment of the present invention, Fig. 2 shows a discharge state when the present invention is not used, and Figs. 3 and 4 show a comparison when the same discharge current is obtained. 5 and 6 are cross-sectional views showing the relationship between dielectric constant and thickness. Figures 5 and 6 are cross-sectional views showing thickness unevenness and voltage density distribution on the dielectric material surface. Figure 7 is a cross-sectional view showing the relationship between dielectric constant and thickness. Figure 7 is a cross-sectional view showing the voltage density distribution and thickness unevenness on the surface of the dielectric material. FIG. 8 is a bottom view of the discharge device of FIG. 7; Description of attachment 1. Discharge member 2. Charged object, 2a, conductor base, 2b
, photoconductor, 3. dielectric, 4. induction electrode, 5. discharge electrode, 6. AC power supply, 7. bias power supply

Claims (1)

【特許請求の範囲】 誘電体と、該誘電体を挾んで延びる誘導電極および放電
電極と、該誘導電極と放電電極との間に交互電圧を印加
して放電電極の近傍にイオンを発生させる交互電圧印加
手段とを有し、少なくとも該誘電体の誘導電極巾に対向
する領域において、誘電体材料の比誘電率をε、前記誘
導電極と放電電極に挾まれた誘電体材料の厚みをＴ、平
均厚みをｔｏとした時、 Ｔｏ−（α／１００）Ｔｏ＜ｔｏ＋（α／１００）ｔｏ
で定義するαに対して、εα≦６０を満たすことを特徴
とする放電装置。[Claims] A dielectric, an induction electrode and a discharge electrode that extend between the dielectric, and an alternate method of generating ions in the vicinity of the discharge electrode by applying alternating voltages between the induction electrode and the discharge electrode. and a voltage applying means, at least in a region of the dielectric opposite to the width of the induction electrode, the dielectric constant of the dielectric material is ε, the thickness of the dielectric material sandwiched between the induction electrode and the discharge electrode is T, When the average thickness is to, To−(α/100)To<to+(α/100)to
A discharge device characterized in that εα≦60 is satisfied for α defined by .