JP3760336B2 - Static elimination method under reduced pressure - Google Patents

Description

【００３５】
これらの実験結果と図４〜図９に示した圧力−放電電流特性図とを対比すれば分かるように、真空室１ａの圧力の低下につれて放電電流が上昇するのに伴い、放電電流が最高域になる圧力８０Ｐａのときには、図１７及び図１８に示すように、プラスの高電圧のみを印加した場合も、マイナスの高電圧のみを印加した場合も、フィルムの表面ばかりでなく裏面もプラス・マイナス両極性とも帯電模様は全く消滅し、高密度に綺麗に除電されていることを示している。
【００３６】
これは、減圧の進行に伴う現象、つまり真空度が高くなる（圧力が低下する）に従い空気が希薄になり、電離する空気量が減少していくのに、しかもプラス・マイナスの一方の極性での放電であるにも拘わらず、除電性能が高まっていく現象は、放電電極からの放電で空気を電離させて、プラス・マイナスのイオンのみで除電していた従来の除電法の考えとは適合せず、真空室１ａ全体が放電プラズマ雰囲気（荷電粒子であるイオンと電子が混在して電気的に中性な状態）になっていて、電気的に中性なプラズマによりフィルムの帯電部分がプラス・マイナス両極性とも同時に除電されるからであると想像される。また、プラズマに電界が印加されると、荷電粒子であるイオンと電子の移動に伴ってプラズマ中に電流が流れてプラズマに導電性が生じ、これが上記のように測定された放電電流を引き起こし、放電電流が最高域になったところがプラズマの導電性が最高に上昇したことと符合すると思われる。
【００３７】
ところが、放電電流は、真空室１ａの圧力の低下に伴い上昇して最高域に達した後、更に圧力を１Ｐａまで下げていくと減衰し、放電電極３の周囲に生じている球形の発光の大きさも収縮するのが観察された。これは、圧力を下げ過ぎると放電電流が低下し、却って除電性能が低下することを示している。
【００３８】
本発明者らは、このような現象の理由を究明するために、圧力の変化に伴う分子及び電子の平均自由行程の変化について計算した。
分子及び電子の平均自由行程は近似的に次式で求められる。
【００３９】
【数１】

【００４０】
ここで、λgは分子の平均自由行程、λeは電子の平均自由行程、Pは圧力[Torr]で、Ｋ[×10^-3]はガスにより異なり、次の表２に示すとおりである。
【００４１】
【表２】

【００４２】
上述したような除電実験を行った環境での空気の平均自由行程を求めたところ表３のようになった。図１０はこれをグラフで表したものである。
【００４３】
【表３】

【００４４】
図１０の圧力−平均自由行程のグラフと、図４、図８及び図９の圧力−放電電流特性のグラフとを対比すれば分かるように、平均自由行程が急激に上昇する圧力域では放電電流も急激な上昇推移を呈し、平均自由行程の上昇推移と放電電流の上昇推移とは符合している。従って、放電電流の急激な上昇は、真空室１ａでの空気の分子数の減少以上に、平均自由行程の急激な上昇が大きく寄与していると言える。しかし、更に圧力が低下したときには、平均自由行程は更に上昇するが、上記のようにマイナス放電電流は急激に減衰しており、これは分子数の減少に伴うイオンの急激な減少の度合いの方が大きくなったためであると思われる。
【００４５】
また、放電電極２・３から抵抗結合用の抵抗６を外した状態で実験したところ、図６及び図７に示した特性のように、減圧下では導電性が向上し、短絡電流に近い放電電流が流れるため、放電電極から大きなプラズマ放電が接地体に向かって流れ、安定なグロー放電を生成することができず、上記と同等の除電効果が得られなかった。
【００４６】
なお、放電電極２・３にコンデンサを接続し、コンデンサを介してプラス又はマイナスの一方の極性のパルス状高電圧を放電電極２・３に印加しても、同様のグロー放電が得られた。
【００４７】
更に、本発明者らは減圧下での除電で用いる放電電極の材質を決定するため、インコネル合金の針電極とタングステン合金の針電極とチタニウム合金の針電極について、圧力を８０Ｐａ、印加電圧をプラスの場合＋５ｋＶ、マイナスの場合−５ｋＶとして耐久試験を行った。
【００４８】
インコネル合金、タングステン合金、チタニウム合金のいずれの場合も針電極の使用前の先端部の形状は、図１９に示すように円錐形に加工されたものであったが、＋５ｋＶをインコネル合金の場合には６７２時間、タングステン合金の場合には６６８時間、チタニウム合金の場合には６２４時間印加した後にそれぞれの針電極を写真撮影したところ、図２０、図２１、図２２にそれぞれ図化したようになった。
【００４９】
また、−５ｋＶを同様にインコネル合金の場合には６７２時間、タングステン合金の場合には６６８時間、チタニウム合金の場合には６２４時間印加した後にそれぞれの針電極を写真撮影したところ、図２３、図２４、図２５にそれぞれ図化したようになった。
【００５０】
プラス高電圧印加時及びマイナス高電圧印加時のいずれの場合も、インコネル合金の針電極の場合は先端部の全体形状は崩れないが、表面に水滴なような溶融部分が現れた。タングステン合金の場合には先端が損壊するとともに、表面がぼろぼろに損傷し、マイナス高電圧を印加したときの方が損傷の程度が大きかった。
【００５１】
チタニウム合金の針電極の場合は、ほとんど変化しなかった。
従って、放電電極の好ましい材質としては、チタニウム合金が良く、次にインコネル合金が良いという結果となった。
【００５２】
【発明の効果】
以上述べたように本発明によれば、帯電物体が強帯電であっても減圧下（真空中）で高性能かつ高密度の除電ができる。また、三次元形状の帯電物体であっても、その内部まで高密度に除電でき、更に装置規模も小さくできる。
【００５３】
また、大気圧下での除電では解決しない場合にも、ある減圧下で除電することで、帯電模様までしかもプラス又はマイナスの一方の極性の高電圧を印加するだけで、プラス・マイナスの帯電極性に関係なくプラス・マイナス両方とも綺麗に除電できるので、実用価値の高い新たな除電方法を提供でき、また電源も簡素になる。
【図面の簡単な説明】
【図１】本発明による方法の模式図である。
【図２】絶縁基板上におけるプラス・マイナスの放電電極の実装構造を示す一部分の斜視図である。
【図３】図２の構造を電極ホルダ内において樹脂埋設して全体として一本の放電電極ユニットとした断面図である。
【図４】真空室を減圧して圧力を下げ、帯電板に流れるプラス放電電流とマイナス放電電流とを別々に測定した圧力−放電電流特性のグラフである。
【図５】図４の一部を対数目盛にして表したグラフである。
【図６】真空室を減圧して一定にし、放電電極にマイナス高電圧を可変して印加し、帯電板に流れる電流と放電電極からの放電電流を測定した、マイナス印加電圧の変化に対する放電電流の特性グラフである。
【図７】同じく、放電電極にプラス高電圧を可変して印加し、帯電板に流れる電流と放電電極からの放電電流を測定した、プラス印加電圧の変化に対する放電電流の特性グラフである。特性グラフである。
【図８】帯電板のみの場合の圧力の変化に対するマイナス放電電流の特性グラフである。
【図９】同じくプラス放電電流の特性グラフである。
【図１０】圧力の変化に伴う空気の分子及び電子の平均自由行程の変化を示すグラフである。
【図１１】プラスチックフィルムを真空室内で除電する前のフィルムの表面に現れたプラス・マイナス両方の帯電模様（青と赤）を示す図である。
【図１２】図１１からプラスの帯電模様のみ（青のみ）を取り出した図である。
【図１３】同じくマイナスの帯電模様のみ（赤のみ）を取り出した図である。
【図１４】プラスチックフィルムを真空室内で除電する前のフィルムの裏面に現れたプラス・マイナス両方の帯電模様（青と赤）を示す図である。
【図１５】図１４からプラスの帯電模様のみ（青のみ）を取り出した図である。
【図１６】同じくマイナスの帯電模様のみ（赤のみ）を取り出した図である。
【図１７】真空室の圧力（真空度）を８０Ｐａにして、放電電極に＋５ｋＶの直流高電圧を印加してフィルムを除電したときの図で、（Ａ）がフィルムの表面、（Ｂ）が裏面である。
【図１８】真空室の圧力（真空度）を８０Ｐａにして、放電電極に−５ｋＶの直流高電圧を印加してフィルムを除電したときの図で、（Ａ）がフィルムの表面、（Ｂ）が裏面である。
【図１９】放電電極である針電極の材質をインコネル合金、タングステン合金、チタニウム合金とした場合の耐久試験において、針電極の使用前の先端部の形状である。
【図２０】プラスを高電圧印加した使用後のインコネル合金針電極の先端部の形状である。
【図２１】プラスを高電圧印加した使用後のタングステン合金針電極の先端部の形状である。
【図２２】プラスを高電圧印加した使用後のチタニウム合金針電極の先端部の形状である。
【図２３】マイナスを高電圧印加した使用後のインコネル合金針電極の先端部の形状である。
【図２４】マイナスを高電圧印加した使用後のタングステン合金針電極の先端部の形状である。
【図２５】マイナスを高電圧印加した使用後のチタニウム合金針電極の先端部の形状である。
【符号の説明】
１ 真空容器
１ａ 真空室
２・３ 放電電極
４ 絶縁基板
５ 導電性ブッシュ
６ 抵抗
７ 電源配線
８ 導電部材
９ 電極ホルダ
１０ 樹脂
１１ 電極ユニット
１２ 直流高電圧電源
１３ 基台
１４ 電流計
Ａ 被除電物
Ｂ 帯電板[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for removing static electricity under reduced pressure below atmospheric pressure.
[0002]
[Prior art]
In conventional static neutralization, air is ionized by discharge to generate positive and negative ions at the same time, and it is common practice to neutralize charged objects with the positive and negative ions. Under reduced pressure where air (gas molecules) becomes diluted In (in a vacuum), since ionization of air is less likely to occur, positive and negative ions are not generated, and it was thought that static electricity cannot be removed.
[0003]
From such an idea, when neutralization efficiency is improved or when a three-dimensional charged surface is neutralized, for example, air is actively sent by blowing air, but it cannot be neutralized with high density. -The problem of charge removal unevenness and reverse charge could not be eliminated for charging (charging pattern) in which both negative polarities were mixed in a complicated manner like a pattern.
[0004]
The present applicant uses an ion-attracting electrode having a two-dimensional spread as described in Japanese Patent No. 2651476 as a method capable of removing charges at high density up to the charged pattern as described above. Positive and negative ions generated at the positive / negative ion generating static elimination electrode by placing a charged object across the charged static elimination electrode and applying a high voltage with positive and negative alternating polarity to the ion attracting electrode alternately. A method of removing electricity by forcibly irradiating a charged object by suctioning with an ion attraction electrode is provided.
[0005]
However, according to this method, an ion attracting electrode larger than the surface area of the charged object is required, so that the scale of the apparatus is increased, and the power supply device for the ion attracting electrode and the positive / negative ion generating charge eliminating electrode is complicated. There are problems such as.
[0006]
Moreover, although a method (for example, see Japanese Patent Publication No. 5-12839) that can eliminate static electricity by irradiating ultraviolet rays has been proposed, it can be applied only in the case of weak charging, and high-density neutralization cannot be expected.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a static eliminating method capable of performing high performance and high density static elimination under reduced pressure (in a vacuum) regardless of whether a charged object is strongly charged or has a three-dimensional shape.
[0008]
[Means for Solving the Problems]
In the static elimination method of the present invention, a discharge electrode to which a capacitor is connected is placed in a vacuum chamber, and a positive or negative high voltage is applied to the discharge electrode via the capacitor, and the discharge of the one polarity is performed. The discharge current generated is detected, the vacuum chamber is depressurized so that the pressure reaches a maximum range from where the discharge current suddenly rises, and glow discharge is generated from the discharge electrode, so that It is characterized in that the charge removal material is discharged in a discharge plasma atmosphere.
[0009]
If a plurality of discharge electrodes are installed side by side in a vacuum chamber and a high voltage having one of the positive and negative polarities is simultaneously applied thereto, the static elimination efficiency is improved.
[0010]
When a capacitor is connected to the discharge electrode, if a pulsed high voltage having one of the positive and negative polarities is applied to the discharge electrode via the capacitor, an effect equivalent to that of the resistance connection is obtained.
[0011]
When the material of the discharge electrode is a titanium alloy or an inconel alloy, the discharge electrode is less damaged and worn.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
FIG. 1 shows a schematic diagram of the method according to the invention. A plurality of needle-like (two in the figure) discharge electrodes 2 and 3 are installed at predetermined positions in the vacuum vessel 1 with a predetermined interval and the tips directed in the same direction. Specifically, as shown in FIG. 2, these discharge electrodes 2 and 3 are held in parallel on the insulating substrate 4 by inserting the base end portion into a bottomed conductive bush 5 implanted in the insulating substrate 4. In addition, a resistor 6 mounted on the back surface of the insulating substrate 4 is connected to each of the discharge electrodes 2 and 3 in order to achieve so-called resistance coupling.
[0014]
Further, power supply wirings 7 are printed on both side edges of the insulating substrate 4, and input ends of the power supply wirings 7 on both sides are connected to each other by a conductive member 8 and connected to a high voltage power supply cable (not shown). A high voltage having one of the positive and negative polarities can be applied to 2 and 3 via the power supply wiring 7. As shown in FIG. 3, the insulating substrate 4 is embedded in the resin 10 together with the conductive bush 5 and the resistor 6 in the electrode holder 9 having a C-shaped cross section so that the tip ends of the discharge electrodes 2 and 3 protrude from the resin surface. Thus, one electrode unit 11 is formed as a whole. The discharge electrodes 2 and 3 are fixedly installed at predetermined positions in the vacuum vessel 1 by fixing the electrode unit 11 horizontally on the gantry in the vacuum vessel 1.
[0015]
The high-voltage power supply cable connected to the input end of the power supply wiring 7 is electrically connected to a DC high-voltage power supply 12 outside the vacuum vessel 1, and a DC high voltage having one of positive and negative polarity is applied to the discharge electrodes 2 and 3. They are simultaneously applied through the resistor 6.
[0016]
The DC high-voltage power supply 12 is configured to boost using a self-excited oscillation circuit and a booster circuit and rectify it using a voltage doubler rectifier circuit to generate a positive or negative DC high voltage.
[0017]
The vacuum vessel 1 is transparent so that it can be seen through from the outside, but its base 13 is opaque. The inside of the vacuum vessel 1, that is, the vacuum chamber 1a, can be gradually reduced to a vacuum pressure (below atmospheric pressure) steplessly by an external vacuum pump (not shown).
[0018]
The static elimination method of the present invention uses such a vacuum static elimination device, puts the static elimination object A in the vacuum chamber 1a, and applied a DC high voltage having one of the positive and negative polarities to the discharge electrodes 2 and 3. While the vacuum chamber 1a is depressurized until glow discharge is generated from the discharge electrodes 2 and 3, the object A to be discharged is discharged in the discharge plasma atmosphere in the vacuum chamber 1a. In the following, experiments conducted by the present inventors and results thereof will be described.
[0019]
A precharged object A (plastic film) is placed in the vacuum chamber 1a so as to be opposed to the discharge electrodes 2 and 3 by a distance L1 to increase the degree of vacuum in the vacuum chamber 1a. 3. Apply a DC high voltage of positive or negative polarity to 3 for about 1 second to conduct a static elimination experiment on the object A to be removed. The state after static elimination was confirmed.
[0020]
Further, in order to measure the discharge current, a metal charging plate B is set up vertically in the vacuum chamber 1a with a distance L2 further behind the object to be discharged A, and an ammeter 14 is connected to the charging plate B. And the pole of the ammeter on the side opposite to the connection side was grounded.
[0021]
FIG. 4 shows that the charging plate B is applied when a positive DC high voltage is applied to the discharge electrodes 2 and 3 by reducing the pressure (kPa) by reducing the pressure inside the vacuum vessel 1a under the following conditions. It is a graph of the pressure-discharge current characteristic which measured separately the positive discharge current (microampere) which flows, and the negative discharge current (microampere) which flows into charging board B when a minus direct current high voltage is impressed. FIG. 5 is a graph showing a part of the logarithmic scale.
[0022]
50mm distance between discharge electrodes 2 and 3
Applied voltage to discharge electrodes 2 and 3 + 5kV for positive, -5kV for negative
Distance L1 between discharge electrodes 2 and 3 and object A to be removed 50 mm
Charging plate B size 150 × 150mm
Distance L2 between object A to be charged and charging plate B 50 mm
Material of charging plate B Resistance value of stainless steel resistor 6 200MΩ
[0023]
As shown in FIGS. 4 and 5, both the positive discharge current when a positive DC high voltage is applied and the negative discharge current when a negative DC high voltage is applied rise rapidly from around 20 kPa. A sudden increase in the amount of blue-violet emission due to glow discharge from between the discharge electrodes 2 and 3 is observed with the naked eye, and the light emission from the discharge electrodes 2 and 3 spreads in a spherical shape from the tip of the needle. It was observed that the sphere of light emission expanded and expanded with a rapid rise of. This is presumably because plasma is generated in the vacuum chamber 1a. Such a positive or negative discharge current rise continues even if the pressure is further lowered, and the positive discharge current and the negative discharge current have almost the same rising curve until reaching the highest range, but the positive discharge current is the highest. Although the negative discharge current does not attenuate so much from the region, the negative discharge current rapidly attenuates as the pressure further decreases, and the magnitude of the spherical light emission around the discharge electrodes 2 and 3 contracts with the attenuation. Was observed.
[0024]
FIG. 6 shows that the vacuum chamber 1a is depressurized to 0.01 kPa to be constant, a negative high DC voltage is applied to the discharge electrodes 2 and 3 in a variable manner, the current flowing through the charging plate B and the discharge electrodes 2 and 3 The discharge current of was measured. In FIG. 7, similarly, a positive DC high voltage was applied to the discharge electrodes 2 and 3 in a variable manner, and the current flowing through the charging plate B and the discharge current from the discharge electrodes 2 and 3 were measured. In either case, the bottom surface of the vacuum chamber 1a, that is, the metal surface of the base 13 was insulated with an insulating film, and when the resistance value of the resistor 6 was 200 MΩ, the discharge electrodes 2 and 3 were discharged. 6 and 7, a solid line from 0 to 90 μA indicates a discharge current at the time of a short circuit that flows when the discharge electrodes 2 and 3 are short-circuited.
[0025]
As can be seen from these figures, the positive or negative discharge current when the vacuum chamber 1a is depressurized is a large value compared to that at atmospheric pressure (100 kPa shown in FIG. 4 is the discharge current value at atmospheric pressure, This value is about 1 μA). From this, the electric conductivity due to the electrically neutral plasma has reached the maximum, so that a discharge current close to a short-circuit current can be obtained, and at the same time, the high voltage applied to the discharge electrodes 2 and 3 is either positive or negative. Even with a DC high voltage of only polarity, it is considered that high-density static elimination becomes possible as described later by the action of electrically neutral plasma.
[0026]
FIG. 8 is a characteristic graph of the minus discharge current with respect to a change in pressure (cmHg) when only the charging plate B is used, and FIG. 9 is a characteristic graph of the plus discharge current similarly.
[0027]
Since the charging state of plastic film has a charging pattern with both positive and negative polarities mixed in a complicated manner, it is used for electrostatic copying to visually grasp the charging state and the neutralization state. Two types of toner are used, blue toner is attached to the positive charged polarity portion, and red toner is attached to the negative charged polarity portion, and the pressure in the vacuum chamber 1a is set to 80 Pa, and the surface of the film (discharge electrodes 2 and 3 and The surface charge and the surface charge were observed on the opposite side) and back side (on the opposite side). The DC high-voltage power supply 11 has a power-on time of 1 second, an applied voltage of +5 kV when applying a positive voltage, −5 kV when applying a negative voltage, and a total of four discharge electrodes.
[0028]
FIGS. 11 to 18 show the charging pattern of the film. Actually, both positive and negative polarities are mixed, so the positive charged polarity part appears in blue and the negative charged polarity part appears in red, but it cannot be shown in color, so the charged part is all black. Because it must be expressed, both the positive and negative charged polar parts are all represented in black, only the positive charged polar parts are extracted from them, and the negative charged polar parts are represented only in black. Are extracted and shown in black in three parts. Black shading represents the strength of the charging potential.
[0029]
FIG. 11 is a diagram showing both positive and negative charged patterns (blue and red) appearing on the surface of the film before discharging (in the air) in the vacuum chamber 1a, and FIG. FIG. 13 is a diagram in which only the negative charge pattern (only blue) is extracted, and FIG. 13 is a diagram in which only the negative charge pattern (only red) is extracted.
[0030]
FIG. 14 is a diagram showing both positive and negative charging patterns (blue and red) appearing on the back surface of the film before discharging the film in the vacuum chamber 1a, and FIG. FIG. 16 shows only the pattern (only blue), and FIG. 16 shows only the negative charged pattern (only red).
[0031]
FIG. 17 is a diagram when the pressure (vacuum degree) of the vacuum chamber 1a is 80 Pa and a film is discharged by applying a DC high voltage of +5 kV to the four discharge electrodes, where (A) is the surface of the film, (B) is the back surface, and no charged pattern appeared on both the front and back surfaces.
[0032]
FIG. 18 is a diagram when the film is discharged by applying a DC high voltage of −5 kV to the four discharge electrodes with the pressure (degree of vacuum) in the vacuum chamber 1a being 80 Pa, and (A) is the surface of the film. , (B) is the back surface, and no charging pattern appeared on both the front and back surfaces.
[0033]
The following Table 1 shows the measurement of the surface potential of the film in the same experiment. “Sample 1” is before static elimination, “Sample 2” is negative by applying a positive high voltage, and “Sample 3” is negative. This is a case where the static electricity is removed by applying a high voltage.
[0034]
[Table 1]

[0035]
As can be seen by comparing these experimental results with the pressure-discharge current characteristics shown in FIGS. 4 to 9, the discharge current increases to the highest range as the discharge current increases as the pressure in the vacuum chamber 1a decreases. When the pressure becomes 80 Pa, as shown in FIGS. 17 and 18, not only the surface of the film but also the back surface is plus or minus when only a positive high voltage is applied or only a negative high voltage is applied. In both polarities, the charged pattern disappears completely, indicating that the charge is removed neatly at high density.
[0036]
This is a phenomenon accompanying the progress of decompression, that is, as the degree of vacuum increases (the pressure decreases), the air becomes thinner and the amount of air to be ionized decreases. The phenomenon in which the static elimination performance increases despite the fact that it is a discharge of is compatible with the idea of the conventional static elimination method in which air is ionized by the discharge from the discharge electrode and the static electricity is eliminated only with positive and negative ions. The whole vacuum chamber 1a is in a discharge plasma atmosphere (electrically charged ions and electrons are mixed and electrically neutral), and the charged portion of the film is added by the electrically neutral plasma.・ It is assumed that both negative and negative polarities are discharged at the same time. In addition, when an electric field is applied to the plasma, current flows in the plasma as the ions and electrons that are charged particles move, causing the plasma to become conductive, which causes the discharge current measured as described above, It seems that the point where the discharge current reaches the highest range is consistent with the highest increase in plasma conductivity.
[0037]
However, the discharge current rises as the pressure in the vacuum chamber 1a decreases and reaches the highest range, and then attenuates as the pressure is further reduced to 1 Pa. The spherical light emission generated around the discharge electrode 3 is attenuated. It was observed that the size also contracted. This indicates that if the pressure is lowered too much, the discharge current decreases, and on the contrary, the charge removal performance decreases.
[0038]
In order to investigate the reason for such a phenomenon, the present inventors calculated the change in the mean free path of molecules and electrons accompanying the change in pressure.
The mean free path of molecules and electrons can be approximately calculated by the following equation.
[0039]
[Expression 1]

[0040]
Here, λg is the mean free path of the molecule, λe is the mean free path of the electron, P is the pressure [Torr], and K [× 10 ⁻³ ] varies depending on the gas, as shown in Table 2 below.
[0041]
[Table 2]

[0042]
Table 3 shows the mean free path of air in the environment where the static elimination experiment as described above was performed. FIG. 10 is a graphical representation of this.
[0043]
[Table 3]

[0044]
As can be seen by comparing the pressure-mean free path graph of FIG. 10 with the pressure-discharge current characteristics graphs of FIGS. 4, 8, and 9, the discharge current is increased in the pressure range where the mean free path increases rapidly. Also show a sharp rise, and the mean free path rise and the discharge current coincide with each other. Therefore, it can be said that the rapid increase of the discharge current greatly contributed to the rapid increase of the mean free path more than the decrease of the number of molecules of air in the vacuum chamber 1a. However, when the pressure is further reduced, the mean free path further increases, but the negative discharge current is rapidly attenuated as described above, which is the degree of the rapid decrease in ions accompanying the decrease in the number of molecules. It seems that this is because of
[0045]
Further, when an experiment was conducted in a state where the resistance 6 for resistance coupling was removed from the discharge electrodes 2 and 3, as shown in the characteristics shown in FIG. 6 and FIG. Since a current flows, a large plasma discharge flows from the discharge electrode toward the grounding body, a stable glow discharge cannot be generated, and a charge removal effect equivalent to the above cannot be obtained.
[0046]
A similar glow discharge was obtained even when a capacitor was connected to the discharge electrodes 2 and 3 and a pulsed high voltage having one of the positive and negative polarities was applied to the discharge electrodes 2 and 3 via the capacitor.
[0047]
Furthermore, in order to determine the material of the discharge electrode used for static elimination under reduced pressure, the present inventors added a pressure of 80 Pa and an applied voltage of the Inconel alloy needle electrode, the tungsten alloy needle electrode, and the titanium alloy needle electrode. The durability test was conducted at +5 kV for negative and -5 kV for negative.
[0048]
In any case of Inconel alloy, tungsten alloy, and titanium alloy, the shape of the tip portion before use of the needle electrode was processed into a conical shape as shown in FIG. 19, but +5 kV was used in the case of Inconel alloy. Was photographed after applying 672 hours, 668 hours in the case of tungsten alloy, and 624 hours in the case of titanium alloy, as shown in FIGS. 20, 21, and 22, respectively. It was.
[0049]
Similarly, when -5 kV was applied for 672 hours in the case of Inconel alloy, 668 hours in the case of tungsten alloy, and 624 hours in the case of titanium alloy, each needle electrode was photographed. 24 and FIG. 25, respectively.
[0050]
In both cases of applying a plus high voltage and applying a minus high voltage, in the case of an Inconel alloy needle electrode, the entire shape of the tip portion was not broken, but a molten portion such as a water droplet appeared on the surface. In the case of a tungsten alloy, the tip was damaged and the surface was damaged to a shabby, and the degree of damage was greater when a minus high voltage was applied.
[0051]
In the case of a titanium alloy needle electrode, there was almost no change.
Therefore, as a preferable material for the discharge electrode, a titanium alloy is preferable, and then an Inconel alloy is preferable.
[0052]
【The invention's effect】
As described above, according to the present invention, high-performance and high-density static elimination can be performed under reduced pressure (in a vacuum) even when a charged object is strongly charged. Further, even a charged object having a three-dimensional shape can be discharged with high density up to the inside thereof, and the apparatus scale can be reduced.
[0053]
In addition, even if static electricity removal under atmospheric pressure does not solve the problem, by removing electricity under a certain reduced pressure, it is possible to apply positive or negative charge polarity only by applying a high voltage of one of the positive or negative polarity to the charged pattern. Regardless of whether it is positive or negative, it is possible to remove static electricity neatly, so it is possible to provide a new static elimination method with high practical value, and the power supply is simplified.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a method according to the invention.
FIG. 2 is a partial perspective view showing a mounting structure of plus / minus discharge electrodes on an insulating substrate.
FIG. 3 is a cross-sectional view of a single discharge electrode unit as a whole by embedding resin in the electrode holder in the structure of FIG.
FIG. 4 is a graph of pressure-discharge current characteristics in which a positive discharge current and a negative discharge current flowing through a charging plate are separately measured by reducing the pressure by reducing the vacuum chamber.
FIG. 5 is a graph showing a part of FIG. 4 on a logarithmic scale.
FIG. 6 shows a discharge current corresponding to a change in a negative applied voltage, in which a vacuum chamber is depressurized to be constant, a negative high voltage is variably applied to the discharge electrode, and a current flowing through the charging plate and a discharge current from the discharge electrode are measured. It is a characteristic graph.
FIG. 7 is a characteristic graph of the discharge current with respect to a change in the positive applied voltage, in which a plus high voltage is applied to the discharge electrode in a variable manner and the current flowing through the charging plate and the discharge current from the discharge electrode are measured. It is a characteristic graph.
FIG. 8 is a characteristic graph of a negative discharge current with respect to a change in pressure when only a charging plate is used.
FIG. 9 is a characteristic graph of the positive discharge current in the same manner.
FIG. 10 is a graph showing a change in mean free path of air molecules and electrons accompanying a change in pressure.
FIG. 11 is a diagram showing both positive and negative charging patterns (blue and red) appearing on the surface of the film before the plastic film is neutralized in the vacuum chamber.
12 is a diagram in which only a positive charged pattern (only blue) is extracted from FIG.
FIG. 13 is a view in which only a negative charging pattern (only red) is taken out.
FIG. 14 is a diagram showing both positive and negative charged patterns (blue and red) appearing on the back surface of the film before discharging the plastic film in the vacuum chamber.
15 is a diagram in which only a positive charged pattern (only blue) is extracted from FIG.
FIG. 16 is a diagram in which only a negative charged pattern (only red) is taken out.
FIG. 17 is a view when the film is discharged by applying a +5 kV DC high voltage to the discharge electrode with the vacuum chamber pressure (vacuum degree) set to 80 Pa, (A) is the surface of the film, and (B) is the surface. It is the back side.
FIG. 18 is a diagram when the film is discharged by applying a DC high voltage of −5 kV to the discharge electrode with the pressure (vacuum degree) in the vacuum chamber set to 80 Pa, (A) is the surface of the film, and (B) Is the back side.
FIG. 19 shows the shape of the tip of the needle electrode before use in a durability test when the material of the needle electrode that is the discharge electrode is an Inconel alloy, a tungsten alloy, or a titanium alloy.
FIG. 20 shows the shape of the tip of an Inconel alloy needle electrode after use with high voltage applied to plus.
FIG. 21 shows the shape of the tip of a tungsten alloy needle electrode after use with a high voltage applied to plus.
FIG. 22 shows the shape of the tip of a titanium alloy needle electrode after use with a high voltage applied to plus.
FIG. 23 shows the shape of the tip of the Inconel alloy needle electrode after use with a negative high voltage applied.
FIG. 24 shows the shape of the tip of a tungsten alloy needle electrode after use with a negative high voltage applied.
FIG. 25 shows the shape of the tip of a titanium alloy needle electrode after use with negative high voltage applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Vacuum container 1a Vacuum chamber 2/3 Discharge electrode 4 Insulating substrate 5 Conductive bushing 6 Resistance 7 Power supply wiring 8 Conductive member 9 Electrode holder 10 Resin 11 Electrode unit 12 DC high voltage power supply 13 Base 14 Ammeter A Electric discharge object B Charging plate

Claims (5)

A discharge electrode to which a capacitor is connected is placed in a vacuum chamber, and a high voltage having one of the positive and negative polarities is applied to the discharge electrode via the capacitor, and a discharge current generated by the discharge of the one polarity is detected. The vacuum chamber is depressurized so that the pressure reaches a maximum range from where the discharge current suddenly rises, and glow discharge is generated from the discharge electrode. A method of removing static electricity under reduced pressure, characterized by removing electricity.   2. The method of removing electricity under reduced pressure according to claim 1, wherein a plurality of discharge electrodes are installed side by side in a vacuum chamber, and a high voltage having one of positive and negative polarities is simultaneously applied thereto.   The static elimination method under reduced pressure according to claim 1 or 2, wherein the pressure in the vacuum chamber is reduced to 20 kPa to 1 Pa.   The method for removing static electricity under reduced pressure according to claim 1, 2 or 3, wherein the discharge electrode is made of a titanium alloy.   The method for removing static electricity under reduced pressure according to claim 1, 2 or 3, wherein the material of the discharge electrode is an Inconel alloy.

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