The invention relates to a ionizer, device which neutralizes static electricity buildup on synthetic fibers, sheets, webs, when such materials are processed. Generally, an ionizer has the appearance of a bar, placed across movement direction of the charged material, on the side of the surface where the static charge is buildup. The distance between the ionizer and material varies from one to five inches. Electrically powered ionizers are energized by a high voltage power supply, by means of a high voltage cable. Hot ionizers are named that ones which have the high voltage needles directly connected (jabbed) into the conductor of the high voltage cable. A person who accidentally touches a needle can receive an electric shock. The severity of this shock depends on the current rating (usually limited to 5 milliamperes) of the high voltage power supply. Shockless ionizers are named that ones which have high voltage needles capacitively coupled to the high voltage cable. Due to the small capacitance between the high voltage needle and the conductor of the high voltage cable, the current is limited to few microamperes, and a direct touch of a high voltage needle is painless.
It is known an ionizer, which, in order to discharge or neutralize static electricity, consists of a row of high voltage needles inserted into the conductor of a high voltage cable, and one or two electrodes connected to the ground, which flank the needles row. A high voltage power supply, of 5 to 15 kV, energizes high voltage needles by a high voltage cable. The other terminal of the high voltage power supply is connected to the ground. Between high voltage needles and grounded electrode/s of ionizer occurs a corona discharge, generating nearby positive and negative ions. The charged material passing through ionized area attracts the necessary quantity of ions of opposite polarity, until its charge gets neutral. This type of ionizer is efficient for materials with a slight or average charge. For the materials with a high or a high large static charge this ionizer is not efficient, because all the ions generated in corona discharge are attracted by the charge of material, but the charge is still not entirely balanced this way. The density of ions is maximum in the area where the distance between high voltage needles and grounded electrode/s is minimum. This fact decreases the efficiency of neutralization.
It is also known an ionizer, named induction or passive ionizer (neutralizer), which consists of a row of needles or thin wires connected to the ground. The material moves nearby the ionizer, and his charge creates an electrical field between grounded needles and itself. A breakdown of the air appears when the electrical field at the peaks of the needles exceeds a threshold value. A small electrical discharge occurs between the charged surface and the grounded needles, this way the material gets discharged. The breakdown of the air and small electrical discharge stop in the moment when the value of the electrical field between the charged surface and grounded needles drops under threshold value. Therefore on the material remains a residual charge which is no more possible to be neutralized this way. The induction ionizer is inefficient for the materials with slight static charge, which can not create an electrical field higher than threshold value.
There is also known an ionizer which consists of a row of high voltage needles, connected to a high voltage power supply. On both sides, along of high voltage needles row, are arranged two saw-teeth shape electrodes, connected to the ground. Between the high voltage needles and grounded electrodes takes place a corona discharge, generating positive and negative ions. The materials with a slight static charge get discharged by attracting ions of opposite polarity. High static charges get neutralized mainly by small electrical discharges between the peaks of the teeth of the grounded electrodes and charged material. The materials having an average static charge get neutralized by small electrical discharges to the peaks of grounded electrodes, as well by attracting ions of opposite polarity.
This type of ionizer is not enough efficient because the density of ions is not uniform. The corona discharge is perpendicular to the axis of the ionizer and occurs mainly where the distance between the high voltage needles and grounded electrodes is minimum. The density of ions is maximum in the area where the corona discharge takes place, and lowers to a minimum at the half of the distance between the needles. Consequently, the neutralization of the electrical charge of the material is good in the areas where the ions density is maximum, and decreases in the areas where the ions density is poor. The result of the decreased neutralization in these areas is an increasing of the residual electrical charge on the material.
U.S. Pat. No. 4,216,518 refers to a Capacitively Coupled Static Eliminator with High Voltage Shield. It consists of a grounded metallic U shape housing, which supports high voltage electrode (plate configuration) and surrounding insulation, high voltage needles, capacitively coupled with high voltage electrode and high voltage shield. An AC high voltage power supply energizes high voltage electrode and shield. This ionizer is efficient for neutralization of slight or average static charges. The corona discharge current between high voltage needle and grounded U shape housing is limited by the capacitance between high voltage needle and high voltage electrode and shield. Consequently the quantity of generated ions is limited. For the materials with a high or a very high static charge this ionizer is not efficient, because all the ions generated in corona discharge are attracted by the charge of material, but the charge is still not entirely balanced this way.
In Romanian patent no.96753, 1988, inventor Dan D.C. Botez, is presented an apparatus meant for static charge neutralization consisting of a high voltage AC power supply which energizes by a high voltage cable/s one ionizer or more. Referring strictly to ionizer, it is made in the form of a metallic shape supporting insulating modules. A high voltage needle is introduced through each insulating module and makes contact to the conductor of a high voltage cable, placed in the inner part of the insulating module. Between the insulating modules, on both sides, are inserted thin steel wires connected by metallic shape to the ground. This way, each high voltage needle is located in the middle of a rectangle, whose corners contain the peaks of the grounded wires. Between the high voltage needles and peaks of grounded wires takes place a corona discharge, that generates positive and negative ions. The materials with a slight electrical charge get discharged by attracting ions of opposite polarity. High static charges get neutralized mainly by small electrical discharges between the peaks of the grounded wires and charged material. The materials having an average electrical charge get neutralized by small electrical discharges to the peaks of grounded wires, as well by attracting ions of opposite polarity. This type of ionizer has a good efficiency for small, average as well for high and very high static charges. The disadvantages of this ionizer are: a slightly increased ozone generation, because of intense corona discharge; in the inner part of the insulating module is a short path between the high voltage needle via joint of insulated modules to the grounded metallic shape, where a small electrical discharge can take place. The dirt built up on the top surface of ionizer can develop, between high voltage needles and grounded wires, a path with a lower surface resistance, and consequently a leakage current can appear. If the ionizer is not regularly cleaned, a small electrical discharge is possible to develop on this path.