DE1597897A1 - Discharge device - Google Patents

Description

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The invention relates to a discharge device, in particular to a corona charging arrangement for negatives

Charge carrier.

As is known, corona charging arrangements are widely used in xerography, electrostatic coating technology, and others electrostatic process applied. In electrostatic imaging processes, it is generally necessary to to provide a conductor or photoconductor with a uniform positive or negative charge. The difference between positive and negative corona is particularly important in the previous technology, since each of these corona processes according to a special specific mechanism which has an effect on the nature of the discharge and the results shows the charge of an insulating surface.

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A brief discussion of the mechanism of positive and negative corona discharge is necessary to aid in understanding problems encountered in the prior art required which are solved by the present invention.

Due to naturally occurring ionization processes (bombardment with cosmic rays) there is usually one low number of free electrons and positive ions in the air. Will apply a sufficiently high positive voltage to one conductive wire is applied, so move around it; en free electrons towards him at a speed that sufficient to ionize some of the neutral gas molecules they have hit. In this way additional positive ions and electrons generated. The newly generated electrons are accelerated towards the corona wire and can collide with other neutral gas molecules on their way, creating even more ions and Electrons are generated. As a result of this avalanche process, the wire becomes covered with a shell of electrons and positives Surrounded by ions. The positive ions are repelled by the corona wire due to the positive potential of the latter. Some of these positive ions strike a nearby insulating surface that is connected to a grounded Surface is deposited, whereby it takes on an electrostatic positive charge. In these processes the Corona wire itself is essentially irrelevant for the process of corona generation, except for the generation of the

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required electric field. Changes to the wire diameter act according to the laws of electrostatics on the electric field strength and thus on the properties the corona discharge. Isolated points or other surface irregularities of the wire create localized strong electric fields near the wire. However, these points result in field anomalies that are primarily found in the Close to the wire surface, while the corona-generating process creates a charge envelope at some distance from it Wire builds up. The above description of the positive corona is based on the observation of a blue-white one Sheath of uniform thickness over the entire surface of the wire. Because the positive corona generated is relatively independent Depending on the exact nature of the corona wire that produces it, a normal commercial wire can be a relatively uniform one generate positive corona emission.

The mechanism of the negative corona is completely different. the The amount and pattern of electron emission from the negative corona is more than a property of the wire material and to observe the exact condition of the wire surface. Factors such as dirt stains, oxidized surfaces, changes The crystal structure of the wire, the smoothness of the surface, etc., have an effect on the uniformity of the negative Corona emission off. Regardless of the real causes or theoretical explanations, it can be observed that when the

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the negative voltage of a thin wire, the corona discharge enters and irregular, discrete and almost periodic light emission points glowing in the form of reddish tufts Gas along the wire. On a polished Head, these light points are distributed almost evenly. If the tension continues to rise, they move Leuoht points closer and closer together, their number increasing, in the range of practically applicable voltages, the corona emission but not evenly. The use of higher voltages is undesirable because of the increased generation of ozone. The increase in ozone production is undesirable because ozone is toxic to other components of a copier machine, For example, rubber bands, etc., damaged and generally acts as a strong oxidizing agent. It also occurs at higher levels Stresses the problem of potential destruction of the charged substance by high-energy electron or ion impact processes on.

In contrast to the continuous, even glow of the positive corona, the glow of the negative corona is uneven and consists of irregular, discrete, almost periodic light points. The irregularity of the negative Corona can be achieved by applying a voltage high enough above the onset of the negative corona, as well as by Use of an extremely clean, smooth and even wire or one evenly by sandblasting, for example patterned wire can be reduced somewhat. However, it is

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practically-impossible, the effects of the discrete luminous dots for uniformly charging, for example, a xerographic plate by means of one of the above methods to avoid.

There have been numerous attempts to avoid the Problem of non-uniform negative corona emission carried out. For example, it has been suggested the spacing between the plate to be loaded and the corona wire so as to increase that there is a radial scattering effect, which causes a more uniform charging of the plate. This will be however, the efficiency is reduced and the possible charging speeds are severely restricted. Furthermore are at greater distance, higher voltages are required, and dielectric flashovers create additional problems. Further It has been proposed to sandblast or twist the corona wire into stranded wire for a variety of purposes of emission points to form. To reduce the voltages required for ionization to occur the application of radioactive skins proposed to a To achieve a shift in the relative control voltages. The superposition of a high negative charging voltage with An AC voltage signal was used to avoid the irregularities tried the negative corona emission. It has also been suggested that the wire be inserted in its charge To oscillate or rotate in order to counteract the non-uniform corona emission. Such procedures are

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however, a hindrance for mechanical reasons if higher Loading speeds desired Bind. The air or the gas surrounding the corona wire is also moved with or in Vibration displaced so that the emission of ions and electrons from a respective surface part of the wire is changed will. Each of these procedures resulted in some limited success, each with a loss of performance or Brought complexity with them. In view of the problem of unevenness of negative corona emission hence previous research has focused more on solving the simpler problems of positive corona emission. In order to effectively control the positive corona, electrostatic shields and electrodes have been used, these However, elements only allow a control of the electrons and ions at some distance from their exit point from the Corona wire. Since the previous electrodes and shields generally refer to the positive corona emission, is if they have neither the correct voltage nor the shape to produce a suitable field near a negative one Corona wire provided, as proposed by the present invention, that underlying the invention Problem was nooh due to the previous technology. not recognized, namely it concerns the generation of electrostatic states in the line of a negative corona wire, that of a closer Allow the luminous dots to move closer together at a given voltage and thus lead to a more even charge.

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The invention now relates to a corona discharge device cum applying an even negative electrical charge on a surface to be charged. According to the invention, this device contains a corona discharge electrode connected to a voltage causing the negative discharge and a device for reducing the divergence of the effective, from each emission point of the discharge electrode emerging cones of negative charges, whereby the emission points move closer together and a uniform charge the area to be charged.

An embodiment of the invention is shown below described with reference to the figures. Show it:

the schematic representation of the invention Discharge device,

Fig. 2 is the cross section of the discharge device according to the invention,

Flg. 3 under a) the representation of the credit model at

Corona discharge alone and under b) the luminous pattern in the presence of a suitable field and

Fig. 4 shows a representation of the ύοώ. field lines emanating from a corona discharge wire in another embodiment of the discharge device according to the invention.

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In Pig. 1 and 2 is an embodiment of the invention Device shown, which contains a surface to be charged 4, which consists of a photoconductive insulating material layer 6 and a grounded, electrically conductive plate 8 lying below it. Such areas become general used in the xerographic process. The plate 8 serves as a grounded plane, so that a charge on the insulating Layer 6 is retained. The plate 8 can also with a corresponding change in the existing voltages carry positive or negative voltage. In another embodiment, the underside of the insulating material layer 6 can be Dispensing with the plate 8 are exposed to a positive corona emission. The photoconductive insulating material layer 6 has such a low conductivity that an electrostatic Charge held long enough for practical purposes will. This requires a resistivity at least on the order of 10 ^ 0ha cm for one usual xerographic facility.

At a distance from the surface 4 to be charged, one or more corona charging electrodes 10 are provided. these can have any suitable structure for generating the corona emission, for example the shape of round wires, a mese edge o.a. The distance between the corona electrode 10 and the one to be charged Area 4 is for optimal charging due to the properties of the electrode, its dimensions, the voltages used and determines the environmental conditions. In the preferred execution

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T597897

The shape of the corona electrode becomes a non-caroding one Material with a uniform surface that allows for corona discharge is used and has many different dimensions and can have shapes. A typical corona wire arrangement consists of smooth, 0.09 mm stainless steel wires Starch secured with its ends in a polystyrene insulation block (not shown) or other good insulator and have a mutual distance of 12.7 mm. You are on a single level. Pie corona wires need do not consist of a good leader, rather they are preferential made of a mechanically stable metal. The minimum diameter of the corona wire 10 is determined by considerations determined in terms of mechanical strength. Its maximum diameter is determined by the fact that the voltage required for corona discharge with increasing Wire diameter increases and then the withstand voltage getting closer and closer. Because of the corrosive effect of the corona discharge with the formation of ozone, nitrogen oxides and in the case of moisture, nitric acid as well, the corona wire should preferably be made of a corrosion-resistant material Material.

Within a larger area, the distance between the corona wire 10 and the surface 4 to be charged is not critical, A satisfactory charge is obtained using a stainless wire 0.09 mm in diameter and negative voltage from 4 to 11 kilo-volts between lower plate 8 and corona

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- ίο -

Electrode 10 and air atmosphere reached at 6.35 to 12.7 mm ·

In FIG. 2, the negative pole is a voltage source 14 with the corona electrode 10 for generating a negative one Corona emission electrically connected. The voltage of the voltage source 14 is 6000 in a typical case Volt. The voltage range required for the aforementioned wire diameter to generate a corona discharge is between approximately 4000 and 11000 volts, preferably the voltage is 6000 to 8000 volts. Thinner wires require lower voltages, thicker wires require higher tensions.

On the side of the corona electrode 10 opposite the surface 4 to be charged is a negatively charged metal plate, a grid or a field electrode 12 is provided, which is used to generate a field which is opposite to the normal irregular negative corona emission causes a regular, continuous emission. In the described Arrangement is a negatively charged metal plate 12 to generate this field near the corona wire used, but any other suitable S ^ ruk-, door to be provided for generating an electromagnetic field. For example, parallel strands made of conductive Wires, a woven wire mesh, a flat, polygonal, cylindrical or otherwise curved, continuous, conductive part, a grid formed by openings,

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a continuous insulating surface with embedded Ladders or a plate made of a rigid conductive material such as steel or aluminum join with the appropriate one Voltage can be used. They form the elements generating the electromagnetic field in the vicinity of the corona electrode 10 is such that the voltages used on them do not themselves produce a corona emission. In general, the Electrode plate 12 has a width of 10 to lOOfauhen wire diameter or at least the dimensions of the corona electrode, in order to ensure that the electromagnetic field generated at all points of the cone of the charge emission is effective «The distance between the electrode plate 12 and the corona electrode 10 should be so great that a dielectric Flashover is avoided. It depends on the voltages used. Typical spacing values are on the order of 12.7 mm.

A suitable electromagnetic field can be generated by applying a negative voltage to the voltage source 16 Metal plate 12 is applied. The absolute value of this voltage should be equal to or greater than the voltage of the Corona wire 10. If the voltage source 14 supplies, for example, a negative voltage of 6000 volts compared to the charging surface 4, the voltage source 16 should preferably have a negative voltage between approximately 7000 and 8000 volts for the metal plate 12 to produce a sufficiently repulsive field which is a continuous

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Luminous pattern on the surface 4 to be charged causes it can however, higher voltages of up to approx. 11000 volts can also be used, which, however, must be below that value where dielectric flashovers occur. Lower voltages up to approx. 4000 volts are also possible. There are changes that supplied by the voltage source 16 to the plate 12 Tension required to vary depending on changes in tension 14 of corona wire 10 as well as others Parameters to achieve an optimal setting.

If a sufficiently high negative voltage 14 is applied to the corona wires 10 during operation of the arrangement, calibration results a corona discharge in the form of irregular, discrete, almost periodic luminous points 22 around the corona wire 10. Without wishing to restrict the invention to any specific theoretical explanation of these processes, it is assumed that that the reason for this periodic structure of the negative corona points is that the emission in each case starts at a raised point on the wire where the strongest fields occur. The resulting negative Charges and corresponding fields delay the emission from neighboring points along the corona electrode 10, which are within an area of strong interaction with the former points. The next emission point therefore measures be the point of high field strength that is just outside this area of strong interaction. This area is apparently enlarged by the scattering and defocusing of electrons and negative ions in the gas. Lr is decreased

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through, a repulsive field near the corona wire 10 obtained by applying a negative voltage equal to or greater than that of the corona wire 10 to the metal plate 12 is generated. The reduction in this area of strong interaction appears to occur at least in part because the repulsive field of the plate 12 reduces the radial scattering of the emitted electrons, such as this by the dashed lines in Pig. I is indicated. This suffering therefore diminishes the impact of the emitted Electrons and negative charges on neighboring raised points, and therefore the area of interaction between the light points 22 on the corona wire 10 are narrowed. Me luminous dots 22 move closer together and eventually go one inside the other, thereby improving the uniformity of the charge by providing a continuous luminous pattern all distances arise which are equal to or greater than the distance between the surface 4 to be charged and the corona electrode 10 are. The above-described effect is shown in FIG. 3. Fig. 3a shows the charge pattern of a row irregular, discrete, almost periodic charge points 18 on a surface 4 to be charged when the corona electrode is operated at approx. 6000 volts without a repulsive field. at Generating such a field by applying a voltage of about 7500 volts to the plate 12 results in a continuous Line charge 20 as shown in Fig. 3b.

It was also shown that the generation of a relatively positive

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tive field (by applying a lower negative voltage to the plate 12 than the voltage of the electrode 10) shows an effect similar to that described. Lying for example at the corona electrode 10 approx. 6000 volts, a negative voltage of approx. 4000 volts increases creates a continuous charge pattern. It is believed that negative charges are emitted at the periphery of the cone Charges of each luminous point are bent back and attracted to the plate 12, as in fig. 4- shown, furthermore it is believed that the relatively higher velocities of the charged particles near the axis of the emission cone in the direction perpendicular to the plate prevents any significant scattering of these particles, even if the charges are on the periphery of the cone can be deflected by the field. This process also narrows the radial scattering of the emission cone and the effect on neighboring raised points decreased. This reduces the area of interaction between neighboring luminous points, making them closer move together and create a more even charge. The act of redirecting unwanted charges around the perimeter of the Emission cone through the electrode plate 12 depends on its distance from the electrode 10 and the relative dimensions of these elements. The width of the plate 12 is around several orders of magnitude larger than the diameter of the electrode 10 in order to create an effective field in the area of the electrode 10 to secure. In the special lall that the voltages of the plate 12 and the electrode 10 match, is by the

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Field generates a tangential component of the field strength, which has a focusing effect on the charge emission cone.

From the above description it can be seen that instead of the plate 12 according to the invention, any other suitable Arrangement for generating a field at the level of the negative corona electrode 10 can be used.

When operating the device according to the invention, an electromagnetic field in the vicinity of the negative corona wire β 10 is used to miniaturize the interaction between Adjacent points of the negative corona generated, whereby these points move closer together and into each other pass over. This improves the evenness of the corona pattern on the surface to be charged. The area of interaction «like the neighboring emission points of the negative Corona emission is reduced because the divergence of the cone of emitted charges at each emission point is either due to a repulsive field, a tangential force effect on the charges or by deflecting the charges around the circumference of the cone is reduced by an attractive field, which is somewhat more positive than the corona voltage. To be clearer and For a simpler explanation of the subject of the application, the individual gates were described in accordance with the currently known theory, which, however, is not restricted to the area to affect the invention.

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Above was an embodiment of the invention Device described, but the invention is not limited to this, as the skilled person is aware of the principle on which this is based, further embodiments are possible. All such training will be encompassed by the spirit of the invention.

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Claims (16)

Patent claims: 1. Method of applying a uniform negative electrical charge to a surface to be charged, thereby characterized in that between a corona discharge electrode (10) and the surface to be charged (4) for generating a Field of corona charges one on the corona discharge electrode (10) negative voltage is generated and therewith at one on the surface to be charged (4) opposite Side of the corona discharge electrode (10) arranged field electrode (12) to generate a negative voltage (16) an additional electrostatic field in the area of the corona discharge electrode (10) is switched on, whereby the distance between emission points (22) on the corona discharge electrode (1O) is reduced and a continuous charge pattern (20) is generated on the surface to be charged (4) will. 2. The method according to claim 1, characterized in that the voltage connected to the field electrode (12) (16) an absolute value not less than the negative voltage of the corona electrode (10) is used so that in the area of the corona electrode (10) a repulsive field is generated, which the divergence of the effective, of each emission point of the discharge electrode (10) outgoing cone of negative charges is reduced. BADCSIGINAI 009835/1517 3. The method according to claim 2, characterized in that an absolute voltage value is used for the voltage connected to the field electrode (12) which is not less than the voltage of the corona electrode (10) and both from 7 to 8 Kilo-Yolt is when the voltage of the corona electrode (10) is 6 Kilo-Yolt. 4. The method according to claim 1, characterized in that the voltage connected to the field electrode (12) a negative voltage value between KuIl and the voltage of the corona electrode (10) is used. 5. The method according to claim 1, characterized in that a voltage is switched on for the field electrode (12) Voltage value in the range of 4 to 11 kilo-volts is used. 6. Corona discharge device for use in a method according to one of claims 1 to 5 for applying a uniform negative electrical charge on a surface to be charged, characterized by one on the negative Discharge causing voltage (14) connected corona discharge electrode (10) and through a device (12, 16) to reduce the divergence of the effective, emanating from each emission point (22) of the discharge electrode (10) Cone of negative charges, whereby the emission points (22) move closer together and an even charge (20) 009835/1517 BAD OfUGiNAL - 19 of the ssu loading surface (4) takes place. 7. Corona discharge device according to claim 6, characterized in that that the gate direction (12, 16) to reduce the divergence of the cone of negative charges from a Kiektrode (12) with a width corresponding to at least several times the smallest dimension of the corona electrode (10) and a width they connected negative voltage source (16) with a greater than the voltage of the corona electrode (10) There is tension. 8. Corona discharge device according to claim 6, characterized in that that the gate direction (12, 16) to reduce the divergence of the cone of negative charges is an electrostatic repulsive field at the height of the corona electrode (Iu) generated. 9 * corona discharge device according to claim 8, characterized in that daia the device (12, 16) for spontaneous generation of a electrostatic repulsive field near the corona electrode (10) from a conductive metal plate (12) on the opposite side of the surface to be charged (4) Corona electrode (10) and a negative voltage source (16) connected to it with an absolute voltage value not less than the voltage of the corona electrode (10) consists. 009835/1517 10. Corona discharge device according to .Anspruch 9, characterized in that the voltage of the corona electrode (10) is about 60ÜÜ volts negative and the voltage of the metal plate (12) generating the repelling PeId or the voltage source connected to it (16) is more than 7000 volts negative. 11. Corona discharge device according to claim 6, characterized in that that the device (12, 16) for reducing the divergence of the cone of negative charges from an electrode (12) near the corona electrode (10) and a voltage source (16) connected to it with a negative one Jjpü-nriunjsv.ert between WuIl and the voltage of the corona electrode (Iu) exists. 12. i> .orona-Lntli: .üun _ö seirrichtung sum application of a steady negative electrical charge to a person to be charged , cored by one to one the negative n ^ effecting voltage connected Lorona bleeding electrode (10) and through a side of the corona discharge electrode on the opposite side of the pluche to be charged (4) (It) arranged device (12, 16) for generating an electrostatic field which each of the cone of the corona discharge electrode (10) is more negative Focuses charges and thus reduces the area of interaction between the charge cones. 0 0 9 8 3 5/1517 BATH ORIGINAL 13. Corona discharge device according to claim 12, characterized characterized in that the corona electrode (10) approximately in the middle between the surface to be charged (4) and the Device (12,16) for generating the electrostatic field is arranged. 14. corona discharge device according to claim 13, characterized in that the device (12, 16) for generating the electrostatic field from an electrode generating a repulsive field in the area of the corona electrode (10) (12) ″, the width of which is several orders of magnitude greater than the diameter of the corona electrode (10). 15. Corona discharge device according to claim 13 »characterized in that the device (12, 16) for generating an electrostatic field from an electrode (12) close to the corona electrode (10) and one connected to it Voltage source (16) with a negative voltage value between zero and the voltage of the corona electrode (10) exists. 16. Corona discharge device according to claim 13, characterized in that the device (12, 16) for generating an electrasbatic field from an electrode (12) and a negative voltage source connected to this with a voltage value of 4 to 11 kilo-volts stands. 009835/151 7 lee rs e ite