JPH0823715B2 - Corona generator - Google Patents

Description

FIELD OF THE INVENTION The present invention relates generally to charging devices, and more particularly to devices that generate negative corona.

(Prior Art) In the electrostatographic reproduction apparatus widely used today, the photoconductive insulating member can be charged to a negative potential and then exposed to the optical image of the original document to be copied. This exposure discharges the exposed, ie, photoconductive, insulating surface in the background area, resulting in an electrostatic latent image on the member corresponding to the image area contained in the original document. The electrostatic latent image on the photoconductive surface is then visualized by development with a developing powder called toner in the art. During development, the toner particles are attracted from the carrier particles onto the photoconductive surface by the charge pattern in the image areas of the photoconductive insulating surface to form a powder image. This image is then transferred to a support surface, such as a copy sheet, and subsequently permanently fixed to the copy sheet by heating or pressing. After the toner image is transferred to the support surface, the photoconductive insulating surface is discharged and cleaned of residual toner in preparation for the next imaging cycle.

Various types of charging devices have been used for charging or precharging the photoconductive insulating layer. As a commercial product,
For example, there are various types of corona charging devices, which generate a corona discharge by applying a high voltage of 5,000 to 8,000 volts to a corona wire to disperse an electrostatic charge on the surface of the photoreceptor. Recently developed corona charging devices have the discharge electrode coated with a relatively thick dielectric, such as glass, to substantially block conduction current flow through the corona discharge electrode. Dicorotron) and is described in US Pat. No. 4,086,650. Dispersion of charge to the photoconductive surface is accomplished by displacement current, or capacitive coupling by a dielectric. The flow of charge on a charged surface is
Adjusted by the DC bias applied to the corona shield. During operation, an AC voltage having a voltage of about 5,000 to 7,000 volts and a frequency of about 4 kHz produces a true corona current of 1 to 2 mA, that is, an ion current. This device has the advantage of imparting a uniform negative charge to the photoreceptor and, in addition, is not sensitive to dust contamination and therefore does not require frequent cleaning, making it a relatively inexpensive charging device. is there.

In the two-layer corotron described above, the dielectric-coated corona discharge electrode is a coated wire supported between insulating end blocks, and the device faces the imaging surface on which further charge is distributed. With a conductive auxiliary DC electrode placed. In a typical corona discharge device, the conductive corona electrode is in the form of a thin wire connected to a corona generating power source and supported by an end block, which is typically partially surrounded by an electrically grounded conductive shield. Has been. The surface to be charged is supported on the electrically conductive substrate, spaced from the wire on the opposite side of the shield.

For some types of photoreceptors, it is desirable to have a negative charge, and for other types of photoreceptors, such as selenium alloys, it is often desirable to have a negative precharge before actually being positively charged. Negative precharge is used to prepare the photoreceptor for the next copy cycle by transferring the developed toner image to a copy sheet and cleaning it, then neutralizing the positive charge remaining on the photoreceptor. . Generally, in the above pre-charged corotron, 4,500-6000V (effective value), 400-600Hz
AC voltage can be applied. A typical conventional corona discharge device of this type is generally described in U.S. Pat. No. 2,836,725, in which a conductive corona electrode in the form of a thin wire is connected to a corona generating AC power source.

It has been found that some difficulties occur when using a corona discharge device that produces a negative corona. Although various kinds of nitrogen oxides are generated by corona, it is considered that these nitrogen oxides are absorbed on the solid surface. Specifically, it is believed that these nitrogen oxides are absorbed by the conductive shield as well as the housing of the corona generator. The shield is, in principle, made of any electrical conductor, but is generally made of aluminum. Also, the housing is one of the many structural plastics,
It can be made, for example, from glass-filled polycarbonate. This absorption of nitrogen oxides also occurs during operation by supplying an air stream introduced into the corona generator to remove nitrogen oxides and ozone. In fact, in the process of collecting ozone, the air stream may direct nitrogen oxides to the affected areas of the charging device and some other mechanical components. Also,
If you leave the copier off for a long pause after exposure,
It was found that the absorbed nitrogen oxides gradually desorb, ie the absorption is a physically reversible process. After that, when the operation of the copying machine is restarted, a portion of the surface of the photoconductor that has been facing the corona generating device for the rest period causes a lack of a line image and an image with a low density over the entire width of the photoconductor. There was a defect in the image quality of the copy made.
The mechanism of the interaction between the desorbed nitrogen oxide and the photosensitive layer is not completely understood, but they are, in any case,
It is believed that the charge cannot be retained in the form of an image to be subsequently developed with toner because it interacts with the surface of the photoreceptor to increase lateral conductivity. As a result, the thin line image is blurred or disappears and is not developed as a toner image. This deficiency was generally seen with conventional selenium photoreceptors in which a thin layer of selenium or its alloy was vacuum deposited on the surface of the conductive drum substrate as the imaging surface. In addition, difficulties have been observed with photoreceptor structures such as plates, flexible belts, etc. that can include one or more photoconductive layers in the support base layer. The support base layer can be electrically conductive, or it can be coated with a conductive layer and a photoconductive layer coated thereon. Alternatively, the multilayer conductive imaging photoreceptor can be composed of at least two electroworking layers, a photoelectric layer, or charge generating layer, and a charge transport layer, generally attached to the conductive layer. For more details on the above layers, see US Pat. No. 4,265,990. In the various structures described above, some layers can be deposited in very thin layers using vacuum deposition.

Also, the long exposure of the photoreceptor to the desorbing nitrogen oxides for long periods of time leads to severe loss of lines or blurring of lines. Although the mechanism is not completely understood, it was observed that even after a relatively short use time (15 minutes) and a rest period (several hours), the absence of light lines and the disappearance of parallel images occurred. Since the reaction between the photoconductor and the nitrogen oxides occurs purely on the surface, the photoconductor can be restored by alcohol cleaning at the initial stage of exposing the photoconductor to the desorbing nitrogen oxides. However, over a long period of time, the reaction penetrates deeply into the photoreceptor layer and cannot be washed off with solvent. So, for example, a copier
When the copier is activated the next morning after being activated for the production of 0,000 copies and then rested overnight, the problem of line defects appears. As mentioned above, the lack can be to some extent reimbursed by rest periods, which can be on the order of days and are unacceptable to the operator.

Similar difficulties are seen in precharged corotrons where a negative DC potential is applied. An attempt to solve this problem by nickel-plating the corotron shield was to combine nickel with nitrogen oxides to form nickel nitrate, a deliquescent salt, which absorbs moisture in the atmosphere during continuous use and wets it. It's not very successful as it can be quite water at the end, forming water droplets and dropping onto the photoreceptor. Further, the nickel nitrate salt is an immature crystalline substance and has weak bonding, rather than a durable film having strong cohesive force. Another attempt to solve a similar problem in a negatively charged AC two-layer corotron device is to first nickel plate the shield and then gold. However, because gold is extremely expensive, the gold plating layer is very thin, and thus the layer has numerous holes and the layers are not continuous. The theory is that gold plating provides a relatively inert surface that does not absorb nitrogen oxides, but because of the thin porous layer of gold, the nickel base layer underneath corrodes, which is not the case with precharged corotrons. Nickel nitrate is likewise generated which causes similar problems and limits service life.

Research Disclosure Journal (Resear
ch Disclosure Journal, No. 19957, November 1980, p. 508, shows that ions generated from corona discharge may interact with photoconductive members and conductive housings to form salts such as nitrates, which are An electrophotographic copier with a corona generating device is described which can have a detrimental effect on the portion of the photoconductive member that was facing the opening of the corona charging device during the rest period.

U.S. Pat. No. 2,574,225 discloses a method of forming oxide coatings on metals and alloys. In particular, aluminum, magnesium, tin, zinc, and their alloys can be rendered resistant to post-growth oxidation by the treatment of oxide coating with 8-quinolinol or its salts.

U.S. Pat. No. 2,813,804 discloses a lead coating that protects metal surfaces from corrosion. In detail, lead has a pH
Deposit metal alloys from a bath containing up to 7 one or more aliphatic primary hydroxy acids.

U.S. Pat. No. 3,392,039 discloses aqueous lithium silicate solutions and methods of making the same.

U.S. Pat. No. 3,862,420 discloses a device for preventing the formation of certain substances within a corona charging device. This particular material especially comprises ammonium nitrate compounds. This device filters ammonia from the air to prevent the reaction of nitrogen oxides and to prevent the formation of ammonium nitrate particles, which are believed to be present at maximum concentration in the corona charging device.

Paper "Recent Electroless Plating", Author EBSanbestre, Me
tal Finishing, August 1962, pages 45-49, 52, describes the use of nickel plating, lead plating, and rectifiers for thermoelectric elements, and page 46 deals with electroless lead plating. Suggests little interest.

U.S. Defense Publication No. T940022 (published November 4, 1975) is a pressurization that removes amine contaminants that cause image deficiency in selenium alloy photoreceptors with filtration materials such as activated carbon and hopcalite. A filtered xerographic device is disclosed.

Therefore, an object of the present invention is to solve a problem associated with the adhesion of nitrogen oxides to a shield or the like when a negative corona discharge is used, that is, a problem that a fine line image is blurred or disappeared on a copy. To provide.

(Means for Solving the Problems) In order to achieve such an object, according to the present invention, there is provided a corona generating device for imparting a negative charge to an image forming surface supported by a conductive base layer kept at a reference potential. Insulation end
At least one elongated electrically conductive corona discharge electrode stretched between the blocks, means for connecting the electrode to a corona generating potential source, and arranged in proximity to the corona discharge electrode,
At least one component coated with a substantially continuous thin dehydrated alkaline coating of an alkali metal silicate that neutralizes nitrogen oxides generated when the electrode is excited. A corona generating device is provided.

(Function) Corona generation that generates a negative corona because the components (for example, shield) of the corona generator are covered with a continuous thin dehydrated alkaline film of alkali metal silicate that neutralizes nitrogen oxides. Even if nitrogen oxides are generated in the machine, the nitrogen oxides are absorbed by the alkali metal silicate film, so that after the rest period of the copying machine, the line on the surface of the photoconductor that the corona generator faced. The problem of the lack of an image on the striped portion is reduced.

(Example) Referring to FIG. 1, the corona generating device 10 of the present invention is
It can be seen that it comprises a corona discharge electrode 11 in the form of a conductive wire 12 with a relatively thick coating 13 of dielectric material.

The surface 14 to be charged as shown may be the photoconductive surface of a conventional xerographic processor. The surface 14 to be charged is supported on a conductive base layer 15 maintained at a reference potential, usually the copier ground potential. Base layer 15
An AC voltage source 18 is connected between the corona wire 12 and the corona wire 12, and the magnitude of the AC voltage is selected so that a corona discharge occurs near the corona wire. A conductive shield 20 is located opposite the chargeable surface and adjacent the corona wire.

A switch 22 connected to the shield 20 can operate the corona generator in either charge neutralization mode or charge dispersion mode, depending on its position. switch
With 22 in the position shown, the corona generator shield 20
Is connected to ground via lead 24. In this position, no DC electric field is generated between the surface 14 and the shield 20, and the corona generator will not allow the surface 14 to remain in contact for many AC cycles.
Acts to neutralize all charges present in.

If you put the switch 22 in either position shown by the broken line,
Since the shield is connected to one terminal of the DC power supply 23 or 27 and the other terminal of the power supply is connected to earth via lead 26, a DC electric field is created between surface 14 and shield 20. In this position, the corona generator operates to disperse a net charge on surface 14, the polarity and amount of this charge being determined by the polarity and magnitude of the DC bias applied to shield 20.

The corona wire 12 can be supported at its ends in a conventional manner by insulating end blocks (not shown) attached to the ends of the shield structure 20. Corona line 12
Are common conductive filament materials such as stainless steel, gold, aluminum, copper, tungsten, platinum,
It can be made with etc. The diameter of the corona wire 12 is not critical per se and can generally range from 0.5-15 mils, with about 9 mils being preferred.

A suitable dielectric material can be used as the coating 13, which does not break down under an applied AC voltage and is resistant to chemical attack under the conditions present in the corona generator. It has been found that the non-organic dielectric has a higher dielectric breakdown strength and a stronger resistance to chemical reaction in the corona generating environment, and therefore exhibits more satisfactory performance than the organic dielectric.

The thickness of the dielectric film 13 used in the corona generating device of the present invention is such that the conduction current, that is, the direct current charging current cannot substantially pass therethrough. Generally, the thickness is in the range of 7 to 30 mils for the combined wire and dielectric thickness, of which the dielectric thickness is 2 to 10 mils. 4H
has a dielectric breakdown strength of 2 KV / mil or more at z
Experiments have shown that glass having a thickness in the range of 5 mils performs satisfactorily as a dielectric coating material.
With decreasing frequency or thickness, the dielectric breakdown strength (volts) usually increases. The glass coating chosen should be free of porosity and inclusions and should be well adherent, ie wettable, to the line to be coated. Other possible coatings include ceramic materials such as alumina, zirconia, boron nitride, beryllium oxide, silicon nitride. Also, an organic induction conductor sufficiently stable in the corona can be used.

The frequency of the AC power supply 18 can be varied over a wide range from the normal power supply of 60 Hz to several MHz. Corona generator is 4K
Experiments were performed by operating at Hz, but it was found to work satisfactorily.

Although shield 20 is shown as having a semi-circular shape, any of the conventional shapes used for corona shields in xerographic charging may be used. Actually shield
The function of 20 can be performed by any conductive member placed in close proximity to the corona line, for example at the base line, its exact placement being important for obtaining satisfactory operation of the corona generator. is not.

When the switch 22 is connected so that the shield 20 is grounded, as shown, the corona generator acts to essentially neutralize any charge present on the surface 14. This is due to the fact that the net DC charging current does not pass through the electrode 11 due to the thick dielectric coating 13 and the line 12.

Referring to FIG. 1, the operation of the corona generating device of the present invention to disperse a particular net charge onto the imaging surface is described by the switch 22
Is performed by moving it to either of the positions indicated by the dashed line, which allows a positive or negative polarity DC potential to be applied between the surface 14 and the shield 20.

In charging action, a typical AC voltage applied to the corona electrode is in the range of 4KV to 7KV at a frequency of 1KHz to 10KHz. The conductive base layer of the imaging member is maintained at ground potential,
A negative DC bias of about 800V-4KV is applied to the shield. For more details on the operation of a two-layer corotron, see US Pat. No. 4,086,650.

Referring again to FIG. 1, the shield 20 neutralizes nitrogen oxides that may be generated when the two-layer corotron is excited, so that at least the upper surface of the shield 20 is a thin continuous dehydrated alkaline alkali metal silicate. It is covered with a film 28. The exact mechanism by which the alkali metal silicate neutralizes nitrogen oxides is not completely understood, but the cations of the alkali metal silicate film combine with nitrogen oxides in an irreversible reaction to form alkali metal nitrates. Therefore, it is considered that the possibility that the photoreceptor is exposed to nitrogen oxides is completely eliminated. Further, it is considered that the silicate anion present is combined with the hydronium ion present in the dehydrated nitrogen oxide to neutralize the hydronium ion. The resulting alkali metal nitrate is not completely insoluble in water and is therefore partially soluble by atmospheric moisture in high humidity environments, but the rigor of this mechanism is to prevent the lack of the aforementioned line image. There is nothing to prevent the good action of. In order to carry out this irreversible neutralization of nitrogen oxides, the alkaline coating must be thick enough so that it does not wear out and limit the operation of the device within a certain period of time. . Therefore, the dehydrated alkaline coating is preferably at least 5 microns thick for acceptable service life. Nitrogen oxides are absorbed by the shield,
The coating is typically deposited to a thickness of about 1 mil or greater to prevent subsequent desorption, but the alkaline coating should be substantially free of porosity and substantially continuous.

The dehydrated alkametal silicate film can be formed on the shield by applying a thin film of an alkali metal silicate aqueous solution to the shield. Upon heating, the liquid film dehydrates into a strong and stiff non-organic adhesive layer to the substrate. Generally, the coating can be applied by spraying or brushing, similar to paint, so that the coating adheres to the shield. Coatings of sodium silicate, potassium silicate, lithium silicate can be made from suitable commercially available aqueous solutions of sodium silicate, potassium silicate, lithium silicate. Generally, a commercially available sodium silicate aqueous solution has a weight ratio of silica to alkali metal acid of about 1.6 to 3.75 and a density of about 35-59 ° Be '(20
℃), solids content about 30-55% weight, and viscosity about 200-8
It is 00 centipoise. In general, commercially available potassium silicate aqueous solution has a weight ratio of silica and alkali metal acid of about 2.
1-2.5, density about 30-40 ° Be ′ (20 ° C), solid content about 25
-40% weight and a viscosity of about 7-1050 centipoise. The weight ratio of silica to alkali metal acid is preferably 2.5 because it shows high water resistance. Generally, an aqueous solution of lithium silicate has a silica / alkali metal acid weight ratio of about 4.6.
~ 5.9, density about 18-36 ° Be ', viscosity about 180 centipoise, and solids content about 22% by weight. For applications where a conductive coating is desired, such as a continuous thin layer over the shield 20 as shown in FIG. 1, it is preferable to add a conductive additive, or pigment, to the aqueous sodium or potassium silicate solution. Any suitable particulate conductive additive or pigment may be used. Typical conductive additives include conductive carbon such as graphite. If desired, water resistance can be increased by adding a heavy metal oxide, a carbonate insolubilizer, an organic polymer, or a filler such as mica.

FIG. 2 shows a preferred embodiment of the two-layer corotron according to the present invention. In FIG. 2, two-layer type corotron wire 30
Is stretched between fixing members 31 whose both ends are firmly fixed to the end block 35. Conductive shield 34
Is made tubular so that it can be slidably attached to the bottom of the housing 39 by the handle 36. The shield 34 is connected to the power supply through sliding contact between a leaf spring connected to a DC pin connector (not shown) and its inner surface. The power supply potential can be positive, negative, or zero (ground), depending on the function of the device. When the shield 34 is inserted into the housing 39, the shield 34 is fixed at a predetermined position by the spring holding member 38. The high voltage contact pin 33 is inserted in the copier,
It becomes the necessary contact point for the AC power supply. Housing 39
In addition to the conductive shield 34, it has two vertical side panels 32 extending the entire length of the two-layer corotron wire. Shield 34
The upper and inner surfaces of the are coated with a substantially continuous thin dehydrated alkaline coating of alkali metal silicate. In addition, the vertical side panels 32 of the housing 39 are also coated with a substantially continuous thin dehydrated alkaline coating 40 of alkali metal silicate. The housing 39 and the side panel 32 can be integrally molded from any suitable material, such as glass fiber filled polycarbonate. If desired, glass fiber-filled polycarbonate side panels may be primed with a suitable plastic primer to enhance the adhesion between the hydrophilic alkali metal silicate coating and the hydrophobic polycarbonate. Preferably, the primer is Krylon Multipurpose Charcoal Black 13 sold by Borden Inc.
It should contain large amounts of silica or silicates, such as 16.

A comparative test was conducted with the apparatus shown in FIG. In the first sample, a two-layer corotron device that uses a housing integrally molded from glass fiber-containing polycarbonate and an aluminum conductive shield, and is not coated with an alkali metal silicate film is left on the Xerox 1075 copier. And made about 10,000 copies. After making the image, the copier was stopped, rested overnight, and the operation was resumed the next morning.At rest, a lack of lines and a decrease in the density of the line image were observed across the narrow portion of the photoconductor facing the charging device. Was done. This is due to the low surface charge density and correspondingly low mass of developed toner per unit area. This lack of image was repeated for each rotation of the photoreceptor.

To test the effect of an alkaline coating of an alkali metal silicate according to the invention, half of the aluminum pieces were coated with a sodium silicate solution and the other half were uncoated.
It was placed on the elongated slot of a layered corotron charger and operated for about 1000 hours. After that, the aluminum piece was taken out, and left for about 1 hour at a distance of about 0.06 inch from the same photoreceptor. The photoreceptor was then charged and exposed to the image pattern, with no missing problems occurring for those portions of the photoreceptor located near the portions of the aluminum pieces coated with the sodium silicate solution. However, the part of the photoreceptor that was facing the uncoated part of the aluminum strip showed signs of a lack problem because the line image was blurred in that area. The sodium silicate solution used for this test was the Acheson Colloid Company.
Electrodag 181 sold by Oid Company, Port Huron, Michigan), an aqueous dispersion of sodium silicate binder and semi-colloidal graphite that cures at 400 ° C. for 1 hour to form a hard layer on the surface. Electrodag 181 has a weight ratio of silica to alkali metal acid of 2.0, a density of 11 pounds / gallon, a solid content including graphite of 36.0% by weight, and a viscosity of 18 centipoise. First wash the aluminum strips to remove contaminants such as oil and chemical deposits and dry,
This solution was applied. The sodium silicate solution was applied by brush coating and dried at 100 ° C. for about 1 hour to remove excess water. The application of the alkali metal silicate solution can be carried out not only by brush coating but also by ordinary spray coating or dip coating.

FIG. 3 shows an alternative embodiment according to the invention, in particular the line
Reference numeral 44 shows a single wire corotron device stretched between insulating end block assemblies 42,43. The grounded conductive shield 46 increases the available ion density for conduction.
Since no charge is deposited on the shield, the voltage between the shield and the line remains constant and a constant density of ions is generated by the line. The effect of a grounded shield is to increase the amount of current flowing into the plate. Corona line
One end of 44 is secured to port 52 of the end block assembly and the other end is secured to port 50 of the second end block assembly. Line 44 is a corona potential source via lead 55 from the second end block assembly of the corona generator.
Connected to 48. This device can be used as a corona generator for AC pre-charging, in which case the corotron shield 46 is coated with a thin dehydrated alkaline coating of alkali metal silicate.

The two-layer corotron charging device, especially the one shown in FIG. 2, can be used as a charging device in the concept of a copying machine disclosed in, for example, US Pat. No. 4,318,610.

(Effects of the Invention) As described above, the negative charging device according to the present invention has an advantage of successfully neutralizing nitrogen oxides generated during the charging operation. Although not completely known, it is believed that the ions of alkali metal silicates combine with nitrogen oxides in an irreversible reaction to form alkali metal nitrates.
According to the invention, sodium silicate and potassium silicate have the special advantage that they can be easily purchased in aqueous solution, brushing, spraying and dipping without the use of expensive, long coating equipment. A coating that can be easily applied to the required surface by a simple method such as the following, and that the applied surface is relatively durable, corrosion resistant, water resistant, tough and reacts well. Will be provided. If necessary, conductive additives or pigments such as graphite can be added to make them conductive. This is because when applied from an aqueous solution, it does not form a film, rather it crystallizes, and because the crystals are relatively soluble in water, sodium borate, carbonate used in applications where high humidity cannot occur. Sodium, sodium phosphate, sodium hydroxide, uniform sodium metasilicate (ratio of silica to alkali metal acid
In contrast to protective coatings made from materials such as 1: 1). Moreover, they do not form a thin continuous film and are not durable.

The invention has been described above with reference to its particular embodiment,
It will be apparent to experts in this field that many substitutions, modifications and changes can be made. For example, when applying a negative DC or AC potential to a normal scorotron,
The scorotron grid can be coated with an alkali metal silicate. Accordingly, modifications and alternatives falling within the spirit and scope of the claimed invention are considered to be covered by the present invention.

[Brief description of drawings]

FIG. 1 is a sectional view of a corona generator according to the present invention, FIG. 2 is a perspective view of a preferred embodiment of a two-layer corotron according to the present invention, and FIG. 3 is another preferred embodiment of a corotron according to the present invention. It is a perspective view of an example. 10 …… Corona generator, 11 …… Corona discharge electrode, 12 ……
Wire (corona wire), 13 ... Dielectric coating, 14 ... Surface to be charged (photoconductive surface), 15 ... Conductive base layer, 18 ...
AC power supply, 20 ... Conductive shield, 22 ... Switch, 23
...... DC power supply, 24 ...... lead wire, 26 ...... lead wire, 27 ...
… DC power supply, 30 …… 2-layer type corotron wire, 31 …… Fixing material, 32 …… Side panel, 33 …… High-voltage contact pin, 34 ……
Conductive shield, 35 …… End block, 36 …… Handle, 38 …… Spring holding member, 39 …… Housing, 40 ……
Paint, 42, 43 ... end block assembly, 44 ... wire (corona wire), 46 ... conductive shield, 48 ... corona potential source, 50, 52 ... port, 55 ... lead wire.

Claims (10)

[Claims] 1. A corona generator for imparting a negative charge to an imaging surface supported by a conductive base layer held at a reference potential, wherein at least one elongated conductive material stretched between insulating end blocks. A corona discharge electrode, a means for connecting the electrode to a corona generating potential source, and an alkali metal silicate that is arranged in proximity to the corona discharge electrode and neutralizes nitrogen oxides generated when the electrode is excited. A corona generating device comprising: a substantially continuous thin dehydrated alkaline coating and at least one component. 2. The dehydrated alkaline coating has a weight ratio of silica to alkali metal oxide of about 1.6 to 3.75 and a density of about 35 to 6.
The corona generating device according to claim 1, which is a dehydration product of an aqueous solution of sodium silicate having a viscosity of about 200 to 800 centipoise at 0 ° Be '(20 ° C). 3. The dehydrated alkaline film has a weight ratio of silica to alkali metal oxide of about 2.1 to 2.5 and a density of about 30 to 40.
The corona generator according to claim 1, which is a dehydration product of an aqueous potassium silicate solution having a temperature of Be '(20 ° C) and a viscosity of about 7 to 1050 centipoise. 4. The corona generating device according to claim 3, wherein the weight ratio of the silica to the alkali metal oxide is 2.5. 5. The corona generator according to claim 2, wherein the weight ratio of the silica to the alkali metal oxide is 2. 6. The thickness of the silicate coating is at least 5.
The corona generating device according to claim 1, wherein the corona generating device has a size of micron. 7. The at least one component encloses most of the corona discharge electrode and is longitudinally apertured to allow ions generated from the electrode to be directed to the surface to be charged. The corona generating device according to claim 1, wherein the corona generating device comprises a conductive shield. 8. The corona discharge electrode comprises a thin wire coated at least in a discharge region with a dielectric material, the conductive shield having means coupled for connection to a potential source. The corona generating device according to claim 1. 9. The shield is flat on the side with the corona discharge electrode and is adjacent to the shield to form a longitudinal opening to allow ions exiting the electrode to be directed to the surface to be charged. 7. An insulating housing having one side surface, wherein the two side surfaces of the insulating housing are coated with a substantially continuous thin dehydrated alkaline coating of alkali metal silicate. The corona generating device according to the item. 10. The insulating housing has two flat side surfaces, and the two side surfaces and the flat shield surround the corona discharge electrode with three surfaces. The corona generating device according to claim 9.