US3612862A

US3612862A - Electrostatically charging method

Info

Publication number: US3612862A
Application number: US821699A
Authority: US
Inventors: Masanari Suzuki
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1968-05-08
Filing date: 1969-05-05
Publication date: 1971-10-12
Anticipated expiration: 1988-10-12
Also published as: DE1923307A1; FR2008069A1; GB1270461A

Abstract

An electrostatically charging method for charging a light sensitive layer copy sheet, which is positioned close to a charging grid including the steps of generating spike-shaped voltage pulses each having sharp rise and fall portions and a pinpointed peak, and applying said pulses to the charging grid for generating a corona thereat, and thereby imparting an electrostatic charge to the light sensitive layer of the copy sheet.

Description

United States Patent Inventor Masanari Suzuki Kanagawa-ken, Japan Appl. No. 821,699

Filed May 5, 1969 Patented Oct. 12, 1971 Assignee Kabushiki Kaisha Ricoh Tokyo, Japan Priority May 8, 1968 Japan 43/30703 ELECTROSTATICALLY CHARGING METHOD 5 Claims, 4 Drawing Figs.

US. Cl ..250/49.5 ZC

Int. Cl G03g 13/02, 603g 15/02 Field of Search 250/495 C; 317/262 A CORONA" GENORATING VOLTAGE UNITED STATES PATENTS 3,076,092 l/1963 Mott 250/49.5 3,390,266 6/1968 Epping 250/495 Primary Examiner-William F. Lindquist Attorney-Burgess, Ryan and Hicks ABSTRACT: An electrostatically charging method for charging a light sensitive layer copy sheet, which is positioned close to a charging grid including the steps of generating spikeshaped voltage pulses each having sharp rise and fall portions and a pinpointed peak, and applying said pulses to the charging grid for generating a corona thereat, and thereby imparting an electrostatic charge to the light sensitive layer of the copy sheet.

PATENTEUnm 12 l97| I 3.612.862

CORONA" GENORATING VOLTAGE FIG.2A

CORONA E V POSITIVE CORONA 1) NEGATIVE CORONA AND 3.

FIG. 20

- NEGATIvE G) 'INVENTOR MASANARI Suzum ELECTROSTATICALLY CHARGING METHOD BACKGROUND OF THE INVENTION The present invention relates to an electrostatically charging method and more particularly to a method for use in electronic photography for imparting the electrostatic charge by the corona discharge to a light-sensitized layer of a copy sheet.

In the electrostatic charge imparting-type electronic photography, it is generally required that the light-sensitized layer of a copy sheet is imparted with the electrostatic charge immediately prior to its exposure. In the conventional method of the type described above, a pair of wire or needle electrodes are disposed so as to be spaced apart from a copy sheet interposed therebetween by a suitable distance and a voltage ranging from 5 to 7 kv. is applied across the pair of electrodes so as to generate the corona discharge, thereby electrostatically charging the sensitized layer by the ions generated by the corona discharge. In this case, the positive electrode generates the positive corona, that is, the positive ions, while the negative electrode, the negative corona, that is, the negative ions. Depending upon the types and properties of the sensitized layer of copy sheets, either of the positive or negative corona discharges is utilized. For example, when the sensitized layer is mainly composed of ZnO, the negative discharge is utilized while in case of the sensitized layer consisting of Se, the positive corona discharge is utilized. In case of an electrically conductive copy sheet having a layer of ZnO upon its one surface, the copy sheet is first placed upon an electrically conductive substrate or support with the sensitized layer being directed upwardly and a wire electrode is vertically upwardly spaced apart from the sensitized layer by 10 to mm. so that the sensitized layer may be imparted with the electrostatic charge by the negative corona discharge generated by the wire electrode. Alternatively, the conductive substrate or support may be eliminated. That is, the wire electrode is vertically downwardly spaced apart from the rear surface, that is, the surface opposite to the sensitized layer of the copy sheet by a distance from 10 to 20 mm. so that the positive corona discharge may be generated, thereby imparting the electrostatic charge to the copy sheet. In both of the methods described above, a DC high voltage is applied across a pair of electrodes. The invention however had made an extensive study on the wave forms of the voltage applied 'to the electrodes and found out that the complete DC is not required for imparting the electrostatic charge to the sensitized layer and the pulsating voltage is also satisfactorily used for this purpose. The finding of the inventor has been confirmed by the experiments.

In case of the sensitized layer consisting of ZnO, the layer is imparted with the electrostatic charge by the negative corona discharge as described hereinabove. In this case, even if the wire electrode is used, the point corona discharges are generated along the wire electrode so that the sensitized layer is not uniformly charged. To eliminate this defect, the wire electrode must be spaced apart from the sensitized layer by a greater distance or a plurality of wire electrodes must be used, resulting in the increased power consumption. This phenomenon occurs even with DC or pulsating voltage from 50 to I00 c.p.s.

SUMMARY OF THE INVENTION In brief, the present invention provides an electrostatically charging method for use in electronic photography comprising the step of imparting the electrostatic charge to a light-sensitized layer of a copy sheet by the corona discharge generated by the periodic or nonperiodic repetitive pulse voltages each having a waveform with sharp rise and fall and a pinpointed peak. This waveform is sometimes called a spike waveform. Any convenient or conventional pulse generator may be used when carrying out this invention. One such spike wave-shaped generator is shown in my copending U.S. Pat. application Ser. No. 821,701 which is assigned to the same assignee as this application.

The advantages accrued of the present invention may be enumerated as follows:

1. Uniform charging may be ensured and the power consumption can be made less.

2. Because of the sharp voltage waveform, the initiation of the corona discharge may be accelerated and the repetitive cycle can be shortened so that the high-speed charging may be effected.

3. The pulse voltage is sufficiently high enough for generating the corona discharge, but the energy is less so that the electric shock can be minimized. Even if the spark discharge should be initiated, the sensitized layer will be less damaged.

4. Both of the high-frequency harmonics and the repetitive frequency of the pulse voltage are high so that the coils and other components may be made compact in size.

5. In order to control the magnitude of charge, that is the potential of the sensitized layer, the voltage is increased or the electrode gap is adjusted in case of a sinusoidal wavefonn voltage such as commercially available voltage. In this case, the voltage tends to rise up to a spark discharge potential resulting in the breakdowns of the sensitized layers. However, according to the present invention, the above control may be made only by adjusting the repetitive frequency of the pulse voltage. This simple adjustment method also serves to make the device simple in construction and compact in size.

BRIEF DESCRIPTION OF DRAWING FIG. I shows various waveforms used in corona discharge for explanation and comparison with the charging method of the present invention, and

FIG. 2 shows schematically corona discharges by wire electrodes applied with the voltages having the waveforms as shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 showing various waveforms used in corona discharge for comparison, the voltages are plotted against the time, plotting on the abscissa the time and on the ordinate the voltage. The voltage waveform used in the present inyention is of pulse having sharp rise and fall as shown bymThe waveform@is of the voltage obtained from a commercial power source or a sinusoidal waveform generator while the waveformQDis generated by a relaxation oscillator. The half sinusoid waveform 2 is typically 60 cycles per second. It will be noted that the corona-generating voltage I is much faster than the waveform 2.

FIGS. 2-A, B and C are for illustration of the states of the corona discharge generation by wire electrodes E. In case of the positive corona discharge, as shown in FIG. Z-A, the corona discharge generally surrounds the wire-shaped electrode E regardless of the waveforms of the voltages applied thereto. However, in case of the negative corona discharge, as shown in FIG. 2-B, the point-corona discharges are observed along the wire electrode E so that the light-sensitized layer is not uniformly imparted with the electrostatic charge as described hereinbefore. In order to avoid such nonuniform charging, the wire electrode must be spaced apart from the sensitized layer by a greaterdistance or a plurality of wire electrodes must be disposed, resulting in the increase of the required power. The above undesirable phenomenon is observed especially when the frequency of the voltage applied to the wire electrode pulsates at a rate from 50 to I00 c.p.s. even if the waveforms@and@are varied as shown in FIG. 1.

According to the charging method utilizing the pulse voltageQas shown in FIG. I of the present invention, the pointcorona discharges similar to those shown in FIG. Z-B are generated in case of the negative corona discharge, but the number of such discharges is remarkably increased as compared with that shown in FIG. Z-B. That is, one corona discharge is generated per length of l to 2 cm. in FIG. Z-B while in FIG. 2-C showing the method of the present invention 3 to 4 corona discharges are generated per length of 1 to 2 cm.

Furthermore, according to the present invention, the positive corona discharge surrounding the electrode as shown in FIG. 2-A may be substantially approximated even in case of the negative corona discharge by increasing the repetitive rate of the pulse voltage, so that the uniform charging may be ensured and the electrode may be closely positioned toward the sensitized layer, thereby reducing the required power.

The present invention has been so far described with particular reference to the preferred embodiment thereof, but it is to be understood that the variations and modifications can be effected without departing the true spirit of the present invention as described hereinabove and as defined in the appended claims.

lclaim:

1. An electrostatic charging method for imparting electrostatic charge to a light-sensitive layer copy sheet which is positioned close to a charging grid, comprising the steps of generating voltage pulses, each pulse having a spike shape with sharp rise and fall portions, and pinpointed peaks;

applying said voltage to the charging grid for generating a corona discharge by said voltage pulses on said grid and thereby imparting electrostatic charge to a light-sensitive layer copy sheet. 2. A method according to claim 1, including the step of generating said pulses periodically.

3. A method according to claim 2, including the step of varying the frequency of said pulses to control the corona.

4. A method according to claim 1, including the step of generating said pulses repetitively and nonperiodically.

5. A method according to claim 4, including the step of varying the repetition rate of said pulses to control the corona.

Claims

2. A method according to claim 1, including the step of generating said pulses periodically.
3. A method according to claim 2, including the step of varying the frequency of said pulses to control the corona.
4. A method according to claim 1, including the step of generating said pulses repetitively and nonperiodically.
5. A method according to claim 4, including the step of varying the repetition rate of said pulses to control the corona.