JPH0934211A - Electrophotographic method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase transfer efficiency and to suppress the scattering of toner by attaining destaticization in the front stage of a pretransfer toner electrifier and electrification to the same polarity in the rear stage. SOLUTION: The pretransfer toner electrifier 6 is constituted of first/second electrifying parts 61 and 62, an AC voltage is applied to a first corona wire 611 by a first corona power source 613 and a DC voltage is applied to a second corona wire 621 by a second corona power source 623 as well. When a recording body 1 having a two-color toner image is moved in the direction of the arrow, in the first electrifying part 61, the electrostatic charges of the recording body 1, positively charged red color first toner 41 and negatively charged black color second toner 51 are removed by a positive corona ion selectively passing through a first grid 612 and next, in the second electrifying part 62, both of the red color first toner 41 and the black color second toner 51 are negatively electrified by a negative corona ion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corona charging method in an electrophotographic method, and more particularly to a two-color printing method using positive and negative toners for adjusting the charging polarities of the toners before transferring the two-color toner images. The present invention relates to a pre-transfer toner charging method.

[0002]

2. Description of the Related Art As a method of forming a two-color toner image while a recording medium makes one revolution, positive and negative electrostatic latent images are formed above and below a reference potential of the same charging polarity of the recording medium, respectively. A method of using two kinds of toners of different colors having positive and negative charging polarities is disclosed in JP-A-48-37148. As described above, in the method of forming a two-color toner image using toners having positive and negative charging polarities, it is essential to perform pre-transfer toner charging using corona discharge in order to make the charging polarities of the toners uniform before transfer. is there.

[0003]

Conventionally, as a method of charging toner before transfer, for example, as disclosed in Japanese Patent Application Laid-Open No. 3-164771, DC discharge, simultaneous discharge of DC and AC, etc. are known. . In particular, when the pre-transfer toner is charged to the same polarity as the recording medium, the toner on the charged polarity side is overcharged and at the same time, the charging potential of the recording medium is further increased. The electrostatic repulsive force causes the toner particles to easily scatter around the image, and it is difficult to achieve both the transfer performance and the toner scattering around the image.

In view of the above circumstances, an object of the present invention is to form positive and negative electrostatic latent images above and below a reference potential of the same charge polarity of a recording medium, and to form two types of different colors having positive and negative charge polarities. It is an object of the present invention to provide a pre-transfer toner charging method that achieves both transfer performance and toner scattering in a method of forming a two-color toner image using different types of toner.

[0005]

The above-mentioned object is to form a positive and negative electrostatic latent image on a recording medium charged with either positive or negative polarity, and to make the electrostatic latent image different in color and different. Developing with first and second toners of charging polarity to form a two-color toner image on the recording medium, the toner image is charged to the same polarity by corona discharge by the toner charger before transfer, and then transferred to recording paper In the electrophotographic method for obtaining a two-color image by
This can be achieved by removing the charge amount of the two-color toner image after development from the charge in the front stage of the pre-transfer toner charger and charging the same polarity in the rear stage.

[0006]

According to the present invention, since the charges of the toner and the photoconductor are removed in the former stage, the positive and negative toners have the same condition when the toner in the latter stage is charged, so that the same charging can be performed, and the transfer efficiency of the positive and negative toners can be improved. It is high and it is possible to suppress toner scattering due to excessive charging.

[0007]

【Example】

(Embodiment 1) An embodiment in which the present invention is applied to a laser printer which is an electrophotographic apparatus will be described with reference to the drawings. In FIG. 3, a recording body 1 made of an organic photoconductor rotating clockwise.
Is uniformly charged to −750V by the charger 2. Next, a laser beam 3 modulated by two pieces of image information is irradiated to form a weakly exposed portion of a reference potential of −400V, a strongly exposed portion of a residual potential of −50V, and an unexposed portion of an unexposed potential of −750V.
To form an electrostatic latent image having three level potentials. That is, two positive and negative electrostatic latent images are simultaneously formed above and below the reference potential. The positive electrostatic latent image is the first developing machine 4
Is normally developed by the positively charged red first toner 41, and the negative electrostatic latent image is reversely developed by the negatively charged black second toner 51 of the second developing device 5. At the time of forming the two-color image, a first bias voltage slightly higher than the reference potential is applied to the first developing device 4 by the first power source 42, and a second bias voltage slightly lower than the reference potential is applied to the second developing device 5. The bias voltage is applied by the second power supply 52. The two-color toner image formed on the recording body 1 is negatively charged by the pre-transfer toner charger 6 to have the same polarity, and then electrostatically transferred to the recording paper 8 by the transfer device 7. The residual charge on the surface of the recording body 1 is erased by the erase lamp 9, the residual toner is removed by the cleaner 10, and the process goes to the next step again. The toner image on the recording paper 8 is thermally fixed by the fixing device 11.

FIG. 2 shows a state in which two-color toner images are formed on the surface of the recording medium 1 by development in the two-color electrophotographic method shown in FIG. The positively charged red first toner 41 is developed at a high potential area, and the negatively charged black second toner 51 is developed at a low potential area. By exposing the two-color toner images to the negative corona discharge by the pre-transfer toner charging, the charging polarity of the red first toner 41, which is positively charged, is inverted from positive to negative. If it is attempted to sufficiently reverse the charging polarity of the red first toner 41 to the negative polarity, the black second toner 51, which is already negatively charged, is further exposed to the negative corona ions, so that it becomes excessively negative. Each toner is electrostatically repelled by being charged, and toner scatters. The present invention relates to a pre-transfer toner charging method that achieves both reversal of the charging polarity of the toner and suppression of toner scattering due to excessive charging.

FIG. 1 schematically shows the structure of the pre-transfer toner charger 6. The pre-transfer toner charger 6 is the first
Charging section 61 and second charging section 62, first corona wire 611, second corona wire 621, first grid 6
12 and the second grid 622, the first corona wire 611 is connected to the AC5 by the first corona power source 613.
An alternating voltage of 1 kV and 1 kHz is applied, and the second corona wire 621 is DC-4.
A DC voltage of 5 kV is applied. The first grid power supply 614 applies a ground voltage to the first grid 612, and the second grid power supply 624 applies a DC-500V voltage to the second grid 622. When the recording medium 1 having the two-color toner images shown in FIG. 2 moves the position of the pre-transfer toner charger 6 in the arrow direction, the first
In the charging unit 61, the recording body 1 and the positively charged red first toner 41 and the negatively charged black second toner 51 are charged by the positive corona ions that selectively pass through the first grid 612. The charges are removed, and then the second charging unit 6
In 2 the negative first toner 4 due to negative corona ions
Both the first and black second toners 51 are negatively charged. At this time, the charging potential including the recording body 1 is the second grid 62.
The voltage applied to 2 regulates the voltage to about -500 V to prevent excessive charging. Red first toner 41, black second toner
Since both toners 51 are discharged once and then negatively charged, they have substantially the same charge amount, and both toners can have the same high transfer efficiency and can be prevented from scattering around the image. In addition, the first grid power source 6
14 does not necessarily have to be the ground voltage, and the first grid 612 may be omitted.

(Embodiment 2) FIG. 4 shows a second corona power source 6
23 is connected to the first corona power supply 613. A DC voltage of DC-2 kV was applied by the second corona power source 623. Therefore, an AC voltage on which a DC voltage is superimposed is applied to the second corona wire 621, and the discharge is stable and negatively charged even if the DC voltage is low. Further, since there is an AC component, overcharging can be prevented even if the first grid 612 and the second grid 622 are removed.

(Embodiment 3) In FIG. 5, a first charging section 61 and a second charging section 62 are integrated in a shield 63, and a first charging section 61 and a second charging section 62 are integrated.
The corona wire 630 serving as the corona wire 611 and the second corona wire 621 of the
The AC voltage in which the DC voltage is superimposed is applied by the third and second corona power sources 623. The amount of positive or negative corona ions is adjusted by changing the voltage of the second corona power supply 623. The AC voltage was AC 6 kV and 1 kHz, and the DC voltage was DC-2.5 kV. Therefore corona wire 630
Positive and negative corona ions are released from, but the amount of negative corona ions increases. By applying a positive voltage to the first grid 612 and a negative voltage to the second grid 622, positive corona ions are generated in the first grid 612 in accordance with the potential of the recording medium 1 and the second grid In the area 622, the negative corona ions can be selectively charged. + 200V was applied to the first grid 612, and -500V was applied to the second grid 622. For the recording body 1 having the two color toner images shown in FIG.
Recorder 1 and positively charged red first in 12 parts
Of the toner 41 and the negatively charged black second toner 51 are removed, and then, in the second grid 622, the negative first corona ion causes the red first toner 41 and the black second toner 51. Both are negatively charged. At this time, the charging potential including the recording medium 1 is regulated to about -500 V by the voltage applied to the second grid 622 to prevent excessive charging, and the same high transfer efficiency can be obtained for both toners. It is possible to prevent toner from scattering around the image. First grid 612 and second grid 62
The voltage applied to 2 is adjusted by the voltage applied to the corona wire 630 and the charging potential of the recording body 1. The present embodiment is characterized in that the structure of the pre-transfer toner charger 6 is small.

In the embodiment of the present invention, a negatively charged organic photoconductor is used as the recording body 1. However, the type and charging polarity of the recording body 1 are not limited. Further, the order of developing the positive type and negative type electrostatic latent images may be any order. The numerical values such as the potential on the recording body 1 on which the electrostatic latent image is formed, the corona wire, the voltage applied to the grid, and the frequency of the AC voltage are examples, and other numerical values may be used. The first grid power source 614 and the second grid power source 624 may form a potential difference by using a Zener diode or the like instead of the power source.

[0013]

As described above, according to the present invention, the charge of the toner and the photoconductor is removed in the front stage of the pre-transfer toner charger, so that the positive and negative toners have the same condition when the toner in the rear stage is charged. Therefore, charging can be performed in the same manner, transfer efficiency is high for both positive and negative toners, and toner scattering due to excessive charging can be suppressed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a pre-transfer toner charger that represents an embodiment of the present invention.

FIG. 2 is a diagram showing a toner adhesion state on a recording body to which the present invention is applied.

FIG. 3 is a sectional view of a laser printer to which the present invention is applied.

FIG. 4 is a cross-sectional view of a pre-transfer toner charger showing another embodiment.

FIG. 5 is a cross-sectional view of a pre-transfer toner charger showing another embodiment.

[Explanation of symbols]

1 ... recording medium, 3 ... laser beam, 4 ... first developing machine,
41 ... First toner, 5 ... Second developing device, 51 ... Second toner, 6 ... Pre-transfer toner charger, 61 ... First charging unit, 612. ..First grid, 613 ... First corona power supply, 62 ... Second charging part, 622 ... Second grid, 623 ... Second corona power supply, 630 ... Corona wire, 7 ... Transfer device, 8 ... Recording paper

Claims (3)

[Claims] 1. A positive and negative electrostatic latent image is formed on a recording medium charged with either positive or negative polarity, and the electrostatic latent image is formed of first and second electrostatic latent images of different colors and different charging polarities. An electrophotographic image obtained by developing with toner to form a two-color toner image on a recording medium, transferring the toner image to the same polarity by corona discharge by a toner charger before transfer, and then transferring it to a recording sheet to obtain a two-color image. In the method, the amount of electric charge of the two-color toner image after development is eliminated in the front stage of the pre-transfer toner charger, and is charged to the same polarity in the rear stage. 2. The electrophotographic method according to claim 1, wherein the charging polarity of the two-color toner image by the pre-transfer toner charger is the same as that of the recording medium. 3. The pre-transfer toner charger is composed of one shield case, and a grid is provided in at least one of a front-stage opening and a rear-stage opening that divide the opening opposed to the recording medium in two, thereby positively charging the corona discharge. An alternating current corona discharge that generates ions and negative ions is performed, the charge amount of the two-color toner image is removed at the opening at the front stage, and the same polarity is charged at the opening at the rear stage. 1. The electrophotographic method according to 1.