JPH11119525A - Multicolor image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent sticking of developer to a electrifying-means after the second one by applying biases to the shield and grid of at least the electrifying- means after the second one so that they are equal in potential to the developing DC bias of the preceding developing-means. SOLUTION: Relating to a re-electrifier 5 a high voltage is applied to a corona wire from a high-voltage power source 19 and corona electrification is conducted on the surface of a photoreceptor 1. Because the shield 5b of the re-electrifier 5 is grounded, an electric field in a direction opposite to that of an electric field generated by the corona wire due to a first latent image on the photoreceptor 1 is generated. Negative toner 20 on the surface of the photoreceptor is caused to fly to the shield 5b of the re-electrifier 5 due to the electric field in the opposite direction and soils the shield. To counteract this, the potentials of the grid 23 and shield 5b are made almost equal to the potential of the preceding developing-bias 30, and a developing bias line from the bias power source 30 of the first developing-device 4 is used as it is for baises for the grid 23 and shield 5b of the re-electrifier 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser beam printer and an electrostatic recording apparatus, and more particularly to a multicolor image forming apparatus capable of performing multicolor printing.

[0002]

2. Description of the Related Art Recent images include visible images of different colors,
Many pieces of different information are combined on one sheet of paper, and an image forming apparatus having a plurality of developing devices in advance is on the market.

[0003] In particular, two rotations of the latent image bearing member during one rotation.
There are many techniques that disclose a technique of performing multi-color development with more than one developing device and simultaneously transferring the image to a paper surface. For example, there are U.S. Pat. Nos. 4,576,651 and 4,416,533 in which two or more developing devices perform development while keeping the electric field constant with a DC bias. These documents mainly disclose a method of forming a latent image, and do not suggest a problem during development.

On the other hand, US Pat. No. 4,349,268 and Japanese Patent Application Laid-Open No. 56-144452 published earlier in Japan.
Discloses a technique of using an AC developing bias in non-contact development for the development of the second color, and preventing the first color developed image from being disturbed by rubbing with the second color developer. Japanese Patent Application Laid-Open No. Sho 56-144452 does not disclose the potential for the development of the first color.

As described above, in the conventional image forming apparatus having a plurality of developing devices, a technique for performing the next development so as not to disturb the previously formed developed image has been particularly studied.

Similarly to this intention, US Pat. No. 4,660,961 discloses a technique for increasing the potential of the latent image of a previously developed image. By applying the polarity charge uniformly to the entire surface of the latent image carrier, the latent image potential of the developed image of the first color can be made substantially the same as that of the non-developed portion, and the development of the second color is greatly advanced. The formed image could not be disturbed. This is a so-called one-pass multicolor printing image forming apparatus, which is particularly called a negative-negative recharging system and has been actively studied in recent years.

[0007]

However, the above-mentioned negative-negative recharging method has the following problems. That is, the developer on the latent image carrier scatters and adheres to the shield and / or the grid portion of the recharger when the developer has the same polarity as the developer after forming the first color developed image. Therefore, as the copying process is repeated, dirt accumulates, charging unevenness occurs due to recharger dirt, and the potential of the latent image after recharging does not become substantially the same. There has been a problem that the image is disturbed or develops other than the desired latent image of the second color. Further, the first-color developer is mixed and used in the second-color developing device, which causes a problem that an unclear image is formed.

Accordingly, a main object of the present invention is to provide a multicolor image forming apparatus which can prevent the developer from adhering to the second and subsequent charging means.

It is another object of the present invention to provide a multicolor image forming apparatus which can prevent the developer of the first color from being mixed into the developing means of the second color.

[0010]

The above object is achieved by a multicolor image forming apparatus according to the present invention. In summary, the present invention provides a multicolor image forming apparatus that sequentially develops a plurality of charging units and a plurality of developing units on an image carrier to form a multicolor toner image, and collectively transfers the image onto a transfer material. A multicolor image forming apparatus is characterized in that at least a shield and a grid of the second and subsequent charging means are biased so as to have the same potential as the developing DC bias of the preceding developing means.

According to another aspect of the present invention, a multicolor toner image is formed by sequentially developing a plurality of charging means and a plurality of developing means on an image carrier to form a multicolor toner image and collectively transferring the multicolor toner image onto a transfer material. In the image forming apparatus, there is provided a multicolor image forming apparatus characterized in that a developing DC bias of a first-stage developing unit is used as a bias applied to at least a shield and a grid of the second and subsequent charging units.

It is preferable that an exposing means is provided at least in the second and subsequent charging means, and that simultaneous recharging is performed when recharging. According to another aspect, it is preferable that at least the second and subsequent wires in the charging unit are charged by superimposing an AC bias simultaneously with a DC bias. It is preferable to use a voltage obtained by intermittently superimposing an AC voltage on a DC voltage as the developing bias.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a multicolor image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic configuration diagram showing an electrophotographic image forming apparatus, that is, an electrophotographic apparatus according to Embodiment 1 of the present invention.
In this embodiment, two-color multiple development in which image formation is performed by performing batch transfer after repeating development twice will be described. However, the present invention is also applicable to a full-color image forming apparatus achieved by repeating latent images and development four times. It goes without saying that it can be applied.

In FIG. 1, the electrophotographic apparatus includes a photosensitive member (image carrier) 1 for forming an electrostatic latent image, and the surface of the photosensitive member 1 is charged to a negative potential of about -600 V around the photosensitive member. A first developing device 4 that develops a first electrostatic latent image formed on the photoconductor 1 by a primary charger 2 and a first laser beam 3 to be a first toner image, and a photosensitive member on which a first toner image is formed A secondary charger for charging the body 1 again negatively, that is, a recharger 5;
A second developing device 7 for developing the second electrostatic latent image formed on the photoconductor 1 by the laser beam 6, a transfer charger for transferring the first and second toner images formed on the photoconductor 1 to a transfer material 9 8. A cleaning device 10 for removing toner remaining on the photoconductor 1 is provided.

The exposure apparatus includes semiconductor lasers 12 and 13 for irradiating first and second laser beams 3 and 6 modulated by first and second image signals, respectively. The imaging lens 1 deflected by the rotating polygon mirror 14
5, the photosensitive member 1 is raster-scanned. Note that the first laser beam 3 scans the photoconductor 1 through the imaging lens 15 and further through the reflecting mirror 16 in a raster scan.

In the above configuration, the first latent image formed on the photosensitive member 1 is developed by the first developing device 4 to form a first toner image. Then, recharging is performed by the recharger 5 to form a second latent image, and a second toner image is formed by the second developing device 7. The recording material 9 is supplied in synchronization with the rotation of the photoreceptor 1, and the first and second recording media 9 are actuated by the transfer device 8.
The toner image is transferred to the recording material 9. The recording material 9 is further conveyed to a fixing device 11, where the first and second toner images are fixed and discharged outside the apparatus. After the completion of the transfer, the photoreceptor 1 is cleaned by the cleaning device 10 and used for the next image formation.

More specifically, the surface of the photoreceptor 1 is charged to a negative potential of about -600 V by the primary charger 2 and is irradiated with the first laser beam 3 to be at about -100 V. Further, the first developing device 4 develops with a two-component developer composed of negatively charged red toner and magnetic particles such as a ferrite carrier to form a first toner image.

Next, the surface of the photosensitive member 1 is negatively charged again by the secondary charger 5 so that the potential of the first toner image is -100V.
To -700V. Further, the surface of the photoconductor 1 irradiated with the second laser beam has a voltage of about -100V. Next, an alternating current (AC) is applied between the developing sleeve 7a and the photoconductor 1 by the second developing device 7, which is a jumping developing device.
A bias in which a voltage is superimposed on a direct current (DC) voltage is applied, and the second electrostatic latent image is reversely developed with a negatively charged black one-component magnetic toner to form a second toner image.

Next, the operation of the above-described electrophotographic apparatus will be described with further reference to a schematic diagram showing the surface potential of the photosensitive member in FIG. The photosensitive member 1 is moved by the primary charger 2 as shown in FIG.
As shown in (1), the first electrostatic latent image is uniformly charged to −600 V, and is irradiated with the first laser beam 3 to form a −100 V first electrostatic latent image as shown in FIG. And the first
When the first electrostatic latent image is developed by the developing device 4, FIG.
After the first toner image is formed as shown in (3), the photoreceptor 1 is negatively charged again by the secondary charger 5, whereby the potential of the first toner image is changed as shown in FIG. Is -7
00V and the potential of the first laser non-irradiated portion becomes -900V.

Next, as shown in FIG. 2 (5), a second electrostatic latent image of -100 V is formed by the irradiation of the second laser beam 6, and the second electrostatic latent image is formed by the second developing device 7. It is developed to form a second toner image as shown in FIG.

Then, the first and second toner images are collectively transferred to a transfer material by the transfer charger 8.

Here, the occurrence of dirt on the secondary charger 5, which is the recharger described in the conventional example, will be described in detail with reference to FIG.

FIG. 3 is a schematic diagram of the charge distribution in the photosensitive layer 1a and the substrate 1b generated after the first latent image and the first development of the photosensitive member 1. As shown in FIG. The negative toner image 20 selectively inverted by the first developing device 4 is visualized in a portion of the surface where the charge is small. The negative toner image 20 on the surface of the photoreceptor is adhered in a state where the electrostatic force such as Coulomb force is extremely weak because of the reversal development. In this state, the photoconductor 1 rotates in the direction of arrow A in FIG.
Reach the charging area.

The recharger 5 is applied with a high voltage to the corona wire 5a by the high voltage power supply 19 so that about -700 μA flows, and charges the photoreceptor 1 corona. The general distribution of the direction of the electric field generated by the recharger 5 and the photoconductor 1 at that time is indicated by an arrow in FIG. Since the shield 5b of the recharger 5 is grounded, an electric field opposite to the electric field generated by the corona wire 5a due to the first latent image of the photoconductor 1 is generated in a portion near the photoconductor 1. The negative toner 20 on the surface of the photoreceptor, which adheres in a state where the electrostatic force is extremely weak, flies back to the shield 5b of the recharger 5 due to the electric field in the opposite direction to generate shield dirt. Bold lines).

The corona charging of the recharger 5 causes a positive charge on the substrate 1b of the photoreceptor 1, which generates a Coulomb force on the negative toner 20 on the surface of the photoreceptor. Since the adhesive force with the body 1 sharply increases and overcomes the peeling force of the above-described reverse electric field, not all the negative toner 20 on the surface of the photoreceptor flies back to the shield 5 b of the recharger 5.

Further, toner adhesion to the shield 5b of the recharger 5 on the upstream side in the direction of arrow A in FIG. 3 is considerably reduced.

By repeating the above copying process many times, the wire contamination of the recharger 5 becomes remarkable, and the problem shown in the conventional example occurs.

Therefore, in order to solve the above problem, as shown in FIG. 4, SUS grid lines 23 having a diameter of 100 μm are spaced apart from each other by 1 mm in the axial direction of the drum (longitudinal direction of the photosensitive member) in the recharger 5. The external power supplies 21, 22, and the shield 5 b and the grid 23 of the recharger 5 are
31, it was decided to apply -850 V. Note that the distance between the photoconductor 1 and the grid 23 is approximately 1 mm.

The surface potential of the photosensitive member 1 when the first electrostatic latent image is formed is -600 V at the maximum at the first laser non-irradiation part, -100 V at the minimum at the first laser irradiation part, and only at the first laser irradiation part. After development, the toner layer potential after the first development is approximately -25.
It becomes 0V. Then, after recharging, by applying a grid bias of -850 V as described above, the first laser non-irradiated portion has a maximum of -850 V, and the toner layer potential after the first development has a substantially minimum of -800 V.

In this state, when −850 V is applied to the shield 5 b of the recharger 5 by the external power supplies 21 and 22, the first latent image of the photosensitive member 1 and the first latent image after the first development are applied to the shield 5 b near the photosensitive member 1. Photoconductor 1 after toner layer potential and recharging
An electric field in the same direction as the electric field generated by the corona wire 5a is generated with respect to the first latent image and the toner surface potential after the first development.

As shown in FIG. 4, the negative toner layer on the photoreceptor 1 is pressed against the photoreceptor 1 by the electric field generated by the external power supplies 21 and 22 to act on the shield 5b of the recharger 5. Prevent reverse flight. The recharged negative toner layer is prevented from flying back to the shield 5b of the recharger 5 due to the Coulomb force due to corona charging and the -850V electric field applied to the shield 5b of the recharger 5 as described above. it can.

By applying -850 V to the grid 23 by the external power supply 31, the electric field force for pressing the toner layer after the first development against the photoreceptor 1 works more reliably even in the recharger 5. Immediately after the negative toner on the photoreceptor 1 is exposed to the corona, the electric field force for pressing the toner layer after the first development between the photoreceptor and the grid against the photoreceptor 1 sufficiently acts. 5, the toner 5 can be prevented from flying backward.

External power supply 2 for shield 5b of recharger 5
The voltage applied by the recharger 1 or 22 is the same as or higher than the negative toner surface layer potential on the photoreceptor 1 after recharging, and an electric field in the same direction as the electric field generated by the corona wire 5a is generated. Of the shield 5b can be prevented.

However, the shield 5b of the recharger 5
If the voltage applied to the photosensitive member 1 is too high, the carrier or the oppositely charged positive toner on the first laser non-irradiated portion of the first latent image on the photosensitive member 1 is shielded by the recharger 5 in a portion close to the photosensitive member 1. It was found by experiments that it would fly to 5b.

Table 1 below shows the level of toner contamination on the shield 5b and grid 23 with respect to the voltage applied to the shield 5b and grid 23 of the recharger 5. The first developing device 4 performs solid red copying, A4 copies 100 sheets, and performs recharging.
Thereafter, the shield 5b and the grid 23 were checked for toner contamination. Incidentally, the distance between the tip of the shield and the photoconductor 1 was set to an upper limit of 1.0 mm.

[0037]

[Table 1]

As shown in Table 1, the voltage applied to the shield 5b is 0 to
At −200V, the negative toner recharger 5 on the photoconductor 1
Of the toner due to the reverse flight to the shield 5b,
The applied voltage of the shield 5b is -1000V to -1500V
It can be seen that the carrier 5 on the photoreceptor 1 and the toner that has been reversely charged and inverted by frictional charging (hereinafter referred to as “inverted toner”) stain the shield 5 b of the recharger 5.

Particularly, when the voltage applied to the shield 5b is -20.
Shield contamination at 0 V is caused by the negative recharge of the negative toner on the photoconductor 1 despite the electric field force pressing the surface of the photoconductor 5 from the potential of the shield 5 b and the negative toner on the photoconductor 1. Immediately after the exposure to the corona, the repulsive force of the Coulomb force acts on the toner in the upper layer, and it is considered that the toner overcomes the above-mentioned pressing electric field force and flies back to the shield. That is, it is considered that the toner is caused by a transient phenomenon of being exposed to the negative recharge corona in the recharger 5 and the toner floating in the recharger adheres to the shield 5b of the recharger 5 when the applied voltage is small.

From the above, it was found that the shield applied voltage of the recharger 5 has an appropriate value.

Therefore, based on the above data, the toner adhesion preventing potential was set to the developing bias potential at the preceding stage.
That is, the grid and shield potentials are set to be substantially the same as the developing bias 30 (for DC) in the preceding stage. Specifically, as shown in FIG. The developing bias line was used as it is for the grid and shield bias of the recharger 5.

Hereinafter, the set potential will be described. First, the grid and shield potential of the recharger were set to -500 V from the condition of the toner adhesion preventing potential. Therefore, the first latent image potential was set to -650 V (the Vback potential was set to 150 V) to apply -500 V to the developing DC bias of the first developing device.

With the above set potential, toner adhesion was reduced and good results were obtained.

Since the voltage applied to the shield 5b of the recharger 5 and the grid 23 and the potential after recharging are substantially the same, the latitude of the carrier and the reversal toner on the recharger 5 is very wide. became.

Further, the cost can be reduced by using the bias line in common, and the high voltage line can be easily turned.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, attention was paid to the toner layer potential after the first development. This will be described with reference to FIG.

First, the first latent image potential is set to -6 by the primary charger.
At 50 V (FIG. 6 (1)), when solid exposure is performed, the latent image potential drops to -150V (FIG. 6 (2)). If the development efficiency is 100% during development, the toner surface potential Vt after the first development should be the same as the development bias potential (represented by a dotted line in the figure) (-500 V in the first embodiment). However, since the developing bias used is a rectangular bias in which an alternating voltage is continuously superimposed on a DC voltage, Vt is −
It was 300V. For this reason, a potential difference from the grid of the recharger and the shield bias potential was generated to some extent, and it was not possible to completely prevent toner adhesion (FIG. 6 (3)).

Therefore, in this embodiment, a blank pulse bias capable of increasing Vt, that is, increasing development efficiency, is used.

Hereinafter, the blank pulse bias will be described with reference to FIG.

FIG. 7A shows a rectangular bias in which an alternating voltage is continuously superimposed on the DC voltage used in the first embodiment. On the other hand, FIG. 7 (2) shows a blank pulse bias, which is characterized by intermittent alternation (A) on a direct current (DC) voltage.
C) To superpose a voltage. It is known that when a blank pulse bias is used, the developed toner on the photoreceptor cannot return to the sleeve by simply applying a stripping voltage for a certain period, so that the developing efficiency is increased.

In this embodiment, a double blank pulse bias as shown in FIG.

As a result, as shown in Table 2 below,
The potential of the toner layer after development (= toner surface layer potential-potential after the first exposure) could be increased to substantially the same potential as the bias potential, and the toner adhesion was further reduced compared to Example 1, and good results were obtained.

[0053]

[Table 2]

Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIG.
In this embodiment, as shown in FIG. 8, the recharger 5 is divided into two cases 50 and 51, and an exposing unit 60 is provided above the charging wire 52 in the upstream case 51. In this embodiment, the fuse lamp 60 is simply used.
ED or laser may be used.

By performing the charge removal and simultaneous charging in such a configuration, the current in the drum direction can be increased. As a result,
As shown in Table 3 below, the charge on the surface of the toner on the drum can be increased, so that further improvement is seen, and the toner contamination due to the reverse flight of the shield 5b and the grid 23 of the recharger 5 was completely prevented. Also, by increasing the toner surface charge (improving the mirror power), it was possible to prevent mixing of the developing device in the subsequent stage.

[0056]

[Table 3]

Fourth Embodiment Next, a fourth embodiment of the present invention will be described with reference to FIG.
In this embodiment, as shown in FIG.
9, an AC power supply 19 ′ was added, and AC was superimposed on the charging wire bias of the recharger 5. By superimposing AC, it is also possible to perform simultaneous charge elimination, so that the current in the drum direction can be increased.

As a result, similarly to the third embodiment, toner contamination due to the reverse flight of the shield 5b of the recharger 5 and the grid 23 could be completely prevented. Needless to say, by increasing the toner surface charge, it was possible to prevent the toner from being mixed into the subsequent developing device.

In the above embodiment, the red toner is used for the first developing device and the black toner is used for the second developing device. However, the present invention is not limited to this.

[0060]

As is apparent from the above description, in the multicolor image forming apparatus according to the present invention, at least the second and subsequent charging means are connected to their shields and grids with the same developing bias potential as the preceding stage. Alternatively, by using the developing bias of the preceding stage as it is for the grid and the shield voltage of the recharger, it is possible to prevent the developer from adhering to the second and subsequent charging means, thereby preventing charging unevenness due to contamination of the charging means. Image can be obtained. In particular, the use of a voltage in which an AC voltage is intermittently superimposed on a DC voltage, that is, a blank pulse, as a developing bias, has a further effect. Further, by performing simultaneous static elimination exposure in the recharger, the first color can be obtained. The developer can be prevented from entering the second color developing device, and a clear image can be formed. Further, it is possible to prevent the development image of the first color from being disturbed during the development of the second color and to develop an undesired latent image of the second color, thereby obtaining a good image.

[Brief description of the drawings]

FIG. 1 is a first embodiment of a multicolor printing image forming apparatus according to the present invention.
FIG.

FIG. 2 is a schematic diagram illustrating a surface potential transition of a negative-negative recharge type photosensitive member of the image forming apparatus of FIG. 1;

FIG. 3 is an explanatory diagram showing an outline of generation of recharger contamination.

FIG. 4 is an explanatory diagram showing an example of a conventional measure for preventing recharger contamination.

FIG. 5 is an explanatory diagram illustrating a schematic configuration of a first developing device and a recharger and a charge distribution in a charged region of the recharger in the first embodiment.

FIG. 6 is an explanatory diagram showing a transition of a photoconductor surface potential in Example 2.

FIG. 7 is an explanatory diagram of a developing bias used in Example 2.

FIG. 8 is an explanatory diagram illustrating a configuration of a recharger according to a third embodiment.

FIG. 9 is an explanatory diagram illustrating a configuration of a recharger according to a fourth embodiment.

[Explanation of symbols]

 Reference Signs List 1 photoreceptor (image carrier) 2 primary charger (primary charging unit) 4 first developing device (primary developing unit) 5 recharger (secondary charging unit) 5a corona wire 5b shield 7 second developing device (Secondary developing unit) 19 Bias power supply 23 Grid 30 Bias power supply for first developing device

Claims (5)

[Claims] A multicolor toner image formed by sequentially developing on a plurality of charging means and a plurality of developing means on an image carrier;
In a multi-color image forming apparatus that performs batch transfer onto a transfer material, at least a shield and a grid of the second and subsequent charging units are biased so as to have the same potential as the developing DC bias of the preceding developing unit. Multicolor image forming apparatus. 2. A multi-color toner image is formed on the image carrier by sequentially developing with a plurality of charging means and a plurality of developing means,
In a multi-color image forming apparatus that performs batch transfer onto a transfer material, at least a bias applied to a shield and a grid of the second charging unit and a developing DC of a first-stage developing unit
A multicolor image forming apparatus using a bias. 3. The image forming apparatus according to claim 1, wherein an exposing unit is provided in at least the second and subsequent charging units, and simultaneous recharging is performed at the time of recharging. 4. The image forming apparatus according to claim 1, wherein an AC bias is superimposed and charged simultaneously with a DC bias on at least the second and subsequent wires in the charging unit. 5. The image forming apparatus according to claim 1, wherein a voltage in which an AC voltage is intermittently superimposed on a DC voltage is used as the developing bias.