JPH08146719A - Multicolor image forming device - Google Patents

Abstract

PURPOSE: To prevent the scattering and sticking of a developer to a reelectrifying means by applying a voltage being the potential of a toner layer on a recharged image carrier or above, to the shield of an electrifying means after the first time. CONSTITUTION: The surface potential of a photoreceptor 1 at the time of forming a first electrostatic latent image is up to-600V and down to -100V in a first laser nonirradiating part and the potential of the toner layer after the first development, that is, only a first laser irradiating part. is developed is down to -200V. After reelectrification, the surface potential is up to -950V in the first laser nonirradiating part and a toner potential after the first development is down to -700V. When -850V is applied to the shield 5b of a reelectrifier 5 by an external power source 21, in this state, an electric field having the same direction as that of the electric field generated in the toner layer on the photoreceptor 1 is generated in the shield 5b by a corona wire 5a. Consequently, pressing force against the photoreceptor 1 is exerted on the toner layer thereon, to prevent the toner from being reversely soared up to the reelectrifier 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 or an electrostatic recording device, and more particularly to a multicolor image forming apparatus capable of multicolor printing.

[0002]

2. Description of the Related Art Recent images include visible images of different colors,
It is often the case that different pieces of information are combined and formed on one sheet, and an image forming apparatus that stores a plurality of developing devices in advance is on the market.

Among them, the latent image carrier is rotated two times during one rotation.
There are many publications that disclose a technique of performing multicolor development with one or more developing devices and simultaneously transferring them to the paper surface. For example, there is U.S. Pat. No. 4,527,651 and U.S. Pat. No. 4,416,533, in which development is performed with a constant electric field by a DC bias in both developing devices. These mainly disclose a method for forming a latent image, and do not suggest any problems during development.

On the other hand, US Pat. No. 4,349,268 and JP-A-56-144452, which were previously published in Japan, use an AC developing bias in non-contact development for developing the second color. No. 12650 discloses a technique in which a DC bias is used in non-contact development and a developed image of the first color is prevented from being rubbed and disturbed by a developer of the second color.
Incidentally, JP-A-56-144452 does not describe the potential of the developed image of the first color at all.

As described above, in the conventional multi-development image forming apparatus, the technique of performing the next development so as not to disturb the previously developed image is applied.

Similarly to this meaning, US Pat. No. 4,660,961 is known to disclose a technique for increasing the latent image potential of a previously developed image, which is a developer after formation of a first color developed image. The latent image potential of the first color developed image can be made to be substantially the same as that of the non-developed area by uniformly charging the latent image carrier with the same polarity as that of the above. I was able to avoid disturbing the statue. This is a so-called one-pass multicolor printing image forming apparatus, which has been actively studied in recent years, particularly in a method called a negative-negative recharging system.

[0007]

However, the following problems have been known in the above conventional example. When charged to the same polarity as the developer after the first color development image is formed, the developer on the latent image carrier scatters and adheres to the shield and grid of the recharger, and stains accumulate as the copying process is repeated. Uneven charging occurred due to dirt on the charger. Further, since the latent image potentials after recharging do not become substantially the same potential, there is a problem that the previously developed image is disturbed at the time of developing the second color, or the latent image other than the desired latent image of the second color is developed. . Further, the developer of the first color is mixed in the developing device of the second color, and the developer of the first color is used in the developing device at the time of later development, resulting in unclear image formation. occured.

Therefore, a main object of the present invention is to provide an image forming apparatus capable of preventing the developer from scattering and adhering to the recharging means.

Another object of the present invention is that the developer of the first color is 2
An object of the present invention is to provide an image forming apparatus capable of preventing the mixture of colors into the developing device.

[0010]

The above object can be achieved by a multicolor image forming apparatus according to the present invention. In summary, the present invention is a multicolor image forming apparatus that sequentially charges and develops a plurality of charging units and a plurality of developing units on an image carrier to form multicolor toner images and collectively transfer them onto a transfer material. In the multicolor image forming apparatus, a voltage equal to or higher than the potential of the toner layer on the image carrier after recharging is applied to at least the shield of the second and subsequent charging means. is there.

It is preferable that at least the second and subsequent charging means are provided with a grid and a voltage equal to or higher than the potential of the toner layer on the image carrier after recharging is applied to the grid.

V ₀ : voltage applied to the shield or grid, VT: potential of toner layer on image carrier when passing through each recharging means, VD: passing through each recharging means When the potential of the laser non-irradiated portion on the image carrier is d, the distance between the shield tip of each recharging means or the grid and the image carrier is | (V ₀ −VT) /d|≧0.3.
(V / μm), 0.9 (V / μm) ≧ | (VD−V ₀ ).
It is preferable to apply at least a voltage (V ₀ ) satisfying the expression / d | to the shield or grid of at least the second and subsequent charging means.

It is preferable that the voltages applied to the shield and the grid of at least the second and subsequent charging means are different from each other.

It is preferable that the voltage applied to the shield of the charging means is the same as or smaller than the voltage applied to the grid.

It is preferable that at least the second and subsequent shield ends of the charging means be extended outward along the surface of the image carrier.

[0016] It is preferable that at least the second and subsequent shield ends of the charging means are extended inward so as to face the surface of the image bearing member and narrow it down.

[0017]

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

Embodiment 1 FIG. 1 is a schematic configuration diagram showing an electrophotographic apparatus according to the present invention. In FIG. 1, the electrophotographic apparatus includes a photoconductor (image carrier) 1 that forms an electrostatic latent image, and the primary charging around which the surface of the photoconductor 1 is charged to a negative potential of about -600V. Device 2, a first developing device 4 for developing the first electrostatic latent image formed on the photoconductor 1 by the first laser beam 3 into a first toner image, and the photoconductor 1 on which the first toner image is formed. The secondary charging device 5 for negatively charging again, the second developing device 7 for developing the second electrostatic latent image formed on the photoconductor 1 by the second laser beam 6, the first and the second formed on the photoconductor 1. A transfer charger 8 for transferring the two-toner image onto the transfer material 9 and a cleaning device 11 for removing the toner remaining on the photoreceptor 1 are provided.

The exposure apparatus is equipped with semiconductor lasers 12 and 13 for irradiating the first and second laser beams 3 and 6 modulated by the first and second image signals. The first and second laser beams 3 and 6 are provided. Imaging lens 1 deflected by the rotating polygon mirror 14
The photoconductor 1 is raster-scanned via 6. The first laser beam 3 passes through the imaging lens 16 and further through the reflecting mirror 17 to raster-scan the photoconductor 1.

Next, the operation of the electrophotographic apparatus will be described. As shown in the schematic diagram of FIG. 2A, the photosensitive member 1 is uniformly charged to −600 V by the primary charger 2, and is irradiated with the first laser beam 3 as shown in the schematic diagram of FIG. A first electrostatic latent image of 100V is formed. Then, after the first electrostatic latent image is developed by the first developing device 4 to form the first toner image as shown in the schematic view of FIG. 2C, the photosensitive member 1 is removed by the secondary charger 5. It is again negatively charged, and as a result, as shown in the schematic view of FIG.
The potential of the toner image becomes -700V.

Then, by irradiation of the second laser beam 6, a second electrostatic latent image of -100 V is formed as shown in the schematic view of FIG. 2 (5), and the second electrostatic latent image is formed by the second developing device 7. Are developed to form a first toner image as shown in the schematic view of FIG. Then, by the transfer charger 8, the first
And the second toner image is collectively transferred to the transfer material 9.

Here, the outline of the stain generation of the recharger 5 described in the conventional example will be described in detail with reference to FIG.
This figure is a schematic diagram of the charge distribution in the photosensitive layer 1a and the substrate 1b generated after the first latent image of the photoconductor 1 and the first development, and is selectively applied to a portion of the surface of the photoconductor 1 where the charge is small. The negative toner 20 reversely developed by the first developing device 1 is visualized. The negative toner 20 on the surface of the photoconductor 1 is attached in a state where the electrostatic force such as the Coulomb force is very weak due to the reversal development. In this state, the photoconductor 1 rotates in the direction of the arrow in the figure to reach the charging area of the recharger 5.

In the recharger 5, a high voltage is applied to the corona wire 5a by the high voltage power source 19 so that a constant current of about -700 μA flows, and the photoreceptor 1a is corona charged. FIG. 3 shows a schematic distribution of the directions of the electric fields generated by the recharger 5 and the photoconductor 1 at that time.

Since the shield 5b of the recharging device 5 is grounded, an electric field opposite to the electric field generated by the corona wire 5a is generated by the first latent image of the photosensitive member 1 in the portion close to the photosensitive member 1. The negative toner 20 on the surface of the photoconductor, which adheres with a very weak electrostatic force, flies backward to the shield 5b of the recharging device 5 due to the electric field in the opposite direction, and causes shield contamination.

Next, a corona charge of the recharger 5 is applied to generate a positive charge on the substrate 1b of the photoconductor 1, and this charge causes a Coulomb force on the negative toner 20 on the surface of the photoconductor 1 to cause a photoconductor. Since the adhesive force with 1 rapidly increases and overcomes the above-mentioned peeling force, not all the negative toner 20 on the surface of the photoconductor 1 flies back to the shield 5b of the recharger 5.
Further, the shield 5b of the recharger 5 on the upstream side in the direction of the arrow in the figure
Toner adhesion is considerably reduced. When the above copying process is repeated many times, the wire contamination of the recharging device 5 remarkably occurs, and the problem shown in the conventional example occurs.

In order to solve this problem, in this embodiment, as shown in FIG. 4, -850 V was applied from the external power source 21 to the shield 5b of the recharger 5. The surface potential of the photoconductor 1 when the first electrostatic latent image is formed is maximum − in the first laser non-irradiated portion.
600V, the minimum of -100V at the first laser irradiation part,
Only the first laser irradiation portion is developed, and the toner layer potential after the first development is approximately minimum -200V.

After recharging, the first laser non-irradiated portion has a maximum of -950V, and the toner potential after the first development has a minimum of -700V. In this state, the shield 5 of the recharger 5
When the external power source 21 applies −850 V to the b, the shield 5b near the photoconductor 1 has the first latent image of the photoconductor 1, the toner layer potential after the first development, and the first latent image of the photoconductor 1 after the recharge. An electric field in the same direction as the electric field generated by the corona wire 5a is generated with respect to the image and the toner layer potential after the first development. As a result, the negative toner layer on the photoconductor 1 is pressed by the electric field generated by the external power source 21 against the photoconductor 1, as shown in FIG.
It is possible to prevent the backward flight. As described above, the negative toner layer subjected to the recharging could prevent the Coulomb force due to the corona charging and the −850V electric field applied to the shield of the recharging device 5 from flying back to the shield of the recharging device 5. .

External power supply 21 for the shield 5b of the recharger 5
If the applied voltage is equal to or higher than the negative toner layer potential on the photoconductor 1 after recharging, an electric field in the same direction as the electric field generated by the corona wire 5a is generated, and the shield 5b of the recharger 5 is generated. It is possible to prevent the backward flight. However, if the voltage applied to the shield 5b of the recharging device 5 is increased too much, the carrier adhering to the first laser non-irradiated portion of the first latent image of the photoconductor 1 and the reversely charged positive toner (reversed toner) may be removed. Shield 5b of the recharger 5 near the portion 1
Experiments have shown that it will fly to.

Table 1 below shows the level of toner contamination of the shield 5b with respect to the applied voltage of the shield 5b of the recharger 5. The first developing device 4 was used for solid red and 100 sheets of A4 were copied and recharged, after which the toner stain on the shield 5b was checked. By the way, the distance between the tip of the shield and the photoconductor 1 is ~
It is 1.0 mm.

[0030]

[Table 1]

In Table 1, the applied voltage of the shield is 0 to
At -500V, the negative toner recharger 5 on the photoreceptor 1
Of the toner due to the reverse flight of the toner to the shield 5b,
When the voltage applied to the shield 5b is -1000 to -1500V, the toner on the photoreceptor 1 is reversely charged and inverted by frictional charging or the like (hereinafter referred to as inverted toner).
As a result, the shield 5b of the recharger 5 is soiled.

The voltage applied to the shield of the recharging device 5 must satisfy the following expressions [1] and [2].

| (Vs-VT) / d ₁ | ≧ 0.3 (V / μm) ... [1] 0.9 (V / μm) ≧ | (VD-Vs) / d ₁ | [2] Here, Vs: voltage applied to the shield, VT: negative toner layer potential on the photoconductor 1 when passing through the recharging device 5, VD: passing through the recharging device 5. The potential of the first laser non-irradiated portion on the photoconductor 1 when the photoconductor 1 is present, d ₁ : the distance between the shield tip of the recharger 5 and the photoconductor 1.

By satisfying the above equations [1] and [2], it is possible to prevent backward flight to the shield 5b of the recharging device 5 due to the electric field force applied to the photoconductor 1, and to prevent the carrier or the reverse toner from Recharger 5 that can prevent flying and adhesion to shield 5b and is generated by repeating the copying process many times
It was possible to prevent the wire from getting dirty.

By the way, an external power source 21 applies −850 V to the shield 5b of the recharging device 5 and a copying process is carried out for 50,000 copies of a normal document, but uneven charging due to wire contamination of the recharging device 5 does not occur. Since the latent image potentials after recharging do not become approximately the same potential, there is no problem that the previously developed image is disturbed during the development of the second color or the latent image other than the desired latent image of the second color is developed. . Further, there is no problem that the first color developer is mixed in the second color developing device and an unclear image is formed in the subsequent development.

Example 2 In Example 1, the toner layer after the first development was used as the photosensitive member 1.
It is prevented that the electric field force is applied to the shield 5b of the recharging device 5 (a voltage having the same polarity as that of the toner from the external power source 21 is applied to the shield 5b), and the carrier 5 or the reverse toner shield 5b is prevented from flying back to the shield 5b of the recharging device 5. It is possible to prevent the recharger 5 from flying and adhering to the wire, and to prevent the wire of the recharger 5 from being soiled by repeating the copying process many times.

However, in the first embodiment, especially when the applied voltage of the shield 5b is -200 to -500V, the shield 5b on the downstream side of the recharger 5 in the rotation direction of the photoconductor 1 causes toner contamination due to reverse flight.

This is because the negative toner on the photoconductor 1 is exposed to the negative recharge corona despite the electric field force pressing the surface of the photoconductor 5 from the potential of the negative toner on the shield 5b and the photoconductor 1. Immediately after that, it is considered that the repulsive force of the Coulomb force acts on the toner in the upper layer portion to overcome the above-mentioned pressing electric field force and fly back to the shield. In other words, it is considered that the toner, which is generated by a transient phenomenon of being exposed to the negative recharge corona in the recharger 5, adheres to the shield of the recharger 5 when the applied voltage is small.

Therefore, even in the recharging device, a voltage having the same polarity as that of the toner by the external power source 21 is applied to the shield 5b of the recharging device 5 so that an electric field force for pressing the toner layer after the first development to the photoconductor 1 is exerted. It is necessary to have a means to have the same effect as.

Therefore, in the second embodiment, as shown in FIG.
SUS grid lines 23 having a diameter of 100 μm were arranged in the recharging device 5 at intervals of 1 mm in the drum axial direction. Here, the distance between the drum and the grid is approximately 1 mm. And grid 2
Similarly to the shield, a voltage of the same polarity as that of the toner of −850 V was applied to the toner by the external power source 23.

As a result, the electric field force that presses the toner layer after the first development onto the photoconductor 1 operates more reliably in the recharger 5, so that the negative toner on the photoconductor 1 is recharged negatively. Immediately after the exposure, the electric field force that presses the toner layer after the first development between the drum and the grid onto the photoconductor 1 sufficiently acts, so that the toner reverse flight to the shield 5b of the recharger 5 and the grid 23 is completed. I was able to prevent it.

A model experiment similar to that of Example 1 was conducted.
The results are shown in Table 2. Even if the applied voltage of the shield is -200 to -500V, if the applied voltage of the grid satisfies the following expressions [3] and [4], toner adhesion to the shield 5b of the recharger 5 and the grid 23 is completely prevented. it can.

The voltage applied to the grid of the recharger 5 must satisfy the following expressions [3] and [4].

| (Vg-VT) / d ₂ | ≧ 0.3 (V / μm) ... [3] 0.9 (V / μm) ≧ | (VD-Vg) / d ₂ ... [ 4] Here, Vg: voltage applied to the grid, VT: negative toner layer potential on the photoconductor 1 when passing through the recharging device 5, VD: passing through the recharging device 5. At this time, the potential of the first laser non-irradiated portion on the photoconductor 1, d ₂ : the distance between the shield tip of the recharger 5 and the photoconductor 1.

[0045]

[Table 2]

A model experiment was conducted in the same manner as in Example 1 with respect to the shield stain with respect to the additional voltage of the shield when the voltage applied to the grid satisfied the above expressions [3] and [4]. Table 3 shows the results.

[0047]

[Table 3]

The voltage applied to the shield of the recharger 5 should satisfy the following expressions [5] and [6].

| Vs | ≧ | VT | ... [5] 0.9 (V / μm) ≧ | (VD−Vs) / d ₁ | ... [6] Where, Vs: is applied to the grid Voltage, VT: negative toner layer potential on the photoreceptor 1 when passing through the recharger 5, VD: first laser non-irradiation on the photoreceptor 1 while passing through the recharger 5. Potential of the part, d ₁ : distance between the shield tip of the recharger 5 and the photoconductor 1.

As described above, the grid 23 is attached to the recharger 5.
By providing a voltage that satisfies the expressions [5] and [6], the range of the voltage applied to the shield can be expanded, and the corona wire contamination of the recharger 5 can be extended for a longer period of time. Can be prevented. Further, by providing the recharging device 5 with the grid 23, the recharging potential is easily converged, and even if the corona wire is contaminated to some extent, the recharging potential can be made substantially constant by the potential converging effect on the photoconductor 1 of the grid 23.

By the way, after the recharge when the shield 5b of the recharger 5 and the grid 23 are applied -850V by the external power source 22, the first laser is not charged after the recharge when the maximum -850V is applied in the first laser non-irradiation part. -850V at the non-laser irradiation area
And the toner layer potential after the first development is about -800V at minimum.
Became.

That is, since the potential applied after recharging is substantially the same as the voltage applied to the shield 5b and the grid 23, the latitude of the adhesion of the carrier and the reversal toner to the recharging device 5 becomes very wide. 20 copy steps with normal manuscript
Although the number of sheets was repeated, the charging unevenness due to the wire stain of the recharging device 5 did not occur, and the latent image potential after recharging did not become substantially the same potential, so the image formed previously during development of the second color was disturbed. There was no problem of developing a latent image other than the desired second color image. Further, there is no problem that the unclear image is formed during the subsequent development due to the mixing of the inside of the developing for the first color into the developing unit for the second color.

Embodiment 3 In Embodiment 3, as shown in FIG. 5, the shield end portion 5c of the recharger 5 which is close to the photoconductor 1 is extended along the photoconductor 1, and [1], [2] It is characterized in that a voltage satisfying the formula is applied. As a result, the first latent image on the photoconductor 1 and the negative toner on the surface of the photoconductor 1 that adheres with a very weak electrostatic force after the first development are shielded before receiving the corona charge of the recharging device 5. 5b and the electric field generated between the photoconductor 1 can be moved so that the reverse charge corresponding to the charge of the negative toner can be more injected from the substrate 1b of the photoconductor 1. Then, the Coulomb force due to the opposite charge and the charge of the negative toner can be strengthened, and the adhesive force between the photoreceptor 1 and the negative toner is increased. Therefore, when the negative recharge corona in the recharger 5 is exposed, a floating phenomenon caused by a transient phenomenon occurs. It has become possible to suppress the generation of toner.

Actually, the extension amount of the shield end 5c is
When the same model experiment as in Example 1 was performed without setting the grid to 5 mm, the result was better than that of Example 1. The results are shown in Table 4.

[0055]

[Table 4]

Further, by adopting the shield shape of this embodiment, it is possible to prevent the scattered toner spilled from the first developing device from entering the recharger 5, and the shield shape and the grid are provided. Moreover, by applying a voltage satisfying the expressions [1] and [2] to the shield and the grid, the corona wire contamination of the recharging device 5 can be further extended.

Further, even if the shape of the shield 5b is extended into the recharging device 5 and narrowed down as shown in FIG. 6, if the end 5d of the shield of the recharging device 5 is along the photoreceptor 1. no problem. While the negative toner on the photoconductor 1 is pressed against the photoconductor 1 by the electric field of the shield 5b, at the same time, the corona discharge of the recharger 5 easily concentrates on the edge portion of the shield end portion, so that the negative toner on the photoconductor 1 becomes negative. It is thought that the toner will be easily recharged and the reverse flight will be suppressed.

[0058]

As described above, according to the present invention,
By applying a voltage equal to or higher than the potential of the toner layer on the image carrier after recharging to at least the second and subsequent shields and / or grids of the charging means, By preventing the developer from adhering and repeating the normal copying process, it is possible to prevent charging unevenness due to the wire stain of the recharging device 5 caused by the accumulation of the backward flying toner.

As a result, since the latent image potentials after recharging do not become substantially the same potential, the previously developed image is disturbed at the time of developing the second color, or the latent image other than the desired latent image of the second color is developed. No problems occurred. Furthermore, the problem of unclear image formation during subsequent development due to the mixing of the first color developer into the second color developing device, especially in a negative-negative recharging system in a 1-pass multicolor image forming apparatus. I was able to solve the problem that occurs when using.

Further, by extending the shield shape of the recharger along the photoconductor, the shield electric field for strongly pressing the negative toner onto the photoconductor can be made to work for a long time, and the reverse flight of the toner can be suppressed. . Further, it is possible to prevent the toner scattering from the first developing device from entering the recharging device at the same time.

[Brief description of drawings]

FIG. 1 is a first embodiment of a multicolor printing image forming apparatus according to the present invention.
It is a schematic block diagram which shows.

FIG. 2 is a schematic diagram showing a surface potential transition of a negative-negative recharging type photoconductor of the image forming apparatus of FIG.

FIG. 3 is an explanatory diagram showing an outline of generation of stains on a recharger.

FIG. 4 is an explanatory diagram showing prevention of dirt on the recharger in the first embodiment.

FIG. 5 is an explanatory diagram showing prevention of stains on the recharging device according to the second and third embodiments.

FIG. 6 is an explanatory diagram showing a modified example of the recharger stain prevention of the third embodiment according to the present invention.

[Explanation of symbols]

 1 Photoreceptor (Image Carrier) 2 Primary Charger (Primary Charging Means) 4 First Developing Device (Primary Developing Means) 5 Secondary Charging Device (Secondary Charging Means) 5a Corona Wire 5b Shield 7 Second Development Container (secondary development means) 23 grid

Claims (7)

[Claims] 1. A multicolor image forming apparatus for sequentially charging and developing a plurality of charging means and a plurality of developing means on an image carrier to form a multicolor toner image and transferring the toner images onto a transfer material at a time. Is it the same as the toner layer potential on the image carrier after recharging the shield of the second and subsequent charging means?
A multicolor image forming apparatus characterized by applying a voltage higher than that. 2. A grid is provided on at least the second and subsequent charging means, and a voltage equal to or higher than the potential of the toner layer on the image carrier after recharging is applied to the grid. And a multicolor image forming apparatus. 3. The multicolor image forming method according to claim 1, wherein a voltage (V ₀ ) satisfying the following formula is applied to at least a shield or a grid of the second and subsequent charging means. apparatus. | (V ₀ −VT) /d|≧0.3 (V / μm) 0.9 (V / μm) ≧ | (VD−V ₀ ) / d | where V ₀ ; applied to the shield or grid Voltage, VT; toner layer potential on the image carrier when passing through each recharging means, VD: potential of the laser non-irradiated portion on the image carrier when passing through each recharging means, d: The distance between the shield tip of each recharging means or the grid and the image carrier. 4. The multicolor image forming apparatus according to claim 2, wherein the voltages applied to the shield and the grid of at least the second and subsequent charging means are different from each other. 5. The multicolor image forming apparatus according to claim 4, wherein the voltage applied to the shield of the charging unit is the same as or lower than the voltage applied to the grid. 6. A multicolor image according to any one of claims 1 to 5, wherein at least the second and subsequent shield tip portions of the charging means are extended outward along the surface of the image carrier. Forming equipment. 7. The shield tip portion of at least the second and subsequent charging means is extended inward so as to face the surface of the image carrier so as to be narrowed down. Multi-color image forming apparatus.