JP3140313B2 - Multicolor image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam printer,
The present invention relates to an image forming apparatus such as 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,
In many cases, different information is synthesized and formed on one sheet of paper, and an image forming apparatus containing a plurality of developing devices in advance is on the market.

In particular, there are many techniques that disclose a technique of developing a multicolor image with two or more developing devices during one rotation of an image carrier and simultaneously transferring the image to paper.

[0004] For example, US Pat. No. 4,572,265 in which development is performed with a DC bias to keep the electric field constant in both developing devices.
No. 1 and No. 4416533. These are mainly concerned with a method of forming a latent image, and do not suggest any problems 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.
Japanese Patent Application Laid-Open No. Sho 56-12650 uses a DC bias for non-contact development and slides the developed image of the first color with the developer of the second color. There is known a technology that discloses a technique for preventing rubbing and disturbing. JP-A-56-144452 does not disclose the potential of the developed image of the first color.

As described above, in the conventional multi-developed image forming apparatus, a technique for performing the next development so as not to disturb the previously developed image has been known.

Similarly, US Pat. No. 4,660,961 discloses a technique for increasing the potential of a latent image of a previously developed image. 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 by uniformly applying the polarity charging to the entire surface of the image carrier, and the image developed and formed greatly earlier during the development of the second color is disturbed. Could not be.

This has been actively studied in recent years in a one-bus multicolor printing image forming apparatus, particularly in a method called a negative or negative recharging method.

[0009]

However, the above-described conventional example has the following problems.

When the developer of the first color is charged with the same polarity as the developer after the formation of the developed image, the developer on the image carrier is charged with a secondary charger (recharger).
Problem of scattering and adhesion on the shield and grid part of
As the copying process is repeated, dirt accumulates and uneven charging due to dirt on the secondary charger occurs. Since the latent image potential after recharging does not become substantially the same, the previously developed image is disturbed during the development of the second color. Or develop the image other than the desired latent image of the second color.

Further, the first-color developer is mixed into the second-color developing device, and during the subsequent development, the first-color developer is used in the rear developing device, resulting in unclear image formation. Would.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a multicolor image forming apparatus capable of obtaining a good multicolor image.

[0013]

In order to achieve the above object, according to the present invention, a plurality of charging means and a plurality of developing means sequentially charge and develop an image bearing member. In a multicolor image forming apparatus for forming a multicolor image on the recording medium and transferring the multicolor image onto a recording medium at a time, at least one of a shield and a grid of the second and subsequent charging means is equal to the voltage on the image carrier after recharging. or, by applying a voltage having a large absolute value, and thereby forming an air flow toward the image bearing member from the charging means, the voltage applied to V _O to the charging means, charging hand V _T
Voltage on the image bearing member, a V _D charging hand when passing through the stages
Of the laser non-irradiated part on the image carrier when passing through the step
When the pressure and d are the distance between the charging means and the image carrier, | (V _O
−V _T ) /d|≧0.3 (V / μm) and 0.9
(V / μm) ≧ | a V _O which satisfies _{| (V D -V O) /} d
It is characterized in that it is applied to a charging means.

The air flow from the charging means to the image carrier may be formed over the entire area in the axial direction of the image carrier.

Preferably, the charging means is provided with an air feeding means, and the air flow by the air feeding means is preferably stronger at both axial ends than at the center.

Preferably, the air flow by the air feeding means is made larger than the corona ion wind generated by the corona discharge of the charging means.

The wind speed by the air feeding means is 0.5 m /
sec or more.

[0018]

It is preferable that the wind speed distribution of the air flow toward the image carrier of the charging means is increased toward the upstream side in the traveling direction of the image carrier.

It is preferable that the wind speed of the air flow of the charging means toward the image carrier is gradually increased toward the downstream of the traveling direction of the image carrier.

[0021]

In the multicolor image forming apparatus constructed as described above, by applying a voltage having the same or a large absolute value as the voltage on the image carrier after charging, the image carrier, developer, and charging device are charged. The absolute value of the voltage increases in the order of the means. By forming an air flow from the charging unit to the image carrier, the developer receives a force in the direction of the image carrier. Also, V _O is marked on the charging means.
Voltage pressurized, the image bearing when passing through the charging means V _T
Image bearing when the voltage on the body, a V _D is passing through the charging means
The voltage of the laser non-irradiated part on the body, d is the charging means and the image carrier
When the _{distance, | (V O -V T)} /d|≧0.3 (V /
μm) and 0.9 (V / μm) ≧ | (V _D −V _O ) /
By applying V _O satisfying d | to the charging means,
This prevents the developer from separating from and scattering from the image carrier.

By forming an air flow from the charging means to the image carrier over the entire area in the axial direction of the image carrier, the developer receives a force in the direction of the image carrier over the entire area.

Air charging means is provided in the charging means, and the air flow by the air feeding means is made stronger at both axial end portions than at the central portion, thereby suppressing air wind toward the charging means at both axial end portions due to corona ion wind. Can be

By making the air flow by the air feeding means larger than the corona ion wind generated by the corona discharge of the charging means, the air wind is formed in the direction of the image carrier over the entire area even when the corona ion wind is generated.

The wind speed by the air feeding means is set to 0.5 m /
By setting the time to sec or more, a wind speed stronger than the corona ion wind can be obtained.

By increasing the wind speed distribution of the air flow of the charging means toward the image carrier with respect to the traveling direction of the image carrier toward the upstream side, the discharge can be activated toward the upstream side.

By increasing the wind speed of the air flow of the charging means toward the image carrier gradually toward the charging means located on the downstream side in the traveling direction of the image carrier, even if the amount of the developer becomes large, Is done.

[0028]

【Example】

(Introduction) FIG. 1 is a schematic configuration diagram of an electrophotographic apparatus according to the present invention.

In the figure, 1 is a photosensitive member (image carrier) for forming an electrostatic latent image, 2 is a primary charger for charging the surface of the photosensitive member 1 to a negative potential of about -600 V, 3 is a photosensitive member 1 And the surface of the photoconductor 1 irradiated with the laser beam 3 has a voltage of about -100 V. The first laser beam forms a first electrostatic latent image on the photoconductor 1.

A first developing device 4 for developing the first electrostatic latent image with a two-component developer comprising negatively charged red toner and magnetic particles such as a ferrite carrier to form a first toner image;
Reference numeral 5 denotes a secondary charger for negatively charging the photosensitive member 1 on which the first toner image has been formed again, and the charging increases the potential of the first toner image from -100V to -700V.

At this time, an air flow is sent from the air duct (air sending means) indicated by 50 toward the photoreceptor 1 by the fan 52.

6 irradiates the photoreceptor 1 to apply a second
A second laser beam for forming an electrostatic latent image is applied to the surface of the photoconductor 1 irradiated with the second laser beam 6 by about -100V.
become.

Reference numeral 7 denotes a reversal development of a second electrostatic latent image with a negatively charged black one-component magnetic toner by applying a bias in which an AC voltage is superimposed on a DC voltage between the developing sleeve 7a and the photosensitive member 1. And a second developing device (jumping developing device) 8 for forming a second toner image on the photosensitive member 1.
A transfer charger 11 for transferring the second toner image to the transfer material 9;
Reference numeral denotes a cleaning device that removes toner remaining on the photoconductor 1, and reference numerals 12 and 13 denote semiconductor lasers that irradiate first and second laser beams 3 and 6 modulated by first and second image signals. The first and second laser beams 3 and 6 are polarized by the rotating polygon mirror 14 and raster-scan the photoconductor 1 via the image-defining lens 16. 17 is a reflecting mirror.

Next, the operation of the above electrophotographic apparatus will be described.

The photosensitive member 1 is moved by the primary charger 2 as shown in FIG.
Is uniformly charged to -600 V as shown in FIG.
A first electrostatic latent image of V is formed.

Then, after the first electrostatic latent image is developed by the first developing device 4 to form a first toner image as shown in FIG. 2C, the photosensitive member 1 is formed by the secondary charger 5. It is again negatively charged, thereby causing the first charge as shown in FIG.
The potential of the toner image becomes -700V.

Next, as shown in FIG. 2E, a second electrostatic latent image of -100 V is formed by irradiation of the second laser beam 6, and the second electrostatic latent image is developed by the second developing device 7. Thus, a second toner image is formed as shown in FIG.

Then, the first and second toner images are collectively transferred to the transfer material 9 by the transfer charger 8.

Here, the outline of the generation of dirt on the secondary charger 5 described in the conventional example will be described in detail with reference to FIG.

FIG. 4 is a schematic view of a first latent image of the photosensitive member 1 and a charge distribution in the photosensitive layer and the substrate generated after the first development. The negative toner (developer) 20 reversely developed by the device 4 is visualized.

The negative toner 20 on the surface of the photoreceptor 1 adheres 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 the arrow in FIG. 3A and reaches the charging area of the secondary charger 5.

The secondary charger 5 applies a high voltage to the corona wire 5c from the high voltage power supply 19 at a constant current so as to flow at a constant current of about -700 μA, and charges the photoreceptor 1 corona. FIG. 3A is a schematic distribution diagram of the direction of the electric field generated by the secondary charger 5 and the photoconductor 1 at that time.

Since the shield 5a of the secondary charger 5 is grounded, an electric field opposite to the electric field generated by the corona wire 5c due to the first latent image of the photoconductor 1 is generated in a portion near the photoconductor 1.

Since the negative toner 20 on the surface of the photoreceptor 1 is attached in a state where the electrostatic force is very weak, the negative toner 20 flies back to the shield 5a of the secondary charger 5 due to the electric field in the opposite direction. Causes dirt on the surface.

Next, the corona charging of the secondary charger 5 causes a positive charge to be generated on the substrate of the photoreceptor 1, and this charge generates a Coulomb force in the negative toner 20 on the surface of the photoreceptor 1. 1 is sharply increased, and overcomes the above-mentioned peeling force of the reverse electric field, so that the negative toner 20 on the surface of the photoreceptor 1 is removed.
Not all fly backward to the shield 5a of the secondary charger 5.

Further, the adhesion of the toner 20 to the shield 5a of the secondary charger 5 on the downstream side in the traveling direction (arrow direction) of the photoconductor 1 in FIG. 3A is considerably reduced.

By repeating the above copying process many times, the corona wire 5c of the secondary charger 5 was significantly stained. FIG. 3B is a schematic diagram when air is blown from the air duct 50 in a state where the shield 5a is grounded (the air flow intensity distribution is indicated by 101). Was not improved at all.

(Embodiment 1) For this reason, in Embodiment 1, -850 V is applied by the power supply 21 connected to the shield 5a of the secondary charger 5, and clean air is forced through the filter 51 by the air duct 50. Secondary charger 5
I blew in.

FIG. 4A is a schematic view of the first embodiment.
However, the air duct 50 is omitted for explanation in FIG.

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-irradiated portion, -100 V at the minimum at the first laser irradiated portion, and only at the first laser irradiated portion. After the development, the toner layer potential after the first development is substantially minimum -20.
It becomes 0V.

After the recharging, the maximum potential of the first laser non-irradiated portion is -950 V, and the potential of the toner layer after the first development is substantially the minimum of -700 V.

When a voltage of -850 V is applied to the shield 5a of the secondary charger 5 by the power supply 21 in this state, the first latent image of the photosensitive member 1 and the first latent image after the first development are applied to the shield 5a near the photosensitive member 1. An electric field is generated in the same direction as the electric field generated by the corona wire 5c with respect to the toner layer potential and the first latent image on the photoreceptor 1 after recharging and the toner layer potential after the first development.

As a result, as shown in FIG. 4A, the negative toner layer on the photoreceptor 1 exerts a pressing force against the photoreceptor 1 by the electric field generated by the power supply 21.

As described above, the recharged negative toner layer exerts a pressing force against the photoreceptor 1 by the Coulomb force due to the corona charging and the -850 V electric field applied to the shield 5a of the secondary charger 5.

Further, as shown in FIG. 4B, an air flow (air flow intensity distribution is indicated by 101) toward the photoreceptor 1 is forcibly formed by the air duct 50, and the shield 5a is formed.
As a result, the toner 20 that is about to fly backward can be pressed onto the photoreceptor 1 by wind pressure.

The voltage applied by the power supply 21 to the shield 5a of the secondary charger 5 is equal to or higher than the potential of the negative toner layer on the photoreceptor 1 after recharging.
An electric field in the same direction as the electric field generated by c (direction of the photoconductor 1) is generated, and it is possible to prevent the electric field from flying back to the shield 5a of the secondary charger 5.

However, if the voltage applied to the shield 5a of the secondary charger 5 is too high, the carrier attached to the first laser non-irradiated portion of the first latent image of the photosensitive member 1 or the reversely charged positive toner (inverted toner) It was found from experiments that the) 20 would fly to the shield 5a of the secondary charger 5 near the photoconductor 1.

Table 1 shows the level of toner contamination of the shield 5a with respect to the voltage applied to the shield 5a of the secondary charger 5. Solid red in the first developing device 4, 100 copies in A4,
After recharging, the shield 5a was checked for toner contamination. By the way, the tip of the shield 5a and the photoconductor 1
Is -1.0 mm.

[0059]

[Table 1]

[0060]

[Table 2] In Table 1, the voltage applied to the shield 5a is 0 to -5.
At 00V, toner contamination occurs due to the negative toner 20 on the photoreceptor 1 flying back to the shield 5a of the secondary charger 5 and the voltage applied to the shield 5a is -1000 to -1500.
In the case of V, the shield 5a of the secondary charger 5 is stained by the toner 20 (hereinafter, referred to as an inverted toner) which is reversely charged and inverted by the carrier on the photoreceptor 1 and frictional charging or the like. By generating the airflow toward the body 1, as shown in (Table 2), when the voltage applied to the shield 5a is -500 to -1500V, toner contamination can be sufficiently prevented.

This is because the toner 20 and the carrier which fly backward do not retain the charge which is strongly attached to the photoreceptor 1, so that the toner 20 and the carrier which fly backward also affect the wind pressure. It seems to receive.

As described above, the voltage applied to the shield 5a of the secondary charger 5 needs to satisfy the following equations (Equation 1) and (Equation 2).

[0063]

| (V _s −V _T ) / d ₁ | ≧ 0.3 (V / μm)

[0064]

0.9 (V / μm) ≧ | (V _D −V _s / d ₁ | where V _s is the voltage applied to the shield 5a and V
_T, the secondary charger 5 negative toner layer potential on the photosensitive member 1 when passing through the, V _D, the secondary charging device on the photosensitive member 1 when passing through the 5 first laser non The potential of the irradiation unit, d _1, is the distance between the tip of the shield 5 a of the secondary charger 5 and the photoconductor 1.

During the corona discharge of the secondary charger 5 and the electric field force that presses the photosensitive member 1 that satisfies the above formulas (Equation 1) and (Equation 2), the photosensitive member 1 is directed to the photosensitive member 1 over the entire area within the secondary charger 5. By forming the wind pressure by an air flow, both of them can prevent a reverse flight to the shield 5a of the secondary charger 5 and prevent a carrier and the reverse toner 20 from flying and adhering to the shield 5a. Is repeated many times, thereby preventing the corona wire 5c of the secondary charger 5 from being stained.

Incidentally, a voltage of -850 V is applied to the shield 5a of the secondary charger 5 by an external power source and the air duct 5
The wind speed of the air flow blown into the secondary charger 5 by 0 is 1 m
/ Sec, the copying process was performed on 50,000 sheets of a normal original, but no charging unevenness due to contamination of the corona wire 5c of the secondary charger 5 occurred, and the latent image potential after recharging was substantially the same. Therefore, there was no problem that the previously developed image was disturbed at the time of developing the second color, and there was no problem in developing the image other than the desired latent image of the second color.

Further, the toner 20 (developer) of the first color is mixed into the second developing device 7 of the second color, and during the subsequent development,
There was no problem of unclear image formation.

(Embodiment 2) In the embodiment 1, the electric field force for pressing the toner layer after the first development to the photoreceptor 1 (the same polarity positive voltage as that of the toner 20 by the external power source is applied to the shield 5a of the secondary charger 5) ) To generate an air flow toward the photoconductor 1, thereby preventing the shield 5a of the secondary charger 5 from flying backward, and preventing the shield 5a of the carrier and the reversal toner 20 from flowing.
Thus, the corona wire 5c of the secondary charger 5 caused by repeating the copying process many times was prevented.

However, even if an air flow is forcibly formed toward the photosensitive member 1 by the air duct 50 and a force is applied to the shield 5a to push the toner 20 which is about to fly backward on the photosensitive member 1 by wind pressure, the shield 5a is not affected. When the applied voltage of 5a is -200 to -500V, the shield 5a of the secondary charger 5 on the upstream side in the rotation direction of the photoconductor 1 generates toner stain due to reverse flight.

This is because immediately after the negative toner 20 on the photosensitive member 1 is exposed to the negative recharge corona, when the charge amount is small,
It is considered that the Coulomb repulsion between the toners 20 acts on the toner 20 in the upper layer, and the toner 20 overcomes the above-described electric field force and voltage to fly back to the shield 5a.

That is, the toner 20 floating in the secondary charger 5 due to the transient phenomenon of being exposed to the negative recharge corona in the secondary charger 5 is applied to the shield 5a of the secondary charger 5 by the wind pressure of the air flow. It is considered that they adhere when the applied voltage is small.

It has been found that the effect of the airflow forced toward the photoconductor 1 by the air duct 50 occurs only when there is an electric field force pressing the photoconductor 1.

Therefore, the same polarity voltage as that of the toner 20 from the power source 21 is applied to the shield 5 a of the secondary charger 5 to press the toner layer after the first development to the photoreceptor 1 in the secondary charger 5. It is necessary to provide a means for providing the same effect as that of operating the photoconductor 1, and then, forcibly form an airflow toward the photoconductor 1 by the air duct 50, and force the toner 20 that is about to fly backward on the photoconductor 1 by wind pressure. It is important to impose.

For this reason, in the second embodiment, as shown in FIGS. 5A and 5B, the SUS grid 5b having a diameter of 100 μm is connected to the secondary charger 5 at intervals of 1 mm in the axial direction of the photosensitive member.
It was arranged inside. Here, the distance between the photoconductor 1 and the grid 5b is approximately 1 mm.

Then, an airflow (airflow intensity distribution indicated by 103) toward the photoreceptor 1 was forcibly formed by the air duct 50.

At this time, since the grids 5b are uniformly arranged in the secondary charger 5, an air pressure load is generated, and the air flow distribution is made more uniform in the secondary charger 5.

As a result, the electric field force that presses the toner layer after the first development to the photoconductor 1 works more reliably in the secondary charger 5, and particularly, the negative toner 20 on the photoconductor 1 becomes negative. Immediately after the recharging corona, the electric field force and the wind pressure which press the toner layer between the photoreceptor 1 and the grid 5b after the first development to the photoreceptor 1 sufficiently act.
The reverse flight of the toner 20 to the shield 5a and the grid 5b was completely prevented.

A model experiment similar to that of Example 1 was performed.
The results are shown in (Table 3).

[0079]

[Table 3] Even if the applied voltage of the shield 5a is -200 to -500V, if the applied voltage of the grid 5b satisfies the following expression (2), the adhesion of the toner 20 to the shield 5a of the secondary charger 5 and the grid 5b is completely completed. Can be prevented.

As described above, the voltage applied to the grid 5b of the secondary charger 5 needs to satisfy the following equations (Equation 3) and (Equation 4).

[0081]

| (V _g −V _T ) / d ₂ | ≧ 0.3 (V / μm)

[0082]

0.9 (V / μm) ≧ | (V _D −V _g ) / d ₂ | In this (Expression 4), V _g is the voltage applied to the grid 5b, and V _T is The potential of the negative toner layer on the photoconductor 1 when passing through the secondary charger 5, V _D is the potential of the first laser non-irradiation portion on the photoconductor 1 when passing through the secondary charger 5, d ₂ is the distance between the grid 5 b of the secondary charger 5 and the photoconductor 1.

Next, the shield 5 when the voltage applied to the grid 5b satisfies the above equations (Equation 3) and (Equation 4)
A model experiment was performed in the same manner as in Example 1 for contamination of the shield 5a with respect to the applied voltage a. The results are shown in (Table 4).

[0084]

[Table 4] The voltage applied to the shield 5a of the secondary charger 5 may satisfy the following equations (Equation 5) and (Equation 6).

[0085]

| V _s | ≧ | V _T |

[0086]

[6] 0.9 (V / μm) ≧ | (V D -V s) / d 1 | In this equation (6), V _s is the voltage applied to the shield 5a, V _T, the double negative toner layer potential on the photosensitive member 1 when passing through the next charger 5, V _D, the secondary charger 5
, The potential of the first laser non-irradiated portion on the photoconductor 1 when passing through, d ₁ is the distance between the tip of the shield 5 a of the secondary charger 5 and the photoconductor 1.

When the voltage applied to the grid 5b satisfies the above equations (Equation 3) and (Equation 4), and the air flow toward the photosensitive member 1 is also applied, the contamination of the shield 5a with respect to the applied voltage of the shield 5a. Was subjected to a model experiment in the same manner as in Example 1. The results are shown in (Table 5).

[0088]

[Table 5] As described above, the grid 5b is provided on the secondary charger 5, and a voltage that satisfies the equations (5) and (6) is applied.
By forcibly forming an airflow toward the photoconductor 1 by the air duct 50, it is possible to widen the range of the voltage applied to the shield 5a, and the corona wire 5c of the secondary charger 5 can be extended for a longer time. Dirt can be prevented.

Further, by providing the grid 5b in the secondary charger 5, the recharge potential easily converges, and even if the corona wire 5c is stained to some extent, the photosensitive member 1 on the grid 5b can be used.
Due to the above potential convergence effect, the recharge potential can be made substantially constant.

By the way, after recharging when -850 V is applied to the shield 5a and grid 5b of the secondary charger 5 from an external power source, the maximum voltage becomes -850V in the first laser non-irradiated portion, and the toner layer potential after the first development is applied. Became approximately -800V.

That is, since the potential after recharging is substantially the same as the voltage applied to the shield 5a and the grid 5b, the latitude of the carrier and the reversal toner 20 on the secondary charger 5 is greatly widened.

Normally, a copying process was performed on 200,000 sheets of originals. However, uneven charging due to contamination of the corona wire 5c of the secondary charger 5 did not occur, and the latent image potential after recharging did not become substantially the same. At the time of developing the second color, there was no problem in that the previously developed image was disturbed, and there was no development other than the desired latent image of the second color.

Further, the toner 20 (developer) of the first color is mixed into the second developing device 7 of the second color, and during the subsequent development,
There was no problem of unclear image formation.

(Embodiment 3) Further, usually, the secondary charger 5
6A, a corona ion wind is generated as shown in FIG. 6A, which is not uniform in the axial direction of the photosensitive member 1.

That is, in the central portion of the secondary charger 5, the photosensitive member 1
, And corona ion winds from the photoconductor 1 toward the corona wire 5c were generated at both ends of the secondary charger 5.

Particularly, at both ends of the secondary charger 5, an airflow is generated toward the corona wire 5c, so that the negative toner 20 on the surface of the photoreceptor 1 adhered in a state where the electrostatic force is very weak is strongly disturbed. Or promoted reverse flight.

By repeating the above-described copying process many times, the corona wire 5c of the secondary charger 5 is significantly stained particularly at both ends of the secondary charger 5, and the problem described in the conventional example occurs.

Therefore, in the third embodiment, the corona ion wind at the outlet of the secondary charger 5 close to the photoconductor 1 is measured by using a thermistor anemometer, and the photoconductor 1 is covered over the entire area of the photoconductor 1 in the axial direction.
Clean air was forcibly blown onto the photoreceptor 1 by the air duct 50 so that both ends of the secondary charger 5 were stronger than the center of the secondary charger 5 so that an airflow toward the secondary charger 5 was formed. This air wind distribution is shown in FIG.

Thus, as shown in FIG. 6C, the first latent image on the photosensitive member 1 and the negative toner 20 on the surface of the photosensitive member 1 adhered in a state where the electrostatic force after the first development is very weak. Is applied across the entire width of the secondary charger 5, and a wind pressure is applied to the photosensitive member 1, and dirt generated at both ends of the secondary charger 5 generated by corona ion wind blown into the secondary charger 5, and The image stain of the toner 20 was also prevented.

By the way, when the corona discharge does not occur, the wind speed of the air flow just below the secondary charger 5 by the air duct 50 is 0.5
It was also found from the results of the wind velocity measurement that if the speed was / sec or more, the contamination in the secondary charger 5 could be sufficiently prevented.

Actually, the copying process was performed on 200,000 sheets of a normal original in the same manner as in Example 2. However, uneven charging due to the corona wire 5c of the secondary charger 5 did not occur, and the potential of the latent image after recharging was reduced. Since the potentials are not substantially the same, there is no problem that the previously developed image is disturbed at the time of developing the second color, and that the image is not developed to a desired latent image of the second color.

Further, the toner 20 (developer) of the first color is mixed into the second developing device 7 of the second color, and during the subsequent development,
There was no problem of unclear image formation.

(Embodiment 4) Normally, the corona discharge of the secondary charger 5 is further activated by the flow of air from the outside, so that the discharge is more activated and the charge amount in the air flow inlet is increased. It has been known.

Immediately after the negative toner 20 on the photoreceptor 1 is exposed to the negative recharging corona, when the charge amount is small, the Coulomb repulsion between the toners 20 acts on the toner 20 in the upper layer, and the shield 5a The present invention can be applied to the development shown in the second embodiment in which a dirt is generated by flying backward.

That is, by increasing the airflow in the shield 5a on the upstream side in the rotation direction of the photoconductor 1 in the secondary charger 5, the toner 20 is pressed against the photoconductor 1 by the wind pressure, and the discharge is activated. This makes it possible to instantaneously increase the amount of charge of the toner 20, and it is possible to prevent the dirt that flies back to the shield 5 a by the Coulomb force without providing the grid 5 b.

Actually, as shown in FIG. 7, an experiment was conducted in which the opening of the air duct 50 was narrowed and sprayed only on the shield 5a on the upstream side in the rotation direction of the photosensitive member 1 in the secondary charger 5. It was better than the result of Example 1. The results are shown in (Table 6). The air flow intensity distribution 104 is shown in FIG.
Shown in

[0107]

[Table 6] Furthermore, the secondary charger 5 is provided by disposing a grid 5b and applying a voltage satisfying the formulas (1), (2), (3) and (4) to the shield 5a and the grid 5b. The life of the corona wire 5c can be further extended.

Next, in consideration of negative or negative recharge of two or more colors, if recharge is performed by adhering to the photoreceptor 1 of two or more colors, the amount of toner 20 adhering to the photoreceptor 1 increases. As a result, the amount of toner stains that fly back to the secondary charger 5 increases sharply.

In order to prevent this, it is impossible with a cloning force that works by the square of the distance, and a wind pressure effect of the air flow toward the photoconductor 1 is required. In other words, by sequentially increasing the wind speed of the air duct 50 toward the secondary charging device 5 on the downstream side in the rotation direction of the photoconductor 1, it is possible to prevent toner stains that fly backward to the secondary charging device 5.

By the way, when the corona discharge does not occur, the wind speed of the air flow just below the secondary charger 5 by the air duct 50 is 1.0.
As a result of wind speed measurement, it was also found that if the speed was at least m / sec, contamination in the secondary charger 5 could be sufficiently prevented.

[0111]

The present invention has the above configuration and operation. By applying a voltage having the same or a large absolute value as the voltage on the image carrier after charging, the image carrier, developer, The absolute value of the voltage increases in the order of the charging means. By forming an air flow from the charging means toward the image carrier, the developer receives a force in the direction of the image carrier, and is charged by corona wire contamination of the secondary charger caused by accumulation of reverse flying toner as in the conventional case. A one-pass multicolor printing image forming apparatus, which can prevent unevenness, and can cause an unclear image formation at the time of subsequent development due to mixing of the first color developer into the second color developing apparatus. in particular negative, can solve the problems caused when using a negative re-charging method, electrostatic applying a V _O to the charging means
Pressure, the image bearing member Ueno conductive when passing through the charging means V _T
Pressure, on the image bearing member when passing through the charging means V _D Les
The voltage of the non-irradiated part of the laser, d is the distance between the charging means and the image carrier.
Then, | (V _O −V _T ) /d|≧0.3 (V / μm),
And 0.9 (V / μm) ≧ | (V _D −V _O ) / d |
By applying the added V _O to the charging means, the developer
It does not fly away from the carrier.

By forming the air flow from the charging means to the image carrier over the entire area in the axial direction of the image carrier, the developer is subjected to a force in the direction of the image carrier over the entire area, and is scattered away from the image carrier. Absent.

The charging means is provided with an air feeding means, and the air flow by the air feeding means is made stronger at both axial end portions than at the center portion, thereby suppressing the air wind toward the charging means at both axial end portions due to corona ion wind. Air flow can be averaged over the entire area.

By making the air flow by the air feeding means larger than the corona ion wind generated by the corona discharge of the charging means, the air wind can be formed in the direction of the image carrier over the entire area even when the corona ion wind is generated, and the developer Are not separated from the image carrier and scattered.

The wind speed by the air feeding means is set to 0.5 m /
By setting the time to sec or more, a wind speed stronger than the corona ion wind can be obtained.

[0116]

By increasing the wind speed distribution of the air flow of the charging means toward the image carrier with respect to the traveling direction of the image carrier, the discharge is activated more upstream, so that the grid is not provided. It is possible to prevent the developer from flying back to the shield.

By increasing the wind speed of the air flow of the charging means toward the image carrier toward the charging means located on the downstream side with respect to the traveling direction of the image carrier, it is possible to cope with a large amount of developer. .

[Brief description of the drawings]

FIG. 1 is a schematic view showing a multicolor image forming apparatus according to an embodiment of the present invention.

FIGS. 2A to 2F are schematic diagrams showing changes in the surface potential of an image carrier applied to a multicolor image forming apparatus according to an embodiment of the present invention.

FIG. 3A is a schematic diagram showing a comparative example for explaining the present invention, and FIG. 3B is a schematic diagram with an air duct attached.

FIG. 4A is a schematic diagram showing a direction of an electric field according to the first embodiment of the present invention, and FIG. 4B is a schematic diagram showing an air flow through an air duct according to the first embodiment of the present invention.

FIG. 5A is a schematic diagram illustrating the direction of an electric field according to a second embodiment of the present invention, and FIG. 5B is a schematic diagram illustrating an air flow through an air duct according to the second embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between an axial direction and an air flow according to a third embodiment of the present invention, wherein (a) is a corona ion wind generated by a charging unit, and (b) is formed by an air duct. Air wind, (c) shows a synthetic wind of the air duct and the corona ion wind.

FIG. 7 is a schematic diagram showing a fourth embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor (image carrier) 2 primary charger 5 secondary charger 5 a shield 5 b grid 5 c corona wire 6 second laser beam 7 second developing device 8 transfer charger 9 transfer material (recording medium) 20 toner (developer) 21 power supply 22 power supply 50 air duct (air flow forming means) 51 filter 52 fan

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-177155 (JP, A) JP-A-2-146067 (JP, A) JP-A-61-15163 (JP, A) JP-A-61-163 62076 (JP, A) JP-A-6-161197 (JP, A) JP-A-6-110289 (JP, A) JP-A-6-19279 (JP, A) JP-A-58-1111054 (JP, A) JP-A-61-200556 (JP, A) JP-A-63-106673 (JP, A) JP-A-4-60659 (JP, A) JP-A-4-35151 (JP, U) JP-A-64-9254 (JP, U) Japanese Utility Model 62-142058 (JP, U) Japanese Utility Model 64-15245 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 13/01 G03G 15 / 01-15/01 117 G03G 15/02-15/02 103

Claims (7)

(57) [Claims] 1. A multicolor image which is sequentially charged and developed on an image carrier by a plurality of charging means and a plurality of developing means to form a multicolor image on the image carrier and collectively transfer the image onto a recording medium. In the forming apparatus, a voltage having the same or a large absolute value as the voltage on the image carrier after recharging is applied to at least one of the shield and the grid of the second and subsequent charging means, and and forming an air flow toward the voltage applied to V _O to the charging means, the V _T passes through the charging means
Image bearing member voltage when being, the V _D passes through the charging means
The voltage of the laser non-irradiated part on the image carrier when
When the distance of the electrodeposition unit and the image _{carrier, | (V O -V T)} / d
| ≧ 0.3 (V / μm) and 0.9 (V / μm) ≧
Applying V _O satisfying | (V _D −V _O ) / d |
A multicolor image forming apparatus. 2. The multicolor image forming apparatus according to claim 1, wherein the air flow from the charging means to the image carrier is formed over the entire area in the axial direction of the image carrier. Wherein an air feeding means provided in the charging means, according to claim 1 or 2 the air flow by the air feeding means is characterized by stronger than the central portion of the axial ends
Multi-color image forming apparatus. 4. The multicolor image forming apparatus according to claim 3, wherein the air flow by the air feeding means is made larger than the corona ion wind generated by the corona discharge of the charging means. 5. A wind speed of 0.5 m by an air feeding means.
/ Sec or more.
2. The multicolor image forming apparatus according to 1. Against 6. image carrier traveling direction velocity distribution of the air flow toward the image bearing member charging means, according to any one of claims 1 to 5, characterized in that so large that the upstream side Multicolor image forming apparatus. 7. The charging device according to claim 1, wherein the wind speed of the airflow of the charging means toward the image carrier is gradually increased toward the downstream of the image carrier in the traveling direction of the image carrier. The multicolor image forming apparatus according to any one of Items 6 to 6 .